Products, kinetics, and mechanism of the chlorination of 2,3-dimethylbenzothiophen in acetic acid

Abstract

Chlorination of 2,3-dimethylbenzothiophen in acetic acid in the dark gives 2-chloromethyl-3-methylbenzothiophen quantitatively. The reaction is of zero order in the component which is in excess and of first order in the other. The rate and kinetic form remain unchanged in the presence of aromatic hydrocarbons which are extremely reactive towards chlorine. These facts can be explained if chlorine and 2,3-dimethylbenzothiophen interact rapidly to give an adduct which decomposes slowly to the products. The stability constant of this adduct is estimated to be >10⁶ l. mole^–1. The nature of the adduct and the reaction mechanism are discussed.