Solvent-Free Recyclable Heterogeneous Copper(I) oxide/Zinc oxide (Cu2O/ZnO) nanoflake: C-O Coupling of Phenols With Aryl halides

Solvent-Free Recyclable Heterogeneous Copper(I) oxide/Zinc oxide (Cu2O/ZnO) nanoflake: C-O Coupling of Phenols With Aryl halides | 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 Research Article Solvent-Free Recyclable Heterogeneous Copper(I) oxide/Zinc oxide (Cu2O/ZnO) nanoflake: C-O Coupling of Phenols With Aryl halides Mona Hosseini-Sarvari, Hossein Sheikh, Fatemeh Moeini This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2542002/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Following the need for a straightforward and efficient catalyst for the C-O coupling reaction, we proposed Cu 2 O/ZnO as a new heterogeneous catalyst candidate. We developed a simple green procedure for O-arylation of various phenols from differently substituted aryl halides (X = I, Br, Cl), that was not only solvent and ligand-free but also well-tolerated by various functional groups along with high-yield corresponded products. In addition, the described method benefits from air stability and catalyst recyclability. O-arylation C-O coupling Solvent-free catalyst Copper(I) oxide/Zinc oxide Figures Figure 1 Figure 2 Figure 3 Introduction Many agrochemicals, pharmaceuticals, and polymeric molecules contain diaryl ether linkage. ( 1 , 2 ) Because of its presence in many biologically active natural products, such as anti-HIV chloropeptins, anti-tumor bouvardins, cyclopeptides, and weedicides, the search for their efficient synthesis continues to be of real interest. ( 3 ) As shown in Fig. 1 , some biologically active molecules with diaryl ether links are biologically active. As the traditional approach in the Ullmann method, diaryl ethers are made by combining aryl halides with phenols with a base (potassium or sodium hydroxide) and stoichiometric (or greater) amounts of copper at elevated temperatures (125–300°C) in polar solvents (typically pyridine, DMF, NMP), which are not conducive to the construction of complex molecules. ( 4 – 7 ) To more conveniently synthesize such compounds, Buchwald ( 8 ), Hartwig ( 4 ), Beller ( 9 ), and others reported palladium-catalyzed coupling reactions for diaryl ether synthesis, but these methods still have some limitations. These processes are limited by the use of high reaction temperatures and expensive and noncommercial ligands, whose preparation requires tedious multistep processes that limit their applicability. ( 9 ) The low cost and high efficiency of copper in coupling reactions have made it an ideal replacement for palladium catalysts in Ullmann reactions.( 10 ) As Cu/ligand systems have been developed, these reactions have attracted continuing interest due to their low air and moisture sensitivity and high functional group tolerance. ( 6 ) These methods not only suffer from harsh reaction conditions (longer reaction times, higher temperatures, the requirement of a higher quantity of ligand (50 mol%) and quaternary ammonium salts especially fluorides) but also use highly polar toxic solvents and an excess amount of catalyst causes of more attempt for simple procedures. Since heterogeneous catalysts are easy to recover and recycle, they have gained popularity for fine chemical synthesis in recent years. For the Ullman reaction, a variety of heterogeneous copper catalysts have been used.( 11 – 13 ) For the synthesis of the ether linkage, air-resistant, ligand-free, inexpensive, recyclable catalytic systems are highly desirable due to the economic limitations, the excess use of ligands and additives, and the difficulty of synthesis of the reported catalysts. Results And Discussion As part of our continuing attempts to broaden the scope of nanometal oxides as a catalyst, the efficiency of Cu 2 O/ZnO nanoflake in the synthesis of propargyl amines and N-arylation of nitrogen-containing heterocycles was reported by our group.( 14 – 16 ) Desirous to make these reactions more environmentally benign, we embarked on optimization studies to perform this reaction in the aqueous medium. As will be explained in the current work, we operated Cu 2 O/ZnO nanoflake catalyst for a C-O coupling reaction under solvent-free conditions reaction. Synthesis and characterization of this catalyst were performed by FT-IR spectroscopy, ICP analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area measurement. Table 1 shown some of these results. For example, SEM and TEM image of Cu 2 O/ZnO nanoflake are depicted in Fig. 2 . Table 1 Characterization data for Cu2O/ZnO nanoflake. Column 1 Column 2 XRD Crystallite sizes of Cu 2 O and ZnO, were 21 and 30 nm respectively. BET surface area 14.74 m 2 /g Pore size distribution 2.41 nm TEM 32 nm ICP Contents of Cu and Zn were 47.01 and 21.77% (w/w) respectively. The extraordinary stability of this catalyst toward heat, oxygen, and moisture prompted us to test it as a recyclable, ligand and solvent-free catalyst for the synthesis of diaryl ether derivatives from the corresponding aryl halides and phenols. The coupling of iodobenzene 1a (0.5 mmol) with phenol 2 (0.5 mmol) was investigated as a model reaction to optimize the reaction conditions (Tables 2 and 3 ). Several solvents were examined during our optimization studies, and the best results were obtained under solvent-free conditions (entry 7). Some solvents such as ethanol, toluene, DMF, DMSO, THF, and water, reduced the catalyst's efficiency (Table 2 , entries 1–5). The solvent-free condition seems to be crucial in this reaction based on this observation. Among a wide variety of bases (e.g., KOH, K 2 CO 3 , K 3 PO 4 , Cs 2 CO 3 , NaOAc, KF, Na t - Bu, and NEt 3 ), Cs 2 CO 3 is found the best one (Table 2 , entry 7). Without a catalyst, the reaction failed to proceed despite a prolonged reaction time (Table 2 , entry 15). A catalytic amount of nano Cu 2 O/ZnO nanoflake (0.01 g) is sufficient to obtain the desired product in a high yield. An increase in the amount of catalyst had no effect on the efficiency of the reaction, while a decrease in the amount of catalyst resulted in an obvious decries in the product yield (Table 2 , entry 16–17). Following, we investigated the effect of the temperature, the results are shown in Table 3 . As shown in Tables 2 and 3 , the best results were obtained using Cu 2 O/ZnO nanoflakes (0.01 g) with Cs 2 CO 3 as the base under solventless conditions at 120°C. This is the first time Cu 2 O/ZnO nanoflakes have been used as a catalyst for C-O coupling reactions. Table 2 . The optimization of the reaction conditions. 