Some observations relating to substituent effects in halogenation. Part III. The kinetics of the reaction of diphenylmethane with chlorine acetate in aqueous acetic acid at 25°

Abstract

The reaction of diphenylmethane with chlorine acetate has been examined in acetic acid–water mixtures in the presence of varying amounts of perchloric acid at 25°. In 98 % acetic acid and in the presence of perchloric acid the reactive species are considered to be molecular chlorine acetate and its protonated form. Under these conditions diphenylmethane reacts 21·8 times faster than benzene and gives 40·0 % of the 4- and 59·3 % of the 2-chlorodiphenylmethane. The reaction in 75 % acetic acid in the presence of catalytic amounts of perchloric acid involves protonated forms of hypochlorous acid as chlorinating species, is 29·6 times faster than the reaction with benzene, and gives 63·0 % of the 2- and 37·0 % of the 4-chlorodiphenylmethane. The relative rates and product compositions determine the partial rate factors for the chlorination reactions. Comparison with the results for other electrophilic reagents indicates that the reactions of chlorine acetate result in a higher proportion of ortho-substitution. No addition or side-chain chlorination accompanies these reactions.