A kinetic and equilibrium study of the hydrolysis of Pyrrolidine Green

Abstract

Rate constants and the activation parameters AH* and AS* have been determined for the hydrolysis of Pyrrolidine Green over the pH range 10-1 1. The equilibria associated with the hydrolysis of the dye have been studied over the pH range 0-10 and a reaction scheme is proposed. Equilibrium studies have been extended in the pH range 6.8-7.8 and the thermodynamic parameters AH" and AS" have been obtained.During our studies of sterically hindered basic dyes, we have examined the spectral properties of a range of substituted derivatives of Brilliant Green * and studied their hydrolysis under basic conditions.2 The influence of substituents was such that it was considered of value to investigate the consequences of variation in the terminal basic groups. In this paper, the hydrolysis of Pyrrolidine Green, PG+ (11), over a wide pH range and over the temperature range 293.2-313.2 K is reported.

Kinetics and mechanism of the bleaching of a triarylmethane dye by hydrogen peroxide and water: evidence for intramolecular base catalysis

“…1c, and 2) in going from HD Ϫ to H 2 D around pH 1.31 (the pK a of H 2 D) indicates breaking of the chromophoric system due to protonation of an amine nitrogen. 18 The kinetic analysis must include H 3 D ϩ , eqn. ( 20), even though it is not spectrophotometrically detectable.…”

The effects of cyclic terminal groups in di- and tri-arylmethane dyes. Part 3. Consequences of unsymmetrical substitution in Malachite Green

“…It has been noted that in a solvent of sufficient acidity, Pyrrolidine Green (PG ϩ ) becomes yellow as a consequence of its conversion to the protonated species, PGH 2ϩ . 23 It can be seen from the data in Table 1 that, for the majority of the dyes studied, as the acidity of the solvent is increased there is a progressive but small blue shift of both λ max (x) and λ max (y), presumably as a consequence of the change in polarity of the solvent. Generally, the main absorption band of TPM dyes is displaced to longer wavelengths in non-polar solvents 24,25 as a result of changes in solute-solvent interactions.…”

Extended conjugation in di- and tri-arylmethane dyes. Part 4. Steric and electronic effects in analogues of Malachite Green containing a 2H-1-benzopyran unit

“…Nevertheless, TPM dyes provide many examples of carbocations which are efficiently resonance stabilised and which react at measurable rates with even good nucleophiles. 9, 10 The cationic charge on Malachite Green (MG) 1 is stabilised by conjugation both with substituents in the unsubstituted phenyl ring and with the (dimethylamino)phenyl rings and various attempts have been made to increase the efficiency of this process. Thus, changing the terminal group from dimethylamino in 1 to other dialkylamino 11 and to cyclic amino groups 12 causes red shifts of the main absorption band, largely attributable to increased electron donation by the basic units.…”