1 Entry Solvent Base Time/h Yield% 2 1 DMSO Cs 2 CO 3 24 0 2 DMF Cs 2 CO 3 24 0 3 3 H 2 O Cs 2 CO 3 24 0 4 3 EtOH Cs 2 CO 3 24 0 5 3 THF Cs 2 CO 3 24 0 6 3 CH 3 CN Cs 2 CO 3 6 90 7 Solvent-free Cs 2 CO 3 3 95 8 Solvent-free KOH 24 0 9 Solvent-free K 2 CO 3 24 0 10 Solvent-free Na 2 CO 3 24 0 11 Solvent-free K 3 PO 4 24 0 12 Solvent-free NaOAc 24 0 13 Solvent-free KF 24 0 14 Solvent-free NatBu 24 0 15 4 Solvent-free Cs 2 CO 3 24 0 16 5 Solvent-free Cs 2 CO 3 9 60 17 6 Solvent-free Cs 2 CO 3 3 95 1 Reaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu 2 O/ZnO nanoflake (0.01 g), Cs 2 CO 3 (1 mmol), and solvent (1 mL) at 120 ˚C. 2 Isolated yield. 3 Under reflux condition. 4 Without catalyst. 5 Using 0.005 g of Cu 2 O/ZnO nanoflake. 6 Using 0.02 g of Cu 2 O/ZnO nanoflake. Table 3 The optimization of temperature. 1 Entry Solvent Base Time/h Yield% 2 1 DMSO Cs 2 CO 3 24 0 2 DMF Cs 2 CO 3 24 0 3 3 H 2 O Cs 2 CO 3 24 0 4 3 EtOH Cs 2 CO 3 24 0 5 3 THF Cs 2 CO 3 24 0 6 3 CH 3 CN Cs 2 CO 3 6 90 7 Solvent-free Cs 2 CO 3 3 95 8 Solvent-free KOH 24 0 9 Solvent-free K 2 CO 3 24 0 10 Solvent-free Na 2 CO 3 24 0 11 Solvent-free K 3 PO 4 24 0 12 Solvent-free NaOAc 24 0 13 Solvent-free KF 24 0 14 Solvent-free NatBu 24 0 15 4 Solvent-free Cs 2 CO 3 24 0 16 5 Solvent-free Cs 2 CO 3 9 60 17 6 Solvent-free Cs 2 CO 3 3 95 1 Reaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu 2 O/ZnO nanoflake (0.01 g), Cs 2 CO 3 (1 mmol), and solvent (1 mL) at 120 ˚C. 2 Isolated yield. 3 Under reflux condition. 4 Without catalyst. 5 Using 0.005 g of Cu 2 O/ZnO nanoflake. 6 Using 0.02 g of Cu 2 O/ZnO nanoflake. To explore the scope and generality of the nano Cu 2 O/ZnO nanoflake in C-O cross-coupling reactions, aryl halides and phenols possessing a wide range of functional groups were used in combination with optimized reaction conditions. The results of the study are summarized in Table 4 . It is evident from Table 4 that all the reactions were very clean and that the products obtained were in good to excellent yields. An increase in yield was observed when electron-donating groups such as methyl, ethyl, and methoxy were applied at the ortho, meta, and para positions of the phenol part (Table 4 , entries 2–5), compared to electron-withdrawing groups at the para position (Table 4 , entries 9, 10). Metal-mediated arylations pose a challenge to Ortho-substituted phenols. 15 Gratefully, Ortho-substituted phenol did not hinder the reaction and afforded a good yield of the corresponding product (Table 4 , entries 4, 7). It is worth noting, even after long reaction times, 4-nitrophenol, which bears a strong electron-withdrawing group, field to produce the desired O-arylation reaction, which our previous studies have indicated the same thing is in accordance with earlier studies 16 (Table 4 , entry 11). Therefore, electron-donating groups at para positions on aryl halides decreased the yield (Table 4 , entry 12), however, in the case of electron-withdrawing groups at the para position the yield increased (Table 4 , entries 13, 15, 17, 20). Generally, as compared to aryl iodides, aryl bromides and chlorides were less reactive and yielded moderate to good yields (Table 4 , entries 14–20). It should also be pointed out the reaction was highly chemoselective, for example, the reaction between 1-bromo-4-chlorobenzene, 1-bromo-4-fluorobenzene, and phenol gave 4-chlorodiphenyl ether and 4-fluordiphenyl ether as only products, respectively (Table 4 , entries 18, 19). In Table 5 , we summarize the results of the investigation of the reusability of copper catalysts. After centrifuging and drying the catalyst, there was directly used for subsequent catalytic reactions. Even after five cycles, there was no significant decrease in catalyst activity. The recovered Cu 2 O/ZnO nanoflake contained the following composition after 5th successive reactions: 45.12% (w/w) of Cu, and 21.01% (w/w) of Zn according to ICP analysis, which is comparable to the initial value of Cu 47% (w/w) and Zn 21.75% (w/w). After 5 consecutive cycles of recycling, Cu 2 O/ZnO nanoflakes were analyzed to assess their stability, and XRD patterns before and after five recycling cycles were observed in Fig. 3. Table 5 Reuse-ability of the recovered catalyst. 1 Run Product (%) 2 Catalyst recovery (%) 1 95 98 2 94 96 3 94 96 4 92 94 5 90 92 1 Reaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu 2 O/ZnO nanoflake (0.01 g), Cs 2 CO 3 (1 mmol), and under solvent-free condition. 2 Isolated yield. Methods Synthesis of nano Cu 2 O: General procedure A solution of CuSO 4 dissolved in 50 ml distilled water was steered and heated to 70 ̊C in a water bath for 4 min. Then, N 2 H 4 .H 2 O 1mol/l was slowly added to the suspension until lots of red/brown precipitates were observed. The products were collected by filtration, washed three times with deionized water and absolute ethanol, and dried for 3 hours at 60 ̊C. Synthesis of nano ZnO: General procedure NH 4 OH was added to a solution of Zn(OAc) 2 .2H 2 O and PEG 2000 in water drop wisely at reflux condition for 6 hours. After forming the ZnOH 4 2− intermediate, ZnO crystals form at the interface between substrate and solution by the dehydration of ZnOH 4 2− . After, centrifuging and washing the product with deionized water and absolute ethanol, 90 ml of deionized water was added to the mixture and the resulting solution was refluxed for 8 hours. In the next step, the above solution was cooled to room temperature, centrifuged, and washed. Finally, the nano-rods powders were dried at 100 ̊C in an oven. Synthesis of Cu 2 O/ZnO nanoflake: General procedure To a solution of CuSO 4 in 50 ml distilled water commercially ZnO was added then the above solution was sonicated to achieve a uniform suspension. To ensure that maximum Cu 2+ ions were absorbed on the surface of ZnO the suspension was vigorously steered at room temperature for 50 min. Next, for the removal of free