Enantioselective hydrogenation of ethyl pyruvate over cinchonidine-Pt/Al2O3 catalyst. A reaction kinetic approach

Abstract

A new reaction kinetic approach was used to describe the enantioselective hydrogenation of ethyl pyruvate over cinchona-Pt catalyst. The above reaction was considered as the sum of two parallel reactions: (i) racemic hydrogenation resulting in R-and S-product in equal amount and (ii) enantioselective hydrogenation leading to the exclusive formation of one of the two optically isomers. New terms such as acc diff and k e /k r (where k e and k r are the rate constants of the enantioselective and racemic hydrogenation, respectively) were introduced to characterize the relationship between the enantioselective and the racemic hydrogenation reactions. Results obtained show that the formation of R-product is rate accelerated, while the formation of S-product is decelerated. The results indicate also that the overall rate increase is a kinetic phenomenon and cannot be attributed to the suppression of the poisoning effect of CO or oligomers formed from ethyl pyruvate. The strong rate acceleration effect of achiral tertiary amines (ATAs) added to the reaction mixture was attributed to the decrease of the loss of modifier during the hydrogenation experiments.

Tuning Aryl−CH···O Intermolecular Interactions on Pt(111)

“…3 Kinetics studies show that on the modified surface the reaction leading to (R)-product is accelerated and the reaction leading to (S)-product is decelerated. 36 This may be understood in terms of the model in Scheme 3, in that a pro-S diastereomeric complex places the keto group away from the surface relative to the pro-R complex. Hence, the chemisorption activation of the hydrogenation of the keto carbonyl is decreased in going to the pro-S configuration.…”

Enantioselective hydrogenation of activated ketones in the presence of Pt–cinchona catalysts. Is the proton transfer concept valid?

“…Ethyl pyruvate (EtPy, different batches from Fluka) was distilled under vacuum, 2,3- [19][20][21] while CatASium F214 (Degussa,) were used as received [19,22].…”

Asymmetric transfer hydrogenation of ketones using Ru(0) nanoparticles modified by Chiral Thiones

“…The metal NPs modified by chiral compounds, sometimes referred to as chiral NPs can catalyze the reactions in an enantioselective manner. [14][15][16][17][18] Thus, NPs of Pt, Ir, and Pd modified by cinchona alkaloids have been used for the hydrogenation of ethyl pyruvate [10,13,16,[18][19][20][21][22][23] and other prochiral substrates to give chiral products with over 97% ee in some cases. [24] However, cinchona alkaloid ligands appear to be unique.…”