Kinetics of the reactions of olefins with halogens in aqueous solution. Part II. Reactions of bromine with various olefins, and of hydrogen bromide with some epoxides

Abstract

Kinetic results are reported for the reaction of nine olefins with bromine in aqueous solution. Velocity constants were obtained for reaction with molecular bromine and with tribromide ion, and, for two olefins, also with the ions Br₂Cl^– and BrCl₂^–. The relative amounts of bromohydrin and dibromide produced were determined as a function of bromide ion concentration for eight olefins. For most of the reactions studied here and in previous work there is no correlation between the product composition and the kinetics, and it is concluded that an intermediate formed in the rate-determining step then reacts rapidly with either water or bromide ion. The bromination of diethyl fumarate, however, appears to involve simultaneous electrophilic attack by a bromine molecule and nucleophilic attack by water or bromide ion. Both diethyl furmarate and diethyl maleate give the meso-form of diethyl dibromosuccinate. Kinetic measurements with three epoxides support a cyclic bromonium ion as the intermediate in the reactions between olefins and bromine, but other formulations are possible. The velocity constants for reaction with bromine or tribromide ion, varying over about eleven powers of ten, show an approximate correlation with Taft's σ* substituent constants.