Cu 2+ ions, the mixture was centrifuged and washed with a solution of deionized water and absolute ethanol 3 times. In the next step, the mixture was a suspension in 30 ml of deionized water and heated to 70 ̊C for 5 min. Then N 2 H 4 .H 2 O 1 mol l-1 was added into the suspension drop wisely till lots of red/brown precipitates were observed. The products were filtered after 30 minutes of steering in the water bath, washed 3 times with deionized water and absolute ethanol, and finally dried for 3 hours in the air at 60 ̊C. ICP analysis shows that the Cu and Zn content in the catalyst was 47% and 21.77% respectively. Synthesis of diaryl ether: General procedure A mixture of aryl halide (0.5 mmol), phenol (0.5 mmol), Cs 2 CO 3 (1 mmol), and Cu 2 O/ZnO nanoflake (0.010 g) was put into a preheated oil bath at 120°C for an appropriate period of time. The reaction was found not to be sensitive to air and moisture; hence there was no need for an inert atmosphere. Ethyl acetate (25 mL) was added to the reaction mixture and stirred at room temperature to ensure the product was removed from the catalyst surface. We centrifuged the reaction mixture and washed it with ethyl acetate several times to separate the catalyst. The centrifugate was concentrated under reduced pressure to afford the crude product, which after chromatography on silica gel (n-hexane/ethyl acetate 10/1) gave the corresponding products. Catalyst characterization NMR spectra were recorded on a Bruker Avance DPX-250 ( 1 H NMR 250 MHz and 13 C NMR 62.9 MHz) in pure deuterated solvents with tetramethylsilane (TMS) as internal standards. Scanning electron micrographs were obtained by SEM instrumentation (SEM, XL-30 FEG SEM, Philips, at 20 kV). A transmission electron microscopy TEM was also employed for the TEM (Philips CM10) image. X-ray diffraction (XRD, D8, Advance, Bruker, axs) was used for the characterization of the heterogeneous catalyst. Metal contents were obtained by an ICP analyzer (Varian, vista-pro). The purity determination of the substrates and reaction monitoring was accomplished by TLC on silica gel PolyGram SILG/UV254 plates. Column chromatography was carried out on short columns of silica gel 60 (70–230 mesh) in glass columns (2–3 cm diameter) using 15–30 grams of silica gel per one gram of crude mixture. Chemical materials were purchased from Fluka, Aldrich, and Merck Companies. Conclusion In conclusion, we have presented Cu 2 O/ZnO nanoflake as a suitable catalyst for the O-arylation of various phenols from differently substituted aryl halides (X = Cl, Br, I). This new method showed particular advantages such as (i) using this approach is simple and does not require any protection from air or moisture (ii) excellent coupling yields are achieved. Both electron-withdrawing and electron-donating substituents can be used in ortho-, meta-, or para-positions of the phenol (iii) procedure is efficient in terms of cost and safety since it does not require any additional ligands (iv) the process has been fulfilled under solvent-free conditions and (v) without significant loss of catalytic activity, it can be reusable up to 5 times. Declarations Acknowledgments. The authors gratefully acknowledge the support of this work by the Shiraz University Council. Ethical Approval Ethical approvals is not applicable Competing interests Competing of interest is not applicable Authors' contributions All authors contribute equally in this work. Funding Shiraz University. Availability of data and materials There is no conflict of interest. References Yang Q, Zhao Y, Ma D. Cu-Mediated Ullmann-Type Cross-Coupling and Industrial Applications in Route Design, Process Development, and Scale-up of Pharmaceutical and Agrochemical Processes. Organic Process Research & Development. 2022. Chen T, Xiong H, Yang J-F, Zhu X-L, Qu R-Y, Yang G-F. Diaryl ether: A privileged scaffold for drug and agrochemical discovery. Journal of Agricultural and Food Chemistry. 2020;68(37):9839–77. Swapna K, Murthy SN, Jyothi MT, Nageswar YVD. Recyclable heterogeneous copper oxide on alumina catalyzed coupling of phenols and alcohols with aryl halides under ligand-free conditions. Organic & Biomolecular Chemistry. 2011;9(17):5978–88. Kikelj D. Recent progress in diaryl ether synthesis. Synthesis. 2006;2006(14):2271–85. Cai Q, Zhou W. Ullmann-Ma Reaction: Development, Scope and Applications in Organic Synthesis. Chinese Journal of Chemistry. 2020;38(8):879–93. Bhunia S, Pawar GG, Kumar SV, Jiang Y, Ma D. Selected Copper-Based Reactions for C – N, C – O, C – S, and C – C Bond Formation. Angewandte Chemie International Edition. 2017;56(51):16136–79. Beletskaya IP, Cheprakov AV. Copper in cross-coupling reactions: The post-Ullmann chemistry. Coordination Chemistry Reviews. 2004;248(21–24):2337–64. Aranyos A, Old DW, Kiyomori A, Wolfe JP, Sadighi JP, Buchwald SL. Novel electron-rich bulky phosphine ligands facilitate the palladium-catalyzed preparation of diaryl ethers. Journal of the American Chemical Society. 1999;121(18):4369–78. Hu T, Schulz T, Torborg C, Chen X, Wang J, Beller M, et al. Efficient palladium-catalyzed coupling reactions of aryl bromides and chlorides with phenols. Chemical communications. 2009(47):7330–2. Khalili D, Rezaei M, Koohgard M. Ligand-free copper-catalyzed O-arylation of aryl halides using impregnated copper ferrite on mesoporous graphitic carbon nitride as a robust and magnetic heterogeneous catalyst. Microporous and Mesoporous Materials. 2019;287:254–63. Chen Z, Jiang Y, Zhang L, Guo Y, Ma D. Oxalic diamides and tert-butoxide: Two types of ligands enabling practical access to alkyl aryl ethers via Cu-catalyzed coupling reaction. Journal of the American Chemical Society. 2019;141(8):3541–9. Bartlett ME, Zhu Y, Gaffney UB, Lee J, Wu M, Sharew B, et al. Cu-Catalyzed Phenol O‐Methylation with Methylboronic Acid. European Journal of Organic Chemistry. 2021;2021(41):5661–4. He J, Chen C, Fu GC, Peters JC. Visible-light-induced, copper-catalyzed three-component coupling of alkyl halides, olefins, and trifluoromethylthiolate to generate trifluoromethyl thioethers. ACS catalysis. 2018;8(12):11741–8. Hosseini-Sarvari M, Khanivar A, Moeini F. Magnetically recoverable nano Pd/Fe3O4/ZnO catalyst: preparation, characterization, and application for the synthesis of 2-oxazolines and benzoxazoles. Journal of Materials Science. 