Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions

Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions Davood Nematollahi, Mozhdeh Malmir, Ali Sadatnabi, Sajad Shanehsaz This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6111261/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 May, 2025 Read the published version in Scientific Reports → Version 1 posted 8 You are reading this latest preprint version Abstract An electrochemical Meerwein arylation reaction was reported for the synthesis of aryl-benzoquinone derivatives. In this work, efficient electrochemical synthesis of aryl-benzoquinone derivatives by direct electrolysis of aqueous solution containing hydroquinone and aryldiazonium salts in batch and a homemade continuous-flow cells is reported. In the batch system, the products were obtained in a simple undivided cell equipped with a copper anode and a stainless steel cathode. In the continuous flow system, the products were obtained simply by passing hydroquinone and the aryldiazonium salt through a tube made of copper with a stainless steel rod in the center. All equipment required in both cell types is obtained from common commercial sources. This protocol is green and cost-effective due to the use of electricity and is performed under mild and safe conditions without the use of toxic solvents and catalysts. Physical sciences/Chemistry/Organic chemistry/Methodology Physical sciences/Chemistry/Organic chemistry/Reaction mechanisms Physical sciences/Chemistry/Synthesis Physical sciences/Chemistry/Synthesis/Flow chemistry Physical sciences/Chemistry/Green chemistry/Sustainability Aryldiazonium salt Continuous-flow cell Copper anode Cyclic voltammetry Hydroquinone Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Electrochemistry is a very efficient tool for the synthesis of organic compounds, which has recently attracted the attention of many researchers. 1 – 15 It has been found that in many cases, electrochemical synthesis can be a suitable alternative to chemical synthesis. From another point of view, electrochemical synthesis of organic compounds is well established as an environmentally friendly strategy. Benzoquinones are a group of organic compounds that are involved in important biological activities such as electron transport processes, oxidative phosphorylation and bioenergetic transport. In addition, some of them have anti-cancer, anti-inflammatory and antioxidant activities. 16 Therefore, the synthesis of these compounds can be useful in the development of some medicinal molecules. Among quinones, p -benzoquinones are the simplest members of quinones, which are used in the manufacture of dyes and fungicides. They are also important organic intermediates in the synthesis of pharmaceuticals and fine chemicals. 17 Literature review shows that many researchers have synthesized p -benzoquinones in different routes. 18 – 28 Moore and co-workers reported the synthesis of 1,4-benzoquinones from 4-alkynyl-4-alkoxy (or hydroxy or trimethylsily1oxy) cyclobutenones. 18 The reaction is performed through electrocyclic ring opening of cyclobutenones to (2-alkynylethenyl)ketenes, then ring closing and diradical formation. George et al reported the synthesis of 2-substituted 1,4-benzoquinones via oxidative dearomatisation of para -substituted phenols using singlet oxygen in supercritical CO 2 . 19 The synthesis was carried out in a continuous multi-step in supercritical CO 2 . Saa et al reported an oxidative degradation method by Fremy's salt for the synthesis of quinones. 20 They performed these syntheses using phenols that have both a coordinating group for chelation and an electron withdrawing group in a 1,3-relationship. In 2008, Mathur and co-workers reported the photochemical synthesis of the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones from the reaction of enynes, ( Z )-1-methoxybut-1-ene-3-yne, or isopropenyl acetylene with CO in the presence of Fe(CO) 5 . 21 In 2019, Kim et al. reported the synthesis of benzoquinones from hydroquinones using an activated carbon–molecular oxygen system. 22 In this method, the synthesis of benzoquinone was carried out via the oxidation of hydroquinone by oxygen (1 atm) in xylene (0.1 M) at 120°C for 24 hours. These methods have disadvantages due to the use of highly corrosive and expensive oxidants and solvents. Therefore, some researchers have used electrochemical methods for the synthesis of 1,4-benzoquinones. In 2022, Waldvogel and co-workers reported the electrochemical synthesis of para -benzoquinones from phenols using a continuous flow cell in a water/methanol mixture without the use of a catalyst and chemical oxidizer with 61–99% yield. 23 Nematollahi et al. synthesized a number of mono- and di-substituted p -benzoquinone electrochemically through the oxidation of hydroquinone at carbon anode in the presence of some nucleophiles in a water/acetonitrile mixture. 24 , 25 Raju and co-workers reported the electrochemical synthesis of p -benzoquinones in biphasic medium (water/dichloromethane) from 1,4-dihydroxy benzenes using platinum foil electrodes. 26 In 2023, Zhang et al. reported the synthesis of p -benzoquinones (in moderate to good yields) from the electrochemical oxidation of simple aromatic compounds. 27 Electrolysis was carried out in CH 3 CN/H 2 O (5/1) containing n Bu 4 NBF 4 (0.1 M) and K 2 S 2 O 8 using platinum electrodes applying a constant current of 10 mA at room temperature. Recently, Waldvogel et al. synthesized a number of p -benzoquinones (up to 99% yield) electrochemically in water/methanol mixture through the oxidation of 4-hydroxybenzaldehydes using a graphite anode. 28 Meerwein arylation 29 is one of the most widely used methods for the functionalization of alkenes through radical reactions. In this method, the first step is usually the generation of aryl radicals from various precursors and with different methods. 30 The next step in this method is the reaction of the aryl radical with an alkene and the formation of a radical adduct. In the last step, depending on the conditions, this radical adduct after reduction can react with the electrophile and produces the final product. Or after oxidation, reacts with a nucleophile to form the product or in the presence of a radical scavenger to form the final product (Fig. 1 ) 30 .It should be noted that in this method, aryldiazonium salts are often the source of aryl radicals. A literature survey reveals that the Meerwein method for the arylation of organic compounds has been used in a large number of papers. 30 – 33 Despite the large number of articles, to the best of our knowledge there are no reports on electrochemically induced Meerwein arylation. Considering the advantages mentioned for electroorganic synthesis, 1 – 15 we decided to perform the Meerwein arylation by electrochemical method. In this work, the electrochemical synthesis of aryl-benzoquinone derivatives from the direct electrolysis of an aqueous solution containing hydroquinone in the presence of aryldiazonium salts in both batch and continuous-flow cells is performed. The proposed method is carried out under mild and safe conditions without the use of toxic solvents and catalysts and is very economical due to the use of electricity. Experimental Reagents and apparatus . All syntheses were performed at room temperature by applying a constant current using a Chin PS-303 DC power supply. The solution was stirred with a magnetic stirrer (Rodwell, Monostir, England) during electrolysis. FTIR spectroscopy was used to identify the functional groups of the products. All spectra were recorded from 4000 to 400 cm − 1 with a KBr disk on a Perkin–Elmer GX FTIR spectrometer. All 1 H NMR and 13 C NMR were recorded in CDCl 3 on a Bruker Avance DRX 400 spectrometer. The spectrometer operates at 400 MHz for protons and 100 MHz for carbon. The chemical shifts are reported in ppm ( δ ) at 298 K. All melting points in open capillary tubes were measured using a Model 9100 electrothermal apparatus and are uncorrected. AutoLab®/PGSTAT30 potentiostat/galvanostat (manufactured by Eco Chemie, Utrecht, The Netherlands) was used for cyclic voltammetry studies. Constant current electrolysis was performed using a DC POWER SUPPLY PS-305D power supply. The three-electrode system used for cyclic voltammetry measurements consisted of a glassy carbon disc (diameter 1.8 mm) as a working electrode, a stainless steel wire as an auxiliary electrode and Ag/AgCl (3 M) electrode as a reference electrode. All electrodes are provided by Azar Electrode Company (Iran). Alumina slurry was used to polish the glassy carbon electrode. Electrochemical synthesis of aryl-benzoquinone derivatives was performed in both batch and flow cells. The undivided cylindrical batch cell (100 mL) equipped with a large copper plate (5.5 cm x 2.5 cm) as the anode and a stainless steel rod with a length of 4 cm as a counter electrode (cathode). The continuous flow cell consists of a tube made of copper with a length of 28 cm and diameter of 1.3 cm (as the anode) and a stainless steel rod cathode with the same length and diameter of 1.2 cm in the center as the anode. Chemicals used in this study (aniline, 4-nitroaniline, 4-chloroaniline, 4-bromoaniline, 4-iodoaniline, 4-methoxyaniline, 4-fluoroaniline, hydroquinone and 2-methylhydroquinone) were purchased with purity higher than 98% from Aldrich and Merck. Buffer solutions were prepared according to the recommended procedures, 34 from analytical reagent grade chemicals purchased from Merck and Sigma without further purification. Synthesis of diazonium salt. Sulfuric acid (5 mL) was added to a well-stirred suspension of aniline derivatives (2 mmol) in H 2 O (10 mL). The reaction mixture was cooled to 0–5°C in an ice bath. Then, a cooled solution of sodium nitrite (3 mmol) in H 2 O (5 mL) at 0–5°C was added dropwise to the reaction mixture. At this time, the color of the solution turns yellow, which indicates the formation of diazonium salt. The synthesized diazonium solution (approximate concentration, 0.13 M) is placed in ice bath for use in the next step. Synthesis of aryl-benzoquinone derivatives in batch cell. For the synthesis of aryl-benzoquinone derivatives, first the aqueous solution of sodium acetate (0.15 M) (80 ml) containing hydroquinone (or 2-methylhydroquinone) (2 mmol) was electrolyzed in an undivided cell equipped with a copper plate anode and a stainless steel rod cathode under constant current (current density = 0.5 mA cm − 2 ) (20 mA) for 10 minutes. After this period, 2 ml of the produced diazonium solution is added to the electrochemical cell. Then electrolysis continues and after every 6 minutes, 2 ml of diazonium solution is added to the cell, and these steps continue until the diazonium solution is exhausted. The precipitate was collected by filtration and washed several times with distilled water. The dried precipitate was dissolved in acetone and subjected to preparative TLC (silica gel 60 GF 254), n -hexane/ethyl acetate 45:15]. The products were isolated as yellow powder. Synthesis of aryl-benzoquinone derivatives using undivided tubular flow cell. An undivided tubular flow cell consists of a copper tube as the anode with an inner diameter of 1.3 cm and a length of 28 cm with an area of 114 cm 2 (Fig. 2 ). Inside the copper tube is a stainless steel rod with a diameter of 1.0 cm and a length of 28 cm, with an area of 87.9 cm 2 as a cathode. In this cell, the cathode is surrounded by the anode and the solution is pumped from the bottom of the reactor to the top. The arrangement of anode and cathode is shown in Fig. 2 . In order to produce aryl-benzoquinone, a solution of sodium acetate (0.15 M) (80 mL) containing hydroquinone (2 mmol) along with aryl diazonium salt is passed through the flow cell at a constant flow rate using a syringe pump. The cell volume is 15.2 cm 3 and the volume of the connecting tubes is 17.5 cm 3 . Characteristics of the products 4'-Nitro-[1,1'-biphenyl]-2,5-dione (C 12 H 7 NO 4 ) ( ABQ1 ). Yellow solid; M.p. 152–154°C (Lit. 137°C 35 ); 1 H NMR (400 MHz, DMSO- d 6 ) δ : 8.30 (d, J = 8.7 Hz, 2H), 7.79 (d, J = 8.7 Hz, 2H), 7.10 (d, J = 2.3 Hz, 1H), 7.02 (s, 1H), 6.98 (d, J = 2.3 Hz, 1H); IR (KBr) (cm − 1 ): 2924, 2853, 1726, 1664, 1588, 1517, 1462, 1350, 1095, 865, 695; MS (ESI) m/z (relative intensity); 231 (M + 2H) (72), 230 (M + 1) (10), 229 (M) (57), 183 (52), 149 (100). [1,1'-Biphenyl]-2,5-dione (C 12 H 8 O 2 ) ( ABQ2 ). Yellow solid, M.p. 83–86°C (Lit. 104–106°C 36 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.48 (s, 1H), 7.38 (br, 5H), 7.08–6.87 (m, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ 187.6, 186.6, 146.5, 137.1, 136.4, 136.3, 132.7, 130.2, 129.2, 128.6; IR (KBr) (cm − 1 ): 2922, 1729, 1654, 1594, 1489, 1227, 1092, 843, 746, 696. 