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
a b

Department ofChemistry, University of Ioannina, GR-451 10 Ioannina, Greece Institut für Organische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, D-09596 Freiberg/Sachs., Germany E-mail: kskobrid@cc.uoi.gr

Abstract Anefficient 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. Keywords: Benzoins, benzils, air oxidation, alumina, chemoselectivity

IntroductionBenzils or α-dicarbonyl compounds, in general, are important materials due to their practical applications, i.e. as starting materials for the synthesis of heterocycles1 and as photosensitive agents.2 The oxidation ofbenzoins has been accomplished by several oxidative reagents such as nitric acid, thallium nitrate, copper sulfate, copper acetate, ammonium nitrate, bismuth oxide and bismuth nitrate, iron (II) thiolate and oxone,trichlorooxyvanadium and vanadium oxide, titanium (IV) chloride and triethylamine 3 or by molecular oxygen using microwave irradiation on zeolite A or clayfen,4 or by nickel hydrotalcite activation.5 However, while all these methodscan 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 theoxidative transformation of benzoins 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 [continua]

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