Characterisation of Reactions in Supercritical Difluoromethane

Reactions in scCO2 are frequently limited by the low polarity of the solvent. This may result in low solute/ product solubility or low catalyst activity. The use of more polar sc fluids such as difluoromethane (HFC 32) can circumvent many of these issues and facilitate reactions that are not possible in CO2. We demonstrate the use of HFC 32 for three types of reaction; an esterification reaction, a Friedel Crafts alkylation and the polymerisation of olefins. The extent of each reaction is monitored using a dielectometry technique and solution dielectric constants are used to explain unusual observations in reaction rate and product distribution. It is shown that reactions can be tuned more effectively in HFC 32 than CO2 due to the larger changes in polarisability and hydrogen bonding with pressure. It is, however, shown that in reactions where high solute solubility is observed in both fluids the reaction is unaffected by the solvent and that the clustering of reagent molecules affects the reaction dynamics.