Hydrogenation of nitrile groups in HNBR with a rhodium catalyst

Hydrogenation of nitrile groups in HNBR with a rhodium catalyst | 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 Hydrogenation of nitrile groups in HNBR with a rhodium catalyst Minghui Liu, Ziying Xiong, Hui Wang, Linbao Zhang, Qinmin Pan, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5852950/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 Functional polymer materials show a variety of functional properties, such as chemical reactivity, photosensitivity, conductivity, catalysis, biocompatibility and so on. The polymer containing amine group can be used in many fields such as organic polymer catalyst carrier, sewage adsorption treatment, medicine and pharmacy, biological engineering, etc. We note that the amination of small nitrile groups has formed a relatively mature system, but similar reactions for macromolecular raw materials have not been reported. Based on this, the catalytic hydrogenation of nitrile groups on macromolecules was achieved for the first time, the nitrile group was successfully reduced to an amino group, and an efficient and stable hydrogenation catalytic system of HNBR was successfully developed. The reactivity of the catalytic system was studied, considering the catalyst/polymer ratio, reaction temperature, and hydrogen pressure. The optimal experimental conditions were obtained. The study successfully established a corresponding catalytic system to produce HNBR with a controlled amount of ACN. Within a reaction time of 5 hours at 60°C and 500 psig H 2 , the nitrile content in HNBR systems could be reduced from 40% to less than 10%, without the formation of side products like secondary amines. This reduction process involved the conversion of nitrile groups into primary amines, and a possible mechanism for this transformation was proposed for the first time. The formation of gel during nitrile reduction was also investigated, and a potential mechanism was suggested. Various additives were tested, and it was found that some of them effectively slowed down or prevented gel formation. Among these additives, triphenylphosphine (TPP) was identified as the most effective one. Physical sciences/Chemistry/Materials chemistry Physical sciences/Chemistry/Organic chemistry Physical sciences/Chemistry/Polymer chemistry hydrogenated nitrile butadiene rubber nitrile hydrogenation hydrido rhodium complex triphenylphosphine gel mechanism Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction The route of catalytic hydrogenation on unsaturated double bonds or benzene rings plays an important role in improving the properties of polymers; one of the desirable properties attributed to hydrogenated polymers is their excellent thermal and oxidative stability. For example, poly(cyclohexylidene) (PCHE) prepared by catalytic hydrogenation of polystyrene (PS) has not only improved heat resistance and aging resistance but greatly reduced its optical coefficient so that it can be used in the field of optical media. Hydrogenated Styrene Butadiene Rubber (HSBR) can be obtained by hydrogenating the double bonds present in Styrene Butadiene Rubber (SBR); it exhibits improved thermal, oxidation, ozone, and UV (ultraviolet) resistance. [1–4] Hydrogenated-nitrile-butadiene-rubber (HNBR) is a special rubber prepared by catalytic hydrogenation of Nitrile-butadiene-rubber (NBR). It has excellent mechanical, thermo-oxidative, and chemical-resistant properties over a wide operating temperature range, particularly after long-term exposure to heat, oil, and chemicals. At present, solution hydrogenation is the main method of HNBR preparation. In addition, Wang's research group has carried out in-depth research on the emulsion hydrogenation method. [5–8] Moreover, HNBR has been extensively adopted in industrial sealing for oil field exploration and processing, as well as in rolls used in steel and paper mills. The acrylonitrile (ACN) content serves as a defining factor for the grading of NBR and HNBR. The polarity of the ACN content influences various properties, such as oil and solvent resistance and abrasion resistance. Higher ACN content enhances the resistance to fuels and polar lubricants in HNBR, albeit at the expense of its low-temperature properties. Higher ACN content leads to improvements in properties such as air/gas impermeability, abrasion resistance, tensile strength, and compatibility with other polar polymers. Conversely, lower ACN content reduces fuel and polar lubricant resistance while enhancing the low-temperature properties of HNBR. The hydrogenation of nitrile is a prevalent industrial process employed in producing amines. Amines find extensive utilization in various applications, including solvents, pharmaceutical intermediates, raw materials for resins, textile additives, disinfectants, rubber stabilizers, corrosion inhibitors, and the manufacturing of detergents and plastics. [9] Although multiple methods are available for amine production, catalytic hydrogenation of nitriles is the most widespread. Nowadays, functional polymers have gained significant attention in various fields. One notable area of interest is the introduction of amine groups onto the polystyrene molecular chain. This modification is particularly valuable due to the amine group's strong electron absorption and ease of protolization. Consequently, functional polymers with amine groups hold immense potential in applications, including the separation and purification of organic drugs, biomedical polymers, polymer catalyst carriers, sewage adsorption treatment, and numerous other fields. Currently, there is a wealth of research on reducing small molecule nitriles, particularly focusing on the use of transition metal catalysts. In 1969, Dewhirst pioneered using RuCl 2 (PPh 3 ) 3 and RuH 2 (PMePh 2 ) 4 as catalysts for the hydrogenation of nitriles, utilizing ruthenium as the transition metal. Subsequently, precious metal catalysts, including platinum, palladium, ruthenium, rhodium, and other central atom-based catalysts [10–13] , have been widely employed in this field. Different types of catalyst applications have also been reported. Beller et al. [14–18] have achieved important results in developing pincer metal catalysts for the hydrogenation of aliphatic and aromatic nitriles, and they have also investigated a variety of base metal catalysts supported on metal/non-metallic oxides. In response to the economic considerations associated with precious metal catalysts, the Milstein group [19] endeavored to develop a variety of base metal catalysts with iron and cobalt as the central atom, building upon the knowledge gained from Beller's research. Utilizing the diphoshinoamine(PNP)-iron pincer catalyst and PNNH-cobalt pincer catalyst as a foundation, a novel iron complex was designed, featuring a dibenzylamine PNP ligand and an absence of CO ligands. Additionally, researchers such as Masatoshi Yoshimura et al. [20] have explored the use of bimetallic catalysts for nitrile reduction. It was discovered that the hydrogenation of pentonitrile, in the presence of acetic acid as a solvent and a catalyst consisting of a 1:5 ratio of gold and palladium atoms supported by alumina, exhibited high selectivity towards primary amine formation. Dai [21] gave up the previous idea of designing complex base metal catalysts and instead chose to study a dual catalytic system, HN[CH 2 CH 2 P( i -Pr) 2 ] 2 ( i PrPNHP) ligand to regulate the selectivity of nitrile hydrogenation, and simply treated CoBr 2 with NaHBEt 3 to generate cobalt particles, which can catalyze the hydrogenation of nitrile to primary amine. It has high selectivity and wide functional group tolerance. Juhász [22] investigated the application of supported lanthanum catalysts in nitrile hydrogenation reactions, which showed surprisingly high activity and selectivity. At present, the application research of this catalyst has been extended from benzene nitrile to other nitriles (benzyl cyanide, cinnamonitrile, adipic dinitrile). In this text, we extensively investigate the possibility of employing tris(triisopropylphosphine) hydrido rhodium (I) as a catalyst for hydrogenating HNBR nitrile. This study focuses on using low catalyst concentration under mild reaction conditions to achieve the purpose of macromolecular cyanogen reduction, which was not previously documented in the open literature. We thoroughly explore various experimental conditions and ultimately identify the optimal conditions for the hydrogenation process. RhH[P( i -Pr) 3 ] 3 demonstrates remarkable activity and versatility as a catalyst in multiple areas, including the water gas shift reaction (WGSR) [23,24] and the photochemical dehydrogenation of alcohols, [25,26] among others. 2. Experimental 2.1 Materials Solid and liquid reagents, Rhodium(Ⅲ) chloride hydrate (38.5%wt Rh), triisopropylphosphine (P( i -Pr) 3 , 98%), tetrahydrofuran (THF, HPLC, > 99.9%), triphenylphosphine (TPP, 99%) and Na/Hg amalgam (5%) were purchased from Sigma-Aldrich, NBR (Lanxess, Perbunan T3435). And Nitrogen (N 2 , Ultra High Purity 5.0), Ar (Argon, Ultra High Purity 5.0), and hydrogen (H 2 , Ultra High Purity 5.0) from Praxair. Before the experiment, sodium tablets must be added to THF and reflux to remove water. 2.2 Apparatus A Parr 4560 Mini Benchtop Reactor (300 mL) equipped with a Parr 4842 Controller (assembly of ordinary propeller mixing); a Thermo Nicolet 6700 Fourier Transform Infrared Spectroscopy operated using OMNIC software; a Bruker 300 MHz Nuclear Magnetic Resonance (NMR) equipped with a QNP Probe device was employed for chemical structure analyses; a vacuum Atmospheres Company (VAC) HE493 Dri-Train glove box; and a vacuum Atmospheres Company (VAC) Nexus One glove box. 2.3 Preparation and characterization of RhH[P( i -Pr) 3 ] 3 We improved the synthesis method of Butler [27] and successfully obtained the required catalyst, as follows: ①A mixture of RhCl 3 ·3H 2 O (0.98 g, 4 mmol) and P( i -Pr) 3 (1.6 mL, 8 mmol) was stirred in 35 mL THF for 20 hours at room temperature. A brown solid residue was then obtained by concentration under vacuum; ②THF (35 mL), P( i -Pr) 3 (1.0 mL, 5 mmol), and 1% Na/Hg (40 g) were added sequentially to the brown solid. The mixture was stirred at room temperature for 20 hours. The filtered reaction solution was dried under high vacuum (0.001 mm Hg) to remove excess P( i -Pr) 3 ; ③Recrystallization of the resulting dark brown solid residue from pentane containing free P( i -Pr) 3 (0.5 mL) gave RhH[P( i -Pr) 3 ] 3 as yellow crystals (1.4 g, 60%). The gas for degassing was changed from nitrogen to argon. In the previous experiments, N 2 was used for degassing before introducing the catalyst solution into the system. The catalyst RhH[P( i -Pr) 3 ] 3 could form RhH 3 [P( i -Pr) 3 ] 2 in the presence of H 2 , however, if there is any N 2 present, it will continuously create a dinitrogen compound RhH(N 2 )[P( i -Pr) 3 ] 2 , followed by other reactions if conditions permit. RhH[P( i -Pr) 3 ] 3 was characterized by Fourier transform infrared spectroscopy. As we can see in the Fig. 1 , there are very strongly defined peaks in the 2800 cm − 1 to 3000 cm − 1 region. These peaks are characteristic of the C-H bond in any alkanes, similar to those in the Rh hydrido catalyst's ligand, P( i -Pr) 3 . The small peak at 1980–1986 cm − 1 is the Rh-H bond. There are numerous papers to support this claim, some literature also shows that the characteristic peak of Rh-H bond also appears at 2000-2050cm − 1 . [28–32] The 1300–1500 cm-1 peaks are due to C-H bending. These signals are caused by the planar bending of the bond in 3D space and are caused once again by the ligands attached to the catalyst. There is a noticeable P-H bend in the 1100 cm − 1 to 1200 cm − 1 range, a second C-H bending peak around 900 cm − 1 , and finally, a couple of peaks in the 650–700 cm − 1 range related to the P-C bond of the ligand. 