Azo dyes are by far the most important class of dyes for the coloration of textile materials. Commonly, azo dyes are synthesized via diazotization of an aromatic or a heteroaromatic primary amine in dilute or concentrated mineral acid, followed by coupling of the resultant diazonium salt with an electron-rich nucleophile. In conventional azo dyes synthesis, significant levels of electrolyte are produced following neutralization of the reaction mixture, which poses an environmental problem when the waste is released into receiving waters. Relatively recently, however, it was shown that azo dyes may be synthesized using supercritical carbon dioxide (SC-CO2) and water as the main solvent and diazotizing medium, with the potential to reduce environmental pollution.
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