2015;50(8):3065–74. Hosseini-Sarvari M, Moeini F. Nano copper (i) oxide–zinc oxide catalyzed coupling of aldehydes or ketones, secondary amines, and terminal alkynes in solvent-free conditions. New Journal of Chemistry. 2014;38(2):624–35. Hosseini-Sarvari M, Moeini F. Nano copper (I) oxide/zinc oxide catalyzed N-arylation of nitrogen-containing heterocycles with aryl halides and arylboronic acids in air. RSC advances. 2014;4(14):7321–9. Tables Table 4 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files SI.docx Table4.docx Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-2542002","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":175854311,"identity":"0a01ea36-1ccd-4379-a017-d5cb0d871ee0","order_by":0,"name":"Mona 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the biologically active molecules with a diaryl ether linkage.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/107bff851a959fc59fae16d1.png"},{"id":32995826,"identity":"008cc8b5-0625-4636-b2ce-54148ccd5611","added_by":"auto","created_at":"2023-02-15 18:59:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":379663,"visible":true,"origin":"","legend":"\u003cp\u003ea) SEM and b) TEM images of Cu2O/ZnO nanoflake.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/976d802bf5736ff4a44566b7.png"},{"id":32995828,"identity":"b7037def-b28a-4104-b047-4a2fea047bf7","added_by":"auto","created_at":"2023-02-15 18:59:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":197725,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eThe XRD pattern of Cu2O/ZnO nanoflake: a) before and b) after 5 times reuses\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/96f22dcdbb2f1b8a3ac0eb1b.png"},{"id":33596430,"identity":"87110135-0401-4c8b-ac7c-bc97f2104f53","added_by":"auto","created_at":"2023-03-01 02:29:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":927700,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/88f2bc62-6985-4860-94fd-1e09ea4bdf5c.pdf"},{"id":32995879,"identity":"671c5dd9-568d-48c6-b13d-00562070c51d","added_by":"auto","created_at":"2023-02-15 19:07:27","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":648496,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/f54a56cd973085750b70b5df.docx"},{"id":32995833,"identity":"e6f1d244-7062-4372-9c35-2c5289dcf9d9","added_by":"auto","created_at":"2023-02-15 18:59:29","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":260706,"visible":true,"origin":"","legend":"","description":"","filename":"Table4.docx","url":"https://assets-eu.researchsquare.com/files/rs-2542002/v1/f2e8adb2dc32cc05a451c560.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Solvent-Free Recyclable Heterogeneous Copper(I) oxide/Zinc oxide (Cu2O/ZnO) nanoflake: C-O Coupling of Phenols With Aryl halides","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMany agrochemicals, pharmaceuticals, and polymeric molecules contain diaryl ether linkage. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) Because of its presence in many biologically active natural products, such as anti-HIV chloropeptins, anti-tumor bouvardins, cyclopeptides, and weedicides, the search for their efficient synthesis continues to be of real interest. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, some biologically active molecules with diaryl ether links are biologically active.\u003c/p\u003e \u003cp\u003eAs the traditional approach in the Ullmann method, diaryl ethers are made by combining aryl halides with phenols with a base (potassium or sodium hydroxide) and stoichiometric (or greater) amounts of copper at elevated temperatures (125\u0026ndash;300\u0026deg;C) in polar solvents (typically pyridine, DMF, NMP), which are not conducive to the construction of complex molecules. (\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eTo more conveniently synthesize such compounds, Buchwald (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e), Hartwig (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e), Beller (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e), and others reported palladium-catalyzed coupling reactions for diaryl ether synthesis, but these methods still have some limitations. These processes are limited by the use of high reaction temperatures and expensive and noncommercial ligands, whose preparation requires tedious multistep processes that limit their applicability. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe low cost and high efficiency of copper in coupling reactions have made it an ideal replacement for palladium catalysts in Ullmann reactions.(\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e) As Cu/ligand systems have been developed, these reactions have attracted continuing interest due to their low air and moisture sensitivity and high functional group tolerance. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e) These methods not only suffer from harsh reaction conditions (longer reaction times, higher temperatures, the requirement of a higher quantity of ligand (50 mol%) and quaternary ammonium salts especially fluorides) but also use highly polar toxic solvents and an excess amount of catalyst causes of more attempt for simple procedures. Since heterogeneous catalysts are easy to recover and recycle, they have gained popularity for fine chemical synthesis in recent years. For the Ullman reaction, a variety of heterogeneous copper catalysts have been used.(\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e) For the synthesis of the ether linkage, air-resistant, ligand-free, inexpensive, recyclable catalytic systems are highly desirable due to the economic limitations, the excess use of ligands and additives, and the difficulty of synthesis of the reported catalysts.\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003eAs part of our continuing attempts to broaden the scope of nanometal oxides as a catalyst, the efficiency of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake in the synthesis of propargyl amines and N-arylation of nitrogen-containing heterocycles was reported by our group.