2.4 Hydrogenation and characterization of HNBR nitrile groups The THF solution of HNBR (2.5%wt) was prepared and shaken on a shaker for 24h to dissolve the rubber completely. Hydrogenation of HNBR samples was performed in a Parr 4560 Mini Bench Top Reactor (300 mL) equipped with a Parr 4842 Controller. A designated amount of the desired rubber solution was added to the reaction vessel. After assembling all parts, the reactor was bolted shut and tested for leaks with 100 psig H 2 gas. Once the reactor was assembled and tested for leaks, the vessel was degassed using H 2 gas. To degas the reactor, the reaction vessel was placed in an ice/water mixture, and the gas output valve was connected to a hose placed in a bucket of water. With all valves closed, the reactor was turned on to rotate at 250 rpm. Open the H 2 inlet valve and fill the reactor vessel with 100 psig H 2 gas, then close the hydrogen inlet valve and open the gas output valve to allow H 2 to slowly leak out of the output hose, causing a trail of small bubbles in the bucket of water. Once the pressure in the reactor was at 0 psig and bubbles stopped flowing, the H 2 input valve was opened slightly while the output valve into the water bucket was fully opened. The reactor was kept this way for at least 30 min as H 2 was allowed to flow in and out of the reaction vessel. Once the time was up, both valves were quickly closed, the ice/water mixture was removed, and the vessel was dried. The heating mantle for the reactor was placed over the vessel, and the heater was adjusted to set the reaction temperature. While the reaction vessel reached the desired temperature, a designated amount of catalyst was prepared in a glove box. The catalyst was obtained using a gas-tight syringe under an argon atmosphere. Once the desired temperature was reached, the gas exhaust valve was quickly opened to release pressure built up during heating. The catalyst was quickly taken from the argon environment and inserted into the reactor through a valve. All valves were closed, the temperature was increased if desired, and the pressure was increased to a certain value, usually 500–1000 psig H 2 . FT-IR determined the conversion of carbon-carbon double bonds (hydrogenation degree) of HNBR. In the FT-IR analysis, the sample solution was cast onto a sodium chloride crystal disk. The NaCl disk was dried and a polymer film formed on it before it was ready for FT-IR analysis. The degree of hydrogenation was calculated from the FT-IR spectra according to the peak strength. IR spectra were collected using a Bio-Rad Excalibur 300MXPC spectrometer or a Thermo Scientific Nicolet 6700 spectrometer. Without undergoing any hydrogenation of carbon-carbon double bonds, the content of C ≡ N in both HNBR and NBR is approximately 40% which remains unchanged during the olefinic hydrogenation experiments. The calculation for C = C hydrogenation can be found below: A723 = absorbance at 723cm − 1 A970 = absorbance at 970cm − 1 A2236 = absorbance at 2236cm − 1 $$\:\text{A}\left(723\right)=\frac{\text{A}723}{\text{A}2236}\:\text{a}\text{n}\text{d}\:\text{A}\left(970\right)=\frac{\text{A}970}{\text{A}2236}$$ K(723) = 0.255, a constant specific to this peak K(970) = 2.3, a constant specific to this peak $$\:\text{F}=1+\frac{\text{A}\left(723\right)}{\text{K}\left(723\right)}+\frac{\text{A}\left(970\right)}{\text{K}\left(970\right)}$$ $$\:\text{C}\left(\text{B}\text{R}\right)=\frac{\text{A}\left(970\right)}{\left[\text{K}\left(970\right)\times\:\text{F}\right]}=\text{c}\text{a}\text{r}\text{b}\text{o}\text{n}-\text{c}\text{a}\text{r}\text{b}\text{o}\text{n}\:\text{d}\text{o}\text{u}\text{b}\text{l}\text{e}\:\text{b}\text{o}\text{n}\text{d}\text{s}\:\text{r}\text{e}\text{m}\text{a}\text{i}\text{n}\text{i}\text{n}\text{g}\:\text{i}\text{n}\:\text{H}\text{N}\text{B}\text{R}$$ $$\:\text{C}\left(\text{H}\text{B}\text{R}\right)=\frac{\text{A}\left(723\right)}{\left[\text{K}\left(723\right)\times\:\text{F}\right]}=\text{m}\text{e}\text{t}\text{h}\text{y}\text{l}\text{e}\text{n}\text{e}\:\text{g}\text{r}\text{o}\text{u}\text{p}\text{s}\:\text{f}\text{o}\text{r}\text{m}\text{e}\text{d}\:\text{f}\text{r}\text{o}\text{m}\:\text{h}\text{y}\text{d}\text{r}\text{o}\text{g}\text{e}\text{n}\text{a}\text{t}\text{i}\text{o}\text{n}\:\text{o}\text{f}\:\text{N}\text{B}\text{R}$$ $$\:\text{D}\text{e}\text{g}\text{r}\text{e}\text{e}\:\text{o}\text{f}\:\text{H}\text{y}\text{d}\text{r}\text{o}\text{g}\text{e}\text{n}\text{a}\text{t}\text{i}\text{o}\text{n}\left(\text{m}\text{o}\text{l}\text{\%}\right)=100-\frac{\text{C}\left(\text{B}\text{R}\right)}{\text{C}\left(\text{B}\text{R}\right)+\text{C}\left(\text{H}\text{B}\text{R}\right)}\times\:100$$ However, it should be noted that the content of carbon-nitrogen bonds, which is the internal standard, decreases in the hydrogenation of nitrile groups while it remains unchanged in the hydrogenation of carbon-carbon double bonds. This difference will definitely affect the accuracy of the results of the conversion of nitrile groups. In order to ensure the accuracy of experimental data and results, HNBR was used in the experiments as little (< 5%) carbon-carbon double bonds exist in it; in other words, the peak at 723 cm − 1 (-(CH 2 ) X -) in the IR spectra remains unchanged. So the peak at 723 cm − 1 is used as an internal standard, and the ratio of the peak value (peak height) of the nitrile group (at wavenumber 2236 cm − 1 ) and peak height at 723 cm − 1 is calculated for each sample which is taken during the reaction. It was found that the ratio decreases as the reaction proceeds, which means that the nitrile content is being reduced, and the error is less than 5% which is acceptable. To quickly evaluate the gel formation of the hydrogenated product, filtration with a 0.45 µm syringe filter is used. The detailed method is as below. Attach the 0.45 µm syringe filter to a luer-lock syringe, fill the tube with 5–10 mL rubber solution, and insert the plunger. Push the plunger and press the solution through the filter. If the solution passes the filter, it means there is no gel formation; if not, or only very little passes through, it implies gel is formed after hydrogenation. 3. Results and Discussion 3.1 Activity Testing We have investigated the hydrogenation capacity of the prepared catalyst for HNBR nitrile from the aspects of catalyst dosage, temperature, pressure, and so on. We first investigated the influence of catalyst dosage and selected an empirical condition (60℃, 500psig H 2 ) as the initial condition of the experiment. Adding 0.8 mL catalyst solution, the nitrile content was reduced to 17% within 5 hours. By increasing the catalyst from 0.8 mL to 1.8 mL, C ≡ N% was almost completely removed (reduced to 2%). However, continuing to increase the catalyst amount to 1.8 mL or more does not seem to improve the rate of nitrile reduction. This is probably because the nitrile groups on the surface of HNBR particles have already been hydrogenated, and the excessive Rh cannot get into the inner layers of the rubber particles. One thing to note is that when the catalyst amount is lower than 0.8 mL, almost no reaction was observed because gel formation dominates over the reduction of nitriles. Figure 2 shows the effect of different catalyst loadings. In addition to the effect of catalyst amount, the effect of different temperatures has also been investigated. A series of reactions were carried out at temperatures of 0 o C, 25 o C, 60 o C, 80 o C, 100 o C, 120 o C and 140 o C. At 0 o C, it takes 5 hours to reduce the nitrile percentage from 40–36%; while at room temperature C ≡ Ns can be reduced to 34% within the same period. On increasing the temperature to 60 o C, the catalyst's performance is immensely improved with only 12% nitrile groups remaining after 5 hours of reaction. High temperature induces faster movement of the molecules. However, when the temperature is 80 o C or higher, although the response is much quicker, gel formation occurs even faster such that; the rubber solution became completely gelled after just 1 hour, which made the measurement of the sample very difficult and the actual measured values were very low (as shown in Fig. 3 ). Consequently, 60 o C seems to be the optimal reaction temperature. The effect of hydrogen pressure was also investigated, and the results are shown in Fig. 4 . When the H 2 pressure is low (100 psig and 300 psig), there is not much difference for the rate of nitrile reduction; both curves end up at around 25% of nitrile content after 5 hours. However, the reduction of nitrile becomes much faster when the hydrogen pressure equals 500 psig. The nitrile percentage drops to 10% within 5 hours. The possible reasons for this could be that the concentration of hydrogen becomes higher, and more nitrile groups and hydrogen contact with the metal center of the catalyst. With the increase of pressure to 1400 psig, according to Fig. 4 , the reaction curves go lower and lower; however, the improvement is not as much as for the increase in pressure from 300 psig to 500 psig, which may be concluded that the catalyst mass transfer within the rubber particles mainly controls the hydrogenation rate. The results show that higher hydrogen pressure significantly improves the catalyst's performance. There might be two reasons for this; one is higher pressure increases the solubility of hydrogen in the solvent, which is THF in the current system; the other is that, with the help of high hydrogen pressure, it is much easier for the catalyst molecules to transfer into the interior layers of rubber particles in order to hydrogenate more nitriles inside. For most of the experiments in this study, 500 psig is set to be the optimal reaction pressure. 3.2 Preliminary Study of the Reaction Mechanism After having conducted a large amount of experimental work, a possible reaction mechanism shown in Fig. 5 This study proposes for the first time the hydrogenation of nitrile groups in HNBR. Hydrogenation is performed under 500 psig hydrogen at a temperature of 60 o C using tris(triisopropylphosphine)hydrido-rhodium(I). The addition of hydrogen to the catalytic complex was reported by Yoshida, et al. [33,34] This addition creates a new five-member complex. Butler et al. have reported a similar five-member complex with two chlorine atoms instead of two hydrogen atoms. [27] This shows the complex proposed above is not unreasonable and a likely step in the catalysis of the hydrogenation reaction. The next step is a little more difficult to determine. A likely mechanism for this part of the reaction involves the rhodium complex reacting with the C ≡ N bonds and hydrogen gas to reduce the nitrile to an amine. A more detailed and similar reaction is outlined in the Britannica Encyclopedia regarding the catalytic hydrogenation of an olefin (alkene). This reaction is shown below Fig. 6 . “L” indicates a PPh 3 ligand. Similar additions to double and triple bonds were noted in a thesis paper by Lau, [35] further supporting the proposed reaction mechanism. After several experiments, it was observed that gel formation only occurs when rubber, hydrogen and catalyst are present simultaneously; in other words, gel formed only when the reduction of the nitrile group occurs. It can also be concluded that if there is no reduction of the nitrile group, all the other factors, even air or high temperature, could not initiate cross-linking. It is not by accident that another researcher's finding also confirms the conclusion of the present work. The cause for the crosslink was investigated in three possibilities: (i) crosslinking caused by the hydrogenation of the C ≡ N group, (ii) by the oxidation of C = C double bonds, and (iii) by radicals in the system. With the progress of the investigation in this work, something new has recently been discovered. First, many of the repeat experiments failed, and the nitrile group could not be hydrogenated by the same catalyst at all; second, some NBR or HNBR solution became cross-linked by itself over a short period of time. Those phenomena captured our attention, and the reason was soon found that the THF being used was causing the problem. The THF of bad quality was not stabilized by a stabilizer. In industry, THF is often stabilized with 0.025% butylated hydroxytoluene (BHT) to inhibit the formation of explosive-prone peroxides which causes autoxidation (radical chain reactions that lead to