Stability of Saturated Acyl L-Ascorbates in Aqueous Solution

The decomposition of decanoyl l‐ascorbate was measured at 40 °C and at pH 2 to 9. The decrease in the ascorbate concentration at every pH value was well expressed by the Weibull model. The stability of the ascorbate was the highest at pH 3 and lower at a higher or lower pH. The increase in the concentration of decanoic acid, which was formed through the hydrolysis of the ester bond in the ascorbate, was measured at pH 3, 6, and 9. The hydrolysis could be ignored at a pH equal to or lower than 6, whereas it was significant at pH 9. The initial concentration of the ascorbate scarcely affected its decomposition at pH 5 and 40 °C. The decompositions of acyl ascorbates with acyl chain lengths of 6, 8, 10, and 12 were measured at pH 5 and at different temperatures. The temperature dependency of the rate constant for the decomposition of each ascorbate was analyzed by the Arrhenius equation, and it was shown that the enthalpy‐entropy compensation held for the decomposition of the ascorbates.