The kinetics and mechanisms of aromatic halogen substitution. Part XXIX. Chlorination of aromatic hydrocarbons in slightly aqueous (96%) dioxan

Abstract

The kinetics of the chlorinations of p-xylene, m-xylene, naphthalene, and triphenylene by hypochlorous acid in slightly aqueous (96%) dioxan have been examined. The reactions are catalysed by acids, and for each substrate there is a good linear free-energy correlation between the rate of reaction and the extent of protonation of o-nitroaniline in a similar range (0·2–0·6M) of acidity. The reactions mainly give nuclear chlorination, with up to 10% of side-reactions producing chloride ions. Silver perchlorate further catalyses the acid-catalysed chlorinations; the kinetic results suggest that under these conditions two solvated forms of positive chlorine, probably ClOH₂⁺ and ClAgCl⁺, can act as electrophilic chlorinating species, and that with some of the substrates investigated both these reagents can also give products of hydroxylation, probably by an addition–elimination sequence.