Rate and Product Studies with 1-Adamantyl Chlorothioformate under Solvolytic Conditions

A study was carried out on the solvolysis of 1-adamantyl chlorothioformate (1-AdSCOCl, 1) in hydroxylic solvents. The rate constants of the solvolysis of 1 were well correlated using the Grunwald-Winstein equation in all of the 20 solvents (R = 0.985). The solvolyses of 1 were analyzed as the following two competing reactions: the solvolysis ionization pathway through the intermediate (1-AdSCO)⁺ (carboxylium ion) stabilized by the loss of chloride ions due to nucleophilic solvation and the solvolysis-decomposition pathway through the intermediate 1-Ad⁺Cl^- ion pairs (carbocation) with the loss of carbonyl sulfide. In addition, the rate constants (k_exp) for the solvolysis of 1 were separated into k_1-Ad and k_1-AdSCO through a product study and applied to the Grunwald-Winstein equation to obtain the sensitivity (m-value) to change in solvent ionizing power. For binary hydroxylic solvents, the selectivities (S) for the formation of solvolysis products were very similar to those of the 1-adamantyl derivatives discussed previously. The kinetic solvent isotope effects (KSIEs), salt effects and activation parameters for the solvolyses of 1 were also determined. These observations are compared with those previously reported for the solvolyses of 1-adamantyl chloroformate (1-AdOCOCl, 2). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions calculated using Gaussian 03.