Selective oxidation of benzyl alcohols photocatalyzed by asymmetric cobalt thioporphyrazine supported on alumina

Abstract

The sunlight-powered transformation of alcohols to corresponding carboxylic acids offers a feasible route for fine chemical synthesis. In this work, the asymmetric cobalt tri(2,3-bis(butylthio)maleonitrile)-(1,4-dithiin) porphyrazine (CoPz(SBu)₆(dtn)) was synthesized, more importantly, its single crystal was further obtained by the solvent evaporation method. Then the asymmetric CoPz(SBu)₆(dtn) supported on neutral Al₂O₃ particles to form composite photocatalyst CoPz(SBu)₆(dtn)@Al₂O₃, which possessed strong visible light absorption. Under simulated sunlight irradiation using a xenon lamp, the composite photocatalyst CoPz(SBu)₆(dtn)@Al₂O₃ exhibited excellent photocatalytic activity for selective oxidation of benzyl alcohol to benzoic acid in water under conditions of green H₂O₂ as oxidant and K₂CO₃ as additive. The conversion of benzyl alcohol was up to 53.8 % together with 99 % selectivity of benzoic acid over composite photocatalyst CoPz(SBu)₆(dtn)@Al₂O₃. Meanwhile, this photocatalytic system had feasible substrate generalizability and excellent photocatalytic activity for substituted benzyl alcohols containing both electron-donating and electron-withdrawing substituents. The composite photocatalyst CoPz(SBu)₆(dtn)@Al₂O₃ exhibited excellent photocatalytic durability, which was confirmed by the recycling experiments. This work manifests the asymmetric thioporphyrazine as photocatalyst is feasible in implementing sunlight-powered selective transformation.