A substantially anhydrous reaction mixture for the preparation of (R.sub.1)(R.sub.2).sub.2 Si--CN comprising hydrogen cyanide, (R.sub.1)(R.sub.2).sub.2 Si--X and (R.sub.1)(R.sub.2).sub.2 Si--NH--Si(R.sub.1)(R.sub.2).sub.2 or(R.sub.1)(R.sub.2).sub.2 Si--NH.sub.2, wherein X is Cl, Br, or I, and R is a t-butyl or aryl group, and R.sub.2 is a C.sub.1 -C.sub.6 alkyl group.21.