Amine oxidation. Part XII. Reactions of some NN-dimethylbenzylamine N-oxides with acetic anhydride and of some N-acetoxy-NN-dimethylbenzylammonium perchlorates with acetate ion. The Polonovski reaction

Abstract

The reactions of acetic anhydride with NN-dimethylbenzylamine N-oxide and five of its substituted derivatives (the Polonovski reaction) to give NN-dimethylacetamide, an N-benzyl-N-methylacetamide, and a benzaldehyde have been studied by use of n.m.r. and g.l.c. The effect of the substituents on the relative proportions of debenzylation and demethylation is discussed in terms of a variable transition state in the product-determining step for debenzylation: with an electron-donating group, such as 4-OMe, it is iminium ion-like whereas with the electron-withdrawing 4-NO₂ it has carbanionic character. The preparations of N-acetoxy-NN-dimethylbenzylammonium perchlorate and its 4-Cl and 4-NO₂ derivatives are described. The thermal stability of these salts and their reactions with acetate ion are reported. These data agree with an N-acetoxyammonium ion being the first intermediate in the Polonovski reaction, and with the overall conversion of this ion into acetamides being an ionic process induced by acetate ion. No evidence for any radical intermediates was obtained.