Oxidation of 1-propanol to propionic acid with hydrogen peroxide catalysed by heteropolyoxometalates.

Background: Propionic acid as a very valuable chemical is in high demand, and it is industrially produced via the oxo-synthesis of ethylene or ethyl alcohol and via the oxidation of propionaldehyde with oxygen. It is urgent to discover a new preparation method for propionic acid via a green route. Recyclable amino-acid-based organic–inorganic heteropolyoxometalates were first used to high-efficiently catalyse the selective oxidation of 1-propanol to propionic acid with H₂O₂ as an oxidant. Result: A series of amino-acid-based heteropoly catalysts using different types of amino acids and heteropoly acids were synthesized, and the experimental results showed proline-based heteropolyphosphatotungstate (ProH)₃[PW₁₂O₄₀] exhibited excellent catalytic activity for the selective catalytic oxidation of 1-propanol to propionic acid owing to its high capacity as an oxygen transfer agent and suitable acidity. Under optimized reaction conditions, the conversion of 1-propanol and the selectivity of propionic acid reached 88% and 75%, respectively. Over four cycles, the conversion remained at >80%, and the selectivity was >60%. (ProH)₃[PW₁₂O₄₀] was also used to catalyse the oxidations of 1-butanol, 1-pentanol, 1-hexanol, and benzyl alcohol. All the reactions had high conversions, with the corresponding acids being the primary oxidation product. Conclusions: Proline-based heteropolyoxometalate (ProH)₃[PW₁₂O₄₀] has been successfully used to catalyse the selective oxidation of primary alcohols to the corresponding carboxylic acids with H₂O₂ as the oxidant. The new developed catalytic oxidation system is mild, high-efficient, and reliable. This study provides a potential green route for the preparation propionic acid. [ABSTRACT FROM AUTHOR]