NATURE OF CARBONIUM ION .2. FURFURYL CATION FROM A THIOCYANATE-ISOTHIOCYANATE ISOMERIZATION

In contrast to the essentially irreversible isomerizations of most alkyl thiocyanates, including benzyl, the isomerization of furfuryl thiocyanate was discovered to proceed to an equilibrium position in which a substantial amount of the starting material was still present. The second component at equilibrium, furfuryl iso thiocyanate, was always predominant, but relative proportions at equilibrium were strongly solvent influenced. Examination of the equilibrium position over a large temperature span revealed an almost negligible temperature dependence in a given solvent. Measurements of the rates of reaction in several solvents showed the isomerization to be in all cases a first-order process but accelerated by the more nucleophilic solvent, dimethylformamide. A comparison of activation parameters for forward and reverse reactions revealed that the favoring of isothiocyanate at equilibrium is based only on a slightly more favorable activation entropy for the forward reaction. © 1969, American Chemical Society. All rights reserved.