Reductive coupling of nitrobenzene to azo- and azoxy-benzene for antioxidants, dyes, etc.

摘要

A process for the reductive coupling of nitrobenzene (NB) to give azobenzene (AB) and azoxybenzene (AOB), comprises passing NB with gaseous, hydrogen-free reducing agent(s) (RA) at elevated temperature in the gas phase over a heterogeneous redox catalyst in its reduced or partly reduced form. The catalyst contains active metal(s) of Bi, V, Cr, Mn, Fe, Co, Pb, Mo, Ce, U, Sn, Sb, Cu, La, W, Nb, Pd, Pt, Ni and/or In, and the average oxidation state of the active metal before contact with NB and RA is at least 0.5 below the maximum oxidation state which is stable under the reaction conditions. Also claimed is (i) a similar process in which the NB is deoxygenated by passing over a redox catalyst as above in the absence of any free gaseous RA and in amounts such that the catalyst is not completely spent; and (ii) redox catalysts as above.