Mechanisms for Liquid Phase Hydrolyses of Chlorobenzene and Halotoluenes¹

Abstract

A study of the rearrangements which occur during the high temperature liquid phase hydrolyses of the halotoluenes has shown that the extent of rearrangement is a sensitive function of temperature, base strength and the nature of the halogen. These hydrolyses involve either a benzyne (elimination-addition) mechanism, which gives both rearranged and unrearranged products, or an S_N2-type mechanism. The S_N2-type mechanism was found to be favored at lower temperatures, in the presence of weaker bases and with the more easily ionizable halogens. By suitable choice of conditions, one or the other reaction could be made to occur almost exclusively. Chlorobenzene-1-^(14)C, with 4 M sodium hydroxide solution at 340º, gave 58 ± 1% phenol-1-^(14)C and 42 ± 1% phenol-2-^(14)C, which indicates that under these conditions the benzyne mechanism predominates but is not the exclusive reaction path.