Spectroscopic Determination of Acid Dissociation Constants of Some Pyridyl Shiff Bases

Abstract

The acid dissociation constants (pK a ) of eight biologically active pyridyl Shiff bases were determined using a UV-vis spectroscopic technique at 25 ( 0.1 °C. The first acidity constants (pK a1 ) of the 2- 7), and 2-[2-aza-2-(5-methyl-(2-pyridly))vinyl]-4,6-dinitrophenol (8) are found to be associated with the protonation of phenolate oxygen. The second acidity constants (pK a2 ) are found to correspond to protonation of pyridine nitrogen for compounds 5, 6, and 7 and oxoprotonation for molecules 1, 2, 3, 4, and 8. The third acidity constants (pK a3 ) are found to be associated with the protonation of pyridine nitrogen for compounds 1, 3, 7, and 8 and amino protonation for molecules 2 and 5. For molecules 4 and 6, it is associated with oxo protonation. The contribution of the ketoamino tautomeric form was found to be considerably important.

Acetone (2-nitrophenyl)hydrazone

“…Schiff bases have been used extensively as ligands in the field of coordination chemistry (Ogretir et al, 2006). As dinegatively charged ligands, Schiff bases show potential as antimicrobial and anticancer agents (Tarafder et al, 2000;Deschamps et al, 2003) and so have biochemical and pharmacological applications.…”

Synthesis, Characterization and Spectroscopic Studies on Azo-Hydrazone Tautomerism and Acidity Constants of Certain 4-(Phenyldiazenyl) Benzene-1,3-Diol Derivatives

“…This method for measuring pKa values was chosen for its sensitivity. We have conducted several similar studies for previous [30,[36][37][38].…”

(E)-5-Phenyl-N′-(1-phenylethylidene)-1H-pyrazole-3-carbohydrazide

“…For general background, see: Ogretir et al (2006); Tarafder et al (2000); Deschamps et al (2003); Wu et al (2006). For related literature, see: Yang & Raptis (2003); Ali et al (2005).…”