Solvent effects on the reaction rate and selectivity of synchronous heterogeneous hydrogenation of cyclohexene and acetone in ionic liquid/alcohols mixtures

Synchronous heterogeneous catalytic hydrogenation of cyclohexene and acetone, catalyzed by Pt/Al2O3, 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 kvs.π* (dipolarity/polarizibility) gives reasonable results in the solution. The increase of the reaction rate with π* is attributed to the non-polar nature of the reactants.

Graphical abstractSynchronous heterogeneous catalytic hydrogenation of cyclohexene and acetone, catalyzed by Pt/Al2O3, 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.Figure optionsDownload full-size imageDownload high-quality image (59 K)Download as PowerPoint slideSelectivity of the hydrogenation reaction (S = kcycl./kacet.) in ■ ethanol–RTIL and ▴ propan-1-ol–RTIL mixtures at 25 °C.