Oxidation of Benzyl Alcohols by Monomeric Iron Phthalocyanine Complexes: Substituents’ Effect on Their Catalytic Performance

Iron phthalocyanines tetra substituted with either electron-donating n-hexyloxy or electron-withdrawing n-hexylsulfonyl substituents were prepared and tested as oxidation catalysts for benzyl alcohol, 4-bromobenzyl alcohol, 4-methylbenzyl alcohol and 4-tert-butylbenzyl alcohol. Oxidation reactions were performed at room temperature in acetonitrile, acetone, ethanol, toluene, and the best result was obtained in acetonitrile. Oxidation of alcohols using tert-butyl hydroperoxide as an oxidant in the presence of these iron(II) phthalocyanines resulted in the production of corresponding benzaldehyde and benzoic acid. When comparing the substituent effect, the hexylsulfonyl electron-withdrawing substituted phthalocyanine complex exhibited better catalytic performance in acetonitrile for all benzylic alcohol derivatives. It showed that electron-withdrawing substituted iron(II) phthalocyanine tends to produce benzaldehydes, while electron-donating substituted iron(II) phthalocyanine produced benzoic acid. This kind of catalytic system is suitable for the oxidation of benzylic alcohols to produce benzaldehyde and benzoic acid derivatives.