The equilibrium distribution of acyl groups between primary and secondary hydroxyl positions in partial esters

Abstract

In a previous paper the authors discussed the concept of the “relative esterifiability” of primary and secondary hydroxyl groups and demonstrated its utility in predicting the composition of partial glycerides under ester-interchange equilibrium conditions. The concept is clarified and expanded in the present paper. The compositions of partial glycerides at ester-interchange equilibrium are calculated using the estimated reactivities of the primary and secondary hydroxyls at 100 and 220C, and are compared to the composition calculated assuming equal hydroxyl reactivity. Base catalyzed esterification of propylene glycol with fatty acids is shown to be accompanied by rapid ester-interchange. As with glycerol partial esters, the relative esterifiability of the primary hydroxyl of propylene glycol exceeds that of the secondary.