Linear free energy ortho-correlations in the thiophen series. Part IV. Kinetics of alkaline hydrolysis of some methyl 3-substituted thiophen-2-carboxylates in aqueous methanol

Abstract

The rate constants for the alkaline hydrolysis of some methyl 3-substituted thiophen-2-carboxylates (I)(substituents OMe, Me, SMe, H, I, Br, SOMe, and SO₂Me) in methanol–water (80% v/v) have been determined. The logarithms of the rate constants give an excellent straight line when plotted against the pK_a values of the corresponding acids (slope 1.91) and obey an equation of the Yukawa–Tsuno type (ρ+ 2.77, r⁺ 0.44, R 0.996), confirming the marked difference in behaviour between ortho-like substituted thiophen and benzene derivatives.