Cleavage of ethers in an ionic liquid. Enhancement, selectivity and potential application

Abstract

The cleavage of a series of ethers was examined in an ionic liquid containing hydrogen bromide. Reactions that did not proceed in either water or DMSO were found to proceed readily in this system, with notable selectivity between the cleavage of the different ether types examined herein. Increasing the proportion of water in the reaction mixture dramatically decreased the rate constant of ether cleavage; this could, in part, be attributed to a decrease in the solvent stabilisation of the transition state. Through analysis of the electronic requirements of the reaction (using substrates containing substituents with different Hammett parameters) and observation of rate enhancements for an ortho substituted system, the importance of the extent of protonation of the ether prior to nucleophilic attack was demonstrated.