The isomerization of n-butenes catalyzed by RhCl(PPh3)3-I. The isomerization of 2-butenes

In dichloromethane solution, cis- and trans-2-butene are catalytically isomerized by RhCl(PPh₃)₃. The slow reaction reaches the thermodynamic equilibrium of the three possible n-butenes. The isomerization shows a marked induction period. When pure cis-2-butene is isomerized, 1-butene temporarily reaches twice the equilibrium concentration. The kinetic data suggest that RhCl(PPh₃)₃ is not the catalytically active species. Dissociation of the original rhodium complex appears to be a requirement for the isomerization of the olefins.     

Hydroformylation of Olefins by a Rhodium Single‐Atom Catalyst with Activity Comparable to RhCl(PPh3)3

Homogeneous catalysts generally possess superior catalytic performance compared to heterogeneous catalysts. However, the issue of catalyst separation and recycling severely limits their use in practical applications. Single‐atom catalysts have the advantages of both homogeneous catalysts, such as “isolated sites”, and heterogeneous catalysts, such as stability and reusability, and thus would be a promising alternative to traditional homogeneous catalysts. In the hydroformylation of olefins, single‐atom Rh catalysts supported on ZnO nanowires demonstrate similar efficiency (TON≈40000) compared to that of homogeneous Wilkinson's catalyst (TON≈19000). HAADF‐STEM and infrared CO chemisorption experiments identified isolated Rh atoms on the support. XPS and XANES spectra indicate that the electronic state of Rh is almost metallic. The catalysts are about one or two orders of magnitude more active than most reported heterogeneous catalysts and can be reused four times without an obvious decline in activity.     

Homogeneous catalytic hydrogenation of liquid carboxylated nitrile rubber

Homogeneous catalytic hydrogenation of olefinic bonds in liquid carboxylated nitrile rubber (L-XNBR) has been carried out selectively in the presence of nitrile and carboxyl functionality using a six-membered cyclopalladate complex of 2-benzoyl pyridine as catalyst. The degree of hydrogenation has been calculated from IR and NMR spectroscopic studies. For example, 68% hydrogenation has been obtained for a sample (containing 0.057 carboxyl equivalent/100 g and 26.1% acrylonitrile) under 2.7 MPa hydrogenation pressure, 0.18 mmol/L catalyst, at 333 K for 1 h in acetone solution. The overall extent of hydrogenation depends on the catalyst-to-double-bond ratio. The kinetics of hydrogenation of L-XNBR has been investigated. The reaction exhibits a pseudo-first order dependence on the concentration of the substrate. The rate constant of the reaction is reduced by the increase in carboxyl and nitrile content of the polymer. The effect of temperature on reaction kinetics has also been studied and the activation energy of hydrogenation of L-XNBR is 20.2 kJ/mol. Intrinsic viscosity of the polymer remains unchanged during the reaction. A significant lowering of the glass transition temperature and improvement of thermal stability have been observed on hydrogenation. © 1992 John Wiley & Sons, Inc.     

Crosslinker free thermally induced crosslinking of hydrogenated nitrile butadiene rubber

Hydrogenated nitrile butadiene rubbers (HNBRs) are hydrogenated copolymers of acrylonitrile and butadiene, which are often used in composites or polymer blends. These copolymers are usually cured with peroxides or vulcanized with sulfur to reinforce their mechanical resistance and improve their chemical stability. However, using such crosslinking reagents can be problematic for high value systems where residual H₂O₂ or S can be detrimental for the application. To address this limitation, we studied the thermally induced crosslinking of HNBR at high temperature (240 °C) with oxygen. To understand the impact of conditions (temperature, time, and atmosphere) on the chemical structure and the mechanical properties of HNBR, different thermal treatments were investigated. We show that HNBR forms a ladder structure during treatment in the presence of O₂ which result in a reinforcement of the elastomer. Tensile tests and DSC show both alkene and nitrile moieties are involved in the reaction, leading to a mechanical resistance comparable with a HNBR crosslinked with peroxides or sulfur. These findings will help achieving a better control on the crosslinking to provide HNBRs with desired properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1825–1833     

Reduction of nitriles with 2-propanol in presence of RhCl(PPh3)3 and RuCl2(PPh3)3

Conclusions The complexes RhCl(PPh₃)₃ and RuCl₂(PPh₃)₃ catalyze hydrogen transfer from 2-propanol to the C N bond of benzonitrile and capronitrile. The reduction rate of the aromatic nitrile is higher than that of the aliphatic nitrile.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1894–1895, August, 1976.     

