Degradation of Ascorbic Acid in Aqueous Solution

Abstract

An HPLC method, for the simultaneous determination of the degradation products of ascorbic acid, was employed to investigate the degradation of ascorbic acid in aqueous solution at different pH values. After ascorbic acid aqueous solutions were heated at 100 °C for 2 h, four main degradation products, furfural, 2-furoic acid, 3-hydroxy-2-pyrone, and an unidentified compound, were separated and determined. In an acid aqueous solution, ascorbic acid was converted to 2-furoic acid and 3-hydroxy-2-pyrone via dehydroascorbic acid under aerobic conditions, whereas under anaerobic conditions, ascorbic acid degraded to furfural. Low pH conditions favored the formation of furfural, 2-furoic acid, and 3-hydroxy-2-pyrone; at extremely low pH (i.e., pH 1), the formation of furfural dominated. In an alkaline aqueous solution, the unknown compound became the main degradation product of ascorbic acid; at pH 10, only very small amounts of furfural and 3-hydroxy-2-pyrone with no 2-furoic acid were detected. Our results suggest that, in a hydrogen-ion-catalyzed environment, the anaerobic degradation of ascorbic acid to furfural is the main degradation pathway in an aqueous solution. Keywords: Ascorbic acid; dehydroascorbic acid; degradation; furfural; 2-furoic acid; 3-hydroxy-2-pyrone; HPLC