DIFFUSION-CONTROLLED REACTIONS IN SUPERCRITICAL CHF3 AND CO2/ACETONITRILE MIXTURES

We present results of the triplet-triplet annihilation (TTA) process of benzophenone (Ph2C=O) and the self-termination reaction of benzyl radical (PhCH2) to investigate the possibility of diffusion-controlled processes being hindered or enhanced in supercritical fluids (SCFs) or fluid mixtures. However, both reactions occur essentially at the diffusion-control limit in supercritical fluoroform (CHF3) and carbon dioxide (CO2) doped with 1 mol % acetonitrile (CH3CN) when spin statistical factors are taken into account. The reaction kinetics were measured by laser flash photolysis at various pressures above the critical pressure along three isotherms. This study corroborates our earlier report of these reactions in supercritical CO2 and ethane (C2H6). In all of the fluids and fluid mixture, the locally higher density of the solvent around the solutes in no way enhances or slows the bimolecular annihilation or termination reaction. In addition, there is no evidence of enhanced solute-solute interaction. Finally, we studied the photocleavage of dibenzyl ketone (DBK) and the subsequent decarbonylation of the phenylacetyl radical (PhCH2CO) and did not observe any enhanced cage effects or anomalous behavior due to the increased local density.