The chemistry of some heterocyclic analogues of triphenylmethane dyes

Abstract

A comprehensive series of triphenylmethane dyes has been synthesised in which the phenyl ring of Malachite Green has been replaced by a 5- or 6- membered heterocycle containing nitrogen, oxygen or sulphur as hetetâacoins. The visible absorption spectra of the dyes have been correlated with the electronic and structural features of the molecules.
Novel analogues of Malachite Green have been prepared containing terminal pyrrolidine and N-methylpiperazine groups. Differences in the electronic absorption spectra of the parent dyes have been compared with those of related systems and the differences have been interpreted in terms of the inductive effects and relative basicities of the terminal groups.
The observed spectral changes for the Pyrrolidine Green and N-methylpiperazine Green series are in general agreement with the published data for the analogous Malachite Green and Brilliant Green derivatives.
Where substitution occurs in the meta- and para- positions of the phenyl ring, the wavelength of maximum absorption bears a linear relationship to the appropriate Hammett substituent constant. Observed Xmax(x) values for disubstituted compounds are in good agreement with the values calculated on the basis of additivity of substituent effects.
The spectral changes of the x-band arising from ortho- substitution are consistent with the relief of steric hindrance by rotation of the phenyl ring.
A study of bridged analogues of Malachite Green in which the dimethylaminophenyl rings are joined by an ethane or ethene unit across the 2'- and 2"- positions has been initiated. To gain experience with the syster comprehensive series of carbinols containing the dibenzosuberone and dibenzosuberenone moieties have been synthesised. A successful route to
the 2,2'-ethano-bridged anologue of 4,4'-dimethoxybenzophenone has been developed and several dye bases have been prepared from this ketone. However, elaboration of this synthesis to the corresponding bisdimethylamino derivative failed to yield the ketone.