Kinetic study in water-ethylene glycol cationic, zwitterionic, nonionic, and anionic micellar solutions

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Chemical Kinetics

Background:

• Micellar catalysis is crucial for understanding reaction mechanisms in complex media.
• Phenyl chloroformate hydrolysis provides a model system for studying reaction kinetics in varying environments.
• Ethylene glycol (EG) as a co-solvent can significantly alter micellar properties and interfacial characteristics.

Purpose of the Study:

• To investigate the spontaneous hydrolysis of phenyl chloroformate in various micellar systems.
• To determine the effect of water-ethylene glycol (EG) mixtures on reaction kinetics.
• To elucidate the role of micellar properties and EG concentration on reaction pathways.

Main Methods:

• Kinetic studies of phenyl chloroformate hydrolysis.
• Utilizing diverse micellar solutions: cationic, zwitterionic, nonionic, and anionic.
• Employing conductivity, surface tension, spectroscopic, and fluorescence measurements to characterize micellar properties.
• Investigating EG concentrations from 0 to 50 wt %.

Main Results:

• Observed rate constants varied with surfactant concentration and EG content.
• EG significantly impacted critical micelle concentrations, micellar ionization, aggregation numbers, and interfacial polarity.
• A simple pseudophase model effectively explained the kinetic data.
• Reaction acceleration with increased EG was attributed to decreased phenyl chloroformate binding to micelles.

Conclusions:

• Micellar medium effects are governed by charge-charge interactions, polarity, ionic strength, and water content.
• The observed acceleration is primarily due to enhanced contribution from the bulk water-EG phase.
• The rate constant within the micellar pseudophase remained largely unaffected by EG concentration.