Solvolysis of 1-Arylethyl Tosylates. Kinetic and Stereochemical Tests for Solvent Participation

Article abstract of DOI:10.1021/ja00301a023

Solvolytic studies of the 1-arylethyl tosylates 8a (Ar=3-BrC6H4), 8b (Ar=3-CF3C6H4), and 8c (Ar=3,5-(CF3)2C6H3) show that in relatively nonnucleophilic solvents all three substrates have polarimetric rates markedly faster than rates of product formation.These products are largely racemic, but solvolysis of 8c in CF3CO2H gives 6percent net retention.In the more nucleophilic solvents the rates of product formation are close to the polarimetric rates and the products show extensive inversion of configuration.The results are interpreted in terms of an ion-pair mechanism in which nucleophilic solvent attack on the ion pair plays a major role.In the less nucleophilic solvents this attack is rate limiting, whereas attack of the more nucleophilic solvents is fast and initial ionization is rate limiting.Direct displacement by the solvent could contribute to the reactions in the more nucleophilic solvents but is not required by any of the results.The ion-pair mechanism provides a single consistent explanation for the results in all the solvents with all the substrates, and also readily accommodates a variety of other results in the literature, particularly the findings of oxygen and deuterium scrambling, and elimination during solvolysis.