Lanasol dyes and wool fibres. part II: Model studies on the mechanism of dye fixation in an aqueous system

In Part I of this study we investigated the mechanism of the fixation of Lanasol dyes to the various amino acid side chain sites within wool protein using model compounds in a mixed solvent system. As the dyeing of wool is generally carried out in an aqueous system at the boil it was felt that the model system would be more accurate if the compounds studied were water soluble. This paper reports on the synthesis of the sulfonated version of the model reactive dye compound used in Part I of this study and its subsequent reaction with model wool compounds. In addition, a model compound based on benzene sulfonic acid, and an actual commercial Lanasol dye were also reacted. As in the first part of this study the reaction products were isolated by chromatography and then characterized by proton and carbon-13NMR, and electrospray mass spectroscopy. In general the results were consistent with those obtained from the study carried out in the acetone/water solvent system. It was confirmed that the dibromo form of the dye reactive group is only converted to the monobromo form in the presence of model wool compounds and that both forms react with model wool compounds to yield the same products. Amines reacted with the model dyes to form a product containing an aziridine ring - no evidence for the proposed reaction of this ring with a second nucleophilic wool site to form a cross-link between two protein chain segments could be detected. In the few cases where an aziridine ring structure was not formed, the products obtained were found to support a Michael addition (1,4-addition) reaction mechanism. Unlike the results found for the mixed solvent system it was found that the wool models for N-terminal groups did not react with the model dye compounds.