Spectrometric Determination of pKa Values for some Phenolic Compounds in Acetonitrile – Water Mixture

A. Hakan Aktaş*, Nurullah Şanlı, Güzide Pekcan

Department of Chemistry, Faculty of Science & Art, Süleyman Demirel University, 32260 Isparta – Turkey

The pKa values of ten phenolic compounds (phenol, 4-fluorophenol, 4-iodophenol, 3-bromophenol, 4-methylphenol, 4-nitrophenol, 4-ethylphenol, 2-methylphenol, 3-nitrophenol, and 3-methylphenol) in 10% (v/v) acetonitrile-water mixture using spectrometric measurements have been determined. The electronic absorption spectra of phenolic compounds at various pH values (pH 2.0 -11.0) at 200-500 nm intervals were recorded. The calibration of the electrode system was done potentiometrically by Gran’s method. Data were processed using the programme STAR (Stability Constants by Absorbance Readings). The obtained results are in good concordance with literature values.

Key words: phenolic compounds, dissociation constants, spectrometry.