Lauric acid/pentaerythrityl monolaurate: a model melt esterification. Part 1.—Kinetics

Abstract

The study of polyfunctional polycondensates and of the structure of gels is dependent on the availability of link-forming mechanisms which are simple and well understood. Esterification in the melt is a favoured method. Although some melt esterification reactions have been found to be represented by third order kinetics and a mechanism free from measurable complicating effects, the study of esterification of dibasic acids with pentaerythritol (PE) has suggested a substitution effect, whereby each esterified OH accelerates the esterification of the remaining OH in the same PE unit by a factor of about N= 1.5. This effect is here confirmed by kinetic analysis of the (non-polymerisable) model system lauric acid/PE and, in more detail, lauric acid/pentaerythrityl monolaurate. Accurate and automated readings of about 300 conversion/time data per run, based on the pressure of evolved steam, were fitted to rival kinetic models, over a range of compositions and temperatures. Computer analysis in terms of standard deviations strongly supports the validity of the substitution effect (N∼ 1.4). The results are discussed in the context of previous work on esterification in bulk and in dilute solutions.