Electrophilic substitution on the thiophen ring. Part 5. The effect of methyl groups on the kinetics of hydrogen exchange in acidic media

Abstract

The effect of methyl groups on the rate of protodetritiation of 2- and 3-tritiothiophen in perchloric acid has been examined and activation parameters for the reactions have been calculated. The activating effect of a second methyl is non-additive. Reaction at the 3-position is less susceptible to substituent effects than that at the 2-position. With 2-methyl-, 2,4-dimethyl-, and 2,5-dimethyl-thiophen, as well as ring hydrogen exchange, there is slower exchange on certain methyl groups.