Heterocyclic azo dyestuffs in analytical chemistry. Part I. The ligand properties of 2-(2-pyridylazo)-1-naphthol and its sulphonated analogues

Abstract

The preparation, from 2-hydrazinopyridine and the respective 1,2-naphthaquinones, of 2-(2-pyridylazo)-1-naphthol (α-PAN) and its derivatives containing sulphonic acid groups in positions 4 to 8 of the naphthalene ring, respectively, is described. The metal-complexing properties of the dyes are discussed in relationship to the position of the sulphonic acid group, and compared with those of 1-(2-pyridylazo)-2-naphthol (β-PAN). The dye with the sulphonic acid group in position 8 appears to be the most promising colorimetric reagent. All the new dyes are shown to be superior indicators to β-PAN for the complexometric titration of copper.