Humic Acids Aggregates as Microheterogeneus Reaction Media: Alkaline Hydrolysis Reactions

The influence of humic aggregates in water solution upon the chemical stability under basic conditions of different substrates has been reviewed. The kinetic behavior of each substrate has been modelized in terms of micellar pseudophase model.

Quantitative analysis of micellar effect on the reaction rate of cationic triphenylmethine dyes with water according to Berezin’s model

Several approaches quantitatively describe the effect of surfactant micellar solution on the reaction rate. The most used among them are Piszkiewicz’s, Berezin’s, and Pseudophase Ion-Exchange (PIE) models. The last-named was developed by Bunton and Romsted. Piszkiewicz’s model is based on representations of the micellization according to the mass action law with the formation of a catalytic micelle, which consists of some surfactant molecules and a substrate. In our previously paper, this model was used to explain the kinetic micellar effect on the reaction of cationic triphenylmethine dyes with water once again showed the main disadvantages of this approach. Berezin’s model is based on another model of micelle formation viz. the pseudophase model, and the binding of reagents by micelles is considered as the distribution of a substance between two phases. In this work, we aim to consider the applicability of Berezin’s approach for the interaction of malachite green and brilliant green cations with water molecule as a nucleophile in aqueous systems of nonionic, anionic, cationic, and zwitterionic surfactants. On the whole, Berezin's model performed well when applied to the description of the micellar effect on the reaction of similar dye with the hydroxide ion. However, it was revealed that this model does not take into account the change in the local concentration of the HO– ions due to a compression of the double electric layer upon addition of reacting ions to the system, as well as the constant of association of the HO– ions with cationic head groups of surfactant. In this case, when water is used as a nucleophile, the question of the degree of nucleophile binding can be solved differently. The PIE model is also based on a pseudophase model of micellization, but a substrate binding by micelles is considered as an association in a stoichiometric ratio of 1:1, and a nucleophile concentration is expressed in a local concentration based on the neutralization degree of micelles. Given the latter, its approach cannot be applied to the kinetic micellar influence on the reaction of cationic triphenylmethine dyes with water.

SN2 Mechanism of Cationic Micelles on the Hydrolysis of Bis-p-Methoxyphenyl Phosphate Ester

Hydrolysis of bis-p-methoxyphenyl phosphate ester (bis-p-MPPE) was studied in micellar solutions of cityltrimethylammoniumbromide n-C16H33N+(CH3)3Br- (CTABr) at pH-9.0. The hydrolysis followed first order kinetics with respect to bis-p-MPPE concentration. At the concentration of critical micelle concentration (CMC) the rate of hydrolysis increased with increasing CTABr concentration. Surfactant with cationic or polar head group form micelles in water with hydrocarbon like interior or polar groups at the surface and bind cationic solute. The binding constant of micelle for bis-p-MPPE and the rate constant in micellar pseudo phase were determined from kinetic data using the pseudophase model.

Fluorescence quenching of 1-pyrene-carboxaldehyde by iodide ions in the presence of anionic (SDS) and cationic (CTAC) micelles: a quantitative treatment

Applicability of the pseudophase model to photochemical reactions in the presence of receptors (micelles) in spite of the fact that the equilibrium condition between free and bound reactants does not hold.

Effect of Micellar Aggregate on the Kinetics and Mechanism of the Reaction between Ethylene Glycol and Periodate

The oxidation of ethylene glycol by periodate (IO4-) was studied in different micellar aggregates of cetyltrimethylammonium bromide (CTABr) and dodecylamine (DA) by means of UV/Vis spectroscopy. The observed constant Ko was obtained by monitoring the disappearing of ethylene glycol with time at a suitable wavelength under pseudofirst condition. Addition of CTABr and DA inhibits the reaction rate while the kinetic behavior was explained on the association of one of the reactants with the micelles leaving the other reactant in the bulk solution (pseudophase model).