Organic carbonates. Part XI. Conformational and other effects of substitution in the acid-catalysed hydrolysis of highly branched ethylene and trimethylene carbonates

Abstract

The rates, the energies (ΔE^‡), and entropies (ΔS^‡) of activation of the acid-catalysed hydrolysis of 9 highly branched ethylene carbonates, (Ia—h) and (III)—(IV), and 11 trimethylene carbonates (IIa—k) in water at several temperatures have been measured. The trimethylene carbonates show greater reactivity to hydrolysis than do the correspondingly substituted ethylene carbonates, as do other analogous lactones. Alkyl-substitution in the carbon chain causes a decrease in rates of the reaction and an increase in the energy of activation. Analysis of the kinetic and potential energies of the five- and six-membered cyclic carbonates show that the effects of ring-size on rates of the reaction are principally due to the potential energies of activation of the systems. Although at different energy levels, the slopes of the isokinetic plots [a measure of the isokinetic temperature (β)] are significantly similar both in the ethylene and trimethylene carbonates. In the final analysis it was concluded that the effects of analogous substitution in the five- and the six-membered carbonates are primarily of steric nature.