Synthesis of azo compounds

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A highly efficient, metal-free, chemical oxidation of hydrazines using environmentally friendly TCCA as oxidant provides a broad range of azo compounds in THF in excellent yield. This step-economical process offers mild reaction conditions, operational simplicity, high reaction efficiency, and easy scale-up.
Y. Su, X. Liu, J. Yu, G. Cao, R. Zhang, Y. Zhao, D. Huang, K.-H. Wang, C. Huo, Y. Hu, Synthesis, 2020, 52, 1103-1112.

Selectfluor mediates an oxidative dehydrogenation of hydrazine derivatives via N-fluorination and elimination processes to provide azo compounds. This reaction offers simple operation, mild conditions, good functional group tolerance, and high efficiency.
Y. Zhao, S. Li, J. Cui, H. Wang, X. King, Y. Wang, L. Tian, Synthesis, 2022, 54, 5245-5252.

A convenient oxidation of aromatic hydrazides using Bobbitt's salt, a metal-free, recyclable, and commercially available oxoammonium reagent, provides aromatic diazenes. A variety of aryl hydrazides were oxidized within 75 min at room temperature. Computational insight suggests that this oxidation occurs by a polar hydride transfer mechanism.
N. Phadnis, J. A. Molen, S. M. Stephens, S. M. Weierbach, K. M. Lambert, J. A. Milligan, J. Org. Chem., 2024, 89, 5841-5845.

The synthesis of alkyl 2-phenylazocarboxylates largely depended on the stoichiometric use of toxic oxidants. The use of CuCl and DMAP as catalysts enables an environment-friendly aerobic oxidation of alkyl 2-phenylhydrazinecarboxylates to alkyl 2-phenylazocarboxylates under mild conditions.
M. H. Kim, J. Kim, J. Org. Chem., 2018, 83, 1673-1679.

A straightforward, convenient, and efficient oxidative dimerization of aromatic amines enables an easy access to symmetrical and unsymmetrical azobenzenes under extremely mild conditions using a unique and cost-effective iodinating reagent.
Y. Takeda, S. Okumura, S. Minakata, Synthesis, 2013, 45, 1029-1033.

Unsymmetrical and symmetrical bis(hetaryl)azo dyes were prepared by diazotisation-coupling and oxidation reactions in moderate yields. Their absorption maxima were observed in the range of 427-631 nm, being more bathochromic than the corresponding non-hetarylazo derivatives.
M. Wang, K. Funabiki, M. Matsui, Dyes and Pigments, 2003, 57, 77-86.

Treatment of anilines with N-chlorosuccinimide and 1,8-diazabicyclo[5.4.0]undec-7-ene enables a convenient one-step procedure for the synthesis of symmetrical azobenzenes in good yields in minutes.
A. A. John, Q. Lin, J. Org. Chem., 2017, 82, 9873-9876.

A green dehydrogenation of hydrazo compounds using basic alumina or KF/alumina under solvent-free conditions afforded azo compounds in good to excellent yields.
M. Mihara, T. Nakai, T. Iwai, T. Ito, T. Mizuno, Synlett, 2007, 2124-2126.