Continuous and green microflow synthesis of azobenzene compounds catalyzed by consecutively prepared tetrahedron CuBr

• Hong Qin^a,1
• Chengkou Liu^a,1
• Niuniu Lva²
• Wei He^a
• Jingjing Meng^a
• Zheng Fang^a
• Kai Guo^a,b

• ^a College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, No. 30 Puzhu South Road, Nanjing, China
• ^b State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, 211816, China

An environmentally friendly and cross-selective process intensification for the continuous synthesis of symmetric aromatic azo compounds by using self-made cuprous bromide as the catalyst under mild conditions in the microreactor was developed. A novel tetrahedron cuprous bromide catalyst which shows outstanding catalytic activity and satisfactory stability has been synthesized in continuous flow microreactor. The online immobilization of self-made cuprous bromide on the catalyst bed achieved oxidative coupling of aromatic amines (oxygen as oxidant) and high-performance gas–liquid–solid three-phase reaction, which strongly limited the possibility of undesired reaction pathways, improving product selectivity and reducing waste generation. Meanwhile, the yield of azo-coupling reaction was up to 98% under optimized condition. As compared with earlier traditional method (diazotization reaction) for synthesizing azobenzene, the designed micro-flow process displays significant advances in terms of selectivity, waste emissions, sustainability and productivity. The combination of online immobilization of self-made cuprous bromide and precise and safe control through the microreactor provides a green solution for the industrial production of valuable aromatic azo compounds.

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