An Interpretation of the Rate Enhancing Effect of Microwaves – Modelling the Distribution and Effect of Local Overheating – A Case Study

The explanation for the rate enhancing effect of microwave (MW) irradiation is still the subject of controversy. It is, however, agreed that it may involve the possible role of thermal effects. In this article, our explanation is presented using the example of the direct esterification of a cyclic phosphinic acid, modelling the distribution of the local overheatings by exponential functions for the first time, and taking the effect of the overheatings into consideration by the Arrhenius equation. One of the explanatory models described well the experimental rate enhancement observed for the MW-assisted direct esterification of 1-hydroxy-3-methyl-3- phospholene 1-oxide with butanol.