Equilibrium reactions in supercritical difluoromethane

A dielectometry technique is used to follow the extent of two equilibrium reactions in supercritical difluoromethane (sc HFC32), and the validity of the technique is demonstrated in the liquid state and compared to results obtained using gas chromatography -mass spectroscopy (GC-MS). The apparent equilibrium constant for the acid-catalyzed esterification of benzoic acid with 1-butanol decreased as the pressure increased, and this was proposed to be due to clustering at lower solvent density. In supercritical carbon dioxide (sc CO2), the equilibrium constant was similar to that in sc HFC32, despite the large difference in the dielectric constant of the fluids. The solute had a significant effect on the solution dielectric constant, such that the two solutions were similar. An acid-catalyzed aldol condensation reaction was also studied, and the apparent equilibrium constant was observed to change in a manner similar to that observed for the esterification reaction. The overall change in equilibrium constant was less than that observed for the esterification reaction and this was rationalized, in terms of the different dipole moments of the reagents in the two reactions.