A re-examination of the chemical and stereochemical course of the solvolysis of 1-phenylethyl chloride

Abstract

The solvolysis of 1-phenylethyl chloride has been re-examined. The results of previous workers have been confirmed. The reactionis unimolecular and yields 1-phenylethanol, along with a very smallamount of styrene. The stereochemical orientation of thehydrolysis is inversion accompanied by extensive racemisation.The amount of the racemisation increases as the solvent is madeless aqueous. The rate measured polarimetrically is faster thanthe rate measured titrimetrically and the discrepancy between k and k increases as the solvent becomes less aqueous. This study has shown that the racemisation accompanying the solvolysis is not the result of a subsequent racemisation of the alcohol formed with inversion of configuration. Evidence has also been presented to show that the racemisation is not the result of a reaction involving dioxan. Furthermore, the racemisation has been shown not to result from the formation of styrene as an intermediate. The high polarimetric rate cannot be accounted for in terms of a racemising attack on a carbonium ion by dissociated chloride ions. It is concluded that the excess racemisation accompanying the solvolysis is intramolecular, involving a solvent-separatedion aggregate. Product arrises both from attack on dissociated carbonium ions and from attack on these ion aggregates. The rate of exchange with lithium radio-chloride showed an unexpected dependence on the concentration of chloride ions,namely, an increase roughly proportional in more ionising conditions to the three-halves power of the concentration and in less ionising conditions to the second power of the concentration. Implications of this are discussed.