decomposition). THF easily reacts with air (oxygen in air) and produces a very active intermediate which soon forms two peroxides, 4-hydroxybutanoic acid lactone and 3-hydroxytetrahydrofuran, respectively. (Fig. 7 ) Those two peroxides are believed to be the causes of the failed experiments in this study. As per the experiments carried out in this study, adding a small amount of BHT (< 250 ppm) improves the catalyst's performance to some extent and reduces gel formation to some extent. However, BHT is unable to reverse the autoxidation process. Consequently, it is believed that the major factors influencing gel formation in nitrile reduction in HNBR are the nitrile groups, -P( i -Pr) 3 ligands of the catalyst, and the THF peroxides, where the first two play more important roles. This project aims to reduce the percentage of nitrile in HNBR by 5–10%, and to prevent any formation of gel. As discussed many times, gel formation is one of the largest challenges. Fortunately, this study already found that triphenylphosphine (TPP) is a very good additive for the NBR system. First, TPP terminates the hydrogenation of nitrile, and it does not affect the hydrogenation of the remaining carbon-carbon double bonds; the second and most important point is that no visible gel was observed when adding TPP for cases of low nitrile reduction. To minimize the gel formation to as slow as possible while maintaining a relatively fast reaction, all experiments have been carried out at room temperature (25 o C). To make sure that only 5–10% nitrile was reduced, TPP was added at about 50–60 min after the addition of the catalyst (initiation of the reaction). Initially, a small amount of TPP was added, and no promising results were obtained. After increasing the amount of TPP, some very promising results were obtained, shown in Table 1 . These results show that the complete gelling time has been significantly extended overnight to about 2 weeks by adding 5-7.5 g TPP. Figure 8 confirms that the viscosity of the samples with the addition of TPP was much lower than the regular ones. Amounts of TPP of more than 7.5 g were also tested, however no further improvement was observed. Table 1 Effect of TPP on reducing gel formation in HNBR* Experiment batch Catalyst batch TPP** Dosage (g) Duration before C ≡ N reduction ends (after addition of TPP) (hr) Duration before complete gelling (day) K41 #35 5 4 7 K38 #34 7.5 4 10 K47 #35 7.5 2 14 K43 #34 7.5 1 14 *: 0.8 mL catalyst solution (0.06 g, 0.1 mmol Rh), 100 mL 2.5 wt% HNBR in THF, 25 o C, 500 psig H 2 **: TPP was added after 50–60 min of addition of catalyst Regarding the function of TPP, the following dynamic equilibrium has been proposed and is quite likely, RhH(P i Pr 3 ) 3 + PPh 3 RhH(PPh 3 ) 4 + P i Pr 3 As shown above, when TPP is added, TPP ligands start replacing P i Pr 3 ligands of the initial Rh hydrido complex until an equilibrium that lies far to the right is reached which takes at least 1 hour. Since the original catalyst disappears, no more nitriles would be reduced, and consequently no gelling occurs. To avoid any contact with air or oxygen, the product was stored in a glove box filled with argon gas. 3.3 Characterization Figure 9 depicts the FT-IR spectra of hydrogenation of nitrile groups in HNBR with different conversions. The peaks at 2236 cm − 1 and 723 cm − 1 belong to -C ≡ N and saturated -[CH 2 ] n - unit (n > 4) respectively. Since this is HNBR, there are no peaks for unsaturated carbon-carbon bonds at the 920–1000 cm − 1 region. During the hydrogenation reaction, the v(C≡N) decreases and two bumps at 3200–3400 cm − 1 appear which are the classic peaks of primary amines. No secondary amines or other types of amines (widely reported side products) are observed. The 723 cm − 1 peak does not change and the nitrile peak (2236 cm − 1 ) almost disappears when nitrile content is about 10%, which means the catalyst is selectively effective for the hydrogenation of nitrile. The new peak of primary amines confirms that nitrile groups have been successfully converted to amine groups without any side products. 4. Conclusion The hydrogenation of the nitrile group on macromolecules was achieved for the first time, the nitrile group was successfully reduced to an amino group, and an efficient and stable hydrogenation catalytic system of HNBR was successfully developed. The nitrile content can be reduced from 40% to less than 10% within 5 hours at 60 o C and 500 psig H 2 . The nitrile groups have been converted to primary amines. A potential mechanism for nitrile hydrogenation has been proposed for the first time. Gel formation issues exist during a regular procedure, and temperature and catalyst concentration seem to aggravate gel formation. The causes for gel formation during nitrile reduction have been investigated and a possible mechanism was proposed. Some additives have been tested and some of them are found to be effective to slow down or terminate gel formation. TPP is the most effective additive. At last, it is worthwhile to point out that for the first time a successful system has been developed and established for the reduction of the nitrile content of HNBR (macromolecules) without visible gel formation. Now that we have confirmed the possibility of nitrile reduction on polymers, this helps to advance the development of degradable polymers. But there are still some problems, such as poor stability of the catalyst, high price; The product system is easy to gel. In the following studies, we will try to use a cheaper and more stable catalytic system, and explore the performance indexes of the aminoylation products in the follow-up experiments. Declarations Author Contribution M.L. completed all the experimental processes, and M.L. and Z.X. wrote the main manuscript text, H.W. And Q.P. provided part of the theoretical basis, and all authors reviewed the manuscript Data Availability Data is provided within the manuscript files References J. Yan and C. Cao, Advances in the Catalytic Hydrogenation and Properties of Unsaturated Polymers, Macromolecules . 56 (2023), 3774–3808, https://doi.org/10.1021/acs.macromol.2c02333. M. Feng, Z. Luo, S. Yi, H. Lu, C. Lu, C. Li, J. Zhao and G. Cao, Palladium Supported on Carbon Nanotubes Decorated Nickel Foam as the Catalytic Stirrer in Heterogeneous Hydrogenation of Polystyrene, Ind. Eng. Chem . Res. 57 (2018), 16227–16238, https://doi.org/10.1021/acs.iecr.8b03810. H. Xie, X. Li, X. Liu, J. Guo, Hydrogenation and Neutralization of Carboxylic Styrene Butadiene Latexto Form Thermoplastic Elastomer with Excellent Thermooxidation Resistance, J . Appl . Polym . Sci . 83 (2002), 1375–1384, https://doi.org/10.1002/app.10022. Y. He, E. S. Daniels, A. Klein, M. S. El-Aasser, Hydrogenation of Styrene-Butadiene Rubber (SBR) Latexes, J . Appl . Polym . Sci . 64 (1997), 2047–2056, https://doi.org/10.1002/(SICI)1097-4628(19970606)64:103.0.CO;2-3 H. Wang and G. L. Rempel, Organic Solvent-free Catalytic Hydrogenation of Diene-based Polymer Nanoparticles in Latex form: Mass Transfer of Hydrogen in a Semibatch Process, J. Ind. Eng. Chem . 25 (2015), 29–34, https://doi.org/10.1016/j.jiec.2014.10.009. H. Wang, Q. Pan and G. L. Rempel, Diene-based Polymer Nanoparticles: Preparation and Direct Catalytic Latex Hydrogenation, J. Polym. Sci. A. Polym. Chem. 50 (2012), 2098–2110, https://doi.org/10.1002/pola.25982. W. Tong, H. Chen, Y. Zhang, Z. Zhuo, Y. Fu, H. Qi, D. Zhou, Y. Li and H. Wang, Selective Hydrogenation of Nitrile Butadiene Rubber Latex using Catmetium (R) RF 4 Catalyst, Catal. Today . 407 (2023), 80–88, https://doi.org/10.1016/j.cattod.2022.02.015. Y. Wang, F. Cao, Y. Fu, H. Chen, Y. Zhang, C. Wang, Y. Li and H. Wang, Preparation of Diene-based Nanoparticles by Semibatch Microemulsion Polymerization and Their Catalytic Hydrogenation, Catal. Today . 407 (2023), 156–164, https://doi.org/10.1016/j.cattod.2022.01.022. S. Gomez, J. A. Peters and T. Maschmeyer, The Reductive Amination of Aldehydes and Ketones and the Hydrogenation of Nitriles: Mechanistic Aspects and Selectivity Control, Adv. Synth. Catal . 344 (2002), 1037–1057, https://doi.org/10.1002/1615-4169(200212)344:103.0.CO;2-3. P. T. Witte, A New Supported Rhodium Catalyst for Selective Hydrogenation of Nitriles to Primary Amines, Collect. Czech. Chem. Commun . 72 (2007), 468–474, https://doi.org/10.1135/cccc20070468. J. Krupka, J. Drahonsky and A. Hlavackova, Aminocarbene Mechanism of the Formation of a Tertiary Amine in Nitrile Hydrogenation on a Palladium Catalyst, React. Kinet. Mech. Catal . 108 (2013), 91–105, https://doi.org/10.1007/s11144-012-0497-2. K. Lévay, T. Kárpáti and L. Hegedus, Selective Hydrogenation of Benzonitrile and Its Homologues to Primary Amines over Platinum, J. Ind. Eng. Chem . 101 (2021), 279–292, https://doi.org/10.1016/j.jiec.2021.06.002. A. Mukherjee, D. Srimani, Y. Ben-David and D. Milstein, Low-Pressure Hydrogenation of Nitriles to Primary Amines Catalyzed by Ruthenium Pincer Complexes. Scope and Mechanism, ChemCatchem . 9 (2017), 559–563, https://doi.org/10.1002/cctc.201601416. R. Adam, C. B. Bheeter, R. Jackstell and M. Beller, A Mild and Base-Free Protocol for the Ruthenium‐Catalyzed Hydrogenation of Aliphatic and Aromatic Nitriles with Tridentate Phosphine Ligands, ChemCatChem . 8 (2016), 1329–1334, https://doi.org/10.1002/cctc.201501367. C. Bornschein, S. Werkmeister, B. Wendt, H.-J. Jiao, E. Alberico, W. Baumann, H. Junge, K. Junge and M. Beller, Mild and Selective Hydrogenation of Aromatic and Aliphatic (di)nitriles with a well-defined Iron Pincer Complex, Nat. Commun . 5 (2014), 4111, https://doi.org/10.1038/ncomms5111. Z. Ma, V. G. Chandrashekhar, B. Zhou, A. M. Alenad, N. Rockstroh, S. Bartling, M. Beller, R. V. Jagadeesh, Stable and reusable Ni-based nanoparticles for general and selective hydrogenation of nitriles to amines, Chem . Sci . 13 (2022), 10914–10922, https://doi.org/10.1039/d2sc02961h. D. Formenti, R. Mocci, H. Atia, S. Dastgir, M. Anwar, S. Bachmann, M. Scalone, K. Junge, M. Beller, A State-of-the-Art Heterogeneous Catalyst for Efficient and General Nitrile Hydrogenation, Chem . Eur . J. 26 (2020), 15589–15595, https://doi.org/10.1002/chem.202001866. V. G. Chandrashekhar, T. Senthamarai, R. G. Kadam, O. Malina, J. Kaslik, R. Zboril, M. B. Gawande, R. V. Jagadeesh, M. Beller, Silica-supported Fe/Fe–O nanoparticles for the catalytic hydrogenation of nitriles to amines in the presence of aluminium additives, Nat . Catal . 5 (2022), 20–29, https://doi.org/10.1038/s41929-021-00722-x. S. Chakraborty, G. Leitus and D. Milstein, Selective Hydrogenation of Nitriles to Primary Amines Catalyzed by a Novel Iron Complex, Chem. Commun . 52 (2016), 1812–1815, https://doi.org/10.1039/c5cc08204h. M. Yoshimura, A. Komatsu, M. Niimura, Y. Takagi, T. Takahashi, S. Ueda, T. Ichikawa, Y. Kobayashi, H. Okami, T. Hattori, Y. Sawama, Y. Monguchi and H. Sajiko, Selective Synthesis of Primary Amines from Nitriles under Hydrogenation Conditions, Adv. Synth. Catal . 360 (2018), 1726–1732, https://doi.org/10.1002/adsc.201800102. H.-G. Dai and H.-R. Guan, Switching the Selectivity of Cobalt-Catalyzed Hydrogenation of Nitriles, ACS Catal . 8 (2018), 9125–9130, https://doi.org/10.1021/acscatal.8b02645. K. Juhász, K. Lévay, L. Hegedus, D. Balogh-Weiser, L. Pirault-Roy and Z. Hell, Application of Supported Lanthanum Catalysts in the Hydrogenation of Nitriles, React. Kinet. Mech. Catal . 133 (2021), 687–698, https://doi.org/10.1007/s11144-021-02028-2. T. Yoshida, T. Okano and S. Otsuka, Activation of Water-Molecules.4. Generation of Dihydrogen from Water by Rhodium(I) Hydrido and Rhodium(0) Carbonyl-Compounds, J. Am. Chem. Soc . 102 (1980), 5966–5967, https://doi.org/10.1021/ja00538a071. T. Yoshida, T. Okano and Y. Ueda and S Otsuka, Activation of the Water Molecule.5. Rhodium(I) Hydride Catalyzed Water Gas Shift Reaction. Identification of the Elemental Reactions Comprising the Catalytic Cycles, J. Am. Chem. Soc . 103 (1981), 3411–3422, https://doi.org/10.1021/ja00402a027. D. Morton, D. J. Cole-Hamilton, I. D. Utuk, M. Paneque-Sosa and M. Lopez-Poveda, Hydrogen-Production from Ethanol Catalyzed by Group-8 Metal-Complexes, J. Chem. Soc . Dalton Trans . 