Photooxidation and Reduction of Ascorbic Acid Studied by E.S.R.

The photooxidation of ascorbic acid in water at pH 4.5–11.6 was studied using electron spin resonance spectroscopy. In the presence of oxygen, only one radical is detected and its resonance lines are broad. In the absence of O2, better resolution is obtained and a second radical is observed. When N2O or H2O2 is added, the second radical disappears while the concentration of first radical is increased. These results are consistent with a primary photochemical step involving ejection of an electron from the monoanion of ascorbic acid to form the ascorbate. The second radical appears to be formed by addition of a hydrated electron to the monoanion of ascorbic acid.