Oxidation, oxidative esterification and ammoxidation of acrolein over metal oxides: Do these reactions include nucleophilic acyl substitution?

It is known that nucleophilic acyl substitution in the RCOX compounds with “good leaving” groups X is a fundamental and energetically favorable route to carboxylic acid derivatives. When water, alcohols and ammonia are used as nucleophiles, carboxylic acids, esters and amides (or nitriles) are obtained, respectively. On the other hand, the same products are derived from aldehydes upon their catalytic aerobic oxidation, on condition that water, alcohols and ammonia are present in the feed gas. Therefore, one can surmise that nucleophilic substitution reactions are involved intrinsically in the catalytic oxidation reactions. In agreement with this hypothesis we have shown, as an example, that the selfsame catalyst, MoVTeNb mixed oxides, enables successful oxidation, oxidative esterification and ammoxidation of acrolein. The mechanistic aspects of these reactions are considered based on established organic and general chemistry principles.