Jingwei Luo

A multi-pronged mechanistic study of the phosphine-mediated conjugate addition of an alcohol to an acetylenic ester

The conjugate addition of an alcohol to a butynoate ester using an organophosphine catalyst was monitored using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS), together with 31P and 1H NMR spectroscopy. The combination of methods allowed examination of the reaction progress from the perspective of reactants and products (1H NMR) and insights into behaviors of the reaction intermediates and formation of byproducts (31P NMR and MS). The resulting traces could be closely approximated through numerical modeling by appropriate selection of rate constants, and a sound understanding of the mechanism and the means by which oligomeric byproducts are formed allows a rational approach to experimental design.

Mass transfer and convection effects in small-scale catalytic hydrogenation

Rhodium-catalyzed hydrogenation of alkynes was studied under conditions of low concentration of substrate and either one or two equivalents of hydrogen using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS). Four sample vials of the same volume but of different diameter enabled the investigation of the effects of surface area on reaction rates. Running the same experiments with stirring on or off allowed further details to emerge, notably the obvious effects of convection thanks to the localized sampling technique employed. Modelling of the system allowed for a better understanding of the relative importance of the various factors in play (reaction rate, surface area, mass transfer, convection). These factors should be carefully considered when studying or optimizing reactions involving narrow reaction flasks, especially when those flasks are unstirred.