Abstract

Spectrophotometric determination of acidity constants of 1-(2-pyridylazo)-2-naphthol in water and mixed water-organic solvents

Author(s): M.Mazloum Ardakani, S.Lotfei, J.Ghasemi, S.Ghahri Saremi

The acidity constants of 1-(2-pyridylazo)-2-naphthol(o-PAN) in waterorganic solvents mixtures solutions at 250C and an ionic strength of 0.1M have been determined by spectrophotometrically. The organic solvents used were the acetonitrile (AN), dimethyl sulfoxide (DMSO) and dimethyl formamid (DMF).To evaluate the pH–absorbance data, a resolution method based on the combination of soft- and hard-modeling is applied. The acidity constants of all related equilibria are estimated using thewhole spectral fitting of the collected data to an established factor analysismodel. DATAN program was used for determination of acidity constants. Generally, the pKa1 values decreases and pK2 increase with an increase in the content of the organic solvent. There are linear relationships between acidity constants and the mole fraction of different solvents in the mixtures. The effect of solvent properties on acid-base behavior is discussed.