Esterification of pentaerythritol by carboxylic acids

Abstract

Our study of thermal esterification of pentaerythritol by caproic acid in kinetic regime and far from equilibrium has shown that the reaction proceeds via a series of consecutive-parallel steps through the formation of mono-, di- and tri-esters. At the excess of caprioic acid, and at 170 °C, the effective first-order rate constants reduced to a hydroxyl group are approximately equal to $k_{1}^{\text{OH}}$  = 2.0 h⁻¹, $k_{2}^{\text{OH}}$  = 1.0 h⁻¹, $k_{3}^{\text{OH}}$  = 0.84 h⁻¹, and $k_{4}^{\text{OH}}$  = 0.72 h⁻¹. The reaction rates of the consecutive replacements of the OH groups with acid groups during the formation of the monoester are the largest, and decrease for diester and triester formation. The influence of the length and degree of branching of a carboxylic acid residue on the reaction rate of complete esterification is demonstrated: the reaction is slower with a longer (C₅, C₆ and C₈) and more branched (iso-C₅ vs. C₅) acid. The possibility of a catalytic acceleration of the esterification reaction in the presence of a heterogeneous acid–base catalyst is shown.