SOLVOLYSIS RATES AND DEUTERIUM ISOTOPE EFFECTS IN 2,2,2-TRIFLUOROETHANOL-WATER MIXTURES

2,2,2-Trifluoroethanol (TFE)-water is a convenient solvent for the precise conductometric measurement of solvolysis rates. A comparison of results in TFE-water with those in ethanol-water gives a useful indication of the role of changing nucleophilicity in solvolysis reactions. It has been found that the α- and β-deuterium effects in 1-phenylethyl chloride, which in ethanol-water are at or near a maximum characteristic of a limiting reaction, are not much changed in TFE-water. However, for t-butyl-d9 chloride the isotope effects are larger in TFE solutions than in ethanol-water. This is explained on the basis of the incursion of some rate-determining elimination from an ion pair in the TFE solvents. p-Methylbenzyl-α-d2 chloride, and isopropyl-α-d (and -β-d6) p-bromo-benzenesulfonates also show larger effects in TFE-water solvents than in ethanol-water. These results are interpreted in terms of some nucleophilic attack of solvent molecules occurring in the rate-determining steps in the ethanol-water solvents. © 1969, American Chemical Society. All rights reserved.