Collect. Czech. Chem. Commun. 1999, 64, 1253-1261

Construction and Chemometric Analysis of Acidity Function in Perchloric Acid

Eva Jiráskováa, Jiří Kulhánekb, Taťjana Nevěčnáa,* and Oldřich Pytelab

a Department of Inorganic and Physical Chemistry, Palacký University, 771 46 Olomouc, Czech Republic
b Department of Organic Chemistry, University of Pardubice, 532 10 Pardubice, Czech Republic


Four 2,6-disubstituted anilines with CH3, Cl, and NO2 substituents have been synthesized and, together with four commercial substances of the same type, subjected to spectrophotometry to find the concentration ratios of the protonated and non-protonated forms in aqueous perchloric acid of 0.02-10.55 mol dm-3 concentration. By a procedure devised earlier, the acidity function has been constructed and the pKa values calculated. The Principal Component Analysis was applied to the acidity function obtained and on other eight acidity functions of perchloric acid were taken from literature. It was found that the first principal component explained 99.78% of variability, which indicated high degree of similarity of the said functions irrespective of the indicator type and solvent used. The regression dependences acidity function values on the first principle component are very close, the regression coefficient expressing the measure of sensitivity of the indicator to the acidifying medium. The pKa values obtained agree well with the literature data.

Keywords: Acidity functions; 2,6-Disubstituted anilines; Chemometrics; Latent variables; Substituent effects.