Highly efficient oxidation of alcohols to carboxylic acids using a polyoxometalate-supported chromium(III) catalyst and CO₂

Direct catalytic oxidation of alcohols to carboxylic acids is very attractive, but economical catalysis systems have not yet been well established. Here, we show that a pure inorganic ligand-supported chromium compound, (NH₄)₃[CrMo₆O₁₈(OH)₆] (simplified as CrMo₆), could be used to effectively promote this type of reaction in the presence of CO₂. In almost all cases, oxidation of various alcohols (aromatic and aliphatic) could be achieved under mild conditions, and the corresponding carboxylic acids can be achieved in high yield. The chromium catalyst 1 can be reused several times with little loss of activity. Mechanism study and control reactions demonstrate that the acidification proceeds via the key oxidative immediate of aldehydes.