4'-Methoxy-[1,1'-biphenyl]-2,5-dione (C 13 H 10 O 3 ) ( ABQ3 ). Yellow solid, M.p. 108–110°C (Lit. 108–110°C 37 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.91 (d, J = 8.8 Hz, 2H), 7.50 (s, 1H), 7.03 (d, J = 8.8 Hz, 2H), 6.99 (d, J = 8.6 Hz, 2H), 3.92 (s, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 161.1, 158.2, 146.6, 133.0, 127.2, 123.9, 113.8, 55.1; IR (KBr) (cm − 1 ): 2959, 2839, 1601, 1581, 1499, 1465, 1441, 1306, 1251, 1180, 1148, 1042, 1024, 845, 825, 810, 782, 743, 555, 497. 4'-Chloro-[1,1'-biphenyl]-2,5-dione (C 12 H 7 ClO 2 ) ( ABQ4 ). Yellow solid, M.p. 110–112°C (Lit. 127–129°C 38 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.51–7.38 (br, 4H), 6.97–6.77 (br, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.3, 186.3, 144.7, 137.0, 136.6, 136.4, 132.7, 131.0, 130.6, 128.9; IR (KBr) (cm − 1 ): 3069, 1648, 1596, 1492, 1403, 1340, 1305, 1293, 1092, 1016, 976, 904, 855, 842, 822, 790, 728, 564, 508, 470, 419. MS (ESI) m/z (relative intensity); 218 (M) (11), 183 (m – Cl) (100), 155 (19), 136 (21), 101 (14), 82 (38). 4'-Bromo-[1,1'-biphenyl]-2,5-dione (C 12 H 7 BrO 2 ) ( ABQ5 ). Yellow solid; M.p. 84–87°C (Lit. 100–102°C 39 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.52 (d, J = 8.5 Hz, 2H), 7.29 (d, J = 8.6 Hz, 2H), 6.80–6.78 (m, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.3, 186.3, 144.8, 137.0, 136.38, 132.7, 131.8, 130.8, 125.0; IR (KBr) (cm − 1 ): 2926, 1651, 1593, 1489, 1400, 1339, 1292, 1098, 1073, 1012, 978, 906, 852, 789, 709, 501, 425. 4'-Iodo-[1,1'-biphenyl]-2,5-dione (C 12 H 7 IO 2 ) ( ABQ6 ). Yellow solid; M.p. 127–130°C (Lit. 133–135°C 40 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.73 (d, J = 8.5 Hz, 2H), 7.15 (d, J = 8.5 Hz, 2H), 6.81–6.78 (m, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 186.3, 185.2, 143.9, 136.7, 136.0, 135.3, 131.6, 130.0, 129.8, 96.0; IR (KBr) (cm − 1 ): 2923, 1647, 1597, 1580, 1483, 1393, 1385, 1342, 1293, 1260, 1097, 1063, 1008, 975, 910, 849, 784, 698, 606, 548, 428. 4'-Fluoro-[1,1'-biphenyl]-2,5-dione (C 12 H 7 FO 2 ) ( ABQ7 ). M.p. 152–155°C (Lit. 152–155°C 37 ); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.46–7.42 (m, 2H), 7.13–6.79 (m, 5H); IR (KBr) (cm − 1 ): 2924, 1660, 1603, 1508, 1413, 1376, 1330, 1235, 1235, 1162, 1107, 919, 845, 525, 420. 4-Methyl (and 3-methyl ) -4'-nitro-[1,1'-biphenyl]-2,5-dione (C 13 H 9 NO 4 ) ( ABQ8 , two isomers). M.p. 131–133°C; 1 H NMR (400 MHz, CDCl 3 ) δ : 8.25 (d, J = 8.7 Hz, 4H), 7.30 (d, J = 8.8 Hz, 4H), 6.86 (s, 1H), 6.84 (s, 1H), 6.81 (s, 1H), 6.78 (s, 1H), 2.10 (s, 3H), 2.07 (s, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.2, 186.8, 185.7, 147.9, 146.3, 142.6, 141.9, 139.3, 139.2, 136.7, 136.3, 134.1, 133.7, 133.5, 130.7, 130.3, 130.2, 123.6, 123.5, 16.4, 15.6; IR (KBr) (cm − 1 ): 3114, 3068, 2925, 1656, 1592, 1518, 1348, 1304, 1137, 1091, 946, 865, 846, 749, 699, 410. 4'-Chloro-4-methyl (and 3-methyl ) -[1,1'-biphenyl]-2,5-dione (C 13 H 9 ClO 2 ) ( ABQ9 , two isomers); M.p. 64–67°C; 1 H NMR (400 MHz, CDCl 3 ) δ : 7.35 (m, 8H), 6.77 (s, 1H), 6.72 (s, 1H), 6.64 (s, 1H), 6.62 (s, 1H), 2.07 (s, 3H), 2.04 (s, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.8, 187.3, 186.8, 186.5, 146.2, 145.8, 144.9, 144.6, 136.3, 136.2, 133.7, 133.3, 132.74, 132.68, 131.4, 131.0, 130.5, 129.5, 128.8, 128.7, 16.4, 15.5; IR (KBr) (cm − 1 ): 3050, 2974, 1647, 1627, 1594, 1493, 1427, 1404, 1354, 1305, 1231, 1095, 1013, 923, 880, 839, 828, 738, 523, 446, 418. 4'-Bromo-4-methyl (and 3-methyl ) -[1,1'-biphenyl]-2,5-dione (C 13 H 9 BrO 2 ) ( ABQ10 , two isomers); M.p. 84–86°C; 1 H NMR (400 MHz, CDCl 3 ) δ : 7.60 (d, J = 8.3 Hz, 4H), 7.38 (d, J = 6.1 Hz, 4H), 6.87 (s, 1H), 6.81 (s, 1H), 6.73 (s, 1H), 6.71 (s, 1H), 2.16 (s, 3H), 2.13 (s, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.9, 187.3, 186.5, 186.8, 146.2, 145.9, 144.7, 137.4, 136.5, 136.4, 133.7, 133.3, 132.8, 132.7, 131.8, 131.7, 131.5, 131.2, 130.8, 130.7, 129.8, 124.8, 124.6, 16.4, 15.5; IR (KBr) (cm − 1 ): 2928, 1654, 1630, 1594, 1429, 1398, 1189, 1073, 1010, 917, 828, 458. 4'-Iodo-4-methyl (and 3-methyl ) -[1,1'-biphenyl]-2,5-dione (C 13 H 9 IO 2 ) ( ABQ11 , two isomers); 1 H NMR (400 MHz, CDCl 3 ) δ : 7.71 (d, J = 8.0 Hz, 4H), 7.14 (d, J = 6.0 Hz, 4H), 6.77 (s, 1H), 6.71 (s, 1H), 6.64 (s, 1H), 6.62 (s, 1H), 2.06 (s, 3H), 2.0 (s, 3H); 13 C NMR (101 MHz, CDCl 3 ) δ : 187.9, 187.4, 186.7, 186.5, 146.2, 145.9, 145.2, 144.8, 137.73, 137.69, 137.4, 136.5, 136.4, 133.8, 133.3, 132.73, 132.67, 131.3, 130.9, 130.8, 96.8, 16.4, 15.6; IR (KBr) (cm − 1 ): 2922, 1651, 1626, 1599, 1579, 1485, 1396, 1354, 1305, 1231, 1192, 1125, 1061, 1004, 919, 826, 801, 722, 670, 512, 471. Results and Discussion Electrochemical studies. In order to obtain the detailed information about the reaction between p -benzoquinone and aryldiazonium salts, the electrochemical behavior of hydroquinone in the presence of 4-nitrobenzenediazonium sulfate was investigated. Figure 3, part I, curve a, shows the cyclic voltammogram of hydroquinone ( HQ ) (1 mM) in aqueous acidic/ethanol (50/50 v/v) mixture. It should be noted that to record this voltammogram, 1 ml of sulfuric acid (6.1 M) solution was added to 9 ml of HQ solution in a water (phosphate buffer, pH = 2, c = 0.2 M)/ethanol mixture. As expected, the cyclic voltammogram shows a peak related to the oxidation of HQ to p -benzoquinone ( BQ ) (A 1 ) in the anodic scan, and a peak related to the reduction of BQ to HQ (C 1 ) in the cathodic scan. When instead of the sulfuric acid solution, 1 ml of diazonium solution containing sulfuric acid (6.1 M) (see experimental section) is added to the HQ solution, there is a large change in the cyclic voltammogram. (Fig. 3, part I, curves b and c). In these voltammograms, a wide range of potentials is scanned to identify all species that are oxidized or reduced. In the anodic scan and in the first cycle (curve b), the voltammogram shows two well-defined anodic peaks at potentials of 0.64 and 1.28 V. These peaks are related to the oxidation of HQ (A 1 ) and nitrite ion (A N ) 41 (available in diazonium solution), respectively. In this situation, two weak cathode peaks (C 1 and C 2 ) can be seen in the reverse cathodic scan at potentials of 0.83 and 0.62 V, respectively. Cathodic peak C 1 is the counterpart of peak A 1 . In the second cycle of the potential sweep (curve c), a new anodic peak (A 2 ) appears at 0.85 V. This peak is the counterpart of peak C 2 . It should be noted that the same electrochemical behavior observed in the cyclic voltammetry of HQ at different pH values (pH < 8) in the presence of aryldiazonium solution. Since the diazonium solution contains sulfuric acid and changes the pH of the HQ solution, and on the other hand, the HQ / BQ redox system is pH dependent, 42 in the experiment conducted in the absence of diazonium ion (Fig. 2, part I, curve a), sulfuric acid (6.1 M) was added to the HQ solution so that the pH of the HQ solution in the absence of diazonium (curve a) became equal to the pH of the HQ solution in the presence of diazonium (curves b and c). Based on the obtained electrochemical data as well as the spectroscopic data of the product, we propose the following mechanism (Fig. 4, part I) for the oxidation of HQ in the presence of nitrobenzenediazonium sulfate. Accordingly, at the anode surface, HQ loses two electrons and is oxidized to BQ . At the same time, a homolytic dediazonation reaction occurs in the solution. 38,43,44 As a result of this reaction, aryldiazonium salt ( DAZ ) is converted into aryl radical ( ArR ) and dinitrogen molecule. The reaction between BQ and ArR leads to the formation of intermediate INT , which in the next step by losing an electron becomes the final product, nitro-arylbenzoquinone ( ABQ1 ). According to the proposed mechanism, the anodic (A 2 ) and cathodic (C 2 ) peaks are related to the INT / ABQ1 redox couple. It seems that in the absence of reducing agents and metal ions, hemolytic dediazonation of diazonium salt is due to its reaction with HQ . 38 This reaction is shown in Fig. 4, part II. As can be seen, electron transfer between aryldiazonium salt and HQ causes the conversion of aryldiazonium salt to aryl radical. On the other hand, as a result of this reaction, HQ is converted into semiquinone ( SQ ) by losing an electron. Regarding the oxidation of INT and its conversion to the final product ( ABQ1 ), two paths seem possible. The first route is the direct oxidation of INT on the electrode surface and the second route is its indirect oxidation through the reaction with SQ . In contrast to the results obtained in acidic, neutral, and low-alkaline solutions, research conducted at pH ≥ 10 suggests that the reaction follows a different course. Figure 3, part II, curve a, shows the cyclic voltammogram of HQ (1 mM) in aqueous (bicarbonate buffer, pH 10, c = 0.2 M)/ethanol (50/50 v/v) mixture after addition of 1 mL sulfuric acid (6.1 M). The voltammogram recorded under these conditions is similar to the one shown in part I, curve a, except that the peak potentials are shifted towards the negative potentials. When 1 ml of the diazonium solution is added to the HQ solution, there is not much change in the cyclic voltammogram. (Fig. 3, part II, curve b) and only its reversibility decreases. This phenomenon may be caused by the fouling of the electrode surface attributed to the immobilization (or adsorption) of the aryl radicals on the surface of the glassy carbon electrode, which reduces the efficiency of the electrode. 45–47 It seems that as the solution pH increases, the diazonium salt is converted to diazoate and diazohydroxide species, which are much more unstable. Successive hemolytic cleavage of these compounds produces a radical that reacts with the glassy carbon surface. 