Mechanistic studies of chlorination of aromatic compounds using bleach.

Abstract

The mechanism of chlorination of aromatic substances using a two-layer system with bleach as an aqueous phase and a catalyst to ensure phase transfer has been causing controversy for years. The kinetic studies of the chlorination of the a-position in toluene, the o,p-positions in anisole and the ipso-position in bromobenzene were conducted. The obtained reaction orders were mixed "0+1" for anisole and toluene and 2nd for bromobenzene, as well as 1st for chloride ion. The influence of a phase-transfer catalyst and a change of solvent on the rate of anisole chlorination and on its selectivity were also investigated. Based on the kinetic information available, a detailed mechanism is being proposed. The ratio of para-and ortho-isomers in anisole chlorination was calculated theoretically based on the proposed scheme and then compared to the experimental data. A definite correlation between the two series can be regarded as another evidence supporting the idea of a free-radical aromatic substitution mechanism involving both free Cl" and stabilized Cl" as the species reacting in a competitive manner.