Bazı sehiff bazlarının iyonlaşma sabitlerinin spektrofotometrik metotla tayini

Abstract

ABSTRACT Ph. D. Thesis DETERMINATION OF IONIZATION CONSTANTS OF SOME SCHIFF BASES WITH SPECTROPHOTOMERIC METHOD M.AbdülkadirAKAY Ankara University Graduate Scholl of Natural and Applied Sciences Department of Chemistry Supervisor: Prof. Dr. Esma KILIÇ 1995 Page:112 Jury: Prof. Dr. Esma KILIÇ Prof. Dr. Mürşide TUZUN Assoc. Prof.Dr. H. Basri ŞENTÜRK In this study, ionization constants of twenty-two Schiffs bases prepared from salicyialdehyde and mono subsituted anilines were determined spectrophotometrically in ethand- water mixtures of 10, 30, 50 and 70 % ethanol (v/v). The solutions of Schiffs bases containing perchloric acid and 0.1 M sodium perchlorate were titrated with carbondioxide-free standard sodium hydroxide dissolved in the corresponding solvents at 25° C, under nitrogen atmosphere. The pH values and the electronic spectra of Schiffs base solutions were recorded after each addition of titrant These spectra show three isosbestic points. It was first verified by graphic matrix-rank analysis of spectrophotometric titration data that there was indeed no overlap among the various subequilibriaThe corresponding A-diagrams showed the presence of two strictly linear segments for various wavelenghts combinations in the region 230-395 nm. Thus, the overall titration system has the rank s=2. Since all data points fell on one of the two linear segments within the limits of error and A-pH curves displayed flat maxima and plateaus at the pH 5-8, it was concluded that the titration curves could clearly be divided into two single-step subsystems. log Ki and logK2 values related to the ionization of iminnium hydrogen and phenol hydrogen of Schiffs bases were calculated using "the linearization method". The trends in the values of ionization constants were examined in the terms of the nature of the substituents and the mole fraction of ethanol. Furthermore, the applicability of the Hammett equation to the effect of substituents in Schiffs bases is discussed. KEYWORDS: Spectrophotometric titration, Salicyialdehyde, Aniline, Sodium perchlorate, Perchloric acid, Schiffs base, Ionization constants, A-diagrams