3 (1989), 489–495, https://doi.org/10.1002/chin.198924064. E. Delgado-Lieta, M. A. Luke, R. F. Jones and D. J. Cole-Hamilton, The Photochemical Decomposition of Alcohols Catalysted by Tri(isopropyl)phosphine Complexes of Rhodium(I), Polyhedron . 1 (1982), 839–840, https://doi.org/10.1016/0277-5387(82)80020-X. D. C. D. Butler, D. W. Bruce, P. Lightfoot and D. J. Cole-Hamilton, On the Reduction of Rhodium Trichloride in the Presence of Triisopropylphosphine, Can. J. Chem . 2001, 79 , 472–478, https://doi.org/10.1139/cjc-79-5/6-472. D. W. Schiering and J. E. Katon, Characteristic Infrared-Absorption Frequencies of the Enol Group of 1,3-Dicarbonyl Compounds, Appl. Spectrosc . 40 (1986), 1049–1054, https://doi.org/10.1366/0003702864508106. D. W. Schiering and J. E. Katon, The Vibrational-Spectra and Structure of 4-Methyl Oxaloacetate (Carbomethoxypyruvic Acid), J. Mol. Struct . 144 (1986), 25–38, https://doi.org/10.1016/0022-2860(86)80164-8. E. A. Boyd, D. Lionetti, W. C. Henke, V. W. Day and J. D. Blakemore, Preparation, Characterization and Electrochemical Activation of a Model [Cp*Rh] Hydride, Inorg. Chem . 58 (2019), 3606–3615, https://doi.org/10.1021/acs.inorgchem.8b02160. X.-C. Chen, T. Lian, K.-C. Zhao, L. Guo, Y. Lu and Y. Liu, Efficient Hydroaminomethylation of Olefins Catalyzed by Rh-complex Ligated by P, O-hybrid Ligand with Chelating Effect, J. Catal . 411 (2022), 158–166, https://doi.org/10.1016/j.jcat.2022.05.010. C. G. Comadoll, W. C. Henke, J. A. Hopkins Leseberg, J. T. Douglas, A. G. Oliver, V. W. Day and J. D. Blakemore Examining the Modular Synthesis of [Cp*Rh] Monohydrides Supported by Chelating Diphosphine Ligands, Organometallics . 40 (2021), 3808–3818, https://doi.org/10.1021/acs.organomet.1c00525. T. Yoshida, T. Okano, D. L. Thorn, T. H. Tulip, S. Otsuka and J. A. Ibers, Preparations and Reactions of Some Hydridodinitrogentrialkylphosphine Complexes of Rhodium(I)-Structure of a Dinitrogen-Bridged Rhodium(I) Dimer, [RhH(P(i-Pr) 3 ) 2 ] 2 (∝-N 2 ), J. Organomet. Chem . 181 (1979), 183–201, https://doi.org/10.1016/S0022-328X(00)85748-4. T. Yoshida, D. L. Thorn, T. Okano, J. A. Ibers and S. Otsuka, Hydration and Reduction of Carbon-Dioxide by Rhodium Hydride Compounds - Preparation and Reactions of Rhodium Bicarbonate and Formate Complexes, and the Molecular-Structure of RhH 2 (O 2 COH)(P(i-Pr) 3 ) 2 , J. Am. Chem. Soc . 101 (1979), 4212–4221, https://doi.org/10.1021/ja00509a029. C. Lau, Rhodium-Catalyzed Addition of Arylboronic Acids to Nitriles: Application in the Synthesis of Unsymmetrical Polysubstituted Pyridines, University of Toronto. 2011. Additional Declarations No competing interests reported. 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. 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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-5852950","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":439320970,"identity":"3259bbd0-0b79-4f72-9d24-a9b32e50db3c","order_by":0,"name":"Minghui Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuklEQVRIiWNgGAWjYBACPmYGBmYGg39yxGthA2spOGBMghYGkJYPBxIbiNfCzmO6ucDgTnr/7OaDD34w2MnpNjA/e4DfYTxmt2cYPMudcedYsmEPQ7Kx2QE2cwOCWngMmHM3SOSYSTMwHEjcdoCHTYIYLekGpGo5nECKFrYyoJY0wxk30oB+MQD65TCbGV4t/PyHt93m+WMjzz8jGRhiFXZyZsebn+HVggZAQcVMgvpRMApGwSgYBdgBAH/xPCj5o2rlAAAAAElFTkSuQmCC","orcid":"","institution":"CNOOC Enertech Safety \u0026 Environmental Protection Branch","correspondingAuthor":true,"prefix":"","firstName":"Minghui","middleName":"","lastName":"Liu","suffix":""},{"id":439320971,"identity":"59c38afa-011a-41e9-8866-334ab11a60f2","order_by":1,"name":"Ziying Xiong","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Ziying","middleName":"","lastName":"Xiong","suffix":""},{"id":439320972,"identity":"0f5c4be6-aeca-4cfd-a8f9-54f664704f0b","order_by":2,"name":"Hui Wang","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Hui","middleName":"","lastName":"Wang","suffix":""},{"id":439320973,"identity":"b219b856-b0f3-4b49-b00d-95f0b9145959","order_by":3,"name":"Linbao Zhang","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Linbao","middleName":"","lastName":"Zhang","suffix":""},{"id":439320974,"identity":"35a01040-a0c8-4954-9249-658685ccf84b","order_by":4,"name":"Qinmin Pan","email":"","orcid":"","institution":"Soochow University","correspondingAuthor":false,"prefix":"","firstName":"Qinmin","middleName":"","lastName":"Pan","suffix":""},{"id":439320977,"identity":"f8c4011d-9997-4858-bf20-acbea14560e7","order_by":5,"name":"Jiaqi Wang","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Jiaqi","middleName":"","lastName":"Wang","suffix":""},{"id":439320978,"identity":"48c8a6e9-efdb-44f5-a737-3c0ac089bca5","order_by":6,"name":"Garry L. Rempel","email":"","orcid":"","institution":"University of Waterloo","correspondingAuthor":false,"prefix":"","firstName":"Garry","middleName":"L.","lastName":"Rempel","suffix":""}],"badges":[],"createdAt":"2025-01-18 05:23:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5852950/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5852950/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80226645,"identity":"9a2a2cf1-63f2-42a8-9ede-c2e81e902105","added_by":"auto","created_at":"2025-04-09 11:48:12","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52323,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFT-IR spectrum of RhH[P(\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ei\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-Pr)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/18753b50324f6a12b65e9439.jpg"},{"id":80227609,"identity":"96d98fe5-5311-4350-9b3a-47646190c19c","added_by":"auto","created_at":"2025-04-09 11:56:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":18114,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of catalyst dosage on hydrogenation of nitrile groups in HNBR\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e*: 0.8 mL catalyst solution (0.06 g catalyst, 0.1 mmol Rh), 100 mL 2.5 wt% HNBR in THF, 60 \u003csup\u003eo\u003c/sup\u003eC, 500 psig\u003c/p\u003e\n\u003cp\u003e**: the numbers marked after \"#\" symbol in the figure have no special meaning and only represent the experiment batch number, and the same is true in the subsequent figure\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/57d3d617afd62fcd7a5b9be5.png"},{"id":80226647,"identity":"beef7231-f72f-4c77-b8b8-e4567f16e909","added_by":"auto","created_at":"2025-04-09 11:48:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9551,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of temperature on hydrogenation of C≡Ns in HNBR\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e*: 0.8 mL catalyst solution (0.06 g catalyst, 0.1 mmol Rh), 100 mL2.5 wt% HNBR in THF, 500 psig\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/b34e947cff81a7391022ec63.png"},{"id":80226648,"identity":"11905158-90b7-4f56-9551-1273fd10b840","added_by":"auto","created_at":"2025-04-09 11:48:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":11839,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e pressure on hydrogenation of C≡Ns in HNBR\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e*: 0.8 mL catalyst solution (0.06 g catalyst, 0.1 mmol Rh), 100 mL HNBR in THF (2.5 wt%), 60 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/eef32870494c66a2db2e33b8.png"},{"id":80228143,"identity":"de3d643f-2c57-426b-8cf5-2946d257bf3e","added_by":"auto","created_at":"2025-04-09 12:04:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":199764,"visible":true,"origin":"","legend":"\u003cp\u003eProposed potential reaction mechanism for hydrogenation of nitrile groups in HNBR\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/43970dd394ed3d91cb9cd16a.png"},{"id":80226668,"identity":"8510fe4d-e2d6-44be-92db-e43695f435c8","added_by":"auto","created_at":"2025-04-09 11:48:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":88290,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanism for catalytic hydrogenation of alkene\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/f32127091451d471921f32e3.png"},{"id":80227610,"identity":"873bff71-65e1-4cf0-ac75-54fde5712935","added_by":"auto","created_at":"2025-04-09 11:56:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":5295,"visible":true,"origin":"","legend":"\u003cp\u003eOxidation of THF with air\u003c/p\u003e\n\u003cp\u003e(a) THF; (b) unstable intermediate; (c) 4-hydroxybutanoic acid lactone (γ-butyrolactone); (d) 3-hydroxytetrahydrofuran\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/b9eac8037229b50fc0a640d5.png"},{"id":80226652,"identity":"4c1b3069-c6f9-4ba9-a41a-64b00d2b6546","added_by":"auto","created_at":"2025-04-09 11:48:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":8320,"visible":true,"origin":"","legend":"\u003cp\u003eViscosity change of nitrile-reduced HNBR with and without TPP as an additive*\u003c/p\u003e\n\u003cp\u003e*: 1 = before hydrogenation; 2 = 5 hr; 3 = 1 day; 4 = 7 days; 5 = 14 days\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/5c1819415fe6ef803b5e027a.png"},{"id":80226655,"identity":"3ee19d17-0715-44a4-b90e-7afa982e0102","added_by":"auto","created_at":"2025-04-09 11:48:13","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":12143,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra of HNBR with different acrylonitrile content\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/a811d258df40fb69e78adeca.png"},{"id":80785142,"identity":"228e6fec-042a-4526-976c-1ba5583a4d92","added_by":"auto","created_at":"2025-04-17 05:40:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1162786,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5852950/v1/c629ff13-2c40-4690-926b-aff564d02837.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hydrogenation of nitrile groups in HNBR with a rhodium catalyst","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe route of catalytic hydrogenation on unsaturated double bonds or benzene rings plays an important role in improving the properties of polymers; one of the desirable properties attributed to hydrogenated polymers is their excellent thermal and oxidative stability. For example, poly(cyclohexylidene) (PCHE) prepared by catalytic hydrogenation of polystyrene (PS) has not only improved heat resistance and aging resistance but greatly reduced its optical coefficient so that it can be used in the field of optical media. Hydrogenated Styrene Butadiene Rubber (HSBR) can be obtained by hydrogenating the double bonds present in Styrene Butadiene Rubber (SBR); it exhibits improved thermal, oxidation, ozone, and UV (ultraviolet) resistance.\u003csup\u003e[1\u0026ndash;4]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eHydrogenated-nitrile-butadiene-rubber (HNBR) is a special rubber prepared by catalytic hydrogenation of Nitrile-butadiene-rubber (NBR). It has excellent mechanical, thermo-oxidative, and chemical-resistant properties over a wide operating temperature range, particularly after long-term exposure to heat, oil, and chemicals. At present, solution hydrogenation is the main method of HNBR preparation. In addition, Wang's research group has carried out in-depth research on the emulsion hydrogenation method.\u003csup\u003e[5\u0026ndash;8]\u003c/sup\u003e Moreover, HNBR has been extensively adopted in industrial sealing for oil field exploration and processing, as well as in rolls used in steel and paper mills.\u003c/p\u003e \u003cp\u003eThe acrylonitrile (ACN) content serves as a defining factor for the grading of NBR and HNBR. The polarity of the ACN content influences various properties, such as oil and solvent resistance and abrasion resistance. Higher ACN content enhances the resistance to fuels and polar lubricants in HNBR, albeit at the expense of its low-temperature properties. Higher ACN content leads to improvements in properties such as air/gas impermeability, abrasion resistance, tensile strength, and compatibility with other polar polymers. Conversely, lower ACN content reduces fuel and polar lubricant resistance while enhancing the low-temperature properties of HNBR.\u003c/p\u003e \u003cp\u003eThe hydrogenation of nitrile is a prevalent industrial process employed in producing amines. Amines find extensive utilization in various applications, including solvents, pharmaceutical intermediates, raw materials for resins, textile additives, disinfectants, rubber stabilizers, corrosion inhibitors, and the manufacturing of detergents and plastics.