Quadricyclane hydration kinetics in natural waters

Hydration rates of quadricyclane were measured over a pH range of 3 to 8 in phosphate buffer, carbonate buffer, and nitric acid solutions. Norbornadiene was a minor impurity in the quadricyclane, and its hydration rate was also measured. Hydration products were exo−5‐norbornen−2‐ol (bicyclo[2.2.1]hept−5‐ene−2‐ol) and nortricyclyl alcohol (tricyclo[2.2.1.03,5]heptane−2‐ol). Diol formation was not detected. Quadricyclane hydration in solutions containing chloride ions formed the alcohols and their chlorinated analogs. A mechanism consistent with observed kinetics and reaction products involving two carbocation intermediates is proposed. Comparison of reaction rates was used to determine the role of buffer catalysis and chlorination reactions in natural waters. Phosphate buffer catalysis was shown to be important, and rate constants for all phosphate species were calculated. Comparison of hydration rates in nitric acid and carbonate buffer indicated that catalysis by carbonate species for this reaction is unimportant in surface waters. Catalytic effects of other buffers in some natural waters appear possible. Proper buffer selection is important if laboratorymeasured hydration rates of quadricyclane are to be applied to natural water systems.