Kinetics and thermodynamics of hydrolysis of crystal violet at ambient and below ambient temperatures

Hydrolysis reaction was carried out at varying NaOH concentrations of 0.008, 0.016 and 0.024 M, variable temperature of 6 and 21 °C, and constant initial crystal violet (CV) concentration of 2.6 × 10–5 M. Kinetic data of the reaction were generated using UV–Vis Spectrophotometer. Analysis of the reaction kinetics shows that the overall rate order of the hydrolysis reaction was 1st order. The individual rate order of the reaction with respect to NaOH and CV was temperature dependent. At 21 °C the rate order with respect to NaOH and CV were 0.24th and 0.76th, respectively. While at 6 °C the individual rate order were 0.38th and 0.62th with respect to NaOH and CV, respectively. Values of the reaction rate constant (k) at 21 and 6 °C were 7.2 and 1.9 $$\left( {\frac{{{\text{mol}}}}{{\text{L}}}} \right)^{{ - 0.9}} min^{-1}$$ mol L - 0.9 m i n - 1 , respectively. The activation energy of the reaction was determined as 60.57 kJ/mol. The reaction was an endothermic reaction having enthalpy values of 58.13 and 58.29 kJ/mol at 21 and 6 °C, respectively. The entropy and Gibbs free energy of the hydrolysis reaction at ambient temperature of 21 °C were − 64.72 J/mol K and 77.15 kJ/K, respectively. At 6 °C the entropy and Gibbs free energy of the reaction were − 64.29 J/mol K and 76.19 kJ/K, respectively.

Probing the reverse micelle environment with a cationic dye by varying oil and water content of micelles

In the present work, spectroscopic properties of crystal violet (CV) within water-in-hexane sodium base (2-ethyl hexyl) sulfosuccinate (AOT) reverse micellar environment was investigated as a function of water contents (W = [H2O]/[AOT] = 6,10) in AOT and also function of mass fraction of nanodroplet (MFD = 0.01, 0.04, 0.07, and 0.1) by using UV/visible, and fluorescence techniques. A deviation in the absorption spectra of crystal violet at the high CV concentration (0.002 M) was observed in the AOT reversed micelles. The Quenching in the emission intensity of crystal violet at high CV concentration and blue shift in λ_max of fluorescence of dye was observed as a function of MFD in AOT RMs. At high concentration of dye, molecules of CV can be reside interfacial region but near core of AOT. At low dye concentration, the CV molecules also can be in interfacial region but far from core. The Stokes shift of CV at high concentration decreased with mass fraction of nano-droplet (MFD), whereas at the low CV concentration, its variation often increased. The ratio of ground state to the excited state dipole moment of crystal violet dye also affected by the change in W values and MFD values. The change in dipole moment and stokes shift indicates the different environment around CV for different W and MFD values.

Cleavage of Carbofuran and Carbofuran-Derivatives in Micellar Aggregates

In recent years, the stability of carbamate pesticides have been studied by our research group in a wide range of biomimetic microheterogeneous media such as micelles or reverse micelles. These microheterogeneous media included different surfactant species and, hence, different self-assembled structures. In particular, basic hydrolysis of carbofuran and its derivatives have been analysed in the presence of anionic, cationic, non-ionic and reverse micelles. The results obtained from these physicochemical and kinetic studies, as well as a consistent comparison of them, are now summarised.

Kinetics of the oxidation of iodide ion by persulfate ion in the critical water/bis(2-ethylhexyl) sodium sulfosuccinate/n-decane microemulsions

In this work, we studied the kinetics of the oxidation of iodide ion by persulfate ion in the critical water/bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/n-decane microemulsions with the molar ratios of water to AOT being 35.0 and 40.8 via the microcalorimetry at various temperatures. It was found that the Arrhenius equation was valid for correlating experimental measurements in the noncritical region, but the slowing down effect existed significantly in the near critical region. We determined the values of the critical slowing down exponent and found it to be 0.187 ± 0.023 and 0.193 ± 0.032, respectively, which agreed well with the theoretical value of 0.207 predicted by the Griffiths-Wheeler rule for the singularity of the dimer/monomer droplet equilibrium in the critical AOT/water/n-decane microemulsions.

Solvent dependent interactions between droplets in water-in-oil microemulsions

In this paper, we investigated the dilution enthalpies of the droplets in water/AOT/oil microemulsions with oil being isooctane, decane, or cyclohexane by isothermal titration microcalorimetry (ITC). Combining with the results obtained from the study of the water/AOT/toluene system in our previous work, it was found that the enthalpy interactions between droplets for isooctane and decane systems were repulsive, while the enthalpy interactions were attractive for cyclohexane and toluene systems. The repulsive droplet interaction for the isooctane system was also confirmed by static light scattering. The solvents appear to play important roles in varying the droplet enthalpy interactions from positive to negative, and the entropy contribution seems to be dominant for the stability of these microemulsion droplet systems.

Alkaline Fading of Triarylmethyl Carbocations in Self-Assembly Microheterogeneous Media

This review reports on the alkaline fading of crystal violet and other related carbocations in the presence of different microheterogeneous media (micelles, microemulsions and vesicles).