special additives. For example, CoCl2, ZrCl4, I2 and bis(2-bromoethyl)selenium dibromide 6 are effective additives for the reaction. Recently Khurana et al 7 reported that aromatic nitriles could be reduced to primary amines with NaBH4 using NiCl2 as additive. However, this method is not efficient for aliphatic nitriles. Caddick and co-workers 8 introduced a suitable trapping agent such as acetic anhydride or di-tert-butyl dicarbonate to the reaction (NiCl2/NaBH4), the protected primary amines were firstly obtained, and the product amines were formed by subsequent deprotection treatment. In this method, longer synthesis routes were needed and the yields of primary amines are not high enough.
KBH4 is usually used to react with metal salts to prepare metal borides 9 that are used as the catalysts in catalytic hydrogenation. To the best of our knowledge, KBH4 has never been used with additives to enhance its reducing activity in transforming nitriles to amines. On the other hand, Raney nickel is routinely used as catalyst in catalytic hydrogenation 10 and heterogeneous catalytic hydride transfer hydrogenation.11 The scope of its utilization also involves the selective reduction of nitrocompounds, dinitrosubstituted diphenylsulfones, O- and N-benzyl containing nitrocompounds; the conversion of nitro olefins to carbonyl derivatives,12 and the synthesis of halo amines from halo nitro compounds. In these cases, the commonly used hydrogen donors are hydrazine hydrate, hydrazine derivative 13, ammonium formate, formic acid or cyclohexene. In 2002, Gowda et al 14 found that using Raney Ni / N2H4 / HCOOH could transform nitriles to primary amines with the yield of about 70%.
Results and Discussion
In this context, we first report a simple and convenient procedure (Scheme 1) to directly convert the robust aliphatic and aromatic nitriles 1 to the corresponding primary amines 2 with high isolated yields (over 80%) by using Raney Ni / KBH4 system in dry ethanol at mild temperature.
R-CH2NH2dry ethanol, 45min1a-l2a-lRaney Ni/KBH4R-CNR= aliphatic or aromatic substituents
Scheme 1
CNNH21a2aRaney Ni / KBH4dry Ethanol (1)
