Clean synthesis of disperse azo dyes based on peculiar stable 2,6-dibromo-4-nitrophenyl diazonium sulfate

Abstract The development of clean synthetic technology of disperse azo dyes is essential for the dye industry due to ecological and economical demands. In this study, a clean, safe, and low-energy-consumption method for preparing disperse azo dyes based on 2,6-dibromo-4-nitroaniline is presented with excellent yield and short reaction time. The peculiar stable diazonium sulfate of 2,6-dibromo-4-nitroaniline is precipitated from the organic reaction system, and the solid diazonium salt is directly used to synthesize disperse azo dyes. Compared with traditional method, the amount of sulfuric acid used is reduced by 80%, the amount of waste inorganic salt is reduced by 80.9% and the heat released from the reaction system is reduced by 88.5% in the proposed method. The dye structures are verified by 1H NMR, 13C NMR, Fourier transform infrared spectroscopy (FT-IR), and high resolution mass spectrometry (HR-MS). Compared with commercial dyes, the prepared dyes have the same dyeing properties that are sufficient for industrial applications.