\u003csup\u003e[9]\u003c/sup\u003e Although multiple methods are available for amine production, catalytic hydrogenation of nitriles is the most widespread.\u003c/p\u003e \u003cp\u003eNowadays, functional polymers have gained significant attention in various fields. One notable area of interest is the introduction of amine groups onto the polystyrene molecular chain. This modification is particularly valuable due to the amine group's strong electron absorption and ease of protolization. Consequently, functional polymers with amine groups hold immense potential in applications, including the separation and purification of organic drugs, biomedical polymers, polymer catalyst carriers, sewage adsorption treatment, and numerous other fields.\u003c/p\u003e \u003cp\u003eCurrently, there is a wealth of research on reducing small molecule nitriles, particularly focusing on the use of transition metal catalysts. In 1969, Dewhirst pioneered using RuCl\u003csub\u003e2\u003c/sub\u003e(PPh\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e and RuH\u003csub\u003e2\u003c/sub\u003e(PMePh\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e as catalysts for the hydrogenation of nitriles, utilizing ruthenium as the transition metal. Subsequently, precious metal catalysts, including platinum, palladium, ruthenium, rhodium, and other central atom-based catalysts\u003csup\u003e[10\u0026ndash;13]\u003c/sup\u003e, have been widely employed in this field. Different types of catalyst applications have also been reported.\u003c/p\u003e \u003cp\u003eBeller et al.\u003csup\u003e[14\u0026ndash;18]\u003c/sup\u003e have achieved important results in developing pincer metal catalysts for the hydrogenation of aliphatic and aromatic nitriles, and they have also investigated a variety of base metal catalysts supported on metal/non-metallic oxides. In response to the economic considerations associated with precious metal catalysts, the Milstein group\u003csup\u003e[19]\u003c/sup\u003e endeavored to develop a variety of base metal catalysts with iron and cobalt as the central atom, building upon the knowledge gained from Beller's research. Utilizing the diphoshinoamine(PNP)-iron pincer catalyst and PNNH-cobalt pincer catalyst as a foundation, a novel iron complex was designed, featuring a dibenzylamine PNP ligand and an absence of CO ligands. Additionally, researchers such as Masatoshi Yoshimura et al.\u003csup\u003e[20]\u003c/sup\u003e have explored the use of bimetallic catalysts for nitrile reduction. It was discovered that the hydrogenation of pentonitrile, in the presence of acetic acid as a solvent and a catalyst consisting of a 1:5 ratio of gold and palladium atoms supported by alumina, exhibited high selectivity towards primary amine formation. Dai\u003csup\u003e[21]\u003c/sup\u003e gave up the previous idea of designing complex base metal catalysts and instead chose to study a dual catalytic system, HN[CH\u003csub\u003e2\u003c/sub\u003eCH\u003csub\u003e2\u003c/sub\u003eP(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e (\u003csup\u003ei\u003c/sup\u003ePrPNHP) ligand to regulate the selectivity of nitrile hydrogenation, and simply treated CoBr\u003csub\u003e2\u003c/sub\u003e with NaHBEt\u003csub\u003e3\u003c/sub\u003e to generate cobalt particles, which can catalyze the hydrogenation of nitrile to primary amine. It has high selectivity and wide functional group tolerance. Juh\u0026aacute;sz\u003csup\u003e[22]\u003c/sup\u003e investigated the application of supported lanthanum catalysts in nitrile hydrogenation reactions, which showed surprisingly high activity and selectivity. At present, the application research of this catalyst has been extended from benzene nitrile to other nitriles (benzyl cyanide, cinnamonitrile, adipic dinitrile).\u003c/p\u003e \u003cp\u003eIn this text, we extensively investigate the possibility of employing tris(triisopropylphosphine) hydrido rhodium (I) as a catalyst for hydrogenating HNBR nitrile. This study focuses on using low catalyst concentration under mild reaction conditions to achieve the purpose of macromolecular cyanogen reduction, which was not previously documented in the open literature. We thoroughly explore various experimental conditions and ultimately identify the optimal conditions for the hydrogenation process. RhH[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e demonstrates remarkable activity and versatility as a catalyst in multiple areas, including the water gas shift reaction (WGSR)\u003csup\u003e[23,24]\u003c/sup\u003e and the photochemical dehydrogenation of alcohols, \u003csup\u003e[25,26]\u003c/sup\u003e among others.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eSolid and liquid reagents, Rhodium(Ⅲ) chloride hydrate (38.5%wt Rh), triisopropylphosphine (P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e, 98%), tetrahydrofuran (THF, HPLC, \u0026gt;\u0026thinsp;99.9%), triphenylphosphine (TPP, 99%) and Na/Hg amalgam (5%) were purchased from Sigma-Aldrich, NBR (Lanxess, Perbunan T3435). And Nitrogen (N\u003csub\u003e2\u003c/sub\u003e, Ultra High Purity 5.0), Ar (Argon, Ultra High Purity 5.0), and hydrogen (H\u003csub\u003e2\u003c/sub\u003e, Ultra High Purity 5.0) from Praxair. Before the experiment, sodium tablets must be added to THF and reflux to remove water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Apparatus\u003c/h2\u003e \u003cp\u003eA Parr 4560 Mini Benchtop Reactor (300 mL) equipped with a Parr 4842 Controller (assembly of ordinary propeller mixing); a Thermo Nicolet 6700 Fourier Transform Infrared Spectroscopy operated using OMNIC software; a Bruker 300 MHz Nuclear Magnetic Resonance (NMR) equipped with a QNP Probe device was employed for chemical structure analyses; a vacuum Atmospheres Company (VAC) HE493 Dri-Train glove box; and a vacuum Atmospheres Company (VAC) Nexus One glove box.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation and characterization of RhH[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eWe improved the synthesis method of Butler\u003csup\u003e[27]\u003c/sup\u003e and successfully obtained the required catalyst, as follows: ①A mixture of RhCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO (0.98 g, 4 mmol) and P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e (1.6 mL, 8 mmol) was stirred in 35 mL THF for 20 hours at room temperature. A brown solid residue was then obtained by concentration under vacuum; ②THF (35 mL), P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e (1.0 mL, 5 mmol), and 1% Na/Hg (40 g) were added sequentially to the brown solid. The mixture was stirred at room temperature for 20 hours. The filtered reaction solution was dried under high vacuum (0.001 mm Hg) to remove excess P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e; ③Recrystallization of the resulting dark brown solid residue from pentane containing free P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e (0.5 mL) gave RhH[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e as yellow crystals (1.4 g, 60%).\u003c/p\u003e \u003cp\u003eThe gas for degassing was changed from nitrogen to argon. In the previous experiments, N\u003csub\u003e2\u003c/sub\u003e was used for degassing before introducing the catalyst solution into the system. The catalyst RhH[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e could form RhH\u003csub\u003e3\u003c/sub\u003e[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e in the presence of H\u003csub\u003e2\u003c/sub\u003e, however, if there is any N\u003csub\u003e2\u003c/sub\u003e present, it will continuously create a dinitrogen compound RhH(N\u003csub\u003e2\u003c/sub\u003e)[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e, followed by other reactions if conditions permit. RhH[P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e was characterized by Fourier transform infrared spectroscopy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs we can see in the Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, there are very strongly defined peaks in the 2800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 3000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region. These peaks are characteristic of the C-H bond in any alkanes, similar to those in the Rh hydrido catalyst's ligand, P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e. The small peak at 1980\u0026ndash;1986 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is the Rh-H bond. There are numerous papers to support this claim, some literature also shows that the characteristic peak of Rh-H bond also appears at 2000-2050cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003csup\u003e[28\u0026ndash;32]\u003c/sup\u003e The 1300\u0026ndash;1500 cm-1 peaks are due to C-H bending. These signals are caused by the planar bending of the bond in 3D space and are caused once again by the ligands attached to the catalyst. There is a noticeable P-H bend in the 1100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range, a second C-H bending peak around 900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and finally, a couple of peaks in the 650\u0026ndash;700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range related to the P-C bond of the ligand.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Hydrogenation and characterization of HNBR nitrile groups\u003c/h2\u003e \u003cp\u003eThe THF solution of HNBR (2.5%wt) was prepared and shaken on a shaker for 24h to dissolve the rubber completely. Hydrogenation of HNBR samples was performed in a Parr 4560 Mini Bench Top Reactor (300 mL) equipped with a Parr 4842 Controller. A designated amount of the desired rubber solution was added to the reaction vessel. After assembling all parts, the reactor was bolted shut and tested for leaks with 100 psig H\u003csub\u003e2\u003c/sub\u003e gas. Once the reactor was assembled and tested for leaks, the vessel was degassed using H\u003csub\u003e2\u003c/sub\u003e gas. To degas the reactor, the reaction vessel was placed in an ice/water mixture, and the gas output valve was connected to a hose placed in a bucket of water. With all valves closed, the reactor was turned on to rotate at 250 rpm. Open the H\u003csub\u003e2\u003c/sub\u003e inlet valve and fill the reactor vessel with 100 psig H\u003csub\u003e2\u003c/sub\u003e gas, then close the hydrogen inlet valve and open the gas output valve to allow H\u003csub\u003e2\u003c/sub\u003e to slowly leak out of the output hose, causing a trail of small bubbles in the bucket of water.\u003c/p\u003e \u003cp\u003eOnce the pressure in the reactor was at 0 psig and bubbles stopped flowing, the H\u003csub\u003e2\u003c/sub\u003e input valve was opened slightly while the output valve into the water bucket was fully opened. The reactor was kept this way for at least 30 min as H\u003csub\u003e2\u003c/sub\u003e was allowed to flow in and out of the reaction vessel. Once the time was up, both valves were quickly closed, the ice/water mixture was removed, and the vessel was dried. The heating mantle for the reactor was placed over the vessel, and the heater was adjusted to set the reaction temperature.