Nitriles, reaction with LiAlH

A number of organic species, including amides, oximes, and nitriles, undergo reductive amination, a variety of reduction reactions that produce cimines. In general, these processes involve imines, R=N-R, or related species. Reduction processes include hydrogenation using Raney nickel as the catalyst (for nitriles), the reaction with sodium/EtOH (for oximes), and the use of lithium aluminum hydride, LiAlH (for amides or nitriles). Figure 13-16 illustrates the preparation of amphetamine by reductive amination. 

Acid chlorides, R(Ar)COCl, are reduced to R(Ar)CHO by Hj/Pd(S), a moderate catalyst that does not reduce RCHO to RCHjOH (Rosenmund reduction). Acid chlorides, esters (R(Ar)COOR), and nitriles (RC N) are reduced with lithium tri-t-butoxyaluminum hydride, LiAlH[OC(CH3)3]j, at very low temperatures, followed by HjO. The net reaction is a displacement of X by H",... 

With few exceptions, organometalUcs add only once to nitriles (Section 8.6.4). Only if there is a very strong Lewis acid present to activate the anionic intermediate of the first nucleophilic attack will a second addition take place. An example of this second addition is the reduction of nitriles with LiAlH4, which proceeds all the way to the amine (Section 8.6.3). The AIH3 formed from the initial reduction acts as a Lewis acid to catalyze the second addition. This second addition can be prevented by using one equivalent of a less reactive aluminum hydride like LiAlH(OEt)3 or diisobutylaluminum hydride, [(CH3)2CHCH2l2AlH. The reactions in the acidic water workup are the reverse of imine formation (Section 10.5.2). 

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