Kinetic solvent effects on alkaline decolorization of crystal violet in some aquo-organic solvents

Abstract

Rate constants (ks) of alkaline fading of crystal violet (CV+) have been determined at 25 °C by spectrophotometric measurements in aqueous mixtures of some protic, aprotic, and dipolar aprotic cosolvents. Transfer free energies of the substrate (CV+), [Formula: see text], were also determined in some of the solvent systems from solubility measurements of the chloride salt, and by subtracting [Formula: see text] obtained earlier by use of the tetraphenylarsonium tetraphenylboron (TATB) extrathermodynamic assumption. This helped determine transfer free energies of the transition state (X≠), [Formula: see text] values of lyate ion (S−) based on the TATB assumption are already known for all of these solvent systems. The observed log (ks/kw) – composition profiles reveal that the relative solvation of the reacting species rather than the dielectric constant of the solvents dictates the complex variation of the rates of the reaction in these solvent systems. Correlation of [Formula: see text] with [Formula: see text] indicates that the reaction is largely controlled by the relative solvation of S− in most of the cases. But analysis of [Formula: see text] – composition profiles for some of the solvent systems reveals that the non-compensation of the [Formula: see text] contributions of initial-state substrate and of the transition-state complex, which may be considered to be an outer-sphere complex [CV+](S−), is also in accord with what is expected from the relative solvating characteristics of the cosolvents as guided by their respective physico-chemical properties.

Kinetics of malachite green fading in alcohol–water binary mixtures

“…As shown in Table VII, the rate constants of the MG + fading reaction in aqueous glycerol mixtures up to 19.3% increase and then slightly decrease. Similar situation has been found for crystal violet fading in glycerol–water mixtures 19,31. As reported, reaction rates decrease with an increase in viscosity of solvent 32,33.…”

“…A reaction of MG + fading is an electrophile–nucleophile combination reaction. The rate constants for these reactions are correlated by using the Ritchie equation 18,19 where k is the rate constant for the reaction of a given cation with a given nucleophilic system (i.e., given nucleophile in a given solvent). k 0 is the rate constant for the same cation with water in water, and N + is a parameter that is characteristic of the nucleophilic system and is independent of cation.…”

Kinetics of the Reaction of Crystal Violet with Hydroxide Ion in the Critical Solution of 2-Butoxyethanol + Water

“…In recent years, the basic hydrolysis of crystal violet (CV) in aqueous media, , micelles, , alcoholic solutions, and microemulsions , has been studied by UV spectrophotometry, and the kinetics of this reaction are now well-known.…”

Kinetics of malachite green fading in water–ethanol–2‐propanol ternary mixtures

“…A reaction of MG + fading is an electrophile–nucleophile combination reaction. The rate constants for these reactions are correlated by the Ritchie equation 19,20 where k is the rate constant for reaction of a given cation with a given nucleophilic system (i.e., given nucleophile in a given solvent). k 0 is the rate constant for the same cation with water in water, and N + is a parameter, which is characteristic of the nucleophilic system and independent of cation.…”