\u003c/p\u003e \u003cp\u003eWhile the reaction vessel reached the desired temperature, a designated amount of catalyst was prepared in a glove box. The catalyst was obtained using a gas-tight syringe under an argon atmosphere. Once the desired temperature was reached, the gas exhaust valve was quickly opened to release pressure built up during heating. The catalyst was quickly taken from the argon environment and inserted into the reactor through a valve. All valves were closed, the temperature was increased if desired, and the pressure was increased to a certain value, usually 500\u0026ndash;1000 psig H\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eFT-IR determined the conversion of carbon-carbon double bonds (hydrogenation degree) of HNBR. In the FT-IR analysis, the sample solution was cast onto a sodium chloride crystal disk. The NaCl disk was dried and a polymer film formed on it before it was ready for FT-IR analysis. The degree of hydrogenation was calculated from the FT-IR spectra according to the peak strength. IR spectra were collected using a Bio-Rad Excalibur 300MXPC spectrometer or a Thermo Scientific Nicolet 6700 spectrometer. Without undergoing any hydrogenation of carbon-carbon double bonds, the content of C\u0026thinsp;\u0026equiv;\u0026thinsp;N in both HNBR and NBR is approximately 40% which remains unchanged during the olefinic hydrogenation experiments. The calculation for C\u0026thinsp;=\u0026thinsp;C hydrogenation can be found below:\u003c/p\u003e \u003cp\u003eA723\u0026thinsp;=\u0026thinsp;absorbance at 723cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eA970\u0026thinsp;=\u0026thinsp;absorbance at 970cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eA2236\u0026thinsp;=\u0026thinsp;absorbance at 2236cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\text{A}\\left(723\\right)=\\frac{\\text{A}723}{\\text{A}2236}\\:\\text{a}\\text{n}\\text{d}\\:\\text{A}\\left(970\\right)=\\frac{\\text{A}970}{\\text{A}2236}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eK(723)\u0026thinsp;=\u0026thinsp;0.255, a constant specific to this peak\u003c/p\u003e \u003cp\u003eK(970)\u0026thinsp;=\u0026thinsp;2.3, a constant specific to this peak\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\text{F}=1+\\frac{\\text{A}\\left(723\\right)}{\\text{K}\\left(723\\right)}+\\frac{\\text{A}\\left(970\\right)}{\\text{K}\\left(970\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\text{C}\\left(\\text{B}\\text{R}\\right)=\\frac{\\text{A}\\left(970\\right)}{\\left[\\text{K}\\left(970\\right)\\times\\:\\text{F}\\right]}=\\text{c}\\text{a}\\text{r}\\text{b}\\text{o}\\text{n}-\\text{c}\\text{a}\\text{r}\\text{b}\\text{o}\\text{n}\\:\\text{d}\\text{o}\\text{u}\\text{b}\\text{l}\\text{e}\\:\\text{b}\\text{o}\\text{n}\\text{d}\\text{s}\\:\\text{r}\\text{e}\\text{m}\\text{a}\\text{i}\\text{n}\\text{i}\\text{n}\\text{g}\\:\\text{i}\\text{n}\\:\\text{H}\\text{N}\\text{B}\\text{R}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:\\text{C}\\left(\\text{H}\\text{B}\\text{R}\\right)=\\frac{\\text{A}\\left(723\\right)}{\\left[\\text{K}\\left(723\\right)\\times\\:\\text{F}\\right]}=\\text{m}\\text{e}\\text{t}\\text{h}\\text{y}\\text{l}\\text{e}\\text{n}\\text{e}\\:\\text{g}\\text{r}\\text{o}\\text{u}\\text{p}\\text{s}\\:\\text{f}\\text{o}\\text{r}\\text{m}\\text{e}\\text{d}\\:\\text{f}\\text{r}\\text{o}\\text{m}\\:\\text{h}\\text{y}\\text{d}\\text{r}\\text{o}\\text{g}\\text{e}\\text{n}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\:\\text{o}\\text{f}\\:\\text{N}\\text{B}\\text{R}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:\\text{D}\\text{e}\\text{g}\\text{r}\\text{e}\\text{e}\\:\\text{o}\\text{f}\\:\\text{H}\\text{y}\\text{d}\\text{r}\\text{o}\\text{g}\\text{e}\\text{n}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\left(\\text{m}\\text{o}\\text{l}\\text{\\%}\\right)=100-\\frac{\\text{C}\\left(\\text{B}\\text{R}\\right)}{\\text{C}\\left(\\text{B}\\text{R}\\right)+\\text{C}\\left(\\text{H}\\text{B}\\text{R}\\right)}\\times\\:100$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHowever, it should be noted that the content of carbon-nitrogen bonds, which is the internal standard, decreases in the hydrogenation of nitrile groups while it remains unchanged in the hydrogenation of carbon-carbon double bonds. This difference will definitely affect the accuracy of the results of the conversion of nitrile groups. In order to ensure the accuracy of experimental data and results, HNBR was used in the experiments as little (\u0026lt;\u0026thinsp;5%) carbon-carbon double bonds exist in it; in other words, the peak at 723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (-(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003eX\u003c/sub\u003e-) in the IR spectra remains unchanged. So the peak at 723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is used as an internal standard, and the ratio of the peak value (peak height) of the nitrile group (at wavenumber 2236 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and peak height at 723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is calculated for each sample which is taken during the reaction. It was found that the ratio decreases as the reaction proceeds, which means that the nitrile content is being reduced, and the error is less than 5% which is acceptable.\u003c/p\u003e \u003cp\u003eTo quickly evaluate the gel formation of the hydrogenated product, filtration with a 0.45 \u0026micro;m syringe filter is used. The detailed method is as below. Attach the 0.45 \u0026micro;m syringe filter to a luer-lock syringe, fill the tube with 5\u0026ndash;10 mL rubber solution, and insert the plunger. Push the plunger and press the solution through the filter. If the solution passes the filter, it means there is no gel formation; if not, or only very little passes through, it implies gel is formed after hydrogenation.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cstrong\u003e3.1 Activity Testing\u003c/strong\u003e\u003c/h2\u003e\n \u003cp\u003eWe have investigated the hydrogenation capacity of the prepared catalyst for HNBR nitrile from the aspects of catalyst dosage, temperature, pressure, and so on. We first investigated the influence of catalyst dosage and selected an empirical condition (60℃, 500psig H\u003csub\u003e2\u003c/sub\u003e) as the initial condition of the experiment. Adding 0.8 mL catalyst solution, the nitrile content was reduced to 17% within 5 hours. By increasing the catalyst from 0.8 mL to 1.8 mL, C\u0026thinsp;\u0026equiv;\u0026thinsp;N% was almost completely removed (reduced to 2%). However, continuing to increase the catalyst amount to 1.8 mL or more does not seem to improve the rate of nitrile reduction. This is probably because the nitrile groups on the surface of HNBR particles have already been hydrogenated, and the excessive Rh cannot get into the inner layers of the rubber particles. One thing to note is that when the catalyst amount is lower than 0.8 mL, almost no reaction was observed because gel formation dominates over the reduction of nitriles. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows the effect of different catalyst loadings.\u003c/p\u003e\n \u003cp\u003eIn addition to the effect of catalyst amount, the effect of different temperatures has also been investigated. A series of reactions were carried out at temperatures of 0 \u003csup\u003eo\u003c/sup\u003eC, 25 \u003csup\u003eo\u003c/sup\u003eC, 60 \u003csup\u003eo\u003c/sup\u003eC, 80 \u003csup\u003eo\u003c/sup\u003eC, 100 \u003csup\u003eo\u003c/sup\u003eC, 120 \u003csup\u003eo\u003c/sup\u003eC and 140 \u003csup\u003eo\u003c/sup\u003eC. At 0 \u003csup\u003eo\u003c/sup\u003eC, it takes 5 hours to reduce the nitrile percentage from 40\u0026ndash;36%; while at room temperature C\u0026thinsp;\u0026equiv;\u0026thinsp;Ns can be reduced to 34% within the same period. On increasing the temperature to 60 \u003csup\u003eo\u003c/sup\u003eC, the catalyst\u0026apos;s performance is immensely improved with only 12% nitrile groups remaining after 5 hours of reaction. High temperature induces faster movement of the molecules. However, when the temperature is 80 \u003csup\u003eo\u003c/sup\u003eC or higher, although the response is much quicker, gel formation occurs even faster such that; the rubber solution became completely gelled after just 1 hour, which made the measurement of the sample very difficult and the actual measured values were very low (as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Consequently, 60 \u003csup\u003eo\u003c/sup\u003eC seems to be the optimal reaction temperature.\u003c/p\u003e\n \u003cp\u003eThe effect of hydrogen pressure was also investigated, and the results are shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. When the H\u003csub\u003e2\u003c/sub\u003e pressure is low (100 psig and 300 psig), there is not much difference for the rate of nitrile reduction; both curves end up at around 25% of nitrile content after 5 hours. However, the reduction of nitrile becomes much faster when the hydrogen pressure equals 500 psig. The nitrile percentage drops to 10% within 5 hours. The possible reasons for this could be that the concentration of hydrogen becomes higher, and more nitrile groups and hydrogen contact with the metal center of the catalyst. With the increase of pressure to 1400 psig, according to Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the reaction curves go lower and lower; however, the improvement is not as much as for the increase in pressure from 300 psig to 500 psig, which may be concluded that the catalyst mass transfer within the rubber particles mainly controls the hydrogenation rate. The results show that higher hydrogen pressure significantly improves the catalyst\u0026apos;s performance. There might be two reasons for this; one is higher pressure increases the solubility of hydrogen in the solvent, which is THF in the current system; the other is that, with the help of high hydrogen pressure, it is much easier for the catalyst molecules to transfer into the interior layers of rubber particles in order to hydrogenate more nitriles inside. For most of the experiments in this study, 500 psig is set to be the optimal reaction pressure.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Preliminary Study of the Reaction Mechanism\u003c/h2\u003e\n \u003cp\u003eAfter having conducted a large amount of experimental work, a possible reaction mechanism shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e This study proposes for the first time the hydrogenation of nitrile groups in HNBR. Hydrogenation is performed under 500 psig hydrogen at a temperature of 60 \u003csup\u003eo\u003c/sup\u003eC using tris(triisopropylphosphine)hydrido-rhodium(I).\u003c/p\u003e\n \u003cp\u003eThe addition of hydrogen to the catalytic complex was reported by Yoshida, \u003cem\u003eet al.\u003c/em\u003e\u003csup\u003e[33,34]\u003c/sup\u003e This addition creates a new five-member complex. Butler et al. have reported a similar five-member complex with two chlorine atoms instead of two hydrogen atoms.\u003csup\u003e[27]\u003c/sup\u003e This shows the complex proposed above is not unreasonable and a likely step in the catalysis of the hydrogenation reaction. The next step is a little more difficult to determine. A likely mechanism for this part of the reaction involves the rhodium complex reacting with the C\u0026thinsp;\u0026equiv;\u0026thinsp;N bonds and hydrogen gas to reduce the nitrile to an amine. A more detailed and similar reaction is outlined in the Britannica Encyclopedia regarding the catalytic hydrogenation of an olefin (alkene). This reaction is shown below Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. \u0026ldquo;L\u0026rdquo; indicates a PPh\u003csub\u003e3\u003c/sub\u003e ligand. Similar additions to double and triple bonds were noted in a thesis paper by Lau,\u003csup\u003e[35]\u003c/sup\u003e further supporting the proposed reaction mechanism.\u003c/p\u003e\n \u003cp\u003eAfter several experiments, it was observed that gel formation only occurs when rubber, hydrogen and catalyst are present simultaneously; in other words, gel formed only when the reduction of the nitrile group occurs. It can also be concluded that if there is no reduction of the nitrile group, all the other factors, even air or high temperature, could not initiate cross-linking. It is not by accident that another researcher\u0026apos;s finding also confirms the conclusion of the present work. The cause for the crosslink was investigated in three possibilities: (i) crosslinking caused by the hydrogenation of the C\u0026thinsp;\u0026equiv;\u0026thinsp;N group, (ii) by the oxidation of C\u0026thinsp;=\u0026thinsp;C double bonds, and (iii) by radicals in the system.