(\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e) Desirous to make these reactions more environmentally benign, we embarked on optimization studies to perform this reaction in the aqueous medium. As will be explained in the current work, we operated Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake catalyst for a C-O coupling reaction under solvent-free conditions reaction. Synthesis and characterization of this catalyst were performed by FT-IR spectroscopy, ICP analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area measurement. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shown some of these results. For example, SEM and TEM image of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacterization data for Cu2O/ZnO nanoflake.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColumn 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColumn 2\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eXRD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCrystallite sizes of Cu\u003csub\u003e2\u003c/sub\u003eO and ZnO, were 21 and 30 nm respectively.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBET surface area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.74 m\u003csup\u003e2\u003c/sup\u003e/g\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePore size distribution\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.41 nm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTEM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32 nm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eICP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eContents of Cu and Zn were 47.01 and 21.77% (w/w) respectively.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe extraordinary stability of this catalyst toward heat, oxygen, and moisture prompted us to test it as a recyclable, ligand and solvent-free catalyst for the synthesis of diaryl ether derivatives from the corresponding aryl halides and phenols.\u003c/p\u003e \u003cp\u003eThe coupling of iodobenzene \u003cb\u003e1a\u003c/b\u003e (0.5 mmol) with phenol \u003cb\u003e2\u003c/b\u003e (0.5 mmol) was investigated as a model reaction to optimize the reaction conditions (Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Several solvents were examined during our optimization studies, and the best results were obtained under solvent-free conditions (entry 7). Some solvents such as ethanol, toluene, DMF, DMSO, THF, and water, reduced the catalyst's efficiency (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, entries 1\u0026ndash;5). The solvent-free condition seems to be crucial in this reaction based on this observation. Among a wide variety of bases (e.g., KOH, K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, K\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, NaOAc, KF, Na\u003csup\u003e\u003cem\u003et\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e-\u003c/em\u003eBu, and NEt\u003csub\u003e3\u003c/sub\u003e), Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e is found the best one (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, entry 7). Without a catalyst, the reaction failed to proceed despite a prolonged reaction time (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, entry 15). A catalytic amount of nano Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake (0.01 g) is sufficient to obtain the desired product in a high yield. An increase in the amount of catalyst had no effect on the efficiency of the reaction, while a decrease in the amount of catalyst resulted in an obvious decries in the product yield (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, entry 16\u0026ndash;17). Following, we investigated the effect of the temperature, the results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. As shown in Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the best results were obtained using Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflakes (0.01 g) with Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e as the base under solventless conditions at 120\u0026deg;C. This is the first time Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflakes have been used as a catalyst for C-O coupling reactions.\u003c/p\u003e \u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e The optimization of the reaction conditions. \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u003cimg 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\"\u003e\u003c/sup\u003e\u003cbr\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"465\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003eEntry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eBase\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003eTime/h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003eYield%\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eDMSO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eDMF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e3\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e4\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eEtOH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e5\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eTHF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e6\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eCH\u003csub\u003e3\u003c/sub\u003eCN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e95\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eKOH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eK\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eNaOAc\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eKF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eNatBu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e15\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e16\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"24.353448275862068%\"\u003e\n \u003cp\u003e17\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"28.448275862068964%\"\u003e\n \u003cp\u003eSolvent-free\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"18.31896551724138%\"\u003e\n \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"15.948275862068966%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.931034482758621%\"\u003e\n \u003cp\u003e95\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" valign=\"top\" width=\"100%\"\u003e\n \u003cp\u003e\u003csup\u003e1\u003c/sup\u003eReaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO\u0026nbsp;nanoflake\u0026nbsp;(0.01 g), Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (1 mmol), and solvent (1 mL) at 120 ˚C.