Cobalt borides hydrogenation

Adiponitrile undergoes the typical nitrile reactions, eg, hydrolysis to adipamide and adipic acid and alcoholysis to substituted amides and esters. The most important industrial reaction is the catalytic hydrogenation to hexamethylenediarnine. A variety of catalysts are used for this reduction including cobalt—nickel (46), cobalt manganese (47), cobalt boride (48), copper cobalt (49), and iron oxide (50), and Raney nickel (51). An extensive review on the hydrogenation of nitriles has been recendy pubUshed (10). 

Cobalt boride catalysts have been shown to be highly active and selective in the hydrogenation of nitriles to primary amines.103,104 Barnett used Co boride (5%) supported on carbon for the hydrogenation of aliphatic nitriles and obtained highest yields of primary amines among the transition metals and metal borides investigated including Raney Co.104 An example with propionitrile, where a 99% yield of propylamine was obtained in the presence of ammonia, is seen in eq. 7.29. 

High yields of primary amines have also been obtained over cobalt boride as catalyst,26,53,54 which has been found to be not only highly selective but also less inhibited by solvent and ammonia than other cobalt and nickel catalysts in hydrogenation of nitriles.26 The hydrogenation of propionitrile in isopropyl alcohol over cobalt boride (5% on C) in the presence of 15 1 molar ratio of ammonia to the nitrile gave propylamine in a high yield of 99% (eq. 7.29). 

Nitriles have been hydrogenated at low temperatures and pressures over heterogeneou.s and homogeneous catalysts to produce amines, aldehydes, primary alcohols or alkanes. The reduction to produce amines is by far the most widely used transformation. The most commonly used catalysts are Raney nickel, Raney cobalt, nickel boride, cobalt boride, rhodium, palladium or platinum on various supports. Products formed in the hydrogenation of a nitrile (RCN) are determined by the fate of the intermediate... 

While a nickel boride catalyst preferentially saturates the carbon-carbon double bond of a,p-unsaturated aldehydes, the cobalt borides have a tendency to favor carbonyl group hydrogenation. Cinnamaldehyde was hydrogenated to cinnamoyl alcohol in 97% selectivity at 50% conversion and 86% selectivity at 74% conversion over a P-2 cobalt boride (Eqn. 12.7).5 With a P-2W cobalt boride the unsaturated alcohol was produced in 97% selectivity at 73% conversion. The presence of the aromatic ring enhances selectivity in this reaction since the hydrogenation of crotonaldehyde to 2-buten-l-ol occurred with only about a 25% selectivity at under 20% conversion over either catalyst (Eqn. 12.8).54... 

Other Reductions. The (porphinato)irons could realize the reduction of alkenes and alkynes with NaBILj. Various unsaturated carbon-carbon bonds were saturated by meso-tetraphenylporphinatoiron chloride (TPPFe Cl) derivatives (up to 81% yield). Ruthenium(III) complexes also pair with NaBH in the reduction of unsaturated carbon-carbon bonds (as does cobalt boride). In the presence of a catalytic amount of Ru(PPh3)4H2 (0.5-1 mol %) and NaBHj, unsaturated carbon-carbon bonds in a wide variety of alkenes and alkynes were saturated in toluene at 100 Addition of water was required to provide a proton source. Similar systems with RUCI3 in aqueous solution reduce unsaturated bonds under milder conditions. Various unactivated mono- or disubstituted olefins and activated trisubstituted olefins were reduced with RUCI3 (10 mol %) and NaBH4 in THF-H2O at 0 °C to room temperature (eq 36). When the RuCl3-catalyzed reductions of olefins were carried out in aqueous amide solution, unactivated trisubstituted olefins were also hydrogenated. ... 

Monodisperse particles present the advantage of uniform active site distribution and can be considered as models for heterogeneous catalytic reactions. Monodisperse metals, metal oxides or metal borides can now be easily obtained using microemulsions, vesicles, polymers or normal micelles (refs. 1-4). Microemulsions were used to obtain monodisperse particles of platinum (refs. 5-7), palladium (refs. 5,6), rhodium (refs. 5,6), iridium (ref. 5) and gold (ref. 8) by reducing the precursor metal ions with hydrogen, hydrazine, sodium borohydride or solvated electrons. Monodisperse nickel boride (refs. 1,9-12), cobalt boride (refs. 1,10,13-17), nickel-cobalt boride (refs. 1,10,15-17), and mixtures of iron boride and iron oxides (refs. 1,18) were prepared by sodium borohydride reduction of the precursor metal ions. Iron oxides (ref. 19), magnetite (ref. 20), calcium carbonate (ref. 21) and silver chloride (ref. 22) were obtained by precipitation reactions. 

Adiponitrile hydrogenated with 10% cobalt boride (prepared from NaBH4 and GoGlg in water) at 80° in the presence of NHg in a rotating autoclave hexa-methylenediamine. Y 95.7%. B. D. Polkovnikov, L. K. Freidlin, and A. A. Balandin. Izvest. 1959, 1488 G. A. 54, 1264h. 

Catalysts show remarkable product variation in hydrogenation of simple nitriles. Propionitrile, in neutral, nonreactive media, gives on hydrogenation over rhodium-on-carbon high yields of dipropylamine, whereas high yields of tripropylamine arise from palladium or platinum-catalyzed reductions (71). Parallel results were later found for butyronitrile (2S) and valeronitrile (74) but not for long-chain nitriles. Good yields of primary aliphatic amines can be obtained by use of cobalt, nickel, nickel boride, rhodium, or ruthenium in the presence of ammonia (4J 1,67,68,69). 

Nitta et al. compared the selectivity of copper, cobalt, and nickel borides (Cu-B, Co-B, and Ni-B) as well as Raney Ni and Ni-B modified with copper(II) chloride, in the partial hydrogenation of acetylenic compounds.82 The selectivity at 30% conversion... 

P-1 Ni16 and P-1 Co17 boride catalysts have also proved to be good catalysts for the hydrogenation of aromatic hydrocarbons. Table 11.3 compares the activities of these nickel and cobalt catalysts in the hydrogenation of some aromatic hydrocarbons in hydrocarbon solvent at 80°C and the initial hydrogen pressure of 7.8 MPa.18 It is noted that, as in the cases of Raney Ni and Raney Co, P-1 Co boride is generally more active than P-1 Ni boride, except for o-xylene. 

By heating mixtures of cobalt and boron in a current of hydrogen at 1100-1200° C., du Jassoneix 4 has prepared two borides of cobalt, namely, the Sub-boride, CoaB, and the Di-boride, CoB2. The former occurs as brilliant steel-grey needles of density 7-9 at 20° C. These are oxidised by moist air and readily dissolve in nitric acid. The di-boride represents the extreme limit of combination of boron with iron. Evidence of the existence of aMono-boride, CoB, has also been obtained.5... 

The horohydride reduction of a nickel salt solution containing small amounts of other metal salts can lead to co-reduced mixed metal borides that frequently have enhanced catalytic properties when compared to the unmodified nickel boride. The presence of about 2% chromium significantly increased the activity of a P-1 nickel boride toward aldehyde hydrogenation. Molybdenum, tungsten and vanadium modifiers were somewhat less effective than chromium while the presence of a small amount of cobalt had an inhibiting effect on the reaction.22 As the data in Fig. 12.2 show, the amount of chromium responsible for optimum P-1 nickel boride activity depends on the substrate being hydrogenated.39... 

Metal Borides.—Chemical and ESCA studies on hydrogen adducts of cobalt and nickel borides are consistent with the formulations (Co2B)5H3 and (Ni2B)2H3.328... 

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