48 Since the copper anode has been used in macro-scale electrolysis, it is necessary to slightly modify the proposed mechanism in Fig. 4 for the copper anode. In such conditions, it seems that the oxidation of HQ to BQ is done through its electron transfer reaction with copper ions (Fig. 5). Also, these ions can oxidize INT to ABQ1 . On the other hand, the formed cuprous ions (Cu + ) can contribute to the reduction of the aryldiazonium salt ( DAZ ) to the aryl radical ( ArR ) (Fig. 5). The use of a copper anode and the catalytic activity of copper ions in the synthesis of aryl-benzoquinones ( ABQ ) is one of the novel and important aspects of this study. The divalent copper ions generated from the anodic oxidation can oxidize HQ to BQ . On the other hand, the monovalent copper ions generated from this reaction can reduce DAZ to ArR and themselves be oxidized to Cu 2+ . On the other hand, the Cu 2+ ions can act as an oxidant to convert INT to the final product, ABQ1 . The cyclic voltammograms of the product ( ABQ1 ) after separation and purification is shown in Fig. 6. In order to further identify the structure of the product and its electrochemical properties, these voltammograms were recorded in two different conditions. In this figure, to record the voltammogram a, first the potential was scanned from 0.0 V towards more positive values (anodic scan), which led to the appearance of a cyclic voltammogram for a Nernstian reversible process. It should be noted that when the starting potential (0 V) is applied, ABQ1 is reduced to its corresponding nitro-arylhydroquinone ( AHQ1 ) at the electrode surface. The presence of cathodic current at the starting potential (0 V) confirms the reduction of ABQ1. Therefore, during potential scanning, the species present on the electrode surface is NO 2 - AHQ . Accordingly, anodic peak Ap 1 is related to the oxidation of NO 2 - AHQ to ABQ1 , and cathodic peak C p1 is its counterpart and related to the reduction of ABQ1 to NO 2 - AHQ (Fig. 7). In this study, when the cathodic scan is performed first, the shape of the voltammogram changes completely (Fig. 6, curve b). Under these conditions, the cyclic voltammogram shows an irreversible cathodic peak (C N ) and a two reversible redox systems, A p2 /C p2 and A p3 /C p3 . As discussed, when the starting potential (0.0 V) is applied, ABQ1 is reduced to NO 2 - AHQ at the electrode surface. Therefore, during the cathodic potential scan, peak C N corresponds to the reduction of the nitro group in the NO 2 - AHQ molecule to the corresponding hydroxylamine (NHOH- AHQ ). A p2 and C p2 peaks are attributed to NHOH- AHQ /nitroso-arylhydroquinone (NO- AHQ ) redox couple. Based on this A p3 and C p3 peaks are attributed to NO- AHQ /NO- ABQ (Fig. 7). Optimization of reaction conditions. In this part, the effect of factors affecting the yield and purity of the products such as applied current density, amount of electricity, type of electrode and cell and synthesis method has been investigated. The optimization for the synthesis of ABQ1 was carried out by one-factor-at-a-time (OFAT) approach. The amount of electricity consumption is an important factor in the yield and purity of the product. For the synthesis of ABQ1 , first the aqueous solution of sodium acetate (0.15 M) (80 ml) containing HQ (2 mmol) was electrolyzed in an undivided cell equipped with a copper plate anode and a stainless steel rod cathode under constant current (20 mA) for 10 minutes. After this period, 1 ml of the produced 4-nitrobenzenediazonium chloride solution is added to the electrochemical cell. The results of studies is shown in Table 1, entries 1–4. The results show that increasing the amount of electricity consumed from 70 to 190 C increases the yield, but a further increase in electricity decreases the yield of ABQ1 production. Over-oxidation of the product may be the reason for this decrease. Another notable point is that the electricity consumption in these syntheses is lower than the theoretical value, which is due to the oxidation of HQ by excess nitrite ions present in the diazonium solution 49,50 as well as the catalytic activity of copper ions (Fig. 5). The volume of 4-nitrobenzenediazonium chloride solution "added per injection" is another parameter that was optimized, while the total amount of diazonium added was kept constant. Entries 1 and 5–7 show that increasing the sample volume from 0.5 to 3 mL increases production yield. The role of solution pH in the yield of ABQ1 was also investigated (entries 1 and 8–10). It was found that pH of HQ solution has no significant effect on ABQ1 yield. It seems that increasing the strongly acidic solution containing diazonium salt to the HQ solution suppresses the effect of hydroquinone solution pH. Entries 3 and 11–14 show the effect of applied current on ABQ1 production yield. The results show that the yield of ABQ1 increases with increasing applied current due to the increased over-potential for HQ oxidation and then decreases slightly due to over-oxidation of the product, intermediates or solvent. Furthermore, increasing over-potential increases energy consumption and associated costs. Again, the effect of the volume of 4-nitrobenzene diazonium chloride solution "added per injection" was investigated when the electricity consumption was 190 coulombs (entries 3 and 15, 16). The role of anode material in the yield of ABQ1 was also investigated (entries 17–23). It was found that the highest yield is achieved when copper is used as anode. Table 1 Optimization of effective parameters in ABQ1 synthesis in batch cell. Entry Electrolysis time (min) Electricity consumption (C) Increment time a (min) Sample volume (mL) Initial pH of hydroquinone solution Applied current (mA) Anode material Yield % 1 70 84 3 1 sodium acetate b 20 Cu 46.1 2 130 156 6 1 sodium acetate 20 Cu 52.9 3 190 228 9 1 sodium acetate 20 Cu 56.4 4 250 300 12 1 sodium acetate 20 Cu 43.1 5 70 84 1.5 0.5 sodium acetate 20 Cu 38.6 6 70 84 6 2 sodium acetate 20 Cu 71.3 7 70 84 9 3 sodium acetate 20 Cu 71.8 8 70 84 3 1 2 20 Cu 54.1 9 70 84 3 1 5 20 Cu 44.6 10 70 84 3 1 10 20 Cu 51.3 11 190 228 9 1 sodium acetate 5 Cu 46.0 12 190 228 9 1 sodium acetate 10 Cu 47.0 13 190 228 9 1 sodium acetate 15 Cu 57.9 14 190 228 9 1 sodium acetate 25 Cu 55.9 15 190 228 18 2 sodium acetate 20 Cu 71.8 16 190 228 27 3 sodium acetate 20 Cu 51.3 17 130 156 6 2 sodium acetate 20 Zn 37.4 18 130 156 6 2 sodium acetate 20 Al 44.6 19 130 156 6 2 sodium acetate 20 Fe 40.3 20 130 156 6 2 sodium acetate 20 SS c 56.3 21 130 156 6 2 sodium acetate 20 Ag 54.4 22 130 156 6 2 sodium acetate 20 graphite 41.2 23 130 156 6 2 sodium acetate 20 Cu 71.3 a Time interval between two injections. b 0.15 M. c Stainless steel. As mentioned in the previous section and also in Fig. 5, the use of copper anode is one of the innovative aspects of this study due to the catalytic behavior of copper ions. The Cu 2+ ions can oxidize HQ to BQ . On the other hand, the generated Cu + ions can reduce DAZ to ArR and themselves be oxidized to Cu 2+ . On the other hand, Cu 2+ ions can also convert INT to ABQ1 . Such conditions make it possible to achieve maximum yield when using copper anode. At the end of this section, the cell type was evaluated. For this purpose, a divided cell has been used in optimal conditions (entry 6), and the obtained results indicate a decrease in yield from 71–54%. Since the direct reduction of diazonium salts at the cathode surface and the formation of aryl radicals is possible, 51 the decrease in yield is a confirmation that the formation of aryl radicals is also performed through direct reduction of diazonium salts at the cathode. Therefore, the use of a divided cell reduces the yield. Based on this result, we propose Fig. 8 for the cathodic generation (direct) of aryl radicals. The proposed mechanism is categorized as convergent paired mechanism in which the intermediates generated at the anode and cathode interact with each other to form the final product. 9 After optimizing the reaction conditions for the synthesis of ABQ1 , we investigated the substrate range of different aryldiazoniums and hydroquinones. The results of these studies are shown in Table 2. To this end, we reacted a series of aryldiazonium salts with electron-donating or electron-withdrawing groups at the para -position of the benzene ring with hydroquinone as well as 2-methylhydroquinone, leading to the synthesis of the corresponding aryl-benzoquinones in moderate to good yields. Notably, as expected, when unsymmetrical 2-methyl hydroquinone was used, an inseparable mixture of isomers was obtained in moderate yield. These syntheses have also been performed using a flow cell and the effect of factors affecting the yield and purity of the products such as applied current, flow rate, amount of electricity, and time increment have been investigated. The results of studies is shown in Table 3. Table 3 Optimization of effective parameters in ABQ1 synthesis in flow cell. Entry Electrolysis time (min) Electricity consumption (C) Increment time (min) a Sample volume (mL) Flow rate (mL/min) Applied current (mA) Yield % 1 60 72 3 1 80 20 66.7 2 120 144 6 1 40 20 33.4 3 180 216 9 1 26.6 20 26.8 4 60 72 6 2 80 20 88.2 5 60 72 9 3 80 20 47.0 6 120 144 12 2 40 20 40.8 7 120 144 18 3 40 20 33.3 8 60 36 6 2 80 10 42.5 9 60 108 6 2 80 30 57.4 a Time interval between two injections. The arrangement of anode and cathode in the flow cell is shown in Fig. 2. Accordingly, the anode is a copper tube and the cathode is a stainless steel rod. As show in Table 3, the best yield, 88.2% (entry 4) is obtained when the applied current is 20 mA, the flow rate is 80 ml/min, the electricity consumption is 72 C, the sample volume of diazonium salt per injection is 2 mL and the injection interval is 6 minutes. In another cell design, the shape of the cathode and anode in the flow cell was changed. In this way, a stainless steel tube was used as the cathode and a copper rod as the anode. It should be noted that the dimensions of the tube and rod used in this flow cell are similar to Fig. 2. The synthesis of ABQ1 with this new cell configuration provides a yield of 52.3%, which is lower than 88.2%. Conclusion In this work an eco-friendly electrochemical method was developed for the synthesis of some aryl-benzoquinone derivatives. The synthesis of these compounds was carried out through direct electrolysis of aqueous solution containing hydroquinone in the presence of aryl-diazonium salts in both simple batch and a homemade continuous-flow cells. One of the important points in this work is the easy and cheap preparation of all the equipment needed in both types of cells from common commercial sources. This method is very economical due to the use of electricity instead of chemical reagents and is performed in mild conditions and in water without using toxic solvents and catalysts. In addition, in this work, the electrochemical behavior of hydroquinone in the presence of aryldiazonium salt was investigated, and based on the results, a detailed mechanism for the electrochemical Meerwein arylation was presented. Declarations Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability The datasets used and/or analyzed during the current study available from the corresponding author on request. Acknowledgments The authors acknowledge the Bu-Ali Sina University Research Council and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for their support of this work. Author contributions DN: supervision, project administration, resources, writing-review & editing. AS: Project administration. MM: investigation, writing-original draft. SS: investigation. References Waldvogel, S. R., Lips, S., Selt, M., Riehl, B. & Kampf, C. J. Electrochemical arylation reaction. Chem. Rev. 118 , 6706-6765 (2018). Nematollahi, D., Mohamadighader, N., Roshani, M., Hashemi-Mashouf, M. 