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003csup\u003e2\u003c/sup\u003eIsolated yield.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003csup\u003e3\u003c/sup\u003eUnder reflux condition.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003csup\u003e4\u003c/sup\u003e Without catalyst.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e5\u003c/sup\u003eUsing 0.005 g of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO\u0026nbsp;nanoflake.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003csup\u003e6\u003c/sup\u003eUsing 0.02 g of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\u003cbr\u003e\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe optimization of temperature. \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEntry\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBase\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTime/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eYield%\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDMSO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDMF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEtOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTHF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCH\u003csub\u003e3\u003c/sub\u003eCN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eKOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNaOAc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eKF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNatBu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent-free\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003csup\u003e1\u003c/sup\u003eReaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake (0.01 g), Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (1 mmol), and solvent (1 mL) at 120 ˚C.\u003c/p\u003e \u003cp\u003e\u003csup\u003e2\u003c/sup\u003eIsolated yield.\u003c/p\u003e \u003cp\u003e\u003csup\u003e3\u003c/sup\u003eUnder reflux condition.\u003c/p\u003e \u003cp\u003e\u003csup\u003e4\u003c/sup\u003e Without catalyst.\u003c/p\u003e \u003cp\u003e\u003csup\u003e5\u003c/sup\u003eUsing 0.005 g of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake.\u003c/p\u003e \u003cp\u003e\u003csup\u003e6\u003c/sup\u003eUsing 0.02 g of Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo explore the scope and generality of the nano Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake in C-O cross-coupling reactions, aryl halides and phenols possessing a wide range of functional groups were used in combination with optimized reaction conditions. The results of the study are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It is evident from Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e that all the reactions were very clean and that the products obtained were in good to excellent yields.\u003c/p\u003e \u003cp\u003eAn increase in yield was observed when electron-donating groups such as methyl, ethyl, and methoxy were applied at the ortho, meta, and para positions of the phenol part (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 2\u0026ndash;5), compared to electron-withdrawing groups at the para position (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 9, 10). Metal-mediated arylations pose a challenge to Ortho-substituted phenols.\u003csup\u003e15\u003c/sup\u003e Gratefully, Ortho-substituted phenol did not hinder the reaction and afforded a good yield of the corresponding product (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 4, 7). It is worth noting, even after long reaction times, 4-nitrophenol, which bears a strong electron-withdrawing group, field to produce the desired O-arylation reaction, which our previous studies have indicated the same thing is in accordance with earlier studies\u003csup\u003e16\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entry 11). Therefore, electron-donating groups at para positions on aryl halides decreased the yield (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entry 12), however, in the case of electron-withdrawing groups at the para position the yield increased (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 13, 15, 17, 20). Generally, as compared to aryl iodides, aryl bromides and chlorides were less reactive and yielded moderate to good yields (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 14\u0026ndash;20). It should also be pointed out the reaction was highly chemoselective, for example, the reaction between 1-bromo-4-chlorobenzene, 1-bromo-4-fluorobenzene, and phenol gave 4-chlorodiphenyl ether and 4-fluordiphenyl ether as only products, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, entries 18, 19).\u003c/p\u003e \u003cp\u003eIn Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, we summarize the results of the investigation of the reusability of copper catalysts. After centrifuging and drying the catalyst, there was directly used for subsequent catalytic reactions. Even after five cycles, there was no significant decrease in catalyst activity. The recovered Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake contained the following composition after 5th successive reactions: 45.12% (w/w) of Cu, and 21.01% (w/w) of Zn according to ICP analysis, which is comparable to the initial value of Cu 47% (w/w) and Zn 21.75% (w/w). After 5 consecutive cycles of recycling, Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflakes were analyzed to assess their stability, and XRD patterns before and after five recycling cycles were observed in Fig.\u0026nbsp;3.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eReuse-ability of the recovered catalyst.\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRun\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProduct (%)\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCatalyst recovery (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e92\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003e1\u003c/sup\u003eReaction conditions: phenol (0.5 mmol), iodobenzene (0.5 mmol), Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake (0.01 g), Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (1 mmol), and under solvent-free condition.