Studies of Aroyl Hydrazones as indicators

Abstract

A large number of aroylhydraxones were synthesised to study their acid-base indicator properties. The 2,4-dinitrobenzaldehyde derivatives of various acid hydrazides indicated strong indicator properties and were compared with standard indicators in the titration of strong and weak acids with bases. The colourchange of these (hydraxone) indicators were from colourless in acidic media to bright lemon yellow in alkaline solutions. The pH transition ranges were from 8.0 to 10.8 pH units and one part of the indicator solution (0.03%w/v in ethanol) was detectable in 2.5 x 103 parts of water. Dissociation constants (pka values) of the synthesised compounds were determined. The pka values were correlated with Hammett substituent constants and a linear relationship was established. Spectral studies i.e. I.R., U.V. and P.M.R. were also done for the synthesised compounds.