Study of some 2,7-bis (2-hydroxynitrophenylazo) derivatives of chromotropic acid as spectrometric reagents for bismuth (III)

Abstract

Syntheses of four bis-[(O,O1-dihydroxy-nitrophenyl)azo] derivatives of chromotropic acid, namely, 2,7-bis[(2-hydroxy-4-nitrophenyl)azo]-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (4N), 2,7-bis[(2-hydroxy-5-nitrophenyl)azo]-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (5N), 2,7-bis[(2-hydroxy-6-nitrophenyl)azo]-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (6N), and 2,7-bis[(2-hydroxy-3,5-nitrophenyl)azo]-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (3,5N) were attempted. Among these, only 5N-dye was successfully prepared. Thin layer chromatography, elemental analysis, infrared spectrometry and nuclear magnetic resonance were used to confirm the structure of synthesized dye. The 5N-dye was proposed as a EDTA complexometric titration indicator and as a metallochromic reagent for bismuth(III). A visible spectrometric method for bismuth(III) was also systematically developed at pH 2.5, 5N-dye reacted with bismuth(III) instantaneously giving a blue 1:1 metal to dye complex and was stable for at least 24 hours. The complex obeyed Beer's law in the concentration range of bismuth(III) between 20.90 to 146.29 micrograms per 100 millilitre showing a molar absorptivity of 2.3x10x10x10x10 Lmol-1cm-1 at 648 nanometer. Lead(II), manganese(II), zinc(II), nickel(II), cadmium(II), silver(I), cobalt(II), magnesium(II), sodium(I), acetate, chloride, sulfate, and carbonate in the mole ratio of 100:1 did not interfere. A EDTA titration of bismuth(III) using 5N-dye as direct visual indicator gave a satisfactory result comparing to those obtained from xylenol orange method.