Clean Carbonylations in Supercritical Carbon Dioxide. Part 1: Palladium-Catalyzed Alkoxycarbonylation of Allyl Bromide

Palladium-catalyzed alkoxycarbonylation of allyl bromide to unsaturated esters in supercritical carbon dioxide (sc-CO2) was performed and compared with alkoxycarbonylation in organic solvents in this paper. Effects of the catalytic precursor, triphenyl phosphine ligand, base, pressure, and reaction temperature on the reaction yield and selectivity were mainly discussed. The results showed that sc-CO2was a favorable reaction medium for the reaction under lower CO pressure. Small changes, both in the CO2pressure as well as the amount of cosolvent ethanol, can cause drastic changes in both the reaction yield and selectivity. Moreover, FeCl2was found to have a promoting effect as cocatalyst on the reaction. The synergic effect of cosolvent ethanol with FeCl2can lead to an even better result than that in organic solvents.