Low oxidation state ruthenium chemistry : IV. The reactions of M(CO)2(PPh3)3 complexes (M = Fe,Ru) and the hydrogenation and isomerization of alkenes catalyzed by RuL(CO)2(PPh3)2 (L = H2, PPh3)

The complexes M(CO)₂(PPh₃)₃ (I, M = Fe; II, M = Ru) readily react with H₂ at room temperature and atmospheric pressure to give cis-M(H)₂(CO)₂(PPh₃)₂ (III, M = Fe;IV,M = Ru). I reacts with O₂ to give an unstable compound in solution, in a type of reaction known to occur with II which leads to cis-Ru(O₂)(CO)₂(PPh₃)₂(V). Even compound IV reacts with O₂ to give V with displacement of H₂; this reaction has been shown to be reversible and this is the first case where the displacement of H₂ by O₂ and that of O₂ by H₂ at a metal center has been observed. III and IV are reduced to M(CO)₃(PPh₃)₂ by CO with displacement of H₂; Ru(CO)₃- (PPh₃)₂ is also formed by treatment of IV with CO₂, but under higher pressure. Compounds II and IV react with CH₂CHCN to give Ru(CH₂CHCN)(CO)₂- (PPh₃)₂(VI) which reacts with H₂ to reform the hydride IV.cis-Ru(H)₂(CO)₂(PPh₃)₂(IV) has been studied as catalyst in the hydrogenation and isomerization of a series of monoenes and dienes. The catalysts are poisoned by the presence of free triphenylphosphine. On the other hand the ready exchange of H₂ and O₂ on the “Ru(CO)₂(PPh₃)₂” moiety makes IV a catalyst not irreversibly poisoned by the presence of air. It has been found that even Ru(CO)₂(PPh₃)₃(II) acts as a catalyst for the isomerization of hex-1-ene at room temperature under an inert atmosphere.     

The isomerization of n-butenes catalyzed by RhCl(PPh3)3. II. The isomerization of 1-butene

1-butene is catalytically isomerized by RhCl(PPh₃)₃ in dichloromethane solution. The slow reaction starts with an induction period and reaches the equilibrium distribution of the three n-butenes. The pseudo first order reaction rate, as taken from the second half of the reaction, depends on the square root of the catalyst concentration and the inverse of the concentration of free triphenylphosphine. At relatively low butene concentrations the reaction rates fall off. This is interpreted as meaning that a PPh₃—butene ligand exchange equilibrium is essential for the activation of the catalyst. ³¹P n.m.r. spectroscopy suggested that a trans-RhCl(PPh₃)₂(C₄H₈) complex existed in solution. Because of the high cis-2-butene/trans-2-butene ratio formed at the beginning of the reaction the activation of the olefinic double bond is thought to occur via a π-allyl mechanism.     

Determination of carboxyl content in carboxylated nitrile butadiene rubber (XNBR) after degradation via olefin cross metathesis

Carboxyl content in nitrile butadiene rubber (XNBR) has an impact on its application performance. However, its poor solubility makes it difficult to determine the carboxyl content in XNBR due to its high molecular weight. In the present work, olefin cross metathesis was used to degrade XNBR with acrylonitrile (AN) as chain transfer agent for the first time, to solve the solubility problem. After degradation under the optimized condition, with 2% AN and 0.2% catalyst at 60 °C for 30 min, the weight-average molecular weight (M_w) of the product decreased to 0.98 × 10⁴ with distribution (M_w/M_n) of 3.83. Such product was easy to be dissolved, so the carboxyl content in XNBR could be determined with the routine titrimetric analysis methods.     

Network characteristics of hydrogenated nitrile butadiene rubber networks obtained by radiation crosslinking by electron beam

The effects of high-energy radiation on hydrogenated nitrile butadiene rubber (HNBR) copolymer structure and properties were studied. Characterization by FTIR spectroscopy, swelling and mechanical measurements of irradiated and un-irradiated sample permit us to correlate the change in structure with properties. The modifications obtained are dependent on the radiation dose of the incident electron beam. FTIR spectroscopy in absorption mode shows that irradiation of HNBR first induces trans-vinylene bond formation and secondly small amounts of carbonyl (CO) groups. Moreover, more significant changes were observed with swelling method and mechanical behaviour showing the effect of crosslinking on the elastomer.     

