u Acid-base Equilibria of 1-(2-pyridylazo)-2-naphthol in Neutral and Charged Micellar Media

Acid-base equilibria of 1-(2-Pyridylazo)-2-naphthol (PAN) in neutral, cationic and anionic micellar media were investigated by potentiometric method using Calvin-Wilson titration technique. Best fit chemical models obtained using MINIQUAD-75 program showed the presence of both mono-protonated (LH22+) and deprotonated (L-) species of PAN (LH) in solution. The equilibrium constants beta(011) and beta(012) corresponding to the formation of LH and LH2+ species respectively from the most anionic form (L-) of PAN at a temperature of 30.0 +/- 0.1 degrees C and an ionic strength of 0.1 mol. dm(-3) are reported. Several interesting results emerged from the study of the affect of the neutral and charged micelles on the equilibria are explained on the basis of the pseudo phase ionic exchange model, dielectric constant, polarity, hydrophilic and hydrophobic properties of micelles. Species distribution diagrams are generated using HYSS program.