General Papers

ARKIVOC 2006 (x) 102-106

A very simple and chemoselective air oxidation of benzoins to benzils using alumina
Konstantinos Skobridis,*a Vassiliki Theodorou,a and Edwin Weber*b

Department of Chemistry, University of Ioannina, GR-451 10 Ioannina, Greece Institut für Organische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, D-09596 Freiberg/Sachs., GermanyE-mail:

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 asoxidizing 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.Keywords: Benzoins, benzils, air oxidation, alumina, chemoselectivity

Benzils or α-dicarbonyl compounds, in general, are important materials due to their practical applications, starting materials for the synthesis of heterocycles1 and as photosensitive agents.2 The oxidation of benzoins has been accomplished by several oxidative reagents such as nitric acid, thalliumnitrate, copper sulfate, copper acetate, ammonium nitrate, bismuth oxide and bismuth nitrate, iron (II) thiolate and oxone, trichlorooxyvanadium and vanadium oxide, titanium (IV) chloride andtriethylamine 3 or by molecular oxygen using microwave irradiation on zeolite A or clayfen,4 or by nickel hydrotalcite activation.5 However, while all these methods can generate the desired products efficiently,many of the above oxidants are toxic and hazardous metal compounds, generating waste disposal problems. An indirect electrochemical method was, also, recently used for the oxidative transformation ofbenzoins to benzils.6 The cleanest and the most ideal reagent for oxidation reactions would be air. Thus, oxidative transformations of organic compounds effected by air oxygen are attractive from...