Solvent Effects in the Enantioselective Hydrogenation of Ethyl Benzoylformate
- PDF / 580,181 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 17 Downloads / 189 Views
Solvent Effects in the Enantioselective Hydrogenation of Ethyl Benzoylformate Gerson Martin • Pa¨ivi Ma¨ki-Arvela Dmitry Yu. Murzin • Tapio Salmi
•
Received: 24 May 2013 / Accepted: 5 July 2013 Ó Springer Science+Business Media New York 2013
Abstract Solvent effects in the enantioselective hydrogenation of ethyl benzoylformate (EBF) to (R)-ethyl mandelate over (-)-cinchonidine (CD)-modified Pt/Al2O3 catalyst were studied in a semi-batch reactor. Solvents of different nature were used: protic (2-propanol, 1-propanol, 1-octanol and ethanol), aprotic polar (methyl acetate, acetone, ethyl acetate and tetrahydrofuran) and apolar solvents (methyl cyclohexane and toluene). The effects of pure solvents and binary solvent mixtures on hydrogenation rates and enantioselectivity were investigated. The highest enantiomeric excess (ee) of 72 % was obtained in ethyl acetate, decreasing nonlinearly with increasing dielectric constant (e) being close to 20 % in ethanol. The highest value of the initial hydrogenation rate was obtained in the apolar solvents (21 mmol dm-3 min-1g-1 cat ) while the lowest one was observed in tetrahydrofuran (2 mmol dm-3 min-1 g-1 cat ). A kinetic model was proposed for the enantioselectivity dependence on dielectric constant based on Kirkwood treatment. The non-linear dependence of ee on (e) was included in the model to describe quantitatively the variation of ee in different solvents. The results showed a good fit for ee as a function of e. Keywords Enantioselective hydrogenation Solvent effect Pt catalyst Transition state theory Dielectric constant
G. Martin P. Ma¨ki-Arvela D. Yu. Murzin (&) T. Salmi ˚ bo Akademi University, Process Chemistry Centre, A 20500 Turku, Finland e-mail: [email protected]
1 Introduction The hydrogenation of a-ketoesters on supported Pt catalysts modified with cinchona alkaloids was discovered by Orito et al. [1] in 1979 and, since then, detailed studies have been conducted and different substrates have been investigated using Pt-cinchona alkaloid catalytic systems. In case of the hydrogenation of ethyl benzoylformate, only few papers have been recently published. For instance, Barto´k et al. [2] studied the effect of different alkaloids (cinchonidine, cinchonine, quinine, quinidine, a-isocinchonine, a-isocinchonidine and d-isoquinidine) in the hydrogenation of EBF; Sutyinszki et al. [3] found extremely high enantioselectivity (98 %) using Pt/Al2O3 as a catalyst at 25 bar of pressure; Diezi et al. [4] studied the steric effects in the Pt-catalyzed asymmetric hydrogenation of nine different a-ketoesters by variation of the bulkiness at the keto and ester side of the substrates and Sz}oll}osi et al. [5] studied the origin of rate enhancement using methyl benzoylformate as raw material in a continuous-flow-fixed-bed reactor. Solvents have a crucial effect in the production of fine chemicals. Although the presence of solvents in the reaction mixture increases the process costs, the use of solvents in liquid-phase reactions is required to accomplish at least one o
Data Loading...
