Conformation and reactivity. Part V. Kinetics of the esterification with diazodiphenylmethane in methanol, ethanol, or t-pentyl alcohol of the trans-decalincarboxylic acids, of the 4-t-butyl- or 2-methyl-cyclohexanecarboxylic acids, of certain trans-4-substituted cyclohexanecarboxylic acids, and of cyclohexanecarboxylic acid

Abstract

The rates of esterification with diazodiphenylmethane in methanol, ethanol, or t-pentyl alcohol at 30° of the trans-decalincarboxylic acids, of cis- and trans-4-t-butyl-, cis- and trans-2-methyl-cyclohexanecarboxylic acid, of trans-4-X-cyclohexanecarboxylic acid (X = OH, CO₂Et, CO₂Me, Br, or CN), and of cyclohexanecarboxylic acid have been measured. The rate coefficients for the reactions of the trans-decalin-2-carboxylic acids in methanol or in ethanol have nearly the same values as those for the corresponding reactions of their cis- and trans-4-t-butylcyclohexanecarboxylic acid counterparts. Application of Eliel's method indicates that in methanol 69% and in ethanol 79% of cyclohexanecarboxylic acid has the carboxyl group in the equatorial conformation. In t-pentyl alcohol as solvent the agreement between the values for corresponding trans-decalin-2-carboxylic acids and 4-t-butylcyclohexanecarboxylic acids is poor, and the rate coefficient for trans-4-t-butylcyclohexanecarboxylic acid is lower than that for cyclohexanecarboxylic acid. In all three solvents the rate coefficient for the reaction of the decalin-1-axial acid is low because of three “1,3-axial hydrogen atom” interactions, but the rate coefficient for the reaction of the 1-equatorial acid is ∼20% higher than that for the 2-equatorial acid. For each trans-4-X-cyclohexanecarboxylic acid the order of reactivity in the alcohols is MeOH > EtOH > t-C₅H₁₁OH. The polar substituents, X, exert a considerable effect upon reactivity which is greatest for t-pentyl alcohol as solvent. The use of these compounds for evaluating, by extrapolation, the reactivity of an equatorial carboxyl group “subject to no polar effect” is examined.