Stereochemistry of Trifluoroacetolysis of Optically Active 2-Butyl Tosylate. A Test for Hydrogen Bridging

Article abstract of DOI:10.1021/jo00172a017

Trifluoroacetolysis of (R)-(-)-2-butyl tosylate at 25 deg C gives 2-butyl trifluoroacetate with 7 +/- 1percent net inversion.The ratio of the polarimetric and spectrophotometric rate constants is 1.55, and this decreases to 1.05 in the presence of 0.125 M NaO2CCF3.These results are most simply and plausibly interpreted in terms of formation of an ion pair consisting of an open 2-butyl cation and a tosylate anion which gives racemized tosylate by ion-pair return and by elimination/readdition, with competitive nucleophilic solvent attack with a small overall preference for substitution on the side opposite the anion.A published proposal based on deuterium labeling studies that a hydrogen-bridged butyl cation is the predominant intermediate in this reaction does not give a simple prediction of these results.