A study of some derivatives of brilliant green

Abstract

A series of derivatives of Brilliant Green containing substituents in the ortho-position of the phenyl ring has been synthesised, together with some derivatives in which the phenyl ring has been replaced by a heterocyclic ring. The visible absorption spectra of the dyes have been correlated with the electronic and steric effects of the substituents. The effect on the x-band of ortho-substitution is consistent with the relief of steric hindrance by rotation of the phenyl ring.
The perchiorates of a range of ortho-substituted and heterocyclic derivatives of Brilliant Green have been prepared from the corresponding leuco-base or carbinol. A study of the alkaline hydrolysis of each dye has been made under conditions such that pseudo first order kinetics obtained. The effects on the observed rate constant of changing the hydroxide ion concentration, the concentration of the inert salt and the temperature have been observed. The same basic rate law has been determined for most of the dyes.
Multiple Linear Regression Analysis has been applied to the series of ortho-substituted dyes and the rate of hydrolysis has been demonstrated to be dependent mainly on the steric factor, U, derived by Charton. The thermodynamic parameters and have been obtained for the ortho-substituted dyes and the reaction has been shown to be under enthalpy control. An isokinetic relationship has been established providing evidence that most of the orthosubstituted
dyes undergo hydrolysis by the same mechanism.
A value for the steric factor, U, for the ortho-nitro-group has been determined, which shows that this group lies between its coplanar and orthogonal extremes in the dye.
Anomalous behaviour, for which reasoned arguments are presented, has been observed for 2-hydroxy-Brilliant Green, 2,6-dichloro-Brilli-ant Green and 2-Furyl Green.