Tosylate Oxygen Scrambling Associated with Ion-Pair Return in the threo-3-p-Anisyl-2-butyl System

Article abstract of DOI:10.1021/ja00525a028

Ion-pair return involved in acetolysis of threo-3-p-anisyl-2-butyl p-toluenesulfonate (6-OTs) results in racemization of the optically active 6-OTs (k_rac) and equilibration of the sulfonate oxygen atoms of 18O-labeled 6-OTs (k_eq).In this system external ion-pair return is involved.Presumably most, if not all, external ion-pair return is eliminated by 0.03 M LiClO4.The oxygen equilibration to racemization (total measurable return) ratio for internal return, (k_eq/k_rac)_in, is ca. 0.5 and the ratio for external ion-pair return, (k_eq/k_rac)_ex, is ca.1.Acetolysis of 6-OTs is accompanied by some exchange with added 14C-labeled p-toluenesulfonic acid.Exchange is lowered, but not eleminated, by 0.03 M LiClO4 and does not result in loss of diastereomeric configuration, which rules out an S_N2-type exchange process.The residual exchange in the presence of LiClO4 presumably results from external ion-pair return induced by the accumulating p-toluenesulfonic acid produced by acetolysis.