Degradation of the disazo acid dye by the sulfur-containing amino acids of wool fibers

In order to examine the color change of the disazo acid dyeings on wool fibers, C.I. Acid Blue 113 having disazo groups within the molecular structure was used and its characteristics of the color change were studied. The dye degradation was attributed to the reducing effect of the sulfur-containing amino acids within the wool fibers. The degraded moiety of the disazo dye was analyzed using an LC/MS. The mass spectrum showed that the mass of 326.1 corresponded to the dye moiety having monoazo group, which was formed by a reductive degradation of the disazo dye. From the model studies using cystine and cysteine, it was also found that the formation of the monoazo moiety was attributable to the reducing effect of the cystine and the cysteine.