The photochemical decomposition of l-ascorbic acid. II

IN a recent investigation [Kellie & Zilva, 1938] it was shown that in the presence of air, I-ascorbic acid in aqueous solution, when exposed to ultraviolet light, was oxidized without the aid of sensitizers to dehydroascorbic acid.Furthermore, it was found that even in the absence of atmospheric oxygen the exposure to this light brought about a destruction of the vitamin.In the anaerobic experi- ments in which small quantities of ascorbic acid were used the amolunt of dehydroascorbic acid present after the exposure at pH 7 was so small as to throw doubt on its formation.At pH 3 on the other hand although the quantity of ascorbic acid which was decomposed by the ultraviolet light was less than at pH 7, the reduction of the residual solution with H2S produced an appreciable rise in the indophenol-reducing capacity of the solution.That this actinic decomposition of i-ascorbic acid under anaerobic conditions was not due to oxidation brought about by the last traces of 02 which could not be removed by repeated exhaustion and refilling with N2 was shown by the fact that the quan- tities of ascorbic acid which disappeared after prolonged exposure required considerably larger amounts of 02 for their oxidation than those which could possibly be present in solution even without previously removing from it the dissolved air.This observation on the anaerobic photolysis of i-ascorbic acid required further elucidation and experiments for this purpose are described below.In the original investigation ascorbic acid was determined by titration with