The chemistry of heteroarylphosphorus compounds. Part III. The alkaline hydrolysis of heteroarylmethyl analogues of benzyltriphenyl-phosphonium bromide; relative stabilities of heteroarylmethyl carbanions

Abstract

The kinetics of hydrolysis of a series of (heteroarylmethyl)triphenylphosphonium bromides (V)—(VIII)[RPPh₃Br^–(R = 2- or 3-furylmethyl or 2- or 3-thenyl)] which produce triphenylphosphine oxide and the respective methyl-substituted heterocyclic compound, have been studied at different temperatures in aqueous 50% ethanol in the presence of potassium chloride, and the rate data have been compared with those for the hydrolysis of benzyltriphenylphosphonium bromide.

The hydrolysis of all the salts follows a third-order rate law; under the same conditions at 30°, the rates of hydrolysis decrease in the order R = 2-furylmethyl > 2-thenyl > benzyl > 3-thenyl > 3-furylmethyl. The rate data are discussed in terms of the electron-withdrawing nature of the heteroaryl substituent, and the relative stability of the heteroarylmethyl carbanions.