Spectrophotometric determination of some amino heterocyclic donors through charge transfer complex formation with chloranilic acid in acetonitrile

The present study is directed toward a development of simple, rapid and accurate spectrophotometric method for determination of some amino heterocyclic donors. The Charge transfer (CT) interactions between 3-aminopyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-methyl-1,3,4-thiadiazole (AMTD) and 2-amino-5,6-dimethyl-1,2,4-triazine (ADMT) with chloranilic acid (CLA) as π-acceptor have been investigated spectrophotometrically in acetonitrile. Factors controlling the CT-reactions were also studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients were identified with high accuracy and precision. Job's method of continuous variation, spectrophotometric and conductometric titrations were used to identify the composition of the formed CT-complexes. Benesi-Hildebrand (BH) equation has been used to calculate the formation constants of the charge transfer reactions KCT and the molar extinction coefficients ε. Free energy change (ΔGo), oscillator strength (f), transition dipole moment (µ), ionization potential (IP) and charge transfer energy of the formed CT-complexes (ECT) were also determined and evaluated.