Pulse radiolysis to study intermolecular interactions and reactivity in supercritical fluids

The rates of homogeneous reactions in supercritical fluids (SCFs) can be affected by bulk properties of the system, as well as the strength of solvation. The purpose of the work described in this paper is to extend our previous studies of the solvent effect on reactions in SCFs to ionic reactions. We have used pulse radiolysis to measure the rate of reaction of benzhydryl cation (Ph(2)CH(+)) with two cosolvents (tetramethylethylene ((CH3)(2)C=C(CH3)(2)) and triethylamine ((C2H5)(3)N)) in SC CHF3. These results indicate that the rate constants decrease with increasing pressure, which is in agreement with predictions from three different approximation methods. The pressure effect on the ionic reaction of Ph(2)CH(+) with (CH3)(2)C=C(CH3)(2) can be adequately described by relatively simple solution models and there is no indication of preferential solvation of the ion influencing this reaction. However, for the ionic reaction of Ph(2)CH(+) with (C2H5)(3)N, a deviation from the prediction occurring at low pressures at 35 degrees C suggests that Ph(2)CH(+) may be preferentially solvated by (C2H5)(3)N at the lower temperature, indicating that preferential solvation may be cosolvent specific.