Studies in homogeneous catalysis: mechanism of the oxidation of aliphatic aldehydes and ketones catalysed by copper‐pyridine complexes

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Abstract
From kinetic and stoichiometric data the following mechanism is derived for the oxidative steps of the degradation of saturated aldehydes and ketones with oxygen, catalysed by copper‐pyridine complexes in the presence of triethylamine, described in the previous paper.The aldehyde (ketone) is deprotonated by methoxide ions, formed from methanol and triethylamine. The enolate ion co‐ordinates with cupric ion and pyridine to a complex which does not decompose spontaneously. This complex, however, is reactive toward oxygen, yielding an a‐hydroperoxide anion of the carbonyl compound, which decomposes via ionic reactions. The complex is also reactive towards triphenylphosphine, yielding a cuprous phosphine complex and presumably an enolate radical. The dimers of such radicals have been isolated.At high concentrations of oxygen the overall reaction rate is controlled by the rate of formation of the copper‐enolate complex or, if the copper concentration is sufficiently high, by the deprotonation step. In the absence of oxygen the same reactions control the rate of the reaction with triphenylphosphine.