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Additional Declarations No competing interests reported. Supplementary Files Table2.docx Cite Share Download PDF Status: Published Journal Publication published 17 May, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 21 Apr, 2025 Reviews received at journal 18 Apr, 2025 Reviewers agreed at journal 07 Apr, 2025 Reviews received at journal 06 Apr, 2025 Reviewers agreed at journal 06 Apr, 2025 Reviewers invited by journal 04 Apr, 2025 Submission checks completed at journal 04 Apr, 2025 First submitted to journal 25 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6111261","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":439494363,"identity":"8055a8ff-6857-45ac-ad64-2a1cc50d3952","order_by":0,"name":"Davood Nematollahi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYNCCigMwlgSROg6cIVnLwbYDhJQgAXP27sTPH+fdkZefkcD44QeDRT5BLZY9ZzdLHNz2zHDDjQRmyR4GCcsGQloMbuRuAGo5zLhBIoFBGugXA4K2GNx/u/nHwTmH7efPSGD+TZyWG7zbJA42HE5suJHARqQtZ3K3WZw59ix5w5mHbZY9BsRoOX52842Kmju289uTD9/4UVFHWAsSYGwAmkCKhlEwCkbBKBgFOAEA2idARiJCMy8AAAAASUVORK5CYII=","orcid":"","institution":"Bu-Ali Sina University","correspondingAuthor":true,"prefix":"","firstName":"Davood","middleName":"","lastName":"Nematollahi","suffix":""},{"id":439494364,"identity":"9cf3a9cb-9660-4624-8ef0-2569a2728a07","order_by":1,"name":"Mozhdeh Malmir","email":"","orcid":"","institution":"Bu-Ali Sina University","correspondingAuthor":false,"prefix":"","firstName":"Mozhdeh","middleName":"","lastName":"Malmir","suffix":""},{"id":439494365,"identity":"13f865ed-a1bd-49fe-8e21-c9a3c2ca0ce2","order_by":2,"name":"Ali Sadatnabi","email":"","orcid":"","institution":"Bu-Ali Sina University","correspondingAuthor":false,"prefix":"","firstName":"Ali","middleName":"","lastName":"Sadatnabi","suffix":""},{"id":439494366,"identity":"db0491d1-a5d8-4e44-83f7-9762e37a191b","order_by":3,"name":"Sajad Shanehsaz","email":"","orcid":"","institution":"Bu-Ali Sina University","correspondingAuthor":false,"prefix":"","firstName":"Sajad","middleName":"","lastName":"Shanehsaz","suffix":""}],"badges":[],"createdAt":"2025-02-26 08:38:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6111261/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6111261/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-02504-y","type":"published","date":"2025-05-17T15:58:10+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":80316602,"identity":"6fbd6c5c-344e-4893-aa8c-1eb435ca763e","added_by":"auto","created_at":"2025-04-10 12:29:53","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":107562,"visible":true,"origin":"","legend":"\u003cp\u003eReaction pathways in Meerwein arylation.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/a2d3663cf6f61f6a9b6e61fc.png"},{"id":80317239,"identity":"9ad68e6e-1e46-4e0f-8a82-b5b433795ab2","added_by":"auto","created_at":"2025-04-10 12:37:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":641086,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram (above) and the image (below) of the undivided tubular flow cell for the synthesis of aryl-benzoquinone derivatives.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/a328d983823ee2f94f217c21.png"},{"id":80316607,"identity":"4453d9a1-4689-48ce-a100-184e0a102bfd","added_by":"auto","created_at":"2025-04-10 12:29:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":294211,"visible":true,"origin":"","legend":"\u003cp\u003ePart I: Curve a: Cyclic voltammogram of \u003cstrong\u003eHQ\u003c/strong\u003e (1 mM) in a water (phosphate buffer, pH = 2, \u003cem\u003ec\u003c/em\u003e= 0.2 M)/ethanol mixture (50/50 v/v) after addition of 1 mL sulfuric acid (6.1 M). Curves b and c: First and second cycles of cyclic voltammograms of \u003cstrong\u003eHQ\u003c/strong\u003e (1 mM) in a water (phosphate buffer, pH = 2, \u003cem\u003ec\u003c/em\u003e= 0.2 M)/ethanol mixture (50/50 v/v) after addition of 1 mL of prepared diazonium solution (see experimental section). Scan rate: 500 mV/s. Part II: Curve a: Cyclic voltammogram of \u003cstrong\u003eHQ\u003c/strong\u003e (1 mM) in a water (bicarbonate buffer, pH 10, \u003cem\u003ec\u003c/em\u003e = 0.2 M)/ethanol mixture (50/50 v/v) after addition of 1 mL sulfuric acid (6.1 M). Curve b: Cyclic voltammogram of \u003cstrong\u003eHQ\u003c/strong\u003e (1 mM) in a water (bicarbonate buffer, pH 10, \u003cem\u003ec\u003c/em\u003e= 0.2 M)/ethanol mixture (50/50 v/v) after addition of 1 mL of prepared diazonium solution. Scan rate: 100 mV/s. Working electrode: glassy carbon electrode. In all experiments, cells were kept in an ice bath.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/d0561304a7e065980c4f4696.png"},{"id":80316615,"identity":"0e1a69b7-da08-487b-ba7e-7292cef43e48","added_by":"auto","created_at":"2025-04-10 12:29:53","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":308835,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical arylation pathway of hydroquinone and possible homogeneous electron transfer between the species involved in the reaction.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/9881cd811d4e9af014452629.png"},{"id":80318860,"identity":"ac20d114-9fd8-42f6-944c-5e9596c2b2cb","added_by":"auto","created_at":"2025-04-10 13:01:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":287591,"visible":true,"origin":"","legend":"\u003cp\u003eThe possible homogeneous electron transfer between copper ion species and the components involved in the reaction.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/da4dca2ed7101c1686a004a9.png"},{"id":80318861,"identity":"0abf8a5f-d6ce-43bc-bbe5-d2c02d4259ad","added_by":"auto","created_at":"2025-04-10 13:01:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":264867,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of \u003cstrong\u003eABQ1 \u003c/strong\u003e(1 mM) in a water (phosphate buffer, pH = 2, \u003cem\u003ec\u003c/em\u003e = 0.2 M)/ethanol mixture (50/50 v/v) after addition of 1 mL sulfuric acid (6.1 M). (a) Anodic scan has been done first (potential was scanned from +0.0 V to +0.67 V). (b) Cathodic scan has been done first (potential was scanned from 0.0 V to -0.55 V then from -0.55 V to +0.67 V). Scan rate: 25 mV/s. Working electrode: glassy carbon electrode. In all experiments, cells were kept in an ice bath.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/61c2338a2143001633317749.png"},{"id":80317243,"identity":"1b4ebd53-dec9-46bc-8e17-f54e5595deb0","added_by":"auto","created_at":"2025-04-10 12:37:53","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":200302,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical behavior of \u003cstrong\u003eABQ1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/76ba9f402b76337baf6a23c1.png"},{"id":80316620,"identity":"0aee8e56-caa9-4ec1-b461-1cd9b919047e","added_by":"auto","created_at":"2025-04-10 12:29:53","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":351138,"visible":true,"origin":"","legend":"\u003cp\u003eDirect electrochemical generation of NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eArR\u003c/strong\u003e and formation of \u003cstrong\u003eABQ1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/9ee2c5d0ad99ddb8eeb4feb5.png"},{"id":83067873,"identity":"0b375da8-77fc-422a-8644-942a7753c9c9","added_by":"auto","created_at":"2025-05-19 16:07:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4057219,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/b6e11403-81c8-4c3d-b2cf-08c92dca2896.pdf"},{"id":80316606,"identity":"fc8a2e4d-cbba-4aba-9153-a4e55ac92a82","added_by":"auto","created_at":"2025-04-10 12:29:53","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":165371,"visible":true,"origin":"","legend":"","description":"","filename":"Table2.docx","url":"https://assets-eu.researchsquare.com/files/rs-6111261/v1/28b6c31b357f12e1a1e58383.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions","fulltext":[{"header":"Introduction","content":"\u003cp\u003eElectrochemistry is a very efficient tool for the synthesis of organic compounds, which has recently attracted the attention of many researchers. \u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e It has been found that in many cases, electrochemical synthesis can be a suitable alternative to chemical synthesis. From another point of view, electrochemical synthesis of organic compounds is well established as an environmentally friendly strategy. Benzoquinones are a group of organic compounds that are involved in important biological activities such as electron transport processes, oxidative phosphorylation and bioenergetic transport. In addition, some of them have anti-cancer, anti-inflammatory and antioxidant activities.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e Therefore, the synthesis of these compounds can be useful in the development of some medicinal molecules. Among quinones, \u003cem\u003ep\u003c/em\u003e-benzoquinones are the simplest members of quinones, which are used in the manufacture of dyes and fungicides. They are also important organic intermediates in the synthesis of pharmaceuticals and fine chemicals.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Literature review shows that many researchers have synthesized \u003cem\u003ep\u003c/em\u003e-benzoquinones in different routes.\u003csup\u003e\u003cspan additionalcitationids=\"CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26 CR27\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e Moore and co-workers reported the synthesis of 1,4-benzoquinones from 4-alkynyl-4-alkoxy (or hydroxy or trimethylsily1oxy) cyclobutenones.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e The reaction is performed through electrocyclic ring opening of cyclobutenones to (2-alkynylethenyl)ketenes, then ring closing and diradical formation. George et al reported the synthesis of 2-substituted 1,4-benzoquinones via oxidative dearomatisation of \u003cem\u003epara\u003c/em\u003e-substituted phenols using singlet oxygen in supercritical CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e The synthesis was carried out in a continuous multi-step in supercritical CO\u003csub\u003e2\u003c/sub\u003e. Saa et al reported an oxidative degradation method by Fremy's salt for the synthesis of quinones.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e They performed these syntheses using phenols that have both a coordinating group for chelation and an electron withdrawing group in a 1,3-relationship. In 2008, Mathur and co-workers reported the photochemical synthesis of the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones from the reaction of enynes, (\u003cem\u003eZ\u003c/em\u003e)-1-methoxybut-1-ene-3-yne, or isopropenyl acetylene with CO in the presence of Fe(CO)\u003csub\u003e5\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e In 2019, Kim et al. reported the synthesis of benzoquinones from hydroquinones using an activated carbon\u0026ndash;molecular oxygen system.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e In this method, the synthesis of benzoquinone was carried out via the oxidation of hydroquinone by oxygen (1 atm) in xylene (0.1 M) at 120\u0026deg;C for 24 hours. These methods have disadvantages due to the use of highly corrosive and expensive oxidants and solvents. Therefore, some researchers have used electrochemical methods for the synthesis of 1,4-benzoquinones. In 2022, Waldvogel and co-workers reported the electrochemical synthesis of \u003cem\u003epara\u003c/em\u003e-benzoquinones from phenols using a continuous flow cell in a water/methanol mixture without the use of a catalyst and chemical oxidizer with 61\u0026ndash;99% yield.