Formation of charge-transfer complexes with triphenylmethane dye and fractional analysis of aliphatic alkylamines utilizing its thermochromism

Abstract

Molecular tetrabromophenolphthalein ethyl ester (H·TBPE), a triphenylmethane dye, reacts with aliphatic alkylamines to form red charge-transfer complexes in 1, 2-dichloroethane. Its association is based on the basicity of amines and a hydrogen bridge between the nitrogen atom in alkylamines and the phenol group in the TBPE molecule. The primary, secondary and/or tertiary alkylamines form RH₂N·H·TBPE, R₂HN·H·TBPE and R₃N·H·TBPE.The association constants for each amine were determined. On the other hand, all of the charge-transfer complexes studied showed thermochromism with a change in the measuring temperature at 20 and 60°C. The thermodynamic characteristics for each amine family were specific. The thermochromism can be applied to fractional analyses for tertiary amines and secondary amines in the presence of a primary amine.