Journal of Molecular Catalysis A: Chemical 306 (2009) 11–16 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata Solvent effects on the reaction rate and selectivity of synchronous heterogeneous hydrogenation of cyclohexene and acetone in ionic liquid/alcohols mixtures Mohammad Khodadadi-Moghaddam a , Aziz Habibi-Yangjeh b , Mohamad Reza Gholami a,∗ a Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, Iran b Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran article info Article history: Received 2 November 2008 Received in revised form 7 February 2009 Accepted 9 February 2009 Available online 21 February 2009 Keywords: Ionic liquid Heterogeneous catalytic hydrogenation Solvatochromic parameters Solvent effects Selectivity abstract Synchronous heterogeneous catalytic hydrogenation of cyclohexene and acetone, catalyzed by Pt/Al 2 O 3 , was carried out in solutions of 2-hydroxy ethylammonium formate (a room temperature ionic liquid, RTIL) with ethanol and propan-1-ol at 25 ◦ C. Rate constants and selectivity of the reaction (relative to cyclohexene hydrogenation) increase with mole fraction of the ionic liquid (IL). The reactants tendency to the catalyst surface increases by addition of the ionic liquid and thus the reaction rate increases, especially for cyclohexene hydrogenation. Consequently the selectivity to cyclohexene hydrogenation was increased. Single-parameter correlations of log k vs. * (dipolarity/polarizibility) gives reasonable results in the solution. The increase of the reaction rate with * is attributed to the non-polar nature of the reactants. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved. 1. Introduction Selective hydrogenation is an important process both in homo- geneous and heterogeneous catalysis. Its primary target is the hydrogenation of a specific unsaturated bond (e.g., C C, C C or C O), while leaving other unsaturated bonds within the molecule (or in other molecules) unaffected [1]. The selective hydrogenation of a C C bond or a C O bond in a molecule with both a C C bond and a C O bond is important for the preparation of fine chemicals and is of academic interest [2]. The catalytic selective hydrogena- tion of ˛,ˇ-unsaturated aldehydes to the saturated aldehydes is one example. Platinum catalyst is known to be one of the most effective catalysts for this selective hydrogenation. However, such selective reactions become quite problematic when the carbon–carbon dou- ble bond of an a,b-unsaturated aldehyde is conjugated both to a carbonyl group and an aromatic ring. Catalytic hydrogenation is one of the most useful, versatile, and environmentally acceptable reaction routes available for organic synthesis, and the reaction is usually carried out in a liquid-phase using batch type slurry processes and a supported noble metal (Pd, Pt, or Rh) catalyst [3–6]. Major advantages of multi-phase catalytic reactions using solid catalysts include easy separation of catalysts and products, easy recovery and catalyst recycling, and relatively ∗ Corresponding author. Tel.: +98 21 66165314; fax: +98 21 66005718. E-mail address: gholami@sharif.edu (M.R. Gholami). mild operating conditions [7,8]. The performance of noble metal catalysts in liquid-phase hydrogenation is found to be dependent on several factors such as liquid composition (substrate structure, solvent effect, etc.), catalyst nature (active sites composition and morphology, support effect, modifiers, etc.), and reaction condi- tions (temperature, pressure, etc.) [9]. In the production of fine chemicals over heterogeneous catalysts, the choice of the solvent has a crucial impact; a bad selection of the solvent leads to a complete loss of selectivity and/or activity, thus destroying the possible utilization of a potentially efficient process in practice. Therefore, the choice of a solvent and the understand- ing of solvent effects are of central importance and thus require a careful investigation. Solvent effects are widely studied and the phenomena known as solvent effects cover a very broad topic [10,11]. The effects ris- ing from the use of different solvents are observed as variations in activity, selectivity and stereoselectivity. However, several factors can be responsible for these variations, e.g., solubilities of liquid and gaseous reactants and their adsorption on the catalyst surface, competitive adsorption of solvent molecules, interaction of solvent with the reactant(s) either in the liquid-phase or on the catalyst surface as well as catalyst deactivation caused by the solvent [12]. Therefore, the phenomena understood under the label of solvent effects are a combination of very different physical and chemical phenomena and thus it is difficult to understand them completely. Ionic liquids (ILs) are attracting much interest in various areas of chemical synthesis, electrochemistry, separations and biotransfor- 1381-1169/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2009.02.018