Reaction strategies for the enzymatic synthesis of neopentyl glycol diheptanoate.

ABSTRACT

This work describes for the first time the green synthesis of neopentyl glycol diheptanoate in a solvent-free medium via an enzymatic pathway. The process has been carried out in an open-air reactor in order to ease water removal through evaporation and shift the chemical equilibrium towards product formation. The inhibiting effect of high concentrations of heptanoic acid has been put into evidence by a reduction of initial reaction rate when esterification was performed with stoichiometric amounts of substrates. Therefore, in this work different strategies for the stepwise addition of heptanoic acid are proposed, and best results were obtained when stoichiometric quantities of acid were divided in four equal amounts and added when previous batch was consumed. Biocatalyst Novozym® 435 concentration and temperature were optimised, giving yields of 90% in neopentyl glycol diheptanoate when 7.5% (w/w) and 70 °C were used. With a remaining 7% of heptanoic acid (probably caused by the alcohol evaporation) the addition of neopentyl glycol led to a conversion of 95%. Thus, product can be used in cosmetics without further purification and can be labelled as environmentally-friendly synthesized because of its enzymatic origin.