The influence of solvent composition on the rates of E2 elimination and similar reactions in alcohol–water mixtures

The overall rates of E2 elimination of hydrogen bromide from β-phenylethyl bromide and ethylene dibromide by alkoxide and hydroxide ions in methanol– and ethanol–water mixtures have been measured. Similar studies have also been made of the hydrolysis of chloroform and ethylene chlorohydrin which have mechanisms very similar to the E1cB mechanism of elimination. The results for the E2 reactions show a pattern similar to that previously observed for second-order substitution reactions and are given a similar interpretation. The other reactions show no constant pattern of behaviour as the solvent is changed from alcohol to water. The possibility of using the reaction pattern in alkaline alcohol–water mixtures to distinguish between E2 and E1cB mechanisms of elimination is discussed.