Mechanistic Study on Citric Acid-Based Esterification: A Versatile Reaction for Preparation of Hydrophilic Polymers

A kinetic study of the esterification reaction of citric (CA) acid and butyl glycol (BG) with and without catalyst was performed to elucidate the reaction mechanism. Interestingly, different preferences of esterification sites on CA molecules (at α or β position) can be found in either bulk conditions or organic solvents. The density functional theory (DFT) model was used to support this experimental study. Additionally, optimal conditions for the regioselectivity of the reaction of CA toward primary and secondary alcohols, in the presence of scandium triflate as the catalyst, were studied. Choosing the polyesterification conditions optimized from the model reaction, it has been proven that under low temperature (70 °C), it is possible that linear polyester or at least non-cross-linked ones can be obtained from CA and multifunctional alcohols.