Highly Selective and Efficient Conversion of Alkyl Aryl and Alkyl Cyclopropyl Ketones to Aromatic and Cyclopropane Carboxylic Acids by Aerobic Catalytic Oxidation: A Free-radical Redox Chain Mechanism.

Abstract

An efficient and convenient method has been developed for the oxidation of aryl alkyl and cyclopropyl alkyl ketones to aromatic and cyclopropane carboxylic acids by molecular oxygen at atmospheric pressure, catalysed by Mn(NO₃)₂ in combination with Co(NO₃)₂ or Cu(NO₃)₂. This simple, cheap and highly selective process has a general character for the synthesis of carboxylic acids and it is particularly suitable for industrial applications.

Key words

carboxylic acids - kjetones - oxidation by molecular oxygen - free-radical - redox catalysis

References

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14

A large scale procedure: 12 g of acetophenone, 2 mmol of Mn(NO₃)₂, 2 mmol of Co(NO₃)₂ in 100 mL of acetic acid were stirred under oxygen atmosphere at 100 °C and ambient pressure for 6 h. The solution was analysed by GLC, revealing the presence of 0.42 g of unreacted acetophenone. The solution was evaporated and the residue was dissolved in 100 mL of aqueous solution of NaHCO₃; the aqueous phase was extracted with ethyl acetate, then acidified with H₂SO₄ and extracted again with ethyl acetate. By evaporating the solvent 11.1 g of pure benzoic acid (> 99% in GLC) were obtained. Conversion 96.5%, selectivity 93%.