Reactions of Amine Oxides and Hydroxylamines with Sulfur Dioxide

Abstract

Strychnine N-oxide (8; X = H) reacts with sulfur dioxide in benzene to form the sulfitoamine 9 (X = H), which rearranges in boiling water to the substituted sulfamic acid 10 (X = H) by a free-radical mechanism. The sulfamic acid 10 (X = H) is also formed by reaction of strychnine N-oxide with cold aqueous sulfur dioxide, and may be an intermediate in the reduction of the amine oxide by sulfur dioxide in hot water. With aqueous sulfur dioxide at 0°, N,N-dimethylbenzylamine N-oxide gives tertiary amine by reduction and secondary amine and aldehyde by a Polonovski-type reaction; however, N,N-dimethylaniline N-oxide gives tertiary amine, o- and p-dimethylaminobenzene sulfonic acids, but no appreciable amount of secondary amine. The sulfonic acids are probably formed by a free-radical mechanism, since their formation is largely suppressed by the addition of hydroquinone. The reactions of hydroxylamine and of β-phenylhydroxylamine with sulfur dioxide in water have also been studied.