Quadricyclane hydration kinetics in natural waters

Area of Science:

• Environmental Chemistry
• Organic Chemistry

Background:

• Quadricyclane is a strained bicyclic alkene.
• Understanding its hydration is crucial for predicting its fate in natural environments.

Purpose of the Study:

• To investigate the hydration rates of quadricyclane under varying pH conditions.
• To determine the influence of different buffer systems and chloride ions on quadricyclane hydration.
• To propose a reaction mechanism and assess the relevance of buffer catalysis in natural waters.

Main Methods:

• Kinetic measurements of quadricyclane hydration in phosphate buffer, carbonate buffer, and nitric acid solutions (pH 3-8).
• Analysis of hydration products, including alcohols and chlorinated analogs.
• Comparison of reaction rates to evaluate buffer catalysis and chlorination effects.

Main Results:

• Hydration rates were measured across a pH range of 3 to 8.
• Phosphate buffer demonstrated significant catalysis, with rate constants for all phosphate species calculated.
• Carbonate buffer showed minimal catalysis, suggesting it is unimportant in surface waters.
• Chloride ions led to the formation of chlorinated analogs alongside alcohols.

Conclusions:

• A reaction mechanism involving two carbocation intermediates is proposed.
• Phosphate buffer catalysis plays a critical role in quadricyclane hydration.
• Carbonate buffer catalysis is negligible in surface waters.
• Buffer selection is vital for accurate laboratory-to-natural water system rate extrapolation.