Substituent Effects on Absorption Spectra of 7-Amino-4-Hydroxynaphthalene-2- Sulfonic Acid Based Dyes

Abstract

The synthesis of dyes derived from coupling 7-amino-4-hydroxynaphthalene-2-sulfonic acid (a diazonium salt) with different coupling agents (phenol, p-nitrophenol, vanillin and salicylic acid) respectively yielded four different dyes namely; Dye A, 4-hydroxy-7-((2- hydroxyphenyl)diazenyl)naphthalene-2-sulfonicAcid, Dye B, 4-hydroxy-7-((2-hydroxy-5- nitrophenyl)diazenyl)-4-hydroxynaphthalene-2-sulfonic Acid, Dye C, 7-((2-formyl-5-hydroxy-4-methoxyphenyl)diazenyl)-4- hydroxy naphthalene-2-sulfonic Acid and Dye D, 2-hydroxy-6-((5-hydroxy-7-sulfonaphthalene-2-yl)diazenyl)benzoic Acid. The wavelengths of maximum absorption of the dyes were determined in different solvents; water, DMF, ethanol and acetone, their λmax was between 510-600nm. The synthesized dyes were characterized using IR and their melting points determined. The dyes were applied on wool and silk and the effect of pH, time, temperature on the %exhaustion for both fabrics was determined. The optimum pH for absorption of the dyes on both fabrics was 3 & 5, optimum time 50, 75 & 90 minutes and optimum temperature
75 and 90^oC depending on the dye and type of fabric. The Fastness (wash, rub and light) properties of the dyes were also assessed.

Keywords: Diazonium, coupling, exhaustion, fastness