\u003c/p\u003e \u003cp\u003e \u003csup\u003e2\u003c/sup\u003eIsolated yield.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eSynthesis of nano Cu\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO: General procedure\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA solution of CuSO\u003csub\u003e4\u003c/sub\u003e dissolved in 50 ml distilled water was steered and heated to 70 ̊C in a water bath for 4 min. Then, N\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e.H\u003csub\u003e2\u003c/sub\u003eO 1mol/l was slowly added to the suspension until lots of red/brown precipitates were observed. The products were collected by filtration, washed three times with deionized water and absolute ethanol, and dried for 3 hours at 60 ̊C.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of nano ZnO: General procedure\u003c/b\u003e \u003c/p\u003e \u003cp\u003eNH\u003csub\u003e4\u003c/sub\u003eOH was added to a solution of Zn(OAc)\u003csub\u003e2\u003c/sub\u003e.2H\u003csub\u003e2\u003c/sub\u003eO and PEG 2000 in water drop wisely at reflux condition for 6 hours. After forming the ZnOH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e intermediate, ZnO crystals form at the interface between substrate and solution by the dehydration of ZnOH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e. After, centrifuging and washing the product with deionized water and absolute ethanol, 90 ml of deionized water was added to the mixture and the resulting solution was refluxed for 8 hours. In the next step, the above solution was cooled to room temperature, centrifuged, and washed. Finally, the nano-rods powders were dried at 100 ̊C in an oven.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of Cu\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO/ZnO nanoflake: General procedure\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo a solution of CuSO\u003csub\u003e4\u003c/sub\u003e in 50 ml distilled water commercially ZnO was added then the above solution was sonicated to achieve a uniform suspension. To ensure that maximum Cu\u003csup\u003e2+\u003c/sup\u003e ions were absorbed on the surface of ZnO the suspension was vigorously steered at room temperature for 50 min. Next, for the removal of free Cu\u003csup\u003e2+\u003c/sup\u003e ions, the mixture was centrifuged and washed with a solution of deionized water and absolute ethanol 3 times. In the next step, the mixture was a suspension in 30 ml of deionized water and heated to 70 ̊C for 5 min. Then N\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e.H\u003csub\u003e2\u003c/sub\u003eO 1 mol l-1 was added into the suspension drop wisely till lots of red/brown precipitates were observed. The products were filtered after 30 minutes of steering in the water bath, washed 3 times with deionized water and absolute ethanol, and finally dried for 3 hours in the air at 60 ̊C. ICP analysis shows that the Cu and Zn content in the catalyst was 47% and 21.77% respectively.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of diaryl ether: General procedure\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA mixture of aryl halide (0.5 mmol), phenol (0.5 mmol), Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (1 mmol), and Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake (0.010 g) was put into a preheated oil bath at 120\u0026deg;C for an appropriate period of time. The reaction was found not to be sensitive to air and moisture; hence there was no need for an inert atmosphere. Ethyl acetate (25 mL) was added to the reaction mixture and stirred at room temperature to ensure the product was removed from the catalyst surface. We centrifuged the reaction mixture and washed it with ethyl acetate several times to separate the catalyst. The centrifugate was concentrated under reduced pressure to afford the crude product, which after chromatography on silica gel (n-hexane/ethyl acetate 10/1) gave the corresponding products.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCatalyst characterization\u003c/b\u003e \u003c/p\u003e \u003cp\u003eNMR spectra were recorded on a Bruker Avance DPX-250 (\u003csup\u003e1\u003c/sup\u003eH NMR 250 MHz and \u003csup\u003e13\u003c/sup\u003eC NMR 62.9 MHz) in pure deuterated solvents with tetramethylsilane (TMS) as internal standards. Scanning electron micrographs were obtained by SEM instrumentation (SEM, XL-30 FEG SEM, Philips, at 20 kV). A transmission electron microscopy TEM was also employed for the TEM (Philips CM10) image. X-ray diffraction (XRD, D8, Advance, Bruker, axs) was used for the characterization of the heterogeneous catalyst. Metal contents were obtained by an ICP analyzer (Varian, vista-pro). The purity determination of the substrates and reaction monitoring was accomplished by TLC on silica gel PolyGram SILG/UV254 plates. Column chromatography was carried out on short columns of silica gel 60 (70\u0026ndash;230 mesh) in glass columns (2\u0026ndash;3 cm diameter) using 15\u0026ndash;30 grams of silica gel per one gram of crude mixture. Chemical materials were purchased from Fluka, Aldrich, and Merck Companies.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, we have presented Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO nanoflake as a suitable catalyst for the O-arylation of various phenols from differently substituted aryl halides (X\u0026thinsp;=\u0026thinsp;Cl, Br, I). This new method showed particular advantages such as (i) using this approach is simple and does not require any protection from air or moisture (ii) excellent coupling yields are achieved. Both electron-withdrawing and electron-donating substituents can be used in ortho-, meta-, or para-positions of the phenol (iii) procedure is efficient in terms of cost and safety since it does not require any additional ligands (iv) the process has been fulfilled under solvent-free conditions and (v) without significant loss of catalytic activity, it can be reusable up to 5 times.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the support of this work by the Shiraz University Council.