Phosphomolybdic acid as a reoxidant in the palladium(II)-catalysed oxidation of but-1-ene to butan-2-one

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Abstract
Phosphomolybdic and a variety of phosphomolybdovanadic acids were examined as reoxidants for the palladium sulphate-catalysed oxidation of but-1-ene to butan-2-one both in the absence and the presence of oxygen. All of these co-oxidants were approximately equally effective in reoxidising Pd0 to PdII but they varied substantially in their ability to be reoxidised themselves by air under the optimum reaction conditions in aqueous acid. Phosphomolybdovanadate systems were the most effective at a pH > 0, but VIV by itself could not be reoxidised by air under these conditions and therefore the molybdenum must play a vital role. Phosphomolybdic acid, H3[PMo12O40], itself was quite a good co-oxidant under more acid conditions (1 mol dm–3 sulphuric), but 31P n.m.r. spectroscopy showed that in dilute solution it was largely dissociated into phosphoric acid; evidence for the presence under some conditions of other phosphomolybdic acids, which may be related to the active species, is presented.

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