\u003csup\u003e23\u003c/sup\u003e Nematollahi et al. synthesized a number of mono- and di-substituted \u003cem\u003ep\u003c/em\u003e-benzoquinone electrochemically through the oxidation of hydroquinone at carbon anode in the presence of some nucleophiles in a water/acetonitrile mixture.\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e Raju and co-workers reported the electrochemical synthesis of \u003cem\u003ep\u003c/em\u003e-benzoquinones in biphasic medium (water/dichloromethane) from 1,4-dihydroxy benzenes using platinum foil electrodes.\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e In 2023, Zhang et al. reported the synthesis of \u003cem\u003ep\u003c/em\u003e-benzoquinones (in moderate to good yields) from the electrochemical oxidation of simple aromatic compounds.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e Electrolysis was carried out in CH\u003csub\u003e3\u003c/sub\u003eCN/H\u003csub\u003e2\u003c/sub\u003eO (5/1) containing \u003cem\u003en\u003c/em\u003eBu\u003csub\u003e4\u003c/sub\u003eNBF\u003csub\u003e4\u003c/sub\u003e (0.1 M) and K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e using platinum electrodes applying a constant current of 10 mA at room temperature. Recently, Waldvogel et al. synthesized a number of \u003cem\u003ep\u003c/em\u003e-benzoquinones (up to 99% yield) electrochemically in water/methanol mixture through the oxidation of 4-hydroxybenzaldehydes using a graphite anode.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eMeerwein arylation\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e is one of the most widely used methods for the functionalization of alkenes through radical reactions. In this method, the first step is usually the generation of aryl radicals from various precursors and with different methods.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e The next step in this method is the reaction of the aryl radical with an alkene and the formation of a radical adduct. In the last step, depending on the conditions, this radical adduct after reduction can react with the electrophile and produces the final product. Or after oxidation, reacts with a nucleophile to form the product or in the presence of a radical scavenger to form the final product (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e.It should be noted that in this method, aryldiazonium salts are often the source of aryl radicals.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA literature survey reveals that the Meerwein method for the arylation of organic compounds has been used in a large number of papers.\u003csup\u003e\u003cspan additionalcitationids=\"CR31 CR32\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e Despite the large number of articles, to the best of our knowledge there are no reports on electrochemically induced Meerwein arylation. Considering the advantages mentioned for electroorganic synthesis,\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e we decided to perform the Meerwein arylation by electrochemical method. In this work, the electrochemical synthesis of aryl-benzoquinone derivatives from the direct electrolysis of an aqueous solution containing hydroquinone in the presence of aryldiazonium salts in both batch and continuous-flow cells is performed. The proposed method is carried out under mild and safe conditions without the use of toxic solvents and catalysts and is very economical due to the use of electricity.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cp\u003e \u003cb\u003eReagents and apparatus\u003c/b\u003e. All syntheses were performed at room temperature by applying a constant current using a Chin PS-303 DC power supply. The solution was stirred with a magnetic stirrer (Rodwell, Monostir, England) during electrolysis. FTIR spectroscopy was used to identify the functional groups of the products. All spectra were recorded from 4000 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a KBr disk on a Perkin\u0026ndash;Elmer GX FTIR spectrometer. All \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR and \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR were recorded in CDCl\u003csub\u003e3\u003c/sub\u003e on a Bruker Avance DRX 400 spectrometer. The spectrometer operates at 400 MHz for protons and 100 MHz for carbon. The chemical shifts are reported in ppm (\u003cem\u003eδ\u003c/em\u003e) at 298 K. All melting points in open capillary tubes were measured using a Model 9100 electrothermal apparatus and are uncorrected. AutoLab\u0026reg;/PGSTAT30 potentiostat/galvanostat (manufactured by Eco Chemie, Utrecht, The Netherlands) was used for cyclic voltammetry studies. Constant current electrolysis was performed using a DC POWER SUPPLY PS-305D power supply. The three-electrode system used for cyclic voltammetry measurements consisted of a glassy carbon disc (diameter 1.8 mm) as a working electrode, a stainless steel wire as an auxiliary electrode and Ag/AgCl (3 M) electrode as a reference electrode. All electrodes are provided by Azar Electrode Company (Iran). Alumina slurry was used to polish the glassy carbon electrode. Electrochemical synthesis of aryl-benzoquinone derivatives was performed in both batch and flow cells. The undivided cylindrical batch cell (100 mL) equipped with a large copper plate (5.5 cm x 2.5 cm) as the anode and a stainless steel rod with a length of 4 cm as a counter electrode (cathode). The continuous flow cell consists of a tube made of copper with a length of 28 cm and diameter of 1.3 cm (as the anode) and a stainless steel rod cathode with the same length and diameter of 1.2 cm in the center as the anode.\u003c/p\u003e \u003cp\u003eChemicals used in this study (aniline, 4-nitroaniline, 4-chloroaniline, 4-bromoaniline, 4-iodoaniline, 4-methoxyaniline, 4-fluoroaniline, hydroquinone and 2-methylhydroquinone) were purchased with purity higher than 98% from Aldrich and Merck. Buffer solutions were prepared according to the recommended procedures,\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e from analytical reagent grade chemicals purchased from Merck and Sigma without further purification.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of diazonium salt.\u003c/b\u003e Sulfuric acid (5 mL) was added to a well-stirred suspension of aniline derivatives (2 mmol) in H\u003csub\u003e2\u003c/sub\u003eO (10 mL). The reaction mixture was cooled to 0\u0026ndash;5\u0026deg;C in an ice bath. Then, a cooled solution of sodium nitrite (3 mmol) in H\u003csub\u003e2\u003c/sub\u003eO (5 mL) at 0\u0026ndash;5\u0026deg;C was added dropwise to the reaction mixture. At this time, the color of the solution turns yellow, which indicates the formation of diazonium salt. The synthesized diazonium solution (approximate concentration, 0.13 M) is placed in ice bath for use in the next step.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of aryl-benzoquinone derivatives in batch cell.\u003c/b\u003e For the synthesis of aryl-benzoquinone derivatives, first the aqueous solution of sodium acetate (0.15 M) (80 ml) containing hydroquinone (or 2-methylhydroquinone) (2 mmol) was electrolyzed in an undivided cell equipped with a copper plate anode and a stainless steel rod cathode under constant current (current density\u0026thinsp;=\u0026thinsp;0.5 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) (20 mA) for 10 minutes. After this period, 2 ml of the produced diazonium solution is added to the electrochemical cell. Then electrolysis continues and after every 6 minutes, 2 ml of diazonium solution is added to the cell, and these steps continue until the diazonium solution is exhausted. The precipitate was collected by filtration and washed several times with distilled water. The dried precipitate was dissolved in acetone and subjected to preparative TLC (silica gel 60 GF 254), \u003cem\u003en\u003c/em\u003e-hexane/ethyl acetate 45:15]. The products were isolated as yellow powder.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of aryl-benzoquinone derivatives using undivided tubular flow cell.\u003c/b\u003e An undivided tubular flow cell consists of a copper tube as the anode with an inner diameter of 1.3 cm and a length of 28 cm with an area of 114 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Inside the copper tube is a stainless steel rod with a diameter of 1.0 cm and a length of 28 cm, with an area of 87.9 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e as a cathode. In this cell, the cathode is surrounded by the anode and the solution is pumped from the bottom of the reactor to the top. The arrangement of anode and cathode is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In order to produce aryl-benzoquinone, a solution of sodium acetate (0.15 M) (80 mL) containing hydroquinone (2 mmol) along with aryl diazonium salt is passed through the flow cell at a constant flow rate using a syringe pump. The cell volume is 15.2 cm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e and the volume of the connecting tubes is 17.5 cm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eCharacteristics of the products\u003c/h2\u003e \u003cp\u003e \u003cb\u003e4'-Nitro-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eNO\u003csub\u003e4\u003c/sub\u003e) (\u003cb\u003eABQ1\u003c/b\u003e). Yellow solid; M.p. 152\u0026ndash;154\u0026deg;C (Lit. 137\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e6\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 8.30 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.7 Hz, 2H), 7.79 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.7 Hz, 2H), 7.10 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.3 Hz, 1H), 7.02 (s, 1H), 6.98 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.3 Hz, 1H); IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2924, 2853, 1726, 1664, 1588, 1517, 1462, 1350, 1095, 865, 695; MS (ESI) \u003cem\u003em/z\u003c/em\u003e (relative intensity); 231 (M\u0026thinsp;+\u0026thinsp;2H) (72), 230 (M\u0026thinsp;+\u0026thinsp;1) (10), 229 (M) (57), 183 (52), 149 (100).\u003c/p\u003e \u003cp\u003e \u003cb\u003e[1,1'-Biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ2\u003c/b\u003e). Yellow solid, M.p. 83\u0026ndash;86\u0026deg;C (Lit. 104\u0026ndash;106\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.48 (s, 1H), 7.38 (br, 5H), 7.08\u0026ndash;6.87 (m, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 187.6, 186.6, 146.5, 137.1, 136.4, 136.3, 132.7, 130.2, 129.2, 128.6; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2922, 1729, 1654, 1594, 1489, 1227, 1092, 843, 746, 696.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Methoxy-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e13\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) (\u003cb\u003eABQ3\u003c/b\u003e). Yellow solid, M.p. 108\u0026ndash;110\u0026deg;C (Lit. 108\u0026ndash;110\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.91 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.8 Hz, 2H), 7.50 (s, 1H), 7.03 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.8 Hz, 2H), 6.99 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.6 Hz, 2H), 3.92 (s, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 161.1, 158.2, 146.6, 133.0, 127.2, 123.9, 113.8, 55.1; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2959, 2839, 1601, 1581, 1499, 1465, 1441, 1306, 1251, 1180, 1148, 1042, 1024, 845, 825, 810, 782, 743, 555, 497.