Gas-Phase Isotope-Exchange Reactions with Chloride Ion

Article abstract of DOI:10.1021/j100340a021

Gas-phase isotope-exchange reactions of 37Cl^- have been studied in a selected ion flow tube at thermal energy.The S_N2 reaction of 37Cl^- with methyl chloride is immeasurably slow at room temperature, indicating that the transition state is close to or projects above the energy of the reactants.In contrast, the corresponding displacement reactions with chlorotrimethylsilane and chlorodimethylphosphine are facile, indicating that reaction barriers are low and suggesting the possible formation of low-energy intermediates.Exchange with acetyl chloride occurs at a moderate rate while exchange with thionyl chloride occurs at the statistical limit; for sulfuryl chloride only chlorine atom abstraction is observed.Reaction of 37Cl^- with molecular chlorine proceeds in half of the collisions, suggesting formation of Cl3^- from end-on attack; the unique central atom is not exchangeable.Isotope exchange with hydrogen chloride and deuterium chloride occurs with cca. 50 percent efficiency, implicating reaction through a long-lived complex rather than by a direct mechanism.