Selective free radical reactions using supercritical carbon dioxide.

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Supercritical Fluids

Background:

• Alkenes are fundamental organic molecules with diverse reactivity.
• Supercritical fluids, like carbon dioxide, offer unique solvent properties.
• Controlling reaction selectivity is crucial for chemical synthesis.

Purpose of the Study:

• To investigate the modification of alkene reactivity in supercritical carbon dioxide (scCO2).
• To explore the selectivity of alkene reactions with nonpolar free radicals under near-critical conditions.
• To compare the kinetic behavior of different alkenes in scCO2.

Main Methods:

• Measured rate constants for the free radical addition of muonium (a light hydrogen isotope) to alkenes.
• Studied ethylene, vinylidene fluoride, and vinylidene chloride.
• Conducted experiments in supercritical carbon dioxide across varying pressures and temperatures near the critical point.

Main Results:

• Observed critical speeding up for muonium addition to ethylene near the scCO2 critical point.
• Observed critical slowing for muonium addition to halogenated alkenes (vinylidene fluoride and vinylidene chloride).
• Demonstrated pressure and temperature dependence of reaction rates.

Conclusions:

• Supercritical carbon dioxide can significantly tune the reactivity and selectivity of alkenes.
• The solvent effects near the critical point differ between non-halogenated and halogenated alkenes.
• scCO2 provides a tunable medium for controlling alkene chemistry under near-critical conditions.