Aziridines related to some β-adrenergic blocking agents. Kinetics of formation and reaction, and some unusual salt effects

Abstract

The cyclisation rates of some β-chloroethylamines to the aziridine have been measured. Rates and activation parameters are used to demonstrate mechanistic differences between those cyclisations that can, and those that cannot, obtain further assistance from benzylic or neighbouring aryl participation. The reactions of the aziridines with water and thiosulphate ion are studied. While primary products are obtained from one aziridine and secondary products from another, this does not allow a reliable distinction to be made between S_N2 and S_N1 pathways, to which the activation parameters provide a better guide. Unexpectedly large and specific salt effects are found for certain of the aziridine formation and solvolysis reactions. These enable conclusions to be drawn concerning all four transition states, for which tentative activity coefficients are derived. This analysis is incorporated in a scheme that consistently explains rates, salt effects, and activation parameters.