Issue 10, 1972

Mechanism of the photoinduced decarboxylation of carboxylic acids sensitised by aromatic ketones and quinones

Abstract

The rate constants for the decarboxylation of several acids of the type RXCH2CO2H (X = O, S, and NH), sensitised by benzophenone and tetrachloro-p-benzoquinone have been determined. The reactions are considered as occurring via exciplex formation between the carbonyl compound and the acid, and in agreement with this hypothesis, the published values of rate constants for the reaction of triplet benzophenone with substituted hydrocarbons (RXCH3) are very similar to those determined for reaction with the corresponding carboxylic acid. In addition, the rate constants for decarboxylation are in the order expected from a consideration of the ionisation potentials of their corresponding substituted hydrocarbon (RXCH3). The rate constants for reaction with the quinone are higher than those for the corresponding reactions with benzophenone. Decarboxylation of (phenylthio)acetic acid in acetonitrile solution is acid catalysed whereas in benzene solution, acids slightly retard the reaction. This reaction is also quenched by methyl phenyl sulphide. Attention is drawn to the fact that the inefficiency of photoreduction of benzophenone by substituted hydrocarbons (RXCH3) can stem from the hydrogen abstraction reaction being reversible, as well as being due to exciplex formation.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1972, 1357-1362

Mechanism of the photoinduced decarboxylation of carboxylic acids sensitised by aromatic ketones and quinones

R. S. Davidson and P. R. Steiner, J. Chem. Soc., Perkin Trans. 2, 1972, 1357 DOI: 10.1039/P29720001357

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