Conformation and reactivity. Part VI. Kinetics of the acid-catalysed esterification in methanol 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 acid-catalysed esterification in methanol at 30° of the trans-decalincarboxylic acids, of cis- and trans-4-t-butylcyclohexanecarboxylic acid, of cis- and trans-2-methylcyclohexanecarboxylic acid, of trans-4-X-cyclohexanecarboxylic acids (X = OH, CO₂Et, CO₂Me, Br, or CN), and of cyclohexanecarboxylic acid have been measured. The rate coefficient for trans-4-t-butylcyclohexanecarboxylic acid agrees very closely with that for trans-decalin-2β-carboxylic acid but that for the cis-4-t-butyl acid is about 25% greater than that for the trans-decalin-2α-acid. It is therefore concluded that the cis-4-t-butyl acid contains about 1% of the conformation with an equatorial acid group at 30°. Application of Eliel's method indicates that 87–88% of cyclohexanecarboxylic acid has the protonated carboxyl group in the equatorial conformation. trans-Decalin-1α-carboxylic acid shows unexpectedly low reactivity. In the series of trans-4-X-cyclohexanecarboxylic acids electron-attracting substituents slightly retard the reaction.