Abstract
An efficient and facile air oxidation of benzoins in the presence of the heterogeneous catalyst aluminum oxide, avoiding the use of noxious metal compounds as oxidizing agents has been developed. It thus constitutes a very simple, environmentally friendly, clean, economical and selective method for the aerobic preparation of benzils from the corresponding benzoins.
Highlights
Benzils or α-dicarbonyl compounds, in general, are important materials due to their practical applications, i.e. as starting materials for the synthesis of heterocycles[1] and as photosensitive agents.[2]
In order to study the optimization of the reaction conditions and to evaluate the parameters that may affect the reaction, we carried out the oxidation experiments under an air atmosphere using acidic, neutral and basic alumina, i.e. pH 4.5, 7.0 and 9.5, respectively
The reaction rate was found to be strongly influenced by the pH of the alumina, and the best result was obtained with basic aluminum oxide
Summary
Benzils or α-dicarbonyl compounds, in general, are important materials due to their practical applications, i.e. as starting materials for the synthesis of heterocycles[1] and as photosensitive agents.[2]. An indirect electrochemical method was, recently used for the oxidative transformation of benzoins to benzils.[6] The cleanest and the most ideal reagent for oxidation reactions would be air. We describe such an extremely simple and efficient transformation process which is the chemoselective aerobic oxidation of benzoins to benzils, supported by commercially available aluminum oxide as a solid catalyst, without the use of any metal salts as oxidizing agents or other reagents (Scheme 1).
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