Study on ablative properties and mechanisms of hydrogenated nitrile butadiene rubber (HNBR) composites containing different fillers

The ablative properties of hydrogenated nitrile butadiene rubber (HNBR) composites filled with fumed silica, organically modified montmorillonite (OMMT), or expanded graphite (EG) were examined. The HNBR/OMMT composite has the lowest linear ablation rate and the highest mass ablation rate and does not tend to be carbonized. On the other hand, the HNBR/EG composite has the highest linear ablation rate and the lowest mass ablation rate, and is prone to carbonization. The ablative properties of the HNBR/silica composite are between those of HNBR/OMMT and HNBR/EG. From the viewpoint of thermal shielding capability, the HNBR/OMMT has the best ablation resistance. Thermogravimetric analysis (TGA) on different HNBR composites indicated that the filler type has no significant effect on the thermal stability of the composites. To understand the ablation mechanisms, the char layers of different HNBR composites after ablation experiments were characterized by scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS), and wide-angle X-ray diffraction (WAXD). The results showed that the porosity in the char layers of the HNBR/OMMT composite was the highest and the corresponding structure was the loosest of the three composites. The montmorillonite (MMT) dispersed in HNBR experienced phase transition, melting and vaporization when exposed to the flame with the temperature over 2000 °C. Fumed silica only melted at such situation. On the other hand, the EG kept their original crystalline structures after the ablation test. Based on these results, the effect of the filler type on the ablation mechanisms of the HNBR composites was discussed.     

Cyclization of unsaturated aldehydes catalyzed by (PPh3)2Co(Ph2PCH2CH2PPh2)

Catalytic cyclization of ,-unsaturated aldehydes (intramolecular hydroacylation) in the presence of (PPh₃)₂Co(Ph₂PCH₂CH₂PPh₂) gives four-membered and five-membered cycloalkanones. Depending on aldehyde structure the selectivity is 90–97% at 10–100% aldehyde conversion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2565–2568, November, 1989.     

TG-MS analysis of nitrile butadiene rubber blends (NBR/PVC)

Blends of nitrile butadiene rubber (NBR) with polyvinyl chloride (PVC) are widely used in products such as hoses and seals. As part of a project that uses NBR/PVC blends for manufacturing forest fire hoses, blends of NBR/PVC with various inorganic fillers, such as Mg(OH)₂, china clay (organic modified kaolin) and nano clay (organic modified bentonite) were studied by TG-MS. No significant changes were observed to the type of the polymers’ decomposition products, compared to that of NBR/PVC blend without additives. The most remarkable change was the absence of HCl from decomposition products in the presence of the Mg(OH)₂ additive.     

An unusual dimerization of primary unsaturated alcohols catalyzed by RuHCl(CO)(PPh3)3

When primary unsaturated alcohols were treated with a catalytic amount of RuHCl(CO)(PPh3)3 in benzene under reflux, dimerization reactions took place to give alpha-hydroxymethyl ketones as major product.     

Photochemical reactions of (CO)2 (PPh3)MnC5H4Fe(CO)2C5H5 and (CO)2(PPh3)MnC5H4COFe(CO)2C5H5 with PPh3

Conclusions The photochemical reactions of (CO)₂(PPh₃)MnC₅H₄Fe(CO)₂C₅H₅ and (CO)₂(PPh₃)MnC₅H₄COFe(CO)₂C₅H₅ with PPh₃ gave the products of replacing the CO on the Fe atom by PPh₃: respectively (CO)₂(PPh₃)MnC₅H₄Fe (CO)(PPh₃)C₅H₅ and (CO)₂(PPh₃)MnC₅H₄COFe(CO)(PPh₃)C₅H₅.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2813–2815, December, 1977.     

Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber,styrene–butadiene rubber,and polybutadiene rubber

Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene–butadiene rubber (23% styrene content), and with polybutadiene rubber with Na‐montmorillonite clay. The clay was modified with stearyl amine and was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm^?1) in the FTIR spectra. The clay–rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1573–1585, 2004