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthical approvals is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompeting of interest is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contribute equally in this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eShiraz University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere is no conflict of interest.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYang Q, Zhao Y, Ma D. Cu-Mediated Ullmann-Type Cross-Coupling and Industrial Applications in Route Design, Process Development, and Scale-up of Pharmaceutical and Agrochemical Processes. Organic Process Research \u0026amp; Development. 2022.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen T, Xiong H, Yang J-F, Zhu X-L, Qu R-Y, Yang G-F. Diaryl ether: A privileged scaffold for drug and agrochemical discovery. Journal of Agricultural and Food Chemistry. 2020;68(37):9839\u0026ndash;77.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSwapna K, Murthy SN, Jyothi MT, Nageswar YVD. Recyclable heterogeneous copper oxide on alumina catalyzed coupling of phenols and alcohols with aryl halides under ligand-free conditions. Organic \u0026amp; Biomolecular Chemistry. 2011;9(17):5978\u0026ndash;88.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKikelj D. Recent progress in diaryl ether synthesis. Synthesis. 2006;2006(14):2271\u0026ndash;85.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai Q, Zhou W. Ullmann-Ma Reaction: Development, Scope and Applications in Organic Synthesis. Chinese Journal of Chemistry. 2020;38(8):879\u0026ndash;93.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBhunia S, Pawar GG, Kumar SV, Jiang Y, Ma D. Selected Copper-Based Reactions for C \u0026ndash; N, C \u0026ndash; O, C \u0026ndash; S, and C \u0026ndash; C Bond Formation. Angewandte Chemie International Edition. 2017;56(51):16136\u0026ndash;79.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBeletskaya IP, Cheprakov AV. Copper in cross-coupling reactions: The post-Ullmann chemistry. Coordination Chemistry Reviews. 2004;248(21\u0026ndash;24):2337\u0026ndash;64.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAranyos A, Old DW, Kiyomori A, Wolfe JP, Sadighi JP, Buchwald SL. Novel electron-rich bulky phosphine ligands facilitate the palladium-catalyzed preparation of diaryl ethers. Journal of the American Chemical Society. 1999;121(18):4369\u0026ndash;78.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu T, Schulz T, Torborg C, Chen X, Wang J, Beller M, et al. Efficient palladium-catalyzed coupling reactions of aryl bromides and chlorides with phenols. Chemical communications. 2009(47):7330\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhalili D, Rezaei M, Koohgard M. Ligand-free copper-catalyzed O-arylation of aryl halides using impregnated copper ferrite on mesoporous graphitic carbon nitride as a robust and magnetic heterogeneous catalyst. Microporous and Mesoporous Materials. 2019;287:254\u0026ndash;63.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen Z, Jiang Y, Zhang L, Guo Y, Ma D. Oxalic diamides and tert-butoxide: Two types of ligands enabling practical access to alkyl aryl ethers via Cu-catalyzed coupling reaction. Journal of the American Chemical Society. 2019;141(8):3541\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBartlett ME, Zhu Y, Gaffney UB, Lee J, Wu M, Sharew B, et al. Cu-Catalyzed Phenol O‐Methylation with Methylboronic Acid. European Journal of Organic Chemistry. 2021;2021(41):5661\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe J, Chen C, Fu GC, Peters JC. Visible-light-induced, copper-catalyzed three-component coupling of alkyl halides, olefins, and trifluoromethylthiolate to generate trifluoromethyl thioethers. ACS catalysis. 2018;8(12):11741\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosseini-Sarvari M, Khanivar A, Moeini F. Magnetically recoverable nano Pd/Fe3O4/ZnO catalyst: preparation, characterization, and application for the synthesis of 2-oxazolines and benzoxazoles. Journal of Materials Science. 2015;50(8):3065\u0026ndash;74.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosseini-Sarvari M, Moeini F. Nano copper (i) oxide\u0026ndash;zinc oxide catalyzed coupling of aldehydes or ketones, secondary amines, and terminal alkynes in solvent-free conditions. New Journal of Chemistry. 2014;38(2):624\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosseini-Sarvari M, Moeini F. Nano copper (I) oxide/zinc oxide catalyzed N-arylation of nitrogen-containing heterocycles with aryl halides and arylboronic acids in air. RSC advances. 2014;4(14):7321\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 4 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"O-arylation, C-O coupling, Solvent-free catalyst, Copper(I) oxide/Zinc oxide","lastPublishedDoi":"10.21203/rs.3.rs-2542002/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2542002/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFollowing the need for a straightforward and efficient catalyst for the C-O coupling reaction, we proposed Cu\u003csub\u003e2\u003c/sub\u003eO/ZnO as a new heterogeneous catalyst candidate. We developed a simple green procedure for O-arylation of various phenols from differently substituted aryl halides (X\u0026thinsp;=\u0026thinsp;I, Br, Cl), that was not only solvent and ligand-free but also well-tolerated by various functional groups along with high-yield corresponded products. In addition, the described method benefits from air stability and catalyst recyclability.\u003c/p\u003e","manuscriptTitle":"Solvent-Free Recyclable Heterogeneous Copper(I) oxide/Zinc oxide (Cu2O/ZnO) nanoflake: C-O Coupling of Phenols With Aryl halides","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-02-15 18:59:18","doi":"10.21203/rs.3.rs-2542002/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1f8d564f-6f4e-4358-9862-22c9a502446a","owner":[],"postedDate":"February 15th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-03-01T02:29:24+00:00","versionOfRecord":[],"versionCreatedAt":"2023-02-15 18:59:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2542002","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2542002","identity":"rs-2542002","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}