\u003c/p\u003e\n \u003cp\u003eWith the progress of the investigation in this work, something new has recently been discovered. First, many of the repeat experiments failed, and the nitrile group could not be hydrogenated by the same catalyst at all; second, some NBR or HNBR solution became cross-linked by itself over a short period of time. Those phenomena captured our attention, and the reason was soon found that the THF being used was causing the problem. The THF of bad quality was not stabilized by a stabilizer. In industry, THF is often stabilized with 0.025% butylated hydroxytoluene (BHT) to inhibit the formation of explosive-prone peroxides which causes autoxidation (radical chain reactions that lead to decomposition).\u003c/p\u003e\n \u003cp\u003eTHF easily reacts with air (oxygen in air) and produces a very active intermediate which soon forms two peroxides, 4-hydroxybutanoic acid lactone and 3-hydroxytetrahydrofuran, respectively. (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e) Those two peroxides are believed to be the causes of the failed experiments in this study.\u003c/p\u003e\n \u003cp\u003eAs per the experiments carried out in this study, adding a small amount of BHT (\u0026lt;\u0026thinsp;250 ppm) improves the catalyst\u0026apos;s performance to some extent and reduces gel formation to some extent. However, BHT is unable to reverse the autoxidation process. Consequently, it is believed that the major factors influencing gel formation in nitrile reduction in HNBR are the nitrile groups, -P(\u003cem\u003ei\u003c/em\u003e-Pr)\u003csub\u003e3\u003c/sub\u003e ligands of the catalyst, and the THF peroxides, where the first two play more important roles.\u003c/p\u003e\n \u003cp\u003eThis project aims to reduce the percentage of nitrile in HNBR by 5\u0026ndash;10%, and to prevent any formation of gel. As discussed many times, gel formation is one of the largest challenges. Fortunately, this study already found that triphenylphosphine (TPP) is a very good additive for the NBR system. First, TPP terminates the hydrogenation of nitrile, and it does not affect the hydrogenation of the remaining carbon-carbon double bonds; the second and most important point is that no visible gel was observed when adding TPP for cases of low nitrile reduction.\u003c/p\u003e\n \u003cp\u003eTo minimize the gel formation to as slow as possible while maintaining a relatively fast reaction, all experiments have been carried out at room temperature (25 \u003csup\u003eo\u003c/sup\u003eC). To make sure that only 5\u0026ndash;10% nitrile was reduced, TPP was added at about 50\u0026ndash;60 min after the addition of the catalyst (initiation of the reaction). Initially, a small amount of TPP was added, and no promising results were obtained. After increasing the amount of TPP, some very promising results were obtained, shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. These results show that the complete gelling time has been significantly extended overnight to about 2 weeks by adding 5-7.5 g TPP. Figure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e confirms that the viscosity of the samples with the addition of TPP was much lower than the regular ones. Amounts of TPP of more than 7.5 g were also tested, however no further improvement was observed.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEffect of TPP on reducing gel formation in HNBR*\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eExperiment batch\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCatalyst\u003c/p\u003e\n \u003cp\u003ebatch\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTPP** Dosage (g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDuration before C\u0026thinsp;\u0026equiv;\u0026thinsp;N reduction ends (after addition of TPP) (hr)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDuration before complete gelling (day)\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\u003eK41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e#35\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\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eK38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e#34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eK47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e#35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.5\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=\"char\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eK43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e#34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.5\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=\"char\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e*: 0.8 mL catalyst solution (0.06 g, 0.1 mmol Rh), 100 mL 2.5 wt% HNBR in THF, 25 \u003csup\u003eo\u003c/sup\u003eC, 500 psig H\u003csub\u003e2\u003c/sub\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e**: TPP was added after 50\u0026ndash;60 min of addition of catalyst\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eRegarding the function of TPP, the following dynamic equilibrium has been proposed and is quite likely,\u003c/p\u003e\n \u003cp\u003eRhH(P\u003csup\u003ei\u003c/sup\u003ePr\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e + PPh\u003csub\u003e3\u003c/sub\u003e\u0026nbsp; \u0026nbsp;\u003cimg src=\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAANCAYAAAAnigciAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAADESURBVDhPzZWBDYMgEEWvnYAV3IhRYALdgFFkA0eADWAD2IB6lGsbpVpbG33JaVCO/zQkXNIIHMy13A/l/BIxRrDWltF2vPe51qhKYHjXddA0DWity9Pt4AfgGlLKZRncmEQIIbVtmxhjuFlz4fhb+r5/rIMlhEjOufL2SZaohVPtKUE1lQEUqIX/uzBzGIa7RL6OKKWqk/f+ExjOOU/GmDLrRYKYyuwlUQsnZhIEyfwqsRROvJUglprXwN5P+k9wdgDcAFa72I2PwNWHAAAAAElFTkSuQmCC\"\u003e\u0026nbsp; \u0026nbsp;\u0026nbsp; RhH(PPh\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e + P\u003csup\u003ei\u003c/sup\u003ePr\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003eAs shown above, when TPP is added, TPP ligands start replacing P\u003csup\u003ei\u003c/sup\u003ePr\u003csub\u003e3\u003c/sub\u003e ligands of the initial Rh hydrido complex until an equilibrium that lies far to the right is reached which takes at least 1 hour. Since the original catalyst disappears, no more nitriles would be reduced, and consequently no gelling occurs. To avoid any contact with air or oxygen, the product was stored in a glove box filled with argon gas.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Characterization\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e depicts the FT-IR spectra of hydrogenation of nitrile groups in HNBR with different conversions. The peaks at 2236 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e belong to -C\u0026thinsp;\u0026equiv;\u0026thinsp;N and saturated -[CH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003en\u003c/sub\u003e- unit (n\u0026thinsp;\u0026gt;\u0026thinsp;4) respectively. Since this is HNBR, there are no peaks for unsaturated carbon-carbon bonds at the 920\u0026ndash;1000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region. During the hydrogenation reaction, the v(C\u0026equiv;N) decreases and two bumps at 3200\u0026ndash;3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e appear which are the classic peaks of primary amines. No secondary amines or other types of amines (widely reported side products) are observed. The 723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e peak does not change and the nitrile peak (2236 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) almost disappears when nitrile content is about 10%, which means the catalyst is selectively effective for the hydrogenation of nitrile. The new peak of primary amines confirms that nitrile groups have been successfully converted to amine groups without any side products.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe hydrogenation of the nitrile group on macromolecules was achieved for the first time, the nitrile group was successfully reduced to an amino group, and an efficient and stable hydrogenation catalytic system of HNBR was successfully developed. The nitrile content can be reduced from 40% to less than 10% within 5 hours at 60 \u003csup\u003eo\u003c/sup\u003eC and 500 psig H\u003csub\u003e2\u003c/sub\u003e. The nitrile groups have been converted to primary amines. A potential mechanism for nitrile hydrogenation has been proposed for the first time. Gel formation issues exist during a regular procedure, and temperature and catalyst concentration seem to aggravate gel formation. The causes for gel formation during nitrile reduction have been investigated and a possible mechanism was proposed. Some additives have been tested and some of them are found to be effective to slow down or terminate gel formation. TPP is the most effective additive. At last, it is worthwhile to point out that for the first time a successful system has been developed and established for the reduction of the nitrile content of HNBR (macromolecules) without visible gel formation.\u003c/p\u003e \u003cp\u003eNow that we have confirmed the possibility of nitrile reduction on polymers, this helps to advance the development of degradable polymers. But there are still some problems, such as poor stability of the catalyst, high price; The product system is easy to gel. In the following studies, we will try to use a cheaper and more stable catalytic system, and explore the performance indexes of the aminoylation products in the follow-up experiments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.L. completed all the experimental processes, and M.L. and Z.X. wrote the main manuscript text, H.W. And Q.P. provided part of the theoretical basis, and all authors reviewed the manuscript\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript files\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eJ. Yan and C. Cao, Advances in the Catalytic Hydrogenation and Properties of Unsaturated Polymers, \u003cem\u003eMacromolecules\u003c/em\u003e. 56 (2023), 3774\u0026ndash;3808, https://doi.org/10.1021/acs.macromol.2c02333.\u003c/li\u003e\n\u003cli\u003eM. Feng, Z. Luo, S. Yi, H. Lu, C. Lu, C. Li, J. Zhao and G. Cao, Palladium Supported on Carbon Nanotubes Decorated Nickel Foam as the Catalytic Stirrer in Heterogeneous Hydrogenation of Polystyrene, \u003cem\u003eInd. Eng. Chem\u003c/em\u003e. Res. 57 (2018), 16227\u0026ndash;16238, https://doi.org/10.1021/acs.iecr.8b03810.\u003c/li\u003e\n\u003cli\u003eH. Xie, X. Li, X. Liu, J. Guo, Hydrogenation and Neutralization of Carboxylic Styrene Butadiene Latexto Form Thermoplastic Elastomer with Excellent Thermooxidation Resistance, \u003cem\u003eJ\u003c/em\u003e. \u003cem\u003eAppl\u003c/em\u003e. \u003cem\u003ePolym\u003c/em\u003e. \u003cem\u003eSci\u003c/em\u003e. 83 (2002), 1375\u0026ndash;1384, https://doi.org/10.1002/app.10022.\u003c/li\u003e\n\u003cli\u003eY. He, E. S. Daniels, A. Klein, M. S. El-Aasser, Hydrogenation of Styrene-Butadiene Rubber (SBR) Latexes, \u003cem\u003eJ\u003c/em\u003e. \u003cem\u003eAppl\u003c/em\u003e. \u003cem\u003ePolym\u003c/em\u003e. \u003cem\u003eSci\u003c/em\u003e. 64 (1997), 2047\u0026ndash;2056, https://doi.org/10.1002/(SICI)1097-4628(19970606)64:10\u0026lt;2047::AID-APP19\u0026gt;3.0.CO;2-3\u003c/li\u003e\n\u003cli\u003eH. Wang and G. L. Rempel, Organic Solvent-free Catalytic Hydrogenation of Diene-based Polymer Nanoparticles in Latex form: Mass Transfer of Hydrogen in a Semibatch Process, \u003cem\u003eJ. Ind. Eng. Chem\u003c/em\u003e. 25 (2015), 29\u0026ndash;34, https://doi.org/10.1016/j.jiec.2014.10.009.\u003c/li\u003e\n\u003cli\u003eH. Wang, Q. Pan and G. L. Rempel, Diene-based Polymer Nanoparticles: Preparation and Direct Catalytic Latex Hydrogenation, \u003cem\u003eJ. Polym. Sci. A. Polym. Chem.\u003c/em\u003e 50 (2012), 2098\u0026ndash;2110, https://doi.org/10.1002/pola.25982.\u003c/li\u003e\n\u003cli\u003eW. Tong, H. Chen, Y. Zhang, Z. Zhuo, Y. Fu, H. Qi, D. Zhou, Y. Li and H. Wang, Selective Hydrogenation of Nitrile Butadiene Rubber Latex using Catmetium (R) RF 4 Catalyst, \u003cem\u003eCatal. Today\u003c/em\u003e. 407 (2023), 80\u0026ndash;88, https://doi.org/10.1016/j.cattod.2022.02.015.\u003c/li\u003e\n\u003cli\u003eY. Wang, F. Cao, Y. Fu, H. Chen, Y. Zhang, C. Wang, Y. Li and H. Wang, Preparation of Diene-based Nanoparticles by Semibatch Microemulsion Polymerization and Their Catalytic Hydrogenation, \u003cem\u003eCatal. Today\u003c/em\u003e. 407 (2023), 156\u0026ndash;164, https://doi.org/10.1016/j.cattod.2022.01.022.