REARRANGEMENT STUDIES WITH 14C: XIX. THE REACTION OF 2-PHENYL-1-14C-ETHANOL WITH THIONYL CHLORIDE

Abstract

The reaction of 2-phenyl-1-14C-ethanol with thionyl chloride in pyridine, dioxane, toluene, or excess thionyl chloride as solvent gave 2-phenylethyl chloride showing, respectively, about 0, 15, 44, and 48% rearrangement of the 14C-label from the C-1 to the C-2 positions. When reactions of 2-phenyl-1-14C-ethauol or 2-p-anisyl-1-14C-ethanol with thionyl chloride in dioxane or excess thionyl chloride were carried only to partial completion and the undecomposed chlorosulphites hydrolyzed by aqueous sodium hydroxide, the recovered alcohols showed only 0.1 to 0.5% isotope position rearrangement. This indicated a lack of return from ion-pairs to isotopically rearranged 2-arylethylchlorosulphite and suggested that the first stage of ionization may involve ion-pairs with structures that will not result in rearrangement on return to covalent bonding, or that the first ion-pair may decompose faster than it can return to reactant. The possibility that rearrangements via rigidly oriented ion-pairs and via the concerted SNi′ mechanism may represent the two extremes of a graded series is discussed. It is suggested that the relative contributions from the ion-pair and from the SNi′ mechanisms will depend on the stability of the carbonium ion as well as on the nature of the reaction solvent.