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Dielectrometry is used as a novel technique for following the rate of a Friedel-Crafts alkylation reaction in supercritical (sc) difluoromethane. Although the process was not optimized, good product yields were obtained and reaction rates were found to be larger than in CO2 at comparable conditions. The reaction order is determined using the initial rate method and the reaction is shown to be first-order with respect to both anisole and t-butyl chloride. The reaction rate constant is unaffected by pressures above 120 bar but close to the critical pressure the value decreases with increasing pressure. It is also shown that the product distribution for the alkylation of anisole shows significant pressure dependence with substitution at the ortho-position being favored at lower pressures, which is ascribed to hydrogen bonding. This pressure dependency is not observed in sc CO2 or using toluene as a substrate, which supports the idea that hydrogen bonding may be important in the reaction mechanism. The effect of the different reagents and temperature on the rate of the alkylation reaction was also determined.

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.