Enol elimination reactions. Part V. A study of the mechanism of the decarboxylative elimination reactions of some enol sulphonates

Abstract

The rate constants for the fragmentation of a number of sulphonates, Ar¹(Ar²SO₃)CC(CO₂^–)₂, have been measured, and Hammett ρσ plots have been made from these measurements. The ρ⁺ value, for varying the aryl group Ar¹, is –3·1, and the ρ value, for varying the aryl group Ar², is +1·17. The values of m, ΔV‡, and the rate constants are discussed and compared with values derived from related compounds in the literature. The conclusion is drawn that the decarboxylative elimination is a more or less concerted fragmentation reaction in which a substantial build-up of positive charge on a vinyl carbon atom is achieved in the transition state.