\u003c/li\u003e\n\u003cli\u003eS. Gomez, J. A. Peters and T. Maschmeyer, The Reductive Amination of Aldehydes and Ketones and the Hydrogenation of Nitriles: Mechanistic Aspects and Selectivity Control, \u003cem\u003eAdv. Synth. Catal\u003c/em\u003e. 344 (2002), 1037\u0026ndash;1057, https://doi.org/10.1002/1615-4169(200212)344:10\u0026lt;1037::AID-ADSC1037\u0026gt;3.0.CO;2-3.\u003c/li\u003e\n\u003cli\u003eP. T. Witte, A New Supported Rhodium Catalyst for Selective Hydrogenation of Nitriles to Primary Amines, \u003cem\u003eCollect. Czech. Chem. Commun\u003c/em\u003e. 72 (2007), 468\u0026ndash;474, https://doi.org/10.1135/cccc20070468.\u003c/li\u003e\n\u003cli\u003eJ. Krupka, J. Drahonsky and A. Hlavackova, Aminocarbene Mechanism of the Formation of a Tertiary Amine in Nitrile Hydrogenation on a Palladium Catalyst, \u003cem\u003eReact. Kinet. Mech. Catal\u003c/em\u003e. 108 (2013), 91\u0026ndash;105, https://doi.org/10.1007/s11144-012-0497-2.\u003c/li\u003e\n\u003cli\u003eK. L\u0026eacute;vay, T. K\u0026aacute;rp\u0026aacute;ti and L. Hegedus, Selective Hydrogenation of Benzonitrile and Its Homologues to Primary Amines over Platinum, \u003cem\u003eJ. Ind. Eng. Chem\u003c/em\u003e. 101 (2021), 279\u0026ndash;292, https://doi.org/10.1016/j.jiec.2021.06.002.\u003c/li\u003e\n\u003cli\u003eA. Mukherjee, D. Srimani, Y. Ben-David and D. Milstein, Low-Pressure Hydrogenation of Nitriles to Primary Amines Catalyzed by Ruthenium Pincer Complexes. Scope and Mechanism, \u003cem\u003eChemCatchem\u003c/em\u003e. 9 (2017), 559\u0026ndash;563, https://doi.org/10.1002/cctc.201601416.\u003c/li\u003e\n\u003cli\u003eR. Adam, C. B. Bheeter, R. Jackstell and M. Beller, A Mild and Base-Free Protocol for the Ruthenium‐Catalyzed Hydrogenation of Aliphatic and Aromatic Nitriles with Tridentate Phosphine Ligands, \u003cem\u003eChemCatChem\u003c/em\u003e. 8 (2016), 1329\u0026ndash;1334, https://doi.org/10.1002/cctc.201501367.\u003c/li\u003e\n\u003cli\u003eC. Bornschein, S. Werkmeister, B. Wendt, H.-J. Jiao, E. Alberico, W. Baumann, H. Junge, K. Junge and M. Beller, Mild and Selective Hydrogenation of Aromatic and Aliphatic (di)nitriles with a well-defined Iron Pincer Complex, \u003cem\u003eNat. Commun\u003c/em\u003e. 5 (2014), 4111, https://doi.org/10.1038/ncomms5111.\u003c/li\u003e\n\u003cli\u003eZ. Ma, V. G. Chandrashekhar, B. Zhou, A. M. Alenad, N. Rockstroh, S. Bartling, M. Beller, R. V. Jagadeesh, Stable and reusable Ni-based nanoparticles for general and selective hydrogenation of nitriles to amines, \u003cem\u003eChem\u003c/em\u003e. \u003cem\u003eSci\u003c/em\u003e. 13 (2022), 10914\u0026ndash;10922, https://doi.org/10.1039/d2sc02961h.\u003c/li\u003e\n\u003cli\u003eD. Formenti, R. Mocci, H. Atia, S. Dastgir, M. Anwar, S. Bachmann, M. Scalone, K. Junge, M. Beller, A State-of-the-Art Heterogeneous Catalyst for Efficient and General Nitrile Hydrogenation, \u003cem\u003eChem\u003c/em\u003e. \u003cem\u003eEur\u003c/em\u003e. \u003cem\u003eJ.\u003c/em\u003e 26 (2020), 15589\u0026ndash;15595, https://doi.org/10.1002/chem.202001866.\u003c/li\u003e\n\u003cli\u003eV. G. Chandrashekhar, T. Senthamarai, R. G. Kadam, O. Malina, J. Kaslik, R. Zboril, M. B. Gawande, R. V. Jagadeesh, M. Beller, Silica-supported Fe/Fe\u0026ndash;O nanoparticles for the catalytic hydrogenation of nitriles to amines in the presence of aluminium additives, \u003cem\u003eNat\u003c/em\u003e. \u003cem\u003eCatal\u003c/em\u003e. 5 (2022), 20\u0026ndash;29, https://doi.org/10.1038/s41929-021-00722-x.\u003c/li\u003e\n\u003cli\u003eS. Chakraborty, G. Leitus and D. Milstein, Selective Hydrogenation of Nitriles to Primary Amines Catalyzed by a Novel Iron Complex, \u003cem\u003eChem. Commun\u003c/em\u003e. 52 (2016), 1812\u0026ndash;1815, https://doi.org/10.1039/c5cc08204h.\u003c/li\u003e\n\u003cli\u003eM. Yoshimura, A. Komatsu, M. Niimura, Y. Takagi, T. Takahashi, S. Ueda, T. Ichikawa, Y. Kobayashi, H. Okami, T. Hattori, Y. Sawama, Y. Monguchi and H. Sajiko, Selective Synthesis of Primary Amines from Nitriles under Hydrogenation Conditions, \u003cem\u003eAdv. Synth. Catal\u003c/em\u003e. 360 (2018), 1726\u0026ndash;1732, https://doi.org/10.1002/adsc.201800102.\u003c/li\u003e\n\u003cli\u003eH.-G. Dai and H.-R. Guan, Switching the Selectivity of Cobalt-Catalyzed Hydrogenation of Nitriles, \u003cem\u003eACS Catal\u003c/em\u003e. 8 (2018), 9125\u0026ndash;9130, https://doi.org/10.1021/acscatal.8b02645.\u003c/li\u003e\n\u003cli\u003eK. Juh\u0026aacute;sz, K. L\u0026eacute;vay, L. Hegedus, D. Balogh-Weiser, L. Pirault-Roy and Z. Hell, Application of Supported Lanthanum Catalysts in the Hydrogenation of Nitriles, \u003cem\u003eReact. Kinet. Mech. Catal\u003c/em\u003e. 133 (2021), 687\u0026ndash;698, https://doi.org/10.1007/s11144-021-02028-2.\u003c/li\u003e\n\u003cli\u003eT. Yoshida, T. Okano and S. Otsuka, Activation of Water-Molecules.4. Generation of Dihydrogen from Water by Rhodium(I) Hydrido and Rhodium(0) Carbonyl-Compounds, \u003cem\u003eJ. Am. Chem. Soc\u003c/em\u003e. 102 (1980), 5966\u0026ndash;5967, https://doi.org/10.1021/ja00538a071.\u003c/li\u003e\n\u003cli\u003eT. Yoshida, T. Okano and Y. Ueda and S Otsuka, Activation of the Water Molecule.5. Rhodium(I) Hydride Catalyzed Water Gas Shift Reaction. Identification of the Elemental Reactions Comprising the Catalytic Cycles, \u003cem\u003eJ. Am. Chem. Soc\u003c/em\u003e. 103 (1981), 3411\u0026ndash;3422, https://doi.org/10.1021/ja00402a027.\u003c/li\u003e\n\u003cli\u003eD. Morton, D. J. Cole-Hamilton, I. D. Utuk, M. Paneque-Sosa and M. Lopez-Poveda, Hydrogen-Production from Ethanol Catalyzed by Group-8 Metal-Complexes, \u003cem\u003eJ. Chem. Soc\u003c/em\u003e. \u003cem\u003eDalton Trans\u003c/em\u003e. 3 (1989), 489\u0026ndash;495, https://doi.org/10.1002/chin.198924064.\u003c/li\u003e\n\u003cli\u003eE. Delgado-Lieta, M. A. Luke, R. F. Jones and D. J. Cole-Hamilton, The Photochemical Decomposition of Alcohols Catalysted by Tri(isopropyl)phosphine Complexes of Rhodium(I), \u003cem\u003ePolyhedron\u003c/em\u003e. 1 (1982), 839\u0026ndash;840, https://doi.org/10.1016/0277-5387(82)80020-X.\u003c/li\u003e\n\u003cli\u003eD. C. D. Butler, D. W. Bruce, P. Lightfoot and D. J. Cole-Hamilton, On the Reduction of Rhodium Trichloride in the Presence of Triisopropylphosphine, \u003cem\u003eCan. J. Chem\u003c/em\u003e. 2001, \u003cstrong\u003e79\u003c/strong\u003e, 472\u0026ndash;478, https://doi.org/10.1139/cjc-79-5/6-472.\u003c/li\u003e\n\u003cli\u003eD. W. Schiering and J. E. Katon, Characteristic Infrared-Absorption Frequencies of the Enol Group of 1,3-Dicarbonyl Compounds, \u003cem\u003eAppl. Spectrosc\u003c/em\u003e. 40 (1986), 1049\u0026ndash;1054, https://doi.org/10.1366/0003702864508106.\u003c/li\u003e\n\u003cli\u003eD. W. Schiering and J. E. Katon, The Vibrational-Spectra and Structure of 4-Methyl Oxaloacetate (Carbomethoxypyruvic Acid), \u003cem\u003eJ. Mol. Struct\u003c/em\u003e. 144 (1986), 25\u0026ndash;38, https://doi.org/10.1016/0022-2860(86)80164-8.\u003c/li\u003e\n\u003cli\u003eE. A. Boyd, D. Lionetti, W. C. Henke, V. W. Day and J. D. Blakemore, Preparation, Characterization and Electrochemical Activation of a Model [Cp*Rh] Hydride, \u003cem\u003eInorg. Chem\u003c/em\u003e. 58 (2019), 3606\u0026ndash;3615, https://doi.org/10.1021/acs.inorgchem.8b02160.\u003c/li\u003e\n\u003cli\u003eX.-C. Chen, T. Lian, K.-C. Zhao, L. Guo, Y. Lu and Y. Liu, Efficient Hydroaminomethylation of Olefins Catalyzed by Rh-complex Ligated by P, O-hybrid Ligand with Chelating Effect, \u003cem\u003eJ. Catal\u003c/em\u003e. 411 (2022), 158\u0026ndash;166, https://doi.org/10.1016/j.jcat.2022.05.010.\u003c/li\u003e\n\u003cli\u003eC. G. Comadoll, W. C. Henke, J. A. Hopkins Leseberg, J. T. Douglas, A. G. Oliver, V. W. Day and J. D. Blakemore Examining the Modular Synthesis of [Cp*Rh] Monohydrides Supported by Chelating Diphosphine Ligands, \u003cem\u003eOrganometallics\u003c/em\u003e. 40 (2021), 3808\u0026ndash;3818, https://doi.org/10.1021/acs.organomet.1c00525.\u003c/li\u003e\n\u003cli\u003eT. Yoshida, T. Okano, D. L. Thorn, T. H. Tulip, S. Otsuka and J. A. Ibers, Preparations and Reactions of Some Hydridodinitrogentrialkylphosphine Complexes of Rhodium(I)-Structure of a Dinitrogen-Bridged Rhodium(I) Dimer, [RhH(P(i-Pr)\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e(\u0026prop;-N\u003csub\u003e2\u003c/sub\u003e), \u003cem\u003eJ. Organomet. Chem\u003c/em\u003e. 181 (1979), 183\u0026ndash;201, https://doi.org/10.1016/S0022-328X(00)85748-4.\u003c/li\u003e\n\u003cli\u003eT. Yoshida, D. L. Thorn, T. Okano, J. A. Ibers and S. Otsuka, Hydration and Reduction of Carbon-Dioxide by Rhodium Hydride Compounds - Preparation and Reactions of Rhodium Bicarbonate and Formate Complexes, and the Molecular-Structure of RhH\u003csub\u003e2\u003c/sub\u003e(O\u003csub\u003e2\u003c/sub\u003eCOH)(P(i-Pr)\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, \u003cem\u003eJ. Am. Chem. Soc\u003c/em\u003e. 101 (1979), 4212\u0026ndash;4221, https://doi.org/10.1021/ja00509a029.\u003c/li\u003e\n\u003cli\u003eC. Lau, Rhodium-Catalyzed Addition of Arylboronic Acids to Nitriles: Application in the Synthesis of Unsymmetrical Polysubstituted Pyridines, University of Toronto. 2011.\u003c/li\u003e\n\u003c/ol\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":"hydrogenated nitrile butadiene rubber, nitrile hydrogenation, hydrido rhodium complex, triphenylphosphine, gel mechanism","lastPublishedDoi":"10.21203/rs.3.rs-5852950/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5852950/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFunctional polymer materials show a variety of functional properties, such as chemical reactivity, photosensitivity, conductivity, catalysis, biocompatibility and so on. The polymer containing amine group can be used in many fields such as organic polymer catalyst carrier, sewage adsorption treatment, medicine and pharmacy, biological engineering, etc. We note that the amination of small nitrile groups has formed a relatively mature system, but similar reactions for macromolecular raw materials have not been reported. Based on this, the catalytic hydrogenation of nitrile groups on macromolecules was achieved for the first time, the nitrile group was successfully reduced to an amino group, and an efficient and stable hydrogenation catalytic system of HNBR was successfully developed. The reactivity of the catalytic system was studied, considering the catalyst/polymer ratio, reaction temperature, and hydrogen pressure. The optimal experimental conditions were obtained. The study successfully established a corresponding catalytic system to produce HNBR with a controlled amount of ACN. Within a reaction time of 5 hours at 60\u0026deg;C and 500 psig H\u003csub\u003e2\u003c/sub\u003e, the nitrile content in HNBR systems could be reduced from 40% to less than 10%, without the formation of side products like secondary amines. This reduction process involved the conversion of nitrile groups into primary amines, and a possible mechanism for this transformation was proposed for the first time. The formation of gel during nitrile reduction was also investigated, and a potential mechanism was suggested. Various additives were tested, and it was found that some of them effectively slowed down or prevented gel formation. Among these additives, triphenylphosphine (TPP) was identified as the most effective one.\u003c/p\u003e","manuscriptTitle":"Hydrogenation of nitrile groups in HNBR with a rhodium catalyst","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-09 11:48:07","doi":"10.21203/rs.3.rs-5852950/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":"e9c0cefd-afc4-4400-a02e-daa68daa952d","owner":[],"postedDate":"April 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":46767326,"name":"Physical sciences/Chemistry/Materials chemistry"},{"id":46767327,"name":"Physical sciences/Chemistry/Organic chemistry"},{"id":46767328,"name":"Physical sciences/Chemistry/Polymer chemistry"}],"tags":[],"updatedAt":"2025-04-17T05:23:55+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-09 11:48:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5852950","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5852950","identity":"rs-5852950","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}