Microwave assisted solvent free oxidation of hydrobenzoins, benzoins and alcohols with NBS – Al2O3

Jitender M. Khurana; Reema Arora

doi:10.3998/ark.5550190.0009.e20

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Microwave assisted solvent free oxidation of hydrobenzoins, benzoins and alcohols with NBS – Al2O3

Jitender M. Khurana; Reema Arora

Volume 2008, Issue 14, pp. 211-215

DOI: http://dx.doi.org/10.3998/ark.5550190.0009.e20

Paper ID: 08-3349HP

Received on 2008-07-03; Accepted on 2008-09-16; Published on 2008-10-17

Permissions: This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 License. Please contact [email protected] to use this work in a way not covered by the license.

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General Papers ARKIVOC 2008 (xiv) 211-215 Microwave assisted solvent free oxidation of hydrobenzoins, benzoins and alcohols with NBS - Al2O3 Jitender M. Khurana* and Reema Arora Department of Chemistry, Delhi University, Delhi-110007 E-mail: [email protected] Abstract A simple and efficient protocol for microwave-assisted solvent-free oxidation of hydrobenzoins to benzoins or benzils, benzoins to benzils, and alcohols to the corresponding aldehydes or ketones, using N-bromosuccinimide – neutral alumina is reported. Keywords: Oxidation, carbonyl compounds, diols, hydrobenzoins, microwave irradiation. Introduction Oxidation of alcohols to the carbonyl moiety can be achieved by an array of reagents.1 Recently other reagents e.g., cobalt(II) complexes,2 m-iodosylbenzoic acid/RuCl3,3 IBX/n-Bu4N+Br/ CH2Cl2-H2O,4 DABCO/Br2,5 DMSO/N2H4.H2O/I2/H2O/CH3CN,6 have also been reported. Hydrobenzoins and benzoins have also been oxidized with Bi(NO3)-Cu(OAc)2,7 RuCl3/Bromamine-T,8 the Burgess reagent,9 NBS/CCl4/pyridine,10 etc. Many of these reagents lack generality for oxidation of alcohols, benzoins and hydrobenzoins, besides being expensive, and giving low yields and undesirable side products. Microwave-assisted solvent-free chemical reactions on inorganic solid supports have drawn attention recently.11 NBS is an economical and convenient oxidant and has been used in a variety of oxidation reactions.10,12 We have investigated the oxidation of hydrobenzoins, benzoins and alcohols with NBS–Al2O3 in solventfree conditions expedited by microwave irradiation. Results and Discussion We report herein a simple and efficient solvent-free protocol for the microwave- accelerated oxidation of hydrobenzoins, benzoins and alcohols with N-bromosuccinimide–neutral alumina. The reaction conditions were optimized by carrying out reactions of hydrobenzoin (1a) as a model substrate and changing the molar ratios of NBS and Al2O3 besides variable microwave ISSN 1551-7012 Page 211 ©ARKAT USA, Inc.