Cobalt boride

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. 

5% Co Boride—C.104 Charcoal (20 g) in distilled water (8 ml) is soaked for 15 min. Cobalt nitrate (4.2 g) in water (20 ml) is added and the mixture heated gently to dryness. The charcoal is cooled in ice water and sodium borohydride (25 ml of 20% solution) is added slowly to avoid rapid effervescence. The mixture is allowed to stand for 16 h and is filtered, and the catalyst is washed with copious amounts of water, then 

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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 has been used for reducing unsaturated aldehydes to unsaturated alcohols improved results are obtained by addition of ferric chloride or chromium chloride (6S). It is a low-activity catalyst. 

Reactive Sputtering. Nanocomposite films of Ni3N/AlN, CoN/BN, and CoN/ Si3N4 were synthesized by reactive sputtering of a nickel aluminide, a cobalt boride,... 

Monodispersed, 2- to 6-nm-dia- Particles, formed from their metal salts by meter nickel boride, cobalt boride, NaBH4 reduction, were used as catalysts, nickel-cobalt boride, and iron Micellar core size controlled particle sizes... 

Cobalt boride-r-Butylamine-borane, Co2B-(CH3)3CNH2 BH3. 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

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... 

Industrially, borides are prepared in various ways, including reduction of metal oxides by mixtures of carbon and boron carbide, electrolysis in fused salts, and direct combination of the elements. For research purposes, the last method is usually used. Cobalt boride, made in aqueous solution by reduction of Co2+ salts with NaBH4 is an active catalyst for reduction of various substrates.6... 

Petit C and Pileni M P 1997 Nanosized cobalt boride particles control of the size and properties J. Magn. Magn. Mater. 166 82... 

Nitriles are, with few exceptions, not reduced by NaBHa. SulfuratedNaBHa, prepared by the reaction of sodium borohydride with sulfur in THF, is somewhat more reactive than NaBHa, and reduces aromatic nitriles (but not aliphatic ones) to amines in refluxing THF. Further activation has been realized by using the Cobalt Boride system, (NaBHa-CoCD which appears to be one of the best methods for the reduction of nitriles to primary amines. More recently it has been found that Zirconium(IV) Chloride Et2SeBr2, CuSOa, Chlorotrimethylsilane, and l2 are also efficient activators for this transformation. The NaBHa-Et2SeBr2 reagent allows the selective reduction of nitriles in the presence of esters or nitro groups, which are readily reduced by NaBHa-CoCL. 

NaBH4 modified with equimolar amounts of Co salts (see Cobalt Boride) or Ni salts (see Nickel Boride) reduces nitriles to amines. It was found that nitriles could be reduced with NaBH4 in the presence of a catalytic amount (10 mol %) of Ni salts. 

Related Reagents. Cerium(III) Chloride Nickel Boride Potassium Triisopropoxyborohydride Sodium Cyanoboro-hydride Sodium Triacetoxyborohydride Cobalt Boride Lithium Borohydride Lithium Aluminium Hydride Zinc Borohydride Tetramethylammonium Triacetoxyborohydride. 

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