Development of a special SCFX-AnB3L dye and its application in ecological dyeing of silk with supercritical carbon dioxide

Special disperse reactive dyes play an indispensable role in ecological and sustainable dyeing of natural fibers, particularly for silk by employing supercritical carbon dioxide (SCF-CO2) in textile industry. In this work, a special disperse reactive SCFX-AnB3L dye in a red hue involving three moieties of an anthraquinonoid matrix, a bridge group and a dichlorotriazine reactive group was successfully synthesized. The precursor of the target dye was developed by utilizing the intermediates of 1-chloroanthraquinone and N-(2-aminoethyl)-3-methoxybenzenamine, based on a ligand-free Ullmann reaction with metallic copper as a promoter. Then a dichlorotriazine reactive group was grafted onto the dye precursor at a special bridge group via a nucleophilic condensation reaction for achieving the SCFX-AnB3L dye. Moreover, the dye precursor and the final dye were successfully characterized and confirmed by Fourier transform infrared spectroscopy (FTIR), H-1 and C-13 nuclear magnetic resonance spectroscopy H-1 and C-13 NMR), ultraviolet-visible absorption spectroscopy (UV-vis), elemental analysis and liquid chromatography-mass spectrometry (LC-MS). Furthermore, the special dye was applied to an ecological dyeing of silk as well as the contrast substrates of cotton and wool in SCF-CO2. The coloration results indicate that very good adsorption, uptake and fixation behaviors, and the highest color fastness graded at 4-5 in color fading test and 5 grades for staining and dry or wet rubbing tests were observed for the synthesized special dye on silk substrate in comparison with the contrast ones. Particularly, the highest color intensity on the silk substrate was obtained among the tested substrates under an identical dyeing condition.