Ascorbic acid and copper in linoleate oxidation. 11. Ascorbic acid and copper as oxidation catalysts

Both ascorbic acid and copper were strong prooxidants in the oxidation of linoleate in a buffered (pH 7.0) aqueous dispersion at 37OC. Minimum concentrations at which catalytic activity was detected were 1.3 X 10-7 M for coppcr and 1.8 X 10-6 M for ascorbic acid. For concentrations up to lop3 M, the increase in rate of oxidation with increase in concentration of catalyst was greater for ascorbic acid than for copper. Ascorbic acid had maximum catalytic activity at 2.0 X M, but was still prooxidant at the highest concent.-ation tested (5.0 X M ) . Dehydroascorbic acid was a weaker prooxidant than ascorbic acid. Further degradation products of ascorbic acid were not prooxidant. In early stages of the oxidation autocatalytic behavior was observed with copper, but not with ascorbic acid. Ascorbic acid functioned as a true catalyst, i.e., it accelerated the reaction but it was not oxidized simultaneously with the linoleate. It is proposed that the dehydroascorbic acid radical initiates the linoleate oxidation reaction. SUPPLEhf ENT'ARY