Alkyl, alkenyl and cycloalkyl substituted triphenylmethane dyes

Abstract

A series of Malachite Green derivatives containing alkyl an alkenyl substituents in the 2-, 3-. and 4- positions has been synthesised.
Their respective visible absorption spectra have been correlated with the electronic and steric effects of the methyl, ethyl, propyl, butyl and vinyl substituents in the phenyl ring.
The linear relationship between the wavelength of maximum absorption for the x-band of the meta- and para- substituted derivatives of Malachite Green and the respective Hammett substituent constants has been confirmed. The cyclopropyl group is found to produce the largest hypsochromic shift of the x-band for the 4-substituted compounds and this is explained in terms of its unusual electronic contribution.
The effect on the x-band of 2-alkyl and 2,6-Thialkyl substitution is consistent with the relief of steric hindrance by rotation of the phenyl ring. It is noted that the cyclopropyl and isopropyl groups produce somewhat anomalous spectral changes and an explanation is postulated.
The preparation of Crystal Violet and Malachite Green derivatives containing meta- isopropyl substituents has enabled the spectral changes resulting from the steric interaction of substituents with the terminal dimethylamino groups to be determined and by comparison with the parent dyes and the corresponding methyl analogues, the agreement of the spectral
parameters of the ineta- isopropyl derivatives with theoretical considerations is examined.