The light stability of azo dyes and azo dyeings. III. The effect of artificial perspiration on the light stability of reactive and non-reactive derivatives of two selected azo chromophores in aqueous solution

The light stability of two series of azo dyes has been studied in aqueous solution. The first chromophore (A(Chr)) is the coupling product of diazotized ortanilic acid and H-acid, and the second (B(Chr)) is that of diazotized p-anisidine-2-sulfonic acid and J-acid. Bifunctional and monofunctional reactive, as well as non-reactive derivatives, respectively have been exposed to light in aqueous solution. The light stability of the members in the 'A'-group, except A(Chr) and A(DCT) exceeded that of the corresponding members of the 'B'-group. The light stability of the heterobifunctional reactive members of both groups (MCT-VS) could be improved by partial (MHT-VS and MCT-VH) or total (MHT-VH) hydrolysis of the reactive groups, The presence of artificial perspiration in the dye solution very significantly deteriorates the light stability of all the dyes studied. The perspiration induced a decrease in the light stability of the 'A'-group significantly, exceeding that of the 'B'-group; t(50) values, however, are very close to each other subsequent to perspiration-light exposure of all the studied 14 dissolved dyes. (C) 1998 Elsevier Science Ltd.