Tungstophosphoric acid (H 3 PW 12 O 40 ) catalyzed oxidation of organic compounds with NaBrO 3 Ahmad Shaabani * , Maryam Behnam, Ali Hossein Rezayan Department of Chemistry, Shahid Beheshti University, P.O. Box 19396, 4716 Tehran, Iran article info Article history: Received 7 November 2008 Received in revised form 21 December 2008 Accepted 27 December 2008 Available online 10 January 2009 Keywords: Oxidation of organic compounds Heteropoly acid NaBrO 3 abstract The oxidation of organic compounds by NaBrO 3 under heteropoly acid catalysis in aqueous acetonitrile at room temperature has been studied. Primary and secondary aromatic alcohols are converted to alde- hydes and ketones, alkyl arenes and sulfides oxidized to corresponding ketones and sulfoxide, respec- tively. In contrary, thiols undergo oxidative coupling reactions to give disulfides. The reaction was carried out in various solvents or under solvent free conditions. The reaction exhibited better results in terms of the yield and rate in H 2 O/CH 3 CN. Ó 2009 Published by Elsevier B.V. 1. Introduction Oxidation reactions are among the most important transforma- tions in synthetic chemistry and offer important methodology for the introduction and modification of functional groups. During the last two decades, there has been a spectacular development in this field and a large number of novel and useful oxidation reac- tions have been developed. The oxidation of alkyl arenes and alco- hols to their corresponding carbonyl compounds is of significant importance in organic chemistry, both for fundamental research and industrial manufacturing. The world-wide annual production of carbonyl compounds is over 10 million tons and most of these compounds are produced from the oxidation of alkyl arenes and alcohols [1–5]. In recent years, heteropoly acid (HPA) catalysts have received much attention in both academia and industry due to their unique properties. Heteropoly acids offer several advantages in terms of catalytic performance, strong acidity, redox sites and selectivity to a particular reaction product by selective stabilization of the reaction intermediate [6–8]. Considering the corrosiveness, safety, lower waste, and ease of separation and recovery of solid acids, replacement of liquid acid with HPAs have been described in the chemical industries. Therefore, a variety of synthetically useful transformations have been developed for the oxidation of alcohols [9], esterification [10], ring-opening of epoxides [11] and dehydra- tion [12] using HPAs as catalysts. Sodium bromate is commercially available as an inexpensive stable solid, which make it an interesting candidate for the oxidation of organic compounds, in addition to its capability in mul- ti-electron transfer reactions. Although, sodium bromate is thermo- dynamically a strong oxidant, but according to the literature [13] bromate itself is not able to oxidize organic compounds. Standard redox potential of the bromate ion, BrO À 3 , is 0.61 V in neutral and alkaline aqueous solution while in aqueous acidic media, it has a po- tential of 1.52 V. Due to the low standard redox potential in neutral or weak acidic media and also very low solubility in most of organic solvents, it is usually used in aqueous media in the presence of strong acidic co-reactants such as: NaHSO 3 [14], HBr [15], ceriu- m(IV) ammonium nitrate (CAN) [16],H 2 SO 4 [17] and HClO 4 [18]. In spite of their potential utility and solubility in these media, most of these homogeneous acids present limitations, because the use of corrosive reagents, the tedious work-up procedure, and the necessity of the neutralization of strong acidic media, pro- duces a large volume of undesired waste. In addition, the high solution acidity increases the oxidizing power of bromate, and lim- its the selectivity of oxidation reactions. The primary organic prod- ucts of these reactions are often contaminated with a-bromo carbonyl compounds due to the generation of Br 2 in the reaction [19–21]. Therefore, the development of new approaches for the oxidation of organic compounds with NaBrO 3 in the presence of HPA as an efficient and reusable solid acid catalyst will be benefi- cial in the synthesis of organic compounds. In continuation of our interest in exploring oxidation of organic compounds [22–26], we herein report a mild and effective proce- dure for the oxidation of organic compounds using HPA/BrO À 3 in H 2 O/CH 3 CN at room temperature in excellent yields (Scheme 1). 1566-7367/$ - see front matter Ó 2009 Published by Elsevier B.V. doi:10.1016/j.catcom.2008.12.059 * Corresponding author. Fax: +98 21 22431663. E-mail address: a-shaabani@cc.sbu.ac.ir (A. Shaabani). Catalysis Communications 10 (2009) 1074–1078 Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom