SOLVENT EFFECTS ON RATES OF MISCELLANEOUS NUCLEOPHILE-PROMOTED REACTIONS IN AQUEOUS-ALCOHOLIC SOLVENT MIXTURES

The rates of E2 elimination from DDT and SN2 infstitution on allyl bromide by alkoxide and hydroxide ions have been measured using aqueous-alcoholic solvent mixtures. The results are anomalous in terms of previous theories. The E2 hydrogen nucleophilicity order of OEt− > OMe− > OH- towards 2-phenethyl bromide in dioxan has been obtained by extrapolating rates of reaction in alkaline dioxan-alcohol or dioxan-water mixtures to 100% dioxan. The nucleophilicity order contrasts with the basicity order: OEt− > OH− > OMe− but is the same as the carbon nucleophilicity order. The validity is questioned of using similar carbon- nucleophilicity and elimination-reactivity orders as positive evidence for the E2C mechanism of eliminations promoted by weak bases which are also strong carbon nucleophiles. © 1969, CSIRO. All rights reserved.