Acceleration of sulfurous acid oxidation by freezing of aqueous solution

Oxidation of sulfurous acid (H(2)SO(3)) to sulfuric acid (H(2)SO(4)) by dissolved oxygen (O(2)) in an aqueous solution was remarkably enhanced by freezing. The concentration of sulfurous acid in a sample solution which froze in a -10 degreesC refrigerant for 60 min decreased by about 50%, and three freeze/thaw cycles resulted in perfect conversion into sulfuric acid. The difference of reaction rates in -20 degreesC and -10 degreesC refrigerants indicated that the rate-determining step of the reaction was the growth rate of ice formation in the sulfurous acid in an aqueous solution. The yield of sulfurous acid oxidation in a -10 degreesC refrigerant was higher than that in a -20 degreesC refrigerant.