Models for Polyesterification Kinetics. II. Esterification Kinetics in Nonpolar Medium

In order to examine the influence of the polarity of the reaction medium on the polyesterification mechanism, the kinetics of the reaction of 1-octadecanol with octadecanoic acid in octadecanyl octadecanoate is studied with and without p-toluenesulfonic acid catalyst. Without added catalyst the overall order is 2.5 and the orders in acid and in alcohol are 1.5 and 1, respectively. The mechanism consists of an autocatalysis by the acid and involves a nonnegligible dissociation of ion pairs. This differs from the observation made in more polar media. With added p-toluenesulfonic acid, the reaction is first order in alcohol, acid, and catalyst. Activation entropy is the same both for catalyzed and noncatalyzed reactions. The catalytic effect is due to a large decrease of activation enthalpy.