Application of 13C nmr spectroscopy to the elucidation of the electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids

The previously proposed electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids in basic medium must be rejected because of the variation in the carbon chemical shifts and coupling constants with the pH, which shows that the supposed rupture of the furanose rings at pH ～ 9 does not occur. Electrolysis in basic medium yields the same products as those obtained when the pH of the products of the electrolysis in acid medium are raised to pH ～ 11. This suggests that the oxidation mechanisms in acid and basic media are similar. The assigned carbon chemical shifts of the oxidation products in acid medium $\text{3}$ (or $\text{4}$) and in basic medium $\text{5}$ (or $\text{6}$) and $\text{7}$ (or $\text{8}$) are reported.