Selective aromatic chlorination and bromination with N-halogeno amines in acidic solution

Abstract

1,2-Dimethoxybenzene and 3,4-dimethoxytoluene are efficiently chlorinated by N-chlorodialkylamines in sulphuric acid. The reaction has a very marked selectivity for monochlorination of the para-position. The chlorination and bromination of monoalkylbenzenes (toluene, ethyl-, and isopropylbenzenes) under the same conditions is much less selective, but the para/ortho ratio can be reversed going from unsubstituted alkyl groups in the N-halogeno amines to alkyl groups substituted at the β-position by electron-withdrawing groups [morpholine, piperazine, bis(cyanoethyl)amine]. m-Xylene is chlorinated with high selectivity at the 4-position. The nature of the chlorinating species is discussed.