Chelate Formation of 2-(2-Benzoxazolylazo)-1-naphthol with Metal Ions

Abstract

2-(2-Benzoxazolylazo)-1-naphthol(a-BOAN) was synthesized as the new reagent for the determination of trace amounts of metals and the analytical properties ofa-BOAN was quantitatively compared with those of 1-(2-pyridylazo)-2-naphthol(α-PAN), 1-(2-benzothiazolylazo)1-naphthol(α-BTAN) and 2-(2-quinolylazo)-1-naphthol(α-QAN).
Spectrophotometrically det ermined acid dissociation constants of α-BOAN (pK_a1 and pK_a2)in various aqueous dioxane concentration were 0.4689-8.237 n+19.38 n2 and 6.317+3.566 n, respectively, where n is molar fraction of dioxane. Replacement of pyridine ring in α-PAN by benzoxazole ring resulted in a decrease in pKa values of the reagent which accompanied by decrease in metal chelate formation constants. The proton displacement constants of the reagent, however, were found to be higher than those of the other analogous compounds refered above. A study has been made of the extraction of copper and zinc into carbon tetrachloride by α-BOAN. Copper and zinc formed extractable chelates containing a 1 to 2metal-ligand ratio. The extraction constants of the chelates have been determined. The analytical advantages of the use ofα-BOAN in the determination o f metals are outlined.