Kinetics of the reactions of t-butyl chloride and [2H9]t-butyl chloride with silver salts in acetonitrile

Abstract

Reaction of an acetonitrile solution of t-butyl chloride with silver nitrate is only slightly faster than with an equal concentration of silver perchlorate and, for concentrations of silver salt of up to 0.08M, each individual run approximates to overall second-order kinetics. The second-order rate coefficients, approximately equal for the two salts at low concentrations, increase with increasing initial concentration; the increase is more marked with the nitrate salt. Reaction with silver nitrate leads to t-butyl nitrate as well as isobutene, the subsequent elimination reaction of the nitrate ester being relatively slow compared to its rate of formation. Kinetic deuterium isotope effects for [²H₉]t-butyl chloride relative to t-butyl chloride are, for relatively low concentrations of either silver salt, essentially equal (ca. 2.6) to those previously observed for unimolecular decomposition. For reaction with silver nitrate, the magnitude of the isotope effect upon the partitioning between substitution and elimination is consistent with attack upon an intermediate carbonium ion. The pathway is best considered as approximating to the Hughes–Ingold S_N1 Ag⁺(plus E1 Ag⁺) mechanism, with the slightly faster reaction with the moderately nucleophilic nitrate salt reflecting a partial diversion of an intermediate R⁺Cl^–Ag⁺ ion-triplet away from internal return of chloride ion.