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

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◦c depending on the dye and type of fabric. the fastness (wash, rub and light) properties of the dyes were also assessed.