Kinetics and mechanisms of aromatic halogen substitution. Part XXVIII. Environmental effects on rates and products of chlorination of some aromatic hydrocarbons

Abstract

Chlorination of phenanthrene in acetic acid gives a mixture of products of substitution and addition, in which cis-9-acetoxy-10-chloro-9,10-dihydrophenanthrene has been found and estimated by n.m.r. spectroscopy, and 1-, 3-, and 4-chlorophenanthrene have been identified and estimated approximately by infrared spectroscopy. The effects of added electrolytes, and of change in solvent, on the rate of chlorination and on the proportions of adducts and products of substitution have been studied. The results suggest complexities analogous to those involved in the product-determining stages of other reactions involving carbonium ionic intermediates. The effects of added electrolytes on rates and products of the chlorination of biphenyl have also been investigated. Comparison of the effects of change in solvent on the rates and products of chlorination of naphthalene with the corresponding results for phenanthrene establish that the transition state leading to cis-addition can have considerable carbonium ionic character.