Dawson-type polyoxometalates as green catalysts for adipic acid synthesis

•Adipic acid synthesis over Dawson-type polyoxometalates with H2O2 in free solvent.•Formation of new “peroxo-POMox” active species evidenced by 31P NMR spectroscopy.•α-K6P2Mo6W12O62 isomer is the most efficient in cyclohexanol and cyclohexanone oxidation.•α-K6P2Mo6W12O62 gives 69% AA yield from oxidation of 50% cyclohexanol/50% cyclohexanone mixture.

Dawson-type POMs series of formula α- and β-K6P2W18O62 isomers, α1- and α2-K6P2Mo5W13O62 isomers, α-K6P2Mo6W12O62 isomer and α1-K7P2Mo5VW12O62 isomer, have been used as catalysts for the liquid phase oxidation of cyclohexanol, cyclohexanone and cyclohexanol/cyclohexanone mixture to form adipic acid in presence of hydrogen peroxide without solvent, without phase-transfer agents and without adding acid. 31P NMR spectroscopy of different POMs after cyclohexanol oxidation showed the formation of new active species that can be attributed to “peroxo-POMox” form. An adipic acid yield of 69% was obtained from the oxidation of a mixture of cyclohexanol (50%) and cyclohexanone (50%) with α-K6P2Mo6W12O62 isomer.

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