Synthesis of a new heterocyclic dye compound as an indicator in acid and base reactions

Abstract

In the present research, the use of 2-(3-hydroxyamino-2,3-dihydroimidazo[1,2-a]pyridine-2-ylidene)-2-(2-tienyl)acetonitrile as a new acid and base indicator in aquatic environments has been investigated. This compound has been synthesized by the reaction of 3-nitroimidazo [1,2-a] pyridine and 2-(2-thienyl) acetonitrile in a methanol solution by the hydrogen nucleophilic substitution. The aqueous-ethanol solution of this compound shows a change in color by adding acid and an base. For the potential function of this reagent as an indicator, the spectral properties of UV-Vis and the equilibrium of acid and base source have been examined. The results show that the reagent is an amphoteric with two stable ionization factors K_a and K_b with poor acid and base properties. Indicator dissociation constants in aqueous solutions specified by spectrophotometric method are pK_a = 9.73 and pK_b = 11.57. The types of base that can be titrated with this index have been reported. This index has been compared with effective acid and base indexes with similar pH range.