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Chloro-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eClO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ4\u003c/b\u003e). Yellow solid, M.p. 110\u0026ndash;112\u0026deg;C (Lit. 127\u0026ndash;129\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.51\u0026ndash;7.38 (br, 4H), 6.97\u0026ndash;6.77 (br, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.3, 186.3, 144.7, 137.0, 136.6, 136.4, 132.7, 131.0, 130.6, 128.9; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 3069, 1648, 1596, 1492, 1403, 1340, 1305, 1293, 1092, 1016, 976, 904, 855, 842, 822, 790, 728, 564, 508, 470, 419. MS (ESI) \u003cem\u003em/z\u003c/em\u003e (relative intensity); 218 (M) (11), 183 (m \u0026ndash; Cl) (100), 155 (19), 136 (21), 101 (14), 82 (38).\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Bromo-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eBrO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ5\u003c/b\u003e). Yellow solid; M.p. 84\u0026ndash;87\u0026deg;C (Lit. 100\u0026ndash;102\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.52 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 2H), 7.29 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.6 Hz, 2H), 6.80\u0026ndash;6.78 (m, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.3, 186.3, 144.8, 137.0, 136.38, 132.7, 131.8, 130.8, 125.0; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2926, 1651, 1593, 1489, 1400, 1339, 1292, 1098, 1073, 1012, 978, 906, 852, 789, 709, 501, 425.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Iodo-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eIO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ6\u003c/b\u003e). Yellow solid; M.p. 127\u0026ndash;130\u0026deg;C (Lit. 133\u0026ndash;135\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.73 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 2H), 7.15 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 2H), 6.81\u0026ndash;6.78 (m, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 186.3, 185.2, 143.9, 136.7, 136.0, 135.3, 131.6, 130.0, 129.8, 96.0; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2923, 1647, 1597, 1580, 1483, 1393, 1385, 1342, 1293, 1260, 1097, 1063, 1008, 975, 910, 849, 784, 698, 606, 548, 428.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Fluoro-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eFO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ7\u003c/b\u003e). M.p. 152\u0026ndash;155\u0026deg;C (Lit. 152\u0026ndash;155\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.46\u0026ndash;7.42 (m, 2H), 7.13\u0026ndash;6.79 (m, 5H); IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2924, 1660, 1603, 1508, 1413, 1376, 1330, 1235, 1235, 1162, 1107, 919, 845, 525, 420.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4-Methyl\u003c/b\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(and\u003c/span\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003e3-methyl\u003c/span\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e)\u003c/span\u003e \u003cb\u003e-4'-nitro-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e13\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eNO\u003csub\u003e4\u003c/sub\u003e) (\u003cb\u003eABQ8\u003c/b\u003e, two isomers). M.p. 131\u0026ndash;133\u0026deg;C; \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 8.25 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.7 Hz, 4H), 7.30 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.8 Hz, 4H), 6.86 (s, 1H), 6.84 (s, 1H), 6.81 (s, 1H), 6.78 (s, 1H), 2.10 (s, 3H), 2.07 (s, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.2, 186.8, 185.7, 147.9, 146.3, 142.6, 141.9, 139.3, 139.2, 136.7, 136.3, 134.1, 133.7, 133.5, 130.7, 130.3, 130.2, 123.6, 123.5, 16.4, 15.6; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 3114, 3068, 2925, 1656, 1592, 1518, 1348, 1304, 1137, 1091, 946, 865, 846, 749, 699, 410.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Chloro-4-methyl\u003c/b\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(and\u003c/span\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003e3-methyl\u003c/span\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e)\u003c/span\u003e \u003cb\u003e-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e13\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eClO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ9\u003c/b\u003e, two isomers); M.p. 64\u0026ndash;67\u0026deg;C; \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.35 (m, 8H), 6.77 (s, 1H), 6.72 (s, 1H), 6.64 (s, 1H), 6.62 (s, 1H), 2.07 (s, 3H), 2.04 (s, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.8, 187.3, 186.8, 186.5, 146.2, 145.8, 144.9, 144.6, 136.3, 136.2, 133.7, 133.3, 132.74, 132.68, 131.4, 131.0, 130.5, 129.5, 128.8, 128.7, 16.4, 15.5; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 3050, 2974, 1647, 1627, 1594, 1493, 1427, 1404, 1354, 1305, 1231, 1095, 1013, 923, 880, 839, 828, 738, 523, 446, 418.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Bromo-4-methyl\u003c/b\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(and\u003c/span\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003e3-methyl\u003c/span\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e)\u003c/span\u003e \u003cb\u003e-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e13\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eBrO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ10\u003c/b\u003e, two isomers); M.p. 84\u0026ndash;86\u0026deg;C;\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.60 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.3 Hz, 4H), 7.38 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.1 Hz, 4H), 6.87 (s, 1H), 6.81 (s, 1H), 6.73 (s, 1H), 6.71 (s, 1H), 2.16 (s, 3H), 2.13 (s, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.9, 187.3, 186.5, 186.8, 146.2, 145.9, 144.7, 137.4, 136.5, 136.4, 133.7, 133.3, 132.8, 132.7, 131.8, 131.7, 131.5, 131.2, 130.8, 130.7, 129.8, 124.8, 124.6, 16.4, 15.5; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2928, 1654, 1630, 1594, 1429, 1398, 1189, 1073, 1010, 917, 828, 458.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4'-Iodo-4-methyl\u003c/b\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e(and\u003c/span\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003e3-methyl\u003c/span\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e)\u003c/span\u003e \u003cb\u003e-[1,1'-biphenyl]-2,5-dione\u003c/b\u003e (C\u003csub\u003e13\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eIO\u003csub\u003e2\u003c/sub\u003e) (\u003cb\u003eABQ11\u003c/b\u003e, two isomers); \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 7.71 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.0 Hz, 4H), 7.14 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.0 Hz, 4H), 6.77 (s, 1H), 6.71 (s, 1H), 6.64 (s, 1H), 6.62 (s, 1H), 2.06 (s, 3H), 2.0 (s, 3H); \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e: 187.9, 187.4, 186.7, 186.5, 146.2, 145.9, 145.2, 144.8, 137.73, 137.69, 137.4, 136.5, 136.4, 133.8, 133.3, 132.73, 132.67, 131.3, 130.9, 130.8, 96.8, 16.4, 15.6; IR (KBr) (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): 2922, 1651, 1626, 1599, 1579, 1485, 1396, 1354, 1305, 1231, 1192, 1125, 1061, 1004, 919, 826, 801, 722, 670, 512, 471.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eElectrochemical studies.\u003c/strong\u003e In order to obtain the detailed information about the reaction between \u003cem\u003ep\u003c/em\u003e-benzoquinone and aryldiazonium salts, the electrochemical behavior of hydroquinone in the presence of 4-nitrobenzenediazonium sulfate was investigated. Figure 3, part I, curve a, shows the cyclic voltammogram of hydroquinone (\u003cstrong\u003eHQ\u003c/strong\u003e) (1 mM) in aqueous acidic/ethanol (50/50 v/v) mixture. It should be noted that to record this voltammogram, 1 ml of sulfuric acid (6.1 M) solution was added to 9 ml of \u003cstrong\u003eHQ\u003c/strong\u003e solution in a water (phosphate buffer, pH = 2, \u003cem\u003ec\u003c/em\u003e = 0.2 M)/ethanol mixture. As expected, the cyclic voltammogram shows a peak related to the oxidation of \u003cstrong\u003eHQ\u003c/strong\u003e to \u003cem\u003ep\u003c/em\u003e-benzoquinone (\u003cstrong\u003eBQ\u003c/strong\u003e) (A\u003csub\u003e1\u003c/sub\u003e) in the anodic scan, and a peak related to the reduction of \u003cstrong\u003eBQ\u003c/strong\u003e to \u003cstrong\u003eHQ\u003c/strong\u003e (C\u003csub\u003e1\u003c/sub\u003e) in the cathodic scan. When instead of the sulfuric acid solution, 1 ml of diazonium solution containing sulfuric acid (6.1 M) (see experimental section) is added to the \u003cstrong\u003eHQ\u003c/strong\u003e solution, there is a large change in the cyclic voltammogram. (Fig. 3, part I, curves b and c). In these voltammograms, a wide range of potentials is scanned to identify all species that are oxidized or reduced. In the anodic scan and in the first cycle (curve b), the voltammogram shows two well-defined anodic peaks at potentials of 0.64 and 1.28 V. These peaks are related to the oxidation of \u003cstrong\u003eHQ\u003c/strong\u003e (A\u003csub\u003e1\u003c/sub\u003e) and nitrite ion (A\u003csub\u003eN\u003c/sub\u003e)\u003csup\u003e41\u003c/sup\u003e (available in diazonium solution), respectively. In this situation, two weak cathode peaks (C\u003csub\u003e1\u003c/sub\u003e and C\u003csub\u003e2\u003c/sub\u003e) can be seen in the reverse cathodic scan at potentials of 0.83 and 0.62 V, respectively. Cathodic peak C\u003csub\u003e1\u003c/sub\u003e is the counterpart of peak A\u003csub\u003e1\u003c/sub\u003e. In the second cycle of the potential sweep (curve c), a new anodic peak (A\u003csub\u003e2\u003c/sub\u003e) appears at 0.85 V. This peak is the counterpart of peak C\u003csub\u003e2\u003c/sub\u003e. It should be noted that the same electrochemical behavior observed in the cyclic voltammetry of \u003cstrong\u003eHQ\u003c/strong\u003e at different pH values (pH \u0026lt; 8) in the presence of aryldiazonium solution. Since the diazonium solution contains sulfuric acid and changes the pH of the \u003cstrong\u003eHQ\u003c/strong\u003e solution, and on the other hand, the \u003cstrong\u003eHQ\u003c/strong\u003e/\u003cstrong\u003eBQ\u003c/strong\u003e redox system is pH dependent,\u003csup\u003e42\u003c/sup\u003e in the experiment conducted in the absence of diazonium ion (Fig. 2, part I, curve a), sulfuric acid (6.1 M) was added to the \u003cstrong\u003eHQ\u003c/strong\u003e solution so that the pH of the \u003cstrong\u003eHQ\u003c/strong\u003e solution in the absence of diazonium (curve a) became equal to the pH of the \u003cstrong\u003eHQ\u003c/strong\u003e solution in the presence of diazonium (curves b and c).\u003c/p\u003e\n\u003cp\u003eBased on the obtained electrochemical data as well as the spectroscopic data of the product, we propose the following mechanism (Fig. 4, part I) for the oxidation of \u003cstrong\u003eHQ\u003c/strong\u003e in the presence of nitrobenzenediazonium sulfate. Accordingly, at the anode surface, \u003cstrong\u003eHQ\u003c/strong\u003e loses two electrons and is oxidized to \u003cstrong\u003eBQ\u003c/strong\u003e. At the same time, a homolytic dediazonation reaction occurs in the solution.