Cite this: DOI: 10.1039/c3ra41966e Received 22nd April 2013, Accepted 17th May 2013 Selective hydrogenation of the CLC bond of a,b-unsaturated carbonyl compounds over PdNPs–SBA- 15 in a water medium3 DOI: 10.1039/c3ra41966e www.rsc.org/advances Saidulu Ganji, Suresh Mutyala, Chinna Krishna Prasad Neeli, Kamaraju Seetha Rama Rao and David Raju Burri* Well dispersed palladium nanoparticles, with size 3–5 nm, have been immobilized on APTES functionalized SBA-15 and are found to be efficient and selective catalysts for the hydrogenation of the CLC bond of a,b-unsaturated carbonyl compounds with molecular hydrogen at room temperature in a water medium. Introduction With the emergening concerns of environmental pollution and the ever escalating stringent specifications for effluents, there has been a pressing need to develop highly active and selective processes under environmentally benign conditions. From the green chemistry point of view, the use of water as a reaction medium has many advantages such as non-toxicity, non-flamm- ability, abundance etc. 1,2 The development of catalysts that show high activity and selectivity in an aqueous environment is an immense challenge for the scientific community. The catalytic hydrogenation of a,b-unsaturated carbonyl compounds is a process of practical and industrial impor- tance. 3–5 The hydrogenation of both the CLC and the CLO bonds is thermodynamically feasible. The selective hydrogenation of the CLC bond of a,b-unsaturated carbonyl compounds, leaving the CLO group intact, for the production of saturated carbonyl compounds is an important catalytic transformation. Saturated carbonyl compounds are used as intermediates for the synthesis of various biologically active compounds 6 including the synthesis of HIV-I protease inhibitors. 7 In addition, saturated carbonyl compounds like phloretin, a dihydrochalcone, inhibit the growth of Molt-4 human leukemic cells. 8 A few articles can be found in the literature on the selective hydrogenation of a,b-unsaturated carbonyl compounds with palladium, 9 ruthe- nium, 10 rhodium, 11 iridium 12 and other metal complexes. 13 Ondruschka et al. studied extensively the selective hydrogenation of a,b-unsaturated carbonyl compounds with porous glass supported Pd, Pt and Rh catalysts. 14 However, the above cited catalysts are reported using only organic solvents. Bagal et al. 15 and Li et al. 16 reported the chemoselective hydrogenation of a,b-unsaturated carbonyl com- pounds using water as a solvent, but they used sodium formate as a source of hydrogen. Wang et al. 17 reported the hydrogenation of a,b-unsaturated carbonyl compounds over Au–meso-CeO 2 cata- lysts, which efficiently reduces the carbonyl group rather than the CLC bond in water with molecular hydrogen. The use of molecular hydrogen instead of metal hydrides as the hydrogen source in the selective hydrogenation of a,b-unsaturated carbonyl compounds in aqueous medium is challenging in both green chemistry and organic synthesis. Nowadays, mesoporous materials have attracted considerable attention owing to their potential applications in absorption, separation, catalysis etc. 18 Among the family of mesoporous materials, SBA-15 is one of the most ideal catalyst supports due to its high surface area, high porosity and large and uniform pore size. 19 These features provide a consistent and well isolated environment for the growth of nanoparticles, which is of particular interest for size dependent reactions. The incorporation of Pd into the pores of SiO 2 has been reported by several authors. 20 The introduction of the metal salt into the hydrophilic channels of SBA-15 is driven by capillary forces in the presence of an organic solvent. 21 In this approach, several metal and metal oxide nanoparticles have been prepared successfully. 22 The selective hydrogenation of a,b-unsaturated carbonyl compounds to satu- rated carbonyl compounds over Pd–SBA-15 catalysts is not entirely new. 23 However, the reactions are carried out in organic solvents and at high temperatures. Herein, for the first time we report a new approach to prepare well dispersed palladium nanoparticles on APTES modified SBA- 15 by using the hydrophobic solvent dichloromethane as the transport medium. This novel Pd–SBA-15 catalyst exhibited enhanced catalytic activity in the selective hydrogenation of a,b-unsaturated carbonyl compounds to saturated carbonyl compounds in an aqueous medium with molecular hydrogen (Scheme 1). Catalysis Laboratory, Indian Institute of Chemical Technology, Hyderabad-500607, India. E-mail: david@iict.res.in; Fax: +91-40-27160921; Tel: +91-40-27193232 3 Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra41966e RSC Advances COMMUNICATION This journal is ß The Royal Society of Chemistry 2013 RSC Adv. Published on 21 May 2013. Downloaded by INDIAN INSTITUTE OF TECHNOLOGY BOMBAY on 18/06/2013 19:59:08. View Article Online View Journal