Kinetics of Air Oxidation of Sulfurous Acid Salts

Sulfurous acid salts in common with many pharmaceutical antioxidants and oxygen-sensitive drugs undergo oxidation by a radical process. This has important implications in the testing and evaluation of oxidative tendencies of formulations since radical processes are inordinately sensitive to slight amounts (10−6M) of compounds acting as radical inhibitors or initiators. Measurable inhibition of the rate of sulfite oxidation occurred in the presence of 10−6M DMA or DMF; the inhibition is described by an empirical equation. Effect of hydrogen ion concentration on the oxidation of sulfurous acid salts was studied in detail and the results described in terms of a theoretically derived equation. Experimental data are presented in corroboration of the Abel theoretical equations and radical mechanism for sulfite oxidation.