Cis and Trans Isomers of 1-Hydroxyiminoalkylferrocenes and Their Antioxidant Activity

Condensation reactions of acylferrocene with hydroxylamine hydrochloride afforded a series of acylferrocene oximes, 1-hydroxyimino-alkylferrocenes (3a-d) and each separated into cis and trans isomers which has antioxidant activity towards DPPH*. Kinetics parameters (log Z) for the reaction of samples with DPPH were determined. The result indicates that 1-hydroxyiminoalkylferrocenes have antioxidant properties which are related to the stereochemistry of the alpha-substituent hydroxyimino group. Because of a long conjugated chain, resulting in electron delocalization, the antioxidant activity of (3a-d) is better than BHT and enhanced with the increase of compounds concentration of (3a-d), but reduced as the bulkiness of the a-substituent hydroximino group increased. The antioxidant activity of 1-hydroxyimino-alkylferrocene was much higher than that of the precursors (acylferrocenes). Antioxidant activity of cis-isomers is slightly bigger than that of trans-isomers.