\u003csup\u003e38,43,44\u003c/sup\u003e As a result of this reaction, aryldiazonium salt (\u003cstrong\u003eDAZ\u003c/strong\u003e) is converted into aryl radical (\u003cstrong\u003eArR\u003c/strong\u003e) and dinitrogen molecule. The reaction between \u003cstrong\u003eBQ\u003c/strong\u003e and \u003cstrong\u003eArR\u003c/strong\u003e leads to the formation of intermediate \u003cstrong\u003eINT\u003c/strong\u003e, which in the next step by losing an electron becomes the final product, nitro-arylbenzoquinone (\u003cstrong\u003eABQ1\u003c/strong\u003e). According to the proposed mechanism, the anodic (A\u003csub\u003e2\u003c/sub\u003e) and cathodic (C\u003csub\u003e2\u003c/sub\u003e) peaks are related to the \u003cstrong\u003eINT\u003c/strong\u003e/\u003cstrong\u003eABQ1\u003c/strong\u003e redox couple. It seems that in the absence of reducing agents and metal ions, hemolytic dediazonation of diazonium salt is due to its reaction with \u003cstrong\u003eHQ\u003c/strong\u003e.\u003csup\u003e38\u003c/sup\u003e This reaction is shown in Fig. 4, part II.\u003c/p\u003e\n\u003cp\u003eAs can be seen, electron transfer between aryldiazonium salt and \u003cstrong\u003eHQ\u003c/strong\u003e causes the conversion of aryldiazonium salt to aryl radical. On the other hand, as a result of this reaction, \u003cstrong\u003eHQ\u003c/strong\u003e is converted into semiquinone (\u003cstrong\u003eSQ\u003c/strong\u003e) by losing an electron. Regarding the oxidation of \u003cstrong\u003eINT\u003c/strong\u003e and its conversion to the final product (\u003cstrong\u003eABQ1\u003c/strong\u003e), two paths seem possible. The first route is the direct oxidation of \u003cstrong\u003eINT\u003c/strong\u003e on the electrode surface and the second route is its indirect oxidation through the reaction with \u003cstrong\u003eSQ\u003c/strong\u003e. In contrast to the results obtained in acidic, neutral, and low-alkaline solutions, research conducted at pH ≥ 10 suggests that the reaction follows a different course.\u003c/p\u003e\n\u003cp\u003eFigure 3, part II, curve a, shows the cyclic voltammogram of \u003cstrong\u003eHQ\u003c/strong\u003e (1 mM) in aqueous (bicarbonate buffer, pH 10, \u003cem\u003ec\u003c/em\u003e = 0.2 M)/ethanol (50/50 v/v) mixture after addition of 1 mL sulfuric acid (6.1 M). The voltammogram recorded under these conditions is similar to the one shown in part I, curve a, except that the peak potentials are shifted towards the negative potentials. When 1 ml of the diazonium solution is added to the \u003cstrong\u003eHQ\u003c/strong\u003e solution, there is not much change in the cyclic voltammogram. (Fig. 3, part II, curve b) and only its reversibility decreases. This phenomenon may be caused by the fouling of the electrode surface attributed to the immobilization (or adsorption) of the aryl radicals on the surface of the glassy carbon electrode, which reduces the efficiency of the electrode.\u003csup\u003e45–47\u003c/sup\u003e It seems that as the solution pH increases, the diazonium salt is converted to diazoate and diazohydroxide species, which are much more unstable. Successive hemolytic cleavage of these compounds produces a radical that reacts with the glassy carbon surface.\u003csup\u003e48\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eSince the copper anode has been used in macro-scale electrolysis, it is necessary to slightly modify the proposed mechanism in Fig. 4 for the copper anode. In such conditions, it seems that the oxidation of \u003cstrong\u003eHQ\u003c/strong\u003e to \u003cstrong\u003eBQ\u003c/strong\u003e is done through its electron transfer reaction with copper ions (Fig. 5). Also, these ions can oxidize \u003cstrong\u003eINT\u003c/strong\u003e to \u003cstrong\u003eABQ1\u003c/strong\u003e. On the other hand, the formed cuprous ions (Cu\u003csup\u003e+\u003c/sup\u003e) can contribute to the reduction of the aryldiazonium salt (\u003cstrong\u003eDAZ\u003c/strong\u003e) to the aryl radical (\u003cstrong\u003eArR\u003c/strong\u003e) (Fig. 5). The use of a copper anode and the catalytic activity of copper ions in the synthesis of aryl-benzoquinones (\u003cstrong\u003eABQ\u003c/strong\u003e) is one of the novel and important aspects of this study. The divalent copper ions generated from the anodic oxidation can oxidize \u003cstrong\u003eHQ\u003c/strong\u003e to \u003cstrong\u003eBQ\u003c/strong\u003e. On the other hand, the monovalent copper ions generated from this reaction can reduce \u003cstrong\u003eDAZ\u003c/strong\u003e to \u003cstrong\u003eArR\u003c/strong\u003e and themselves be oxidized to Cu\u003csup\u003e2+\u003c/sup\u003e. On the other hand, the Cu\u003csup\u003e2+\u003c/sup\u003e ions can act as an oxidant to convert \u003cstrong\u003eINT\u003c/strong\u003e to the final product, \u003cstrong\u003eABQ1\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eThe cyclic voltammograms of the product (\u003cstrong\u003eABQ1\u003c/strong\u003e) after separation and purification is shown in Fig. 6. In order to further identify the structure of the product and its electrochemical properties, these voltammograms were recorded in two different conditions. In this figure, to record the voltammogram a, first the potential was scanned from 0.0 V towards more positive values (anodic scan), which led to the appearance of a cyclic voltammogram for a Nernstian reversible process. It should be noted that when the starting potential (0 V) is applied, \u003cstrong\u003eABQ1\u003c/strong\u003e is reduced to its corresponding nitro-arylhydroquinone (\u003cstrong\u003eAHQ1\u003c/strong\u003e) at the electrode surface.\u003c/p\u003e\n\u003cp\u003eThe presence of cathodic current at the starting potential (0 V) confirms the reduction of \u003cstrong\u003eABQ1.\u003c/strong\u003e Therefore, during potential scanning, the species present on the electrode surface is NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eAHQ\u003c/strong\u003e. Accordingly, anodic peak Ap\u003csub\u003e1\u003c/sub\u003e is related to the oxidation of NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eAHQ\u003c/strong\u003e to \u003cstrong\u003eABQ1\u003c/strong\u003e, and cathodic peak C\u003csub\u003ep1\u003c/sub\u003e is its counterpart and related to the reduction of \u003cstrong\u003eABQ1\u003c/strong\u003e to NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eAHQ\u003c/strong\u003e (Fig. 7).\u003c/p\u003e\n\u003cp\u003eIn this study, when the cathodic scan is performed first, the shape of the voltammogram changes completely (Fig. 6, curve b). Under these conditions, the cyclic voltammogram shows an irreversible cathodic peak (C\u003csub\u003eN\u003c/sub\u003e) and a two reversible redox systems, A\u003csub\u003ep2\u003c/sub\u003e/C\u003csub\u003ep2\u003c/sub\u003e and A\u003csub\u003ep3\u003c/sub\u003e/C\u003csub\u003ep3\u003c/sub\u003e. As discussed, when the starting potential (0.0 V) is applied, \u003cstrong\u003eABQ1\u003c/strong\u003e is reduced to NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eAHQ\u003c/strong\u003e at the electrode surface. Therefore, during the cathodic potential scan, peak C\u003csub\u003eN\u003c/sub\u003e corresponds to the reduction of the nitro group in the NO\u003csub\u003e2\u003c/sub\u003e-\u003cstrong\u003eAHQ\u003c/strong\u003e molecule to the corresponding hydroxylamine (NHOH-\u003cstrong\u003eAHQ\u003c/strong\u003e). A\u003csub\u003ep2\u003c/sub\u003e and C\u003csub\u003ep2\u003c/sub\u003e peaks are attributed to NHOH-\u003cstrong\u003eAHQ\u003c/strong\u003e/nitroso-arylhydroquinone (NO-\u003cstrong\u003eAHQ\u003c/strong\u003e) redox couple. Based on this A\u003csub\u003ep3\u003c/sub\u003e and C\u003csub\u003ep3\u003c/sub\u003e peaks are attributed to NO-\u003cstrong\u003eAHQ\u003c/strong\u003e/NO-\u003cstrong\u003eABQ\u003c/strong\u003e (Fig. 7).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOptimization of reaction conditions.\u003c/strong\u003e In this part, the effect of factors affecting the yield and purity of the products such as applied current density, amount of electricity, type of electrode and cell and synthesis method has been investigated. The optimization for the synthesis of \u003cstrong\u003eABQ1\u003c/strong\u003e was carried out by one-factor-at-a-time (OFAT) approach. The amount of electricity consumption is an important factor in the yield and purity of the product. For the synthesis of \u003cstrong\u003eABQ1\u003c/strong\u003e, first the aqueous solution of sodium acetate (0.15 M) (80 ml) containing \u003cstrong\u003eHQ\u003c/strong\u003e (2 mmol) was electrolyzed in an undivided cell equipped with a copper plate anode and a stainless steel rod cathode under constant current (20 mA) for 10 minutes. After this period, 1 ml of the produced 4-nitrobenzenediazonium chloride solution is added to the electrochemical cell. The results of studies is shown in Table 1, entries 1–4. The results show that increasing the amount of electricity consumed from 70 to 190 C increases the yield, but a further increase in electricity decreases the yield of \u003cstrong\u003eABQ1\u003c/strong\u003e production. Over-oxidation of the product may be the reason for this decrease. Another notable point is that the electricity consumption in these syntheses is lower than the theoretical value, which is due to the oxidation of \u003cstrong\u003eHQ\u003c/strong\u003e by excess nitrite ions present in the diazonium solution\u003csup\u003e49,50\u003c/sup\u003e as well as the catalytic activity of copper ions (Fig. 5). The volume of 4-nitrobenzenediazonium chloride solution \"added per injection\" is another parameter that was optimized, while the total amount of diazonium added was kept constant. Entries 1 and 5–7 show that increasing the sample volume from 0.5 to 3 mL increases production yield. The role of solution pH in the yield of \u003cstrong\u003eABQ1\u003c/strong\u003e was also investigated (entries 1 and 8–10). It was found that pH of \u003cstrong\u003eHQ\u003c/strong\u003e solution has no significant effect on \u003cstrong\u003eABQ1\u003c/strong\u003e yield. It seems that increasing the strongly acidic solution containing diazonium salt to the \u003cstrong\u003eHQ\u003c/strong\u003e solution suppresses the effect of hydroquinone solution pH. Entries 3 and 11–14 show the effect of applied current on \u003cstrong\u003eABQ1\u003c/strong\u003e production yield. The results show that the yield of \u003cstrong\u003eABQ1\u003c/strong\u003e increases with increasing applied current due to the increased over-potential for \u003cstrong\u003eHQ\u003c/strong\u003e oxidation and then decreases slightly due to over-oxidation of the product, intermediates or solvent. Furthermore, increasing over-potential increases energy consumption and associated costs. Again, the effect of the volume of 4-nitrobenzene diazonium chloride solution \"added per injection\" was investigated when the electricity consumption was 190 coulombs (entries 3 and 15, 16). The role of anode material in the yield of \u003cstrong\u003eABQ1\u003c/strong\u003e was also investigated (entries 17–23). It was found that the highest yield is achieved when copper is used as anode.\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eOptimization of effective parameters in \u003cstrong\u003eABQ1\u003c/strong\u003e synthesis in batch cell.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"9\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEntry\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElectrolysis time (min)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElectricity consumption (C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eIncrement time\u003csup\u003ea\u003c/sup\u003e (min)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample volume (mL)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eInitial pH of hydroquinone solution\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eApplied current (mA)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAnode\u003c/p\u003e\n \u003cp\u003ematerial\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eYield\u003c/p\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e46.