Send Orders for Reprints to reprints@benthamscience.ae Current Catalysis, 2017, 6, 000-000 1 RESEARCH ARTICLE 2211-5447/17 $58.00+.00 ©2017 Bentham Science Publishers Green Oxidation Protocol for Alcohols to Carbonyls by Tert- butylhydroperoxide Over MnO2 Catalysts: Comparison of Bulk and Nanostructure Anand S. Burange 1,2 , Ashtami Jayakumar 3 , Amber J. Sahani 1 , Savita Ladage 4 and Radha V. Jayaram 1,* 1 Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai- 400 019, India; 2 Department of Chemistry, Wilson College, Chowpatty, Mumbai- 400 007, India.; 3 Institute for Intensive Research in Basic Science (IIRBS,Mahatma Gandhi University, Priyadarshini Hills P.O Kottayam, Kerala 686560, India and 4 Homi Bhabha Centre for Science Education,Tata Institute of Fundamental Research,V.N. Purav Marg, Mankhurd, Mumbai 400088, India Abstract: Background: There are various conventional ways for the synthesis of aromatic ketones but suffer from disadvantages like the use of toxic reagents, stoichiometric reagents producing huge amount of byproducts, thus causing hazard to the environment, whereas homogeneous protocols or the noble metal which support catalytic processes are not economically viable. On this ground, an effort was made to develop new green catalytic protocol to overcome these environmental concerns. The catalytic activity of manganese dioxides prepared by different recipes was investigated for the oxidation of allylic and benzylic alcohols. Methods: MnO2 B sample was prepared by calcinations of manganese nitrate while sample ANMnO2 was prepared by the reduction of potassium permanganate using triethanolamine as a reductant. All the samples were well characterized by XRD, SEM, EDX and TEM techniques. All the prepared catalyst samples along with commercial MnO2 were tested for the oxidation of alcohols using TBHP as a clean oxidant, where % conversion and % selectivity were determined by Gas Chromatography. The products were further confirmed by the GC-MS and NMR techniques. Results: Of all the oxides, nano amorphous manganese dioxide exhibited significant catalytic activity and selectivity for the corresponding carbonyls. Change from bulk to nano structure enhanced the catalytic activity because of its higher surface area and change in Mn 3+ / Mn 4+ ratio. The nano amorphous MnO2 (ANMnO2)/TBHP in acetonitrile solvent catalytic system was found to be most efficient with substrate compatibility. In mechanistic investigations, it was observed that from the bulk to the nano structure, Mn 3+ species content in an oxide increased which may play a crucial role in the activity. It was also confirmed by hydrogen peroxide decomposition studies. The catalyst ANMnO2 was found to be reusable for five consecutive cycles with no significant loss in catalytic activity. Conclusion: In conclusion, change in the catalyst’s preparation recipe not only alters the particle size but also affects the ratio of Mn 3+ to Mn 4+ species on the surface as well as on the bulk and thereby catalytic activity. On comparison of initial rate m -2 g of all the catalyst samples for the said reaction, there was no significant difference observed which clearly proved the role of Mn 3+ in catalytic activity. A R T I C L E H I S T O R Y Received: October 13, 2016 Revised: December 31, 2016 Accepted: January 7, 2017 DOI: 10.2174/22115447066661701171223 25 Keywords: Manganese dioxide, amorphous catalysis, nanomaterials, oxidation, nanocatalysis. 1. INTRODUCTION Alcohol oxidation to a carbonyl is one of the most important transformation for the synthesis of variety of intermediates in synthetic organic chemistry [1-2]. Aromatic ketones and carbonyls are usually prepared by Friedel crafts acylation [3-5] or cross-coupling reactions [6-7], apart from *Address correspondence to this author at the Department of Chemistry, Head, Chemistry Department at Institute of Chemical Technology, Matunga, Mumbai, Maharashtra, India; Tel/Fax: + 91 22 3361 2607, +91 22 3361 1020; E-mails: rv.jayaram@ictmumbai.edu.in the oxidation of alcohols. Traditional route for the synthesis of aromatic ketones involves the use of a stoichiometric amount of oxidants such as permanganate and dichromate, but these reagents are toxic and non-ecofriendly causing serious environmental problems [8-10]. Noble metals supported on metal oxides showed promising catalytic activity [11-13], but they are not economically viable. In the last few decades, the stoichiometric reagents for oxidation reaction were gradually replaced by various catalytic systems, including homogeneous and heterogeneous catalysts. This includes many homogeneous