Showing papers by "Donna G. Blackmond published in 1996"
TL;DR: In this paper, it was shown that the reported pressure dependence on enantioselectivity may in fact be reproduced at constant pressure for several systems by varying the rate of gas−liquid mass transfer.
Abstract: Marked shifts in enantioselectivity in the asymmetric hydrogenation of several prochiral substrates were observed as a function of the availability of hydrogen to the catalyst in both heterogeneous and homogeneous catalytic reactions. The key kinetic parameter affecting enantioselectivity was found to be concentration of molecular hydrogen in the liquid phase, [H2], rather than hydrogen pressure in the gas phase, and it was observed that under typical reaction conditions, [H2] could differ widely from its equilibrium saturation value. It was demonstrated that the reported pressure dependence on enantioselectivity may in fact be reproduced at constant pressure for several systems by varying the rate of gas−liquid mass transfer. The general significance of the conclusions suggest that considerations of hydrogen diffusion limitations might be important in other asymmetric hydrogenation studies reported in the literature. For systems where enantioselectivity depends positively on hydrogen pressure, the intrin...
141 citations
TL;DR: In this article, a reaction-driven equilibration of the surface environment for optimal enantioselective catalysis was proposed for these reactions carried out under conditions where moderate enantiorelectivities are observed.
55 citations
TL;DR: In this paper, the authors observed a change in the observed kinetics from the zero-order substrate dependence typical of gas-liquid diffusion control to a positive dependence on substrate concentration, even for a series of reactions carried out at constant pressure.
40 citations
TL;DR: In this paper, examples of enantioselective hydrogenation and selective consecutive hydrogenation reactions are presented to demonstrate the high quality of kinetic data obtainable from reaction calorimetry.
39 citations
TL;DR: In this paper, reaction calorimetry was used for the liquid-phase hydrogenation of a substituted pyrazine compound carried out over supported Pd catalysts, and the concentration profiles developed from fitting the heat flow data to a first-order model were compared with analytical measurements of concentration.
Abstract: Reaction calorimetry was the primary tool in investigations of the liquid-phase hydrogenation of a substituted pyrazine compound carried out over supported Pd catalysts. In addition to providing information about gas-liquid mass transfer limitations, calorimetric measurements provided a kinetic analysis of how product selectivity in this consecutive reaction network may be tuned by changing reaction conditions. Concentration profiles developed from fitting the heat flow data to a first-order model were compared with analytical measurements of concentration, demonstrating the utility of combining independent measurements of reaction progress as a means of assessing the validity of a kinetic model.
2 citations