Trimethylsilyl cyanide

Trimethylsilyl cyanide is the chemical compound with the formula (CH3)3SiCN. This volatile liquid consists of a cyanide group, that is CN, attached to a trimethylsilyl group. The molecule is used in organic synthesis as the equivalent of hydrogen cyanide. It is prepared by the reaction of lithium cyanide and trimethylsilyl chloride:
 * LiCN +  (CH3)3SiCl  &rarr; (CH3)3SiCN  +  LiCl

In its principal reaction, it adds across carbon-oxygen double bonds, for example in an aldehyde:
 * RCHO +  (CH3)3SiCN  &rarr;  RCH(CN)OSi(CH3)3

The product is an O-silylated cyanohydrin.

One use of this reagent is to convert pyridine-N-oxides into 2-cyanopyridine. This transformation is best done in dichloromethane solution using dimethyl carbomyl chloride as the activating electrophile. It is possible to use benzoyl chloride but the yields and regioselectivity of the addition of the cyano group are lower.

Safety
Trimethylsilyl cyanide is treated with care since it hydrolyzes to give hydrogen cyanide:
 * 2 (CH3)3SiCN +  H2O  &rarr;  (CH3)3SiOSi(CH3)3  +  2 HCN