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e52.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e46.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e47.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e57.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e55.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e228\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSS\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003egraphite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e41.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esodium acetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eTime interval between two injections. \u003csup\u003eb\u003c/sup\u003e0.15 M. \u003csup\u003ec\u003c/sup\u003eStainless steel.\u003c/p\u003e\n\u003cp\u003eAs mentioned in the previous section and also in Fig. 5, the use of copper anode is one of the innovative aspects of this study due to the catalytic behavior of copper ions. The Cu\u003csup\u003e2+\u003c/sup\u003e ions can oxidize \u003cstrong\u003eHQ\u003c/strong\u003e to \u003cstrong\u003eBQ\u003c/strong\u003e. On the other hand, the generated Cu\u003csup\u003e+\u003c/sup\u003e ions can reduce \u003cstrong\u003eDAZ\u003c/strong\u003e to \u003cstrong\u003eArR\u003c/strong\u003e and themselves be oxidized to Cu\u003csup\u003e2+\u003c/sup\u003e. On the other hand, Cu\u003csup\u003e2+\u003c/sup\u003e ions can also convert \u003cstrong\u003eINT\u003c/strong\u003e to \u003cstrong\u003eABQ1\u003c/strong\u003e. Such conditions make it possible to achieve maximum yield when using copper anode. At the end of this section, the cell type was evaluated. For this purpose, a divided cell has been used in optimal conditions (entry 6), and the obtained results indicate a decrease in yield from 71–54%. Since the direct reduction of diazonium salts at the cathode surface and the formation of aryl radicals is possible,\u003csup\u003e51\u003c/sup\u003e the decrease in yield is a confirmation that the formation of aryl radicals is also performed through direct reduction of diazonium salts at the cathode. Therefore, the use of a divided cell reduces the yield. Based on this result, we propose Fig. 8 for the cathodic generation (direct) of aryl radicals. The proposed mechanism is categorized as convergent paired mechanism in which the intermediates generated at the anode and cathode interact with each other to form the final product.\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eAfter optimizing the reaction conditions for the synthesis of \u003cstrong\u003eABQ1\u003c/strong\u003e, we investigated the substrate range of different aryldiazoniums and hydroquinones. The results of these studies are shown in Table 2. To this end, we reacted a series of aryldiazonium salts with electron-donating or electron-withdrawing groups at the \u003cem\u003epara\u003c/em\u003e-position of the benzene ring with hydroquinone as well as 2-methylhydroquinone, leading to the synthesis of the corresponding aryl-benzoquinones in moderate to good yields. Notably, as expected, when unsymmetrical 2-methyl hydroquinone was used, an inseparable mixture of isomers was obtained in moderate yield.\u003c/p\u003e\n\u003cdiv\u003e\n \u003cdiv align=\"left\"\u003eThese syntheses have also been performed using a flow cell and the effect of factors affecting the yield and purity of the products such as applied current, flow rate, amount of electricity, and time increment have been investigated. The results of studies is shown in Table 3.\u0026nbsp;\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eOptimization of effective parameters in \u003cstrong\u003eABQ1\u003c/strong\u003e synthesis in flow cell.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"8\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEntry\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElectrolysis time (min)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElectricity consumption (C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eIncrement time (min)\u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample volume (mL)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFlow rate (mL/min)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eApplied current (mA)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eYield\u003c/p\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e66.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e216\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e47.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e42.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e57.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eTime interval between two injections.\u003c/p\u003e\n\u003cp\u003eThe arrangement of anode and cathode in the flow cell is shown in Fig. 2. Accordingly, the anode is a copper tube and the cathode is a stainless steel rod. As show in Table 3, the best yield, 88.2% (entry 4) is obtained when the applied current is 20 mA, the flow rate is 80 ml/min, the electricity consumption is 72 C, the sample volume of diazonium salt per injection is 2 mL and the injection interval is 6 minutes.\u003c/p\u003e\n\u003cp\u003eIn another cell design, the shape of the cathode and anode in the flow cell was changed. In this way, a stainless steel tube was used as the cathode and a copper rod as the anode. It should be noted that the dimensions of the tube and rod used in this flow cell are similar to Fig. 2. The synthesis of \u003cstrong\u003eABQ1\u003c/strong\u003e with this new cell configuration provides a yield of 52.3%, which is lower than 88.2%.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work an eco-friendly electrochemical method was developed for the synthesis of some aryl-benzoquinone derivatives. The synthesis of these compounds was carried out through direct electrolysis of aqueous solution containing hydroquinone in the presence of aryl-diazonium salts in both simple batch and a homemade continuous-flow cells. One of the important points in this work is the easy and cheap preparation of all the equipment needed in both types of cells from common commercial sources. This method is very economical due to the use of electricity instead of chemical reagents and is performed in mild conditions and in water without using toxic solvents and catalysts. In addition, in this work, the electrochemical behavior of hydroquinone in the presence of aryldiazonium salt was investigated, and based on the results, a detailed mechanism for the electrochemical Meerwein arylation was presented.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of competing interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study available from the corresponding author on request.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors acknowledge the Bu-Ali Sina University Research Council and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for their support of this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDN: supervision, project administration, resources, writing-review \u0026amp; editing. 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Grafting of diazonium salts on surfaces: Application to biosensors. \u003cem\u003eBiosensors\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 4 (2020).\u003c/li\u003e\n\u003cli\u003eJohn, P. B. The kinetics and mechanism of oxidation of hydroquinone and chlorohydroquinone in the presence of nitrous acid in aqueous acid solution. \u003cem\u003eJ. Chem. Soc., Perkin Trans. 2\u003c/em\u003e 957-60 (1994).\u003c/li\u003e\n\u003cli\u003eKhalafi, L. \u0026amp; Rafiee, M. Kinetic study of the oxidation and nitration of catechols in the presence of nitrous acid ionization equilibria. \u003cem\u003eJ. Hazard. Mater.\u003c/em\u003e \u003cstrong\u003e174\u003c/strong\u003e, 801-806 (2010).\u003c/li\u003e\n\u003cli\u003eZeng, X. The strategies towards electrochemical generation of aryl radicals, \u003cem\u003eChem. Eur. J.\u003c/em\u003e \u003cstrong\u003e30\u003c/strong\u003e, e202402220 (2024).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 2","content":"\u003cp\u003eTable 2 is available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Aryldiazonium salt, Continuous-flow cell, Copper anode, Cyclic voltammetry, Hydroquinone","lastPublishedDoi":"10.21203/rs.3.rs-6111261/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6111261/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAn electrochemical Meerwein arylation reaction was reported for the synthesis of aryl-benzoquinone derivatives. In this work, efficient electrochemical synthesis of aryl-benzoquinone derivatives by direct electrolysis of aqueous solution containing hydroquinone and aryldiazonium salts in batch and a homemade continuous-flow cells is reported. In the batch system, the products were obtained in a simple undivided cell equipped with a copper anode and a stainless steel cathode. In the continuous flow system, the products were obtained simply by passing hydroquinone and the aryldiazonium salt through a tube made of copper with a stainless steel rod in the center. All equipment required in both cell types is obtained from common commercial sources. This protocol is green and cost-effective due to the use of electricity and is performed under mild and safe conditions without the use of toxic solvents and catalysts.\u003c/p\u003e","manuscriptTitle":"Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-10 12:29:48","doi":"10.21203/rs.3.rs-6111261/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-21T05:29:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-18T06:00:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"26172619405936815115492545912630417257","date":"2025-04-07T11:49:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-07T03:01:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"266584379398215422455212256068698780129","date":"2025-04-07T02:26:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-05T02:11:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-04T05:38:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-03-25T10:33:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a0e3a965-516f-11e9-9e20-12b504df345a","owner":[],"postedDate":"April 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":46787475,"name":"Physical sciences/Chemistry/Organic chemistry/Methodology"},{"id":46787476,"name":"Physical sciences/Chemistry/Organic chemistry/Reaction mechanisms"},{"id":46787477,"name":"Physical sciences/Chemistry/Synthesis"},{"id":46787478,"name":"Physical sciences/Chemistry/Synthesis/Flow chemistry"},{"id":46787479,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"}],"tags":[],"updatedAt":"2025-05-19T16:03:06+00:00","versionOfRecord":{"articleIdentity":"rs-6111261","link":"https://doi.org/10.1038/s41598-025-02504-y","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-05-17 15:58:10","publishedOnDateReadable":"May 17th, 2025"},"versionCreatedAt":"2025-04-10 12:29:48","video":"","vorDoi":"10.1038/s41598-025-02504-y","vorDoiUrl":"https://doi.org/10.1038/s41598-025-02504-y","workflowStages":[]},"version":"v1","identity":"rs-6111261","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6111261","identity":"rs-6111261","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}