Decomposition Kinetics of 6-O-Monoacyl Ascorbate in Air

Abstract

6-O-Monoacyl ascorbates were synthesized by the condensation of L-ascorbic acid with caprylic, capric, lauric, myristic or palmitic acid using immobilized lipase in acetone. The decomposition processes of the acyl ascorbates in air were measured, and the decomposition kinetics were analyzed based on the Weibull equation. The rate constant, k, increased with increasing relative humidity and temperature for all acyl ascorbates; k also depended on acyl chain length, as the decomposition rates of ascorbates increased as acyl chains decreased. The enthalpy-entropy compensation held during the decomposition, suggesting that the decomposition of all acyl ascorbates proceeded by essentially the same mechanism. Furthermore, it was suggested that the oxidative degradation of the ascorbyl moiety of acyl ascorbate primarily proceeded during the decomposition, and was followed by the hydrolysis of the ester bond between the acyl and ascorbyl moieties.