Kinetic study of heterogeneous catalytic hydrogenation of cyclohexene to cyclohexane in ionic liquid–alcohols mixtures

• Published in: Applied catalysis. A, General General, 2008-06, Vol.341 (1), p.58-64
• Main Authors: Khodadadi-Moghaddam, Mohammad, Habibi-Yangjeh, Aziz, Gholami, Mohamad Reza
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Heterogeneous catalytic hydrogenation; Ionic liquid; Solvatochromic parameters; Solvent effects; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2008.02.002

Heterogeneous catalytic hydrogenation of cyclohexene by Pt/Al 2O 3, was carried out in solutions of 2-hydroxyethylammonium formate (a room temperature ionic liquid) mixed with methanol, ethanol and propan-2-ol. The rate constant of the reaction increases with the mole fraction of the ionic liquid. Increase of the reaction rate with π * (dipolarity/polarizibility of solvent) is attributed to the non-polar nature of the reactants. ▪ Heterogeneous catalytic hydrogenation of cyclohexene, catalyzed by Pt/Al 2O 3, was carried out in solutions of 2-hydroxyethylammonium formate (a room temperature ionic liquid, RTIL) mixed with methanol, ethanol and propan-2-ol at 25 °C. The rate constants of the reaction in ionic liquid alcohol mixtures were higher than alcohol alone. First-order rate constant of the reaction in the RTIL relative to propan-2-ol is approximately 28. Furthermore, the rate constant of the reaction increases with the mole fraction of the ionic liquid. Single-parameter correlations of log k vs. normalized polarity parameter ( E T N ), hydrogen-bond acceptor basicity ( β) and hydrogen-bond donor acidity ( α) do not give acceptable results in the solutions. In addition, log k does not show an acceptable dual-parameter correlation with π* (dipolarity/polarizibility, one of the Kamlet–Taft parameters for solvent that shows the dipolarity of the solvent) and α, π* and β and E T N and β. However single-parameter correlation of log k vs. π * gives reasonable results. The increase of the reaction rate with π * is attributed to the non-polar nature of the reactants.