Below is the mechanism of the reduction of an nitrile to amine using LiAlH4 (LAH). I have kept it simple by not going into much details.
Transfer of a hydride ion from lithium aluminum hydride to the carbon atom of the nitrile generates an imine intermediate, which is in equilibrium with the corresponding imino alanate.
The imino alanate converts to the amino alanate after adddition of an additional hydride ion.
Hydrolysis yields the primary amine.
thank you so much for the mechanism :) however, one point- in the last intermediate, can we not show that the N donates an lp to the Al, thus completing its octet - that could be the major contributor to the resonance hybrid of that structure. Furthermore, can't the intermediate react further? After all, there are 2 more H's on the Al if we are to use LiAlH4. that would eventually yield a species with N=Al=N. have you heard of such species? sorry, again, for such weird queries :P
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