SYNTHESIS AND SPECTROANALYTICAL STUDIES OF A NEW heterocyclic ACID-BASE INDICATOR

The new purple dyes of the imidazopyridine series were synthesized by the reaction of 6-chloro-3-nitroimidazo [1, 2-a] pyridine with (4-methylphenyl) acetonitrile in basic MeOH solution via nucleophilic substitution of hydrogen atom. The reagent solution shows a reproducible change in its color due to the addition of acid or base. A UV-Vis spectroscopic characterization and acid-base equilibrium study of the reagent for its possible use as an indicator were investigated. The results show that the reagent is an amphoteric which possesses two ionization constants Kb and Ka of weak basic and acidic properties. The dissociation constants of the indicator in aqueous solution which are determined by spectrophotometric method are pKb, 11.57 and pKa, 9.73. This indicator is compared with existing acid-base indicators effective over the same pH range. Furthermore, conversion of these dyes to new 8- chloro-3-methylpyrido [2 ,1 :2,3] imidazo [4,5-b]quinoline-,12-carbonitriles is reported