Employment of different spectroscopic tools for the investigation of chromium(VI) oxidation of acetaldehyde in aqueous micellar medium

Unraveling the Catalytic Dynamics of Mixed Micellar Assemblies: A Molecular Approach to Green Organic Oxidative Transformation Reaction

The formation of mixed micelles represents a promising strategy to enhance organic reactions in aqueous media, offering a sustainable approach to reaction optimization. This study investigates the catalytic oxidation of cyclohexanol by chromium(VI) under acidic conditions at 27 °C with reaction kinetics monitored using UV-vis spectroscopy. Three readily available surfactants, cationic cetylpyridinium chloride (CPC), non-ionic Brij-35 (polyoxyethylene (23) lauryl ether), and anionic sodium dodecyl sulfate (SDS), were utilized to construct two mixed micellar systems: cationic/non-ionic (CPC: Brij-35) and anionic/non-ionic (SDS: Brij-35). Both mixed micellar systems exhibited significant catalytic activity, with the CPC: Brij-35 system, at an equimolar ratio, enhancing the reaction rate by an impressive 13.97-fold, compared to a 9.87-fold increase observed for the SDS: Brij-35 system. The superior catalytic efficiency of the CPC: Brij-35 assembly is attributed to enhanced micellization, improved solubilization of cyclohexanol, and strong electrostatic interactions between the positively charged CPC and the slightly negatively charged Brij-35, as evidenced by zeta-potential measurements. The kinetic behavior of the reaction was meticulously analyzed via UV-vis spectroscopy, while the micellization phenomena were corroborated through dynamic light scattering, zeta potential analysis, scanning electron microscopy, and 1H NMR spectroscopy. Additionally, the critical micelle concentrations (CMC) of the individual surfactants and their mixed systems were determined by using tensiometric measurements, providing a deeper understanding of the micellization process. The study reveals a plausible reaction mechanism emphasizing the critical role of the reaction zone within mixed micellar assemblies. These findings establish mixed micelles as powerful catalytic platforms, advancing green chemistry through an enhanced reaction efficiency and sustainable processes in aqueous media.

A Comparative Spectral Study on the Interaction of Organic Dye Congo-Red with Selective Aqueous Micellar Media of CPC, Rhamnolipids and Saponin

The present study is an investigation of the solubilising ability of natural and conventional surfactants saponin (sapindus saponin or reetha saponin), Rhamnolipids (RLs) and N-cetylpyridinium chloride (CPC) respectively via dye-surfactant interaction. The ionic dye Congo Red was examined by absorption spectroscopy method for the study. The dye interacted strongly with oppositely charged surfactant N-cetylpyridinium chloride in the pre-micellar concentration range and formed a stable dye-surfactant complex. The thermodynamic parameter, free energy change for all the systems was calculated at a constant temperature of 25°C. The ΔG0 value for N-cetylpyridinium chloride is found to be −33.269 kJ/mol while for saponin and rhamnolipids the values were −16.084 kJ/mol and −26.006 kJ/mol respectively. The values clearly indicate the efficiency of N-cetylpyridinium chloride surfactant compared to the other two surfactants. The present study aims to understand the dye solubilization in surfactant media in order to develop environmentally friendly, green and cost effective techniques.