Hydrazo and azo benzene di:carboxylic acid and salt prodn. - by catalytic redn. of nitrobenzene in aq. soln. of basic potassium cpd. and then oxidn.

摘要

In the prodn. of a soln. of an alkali salt of hydrazobenzene-4,4'-dicarboxylic acid (I) by catalytic redn. of p-nitrobenzoic acid (II) with H2 in the presence of noble metal catalysts in alkaline medium, redn. is carried out in aq. medium contg. basic K cpds. as alkali salt. The aq. medium contains min. 4.8 (wt.) pts. water and 0.3-1.6 pts. KOH or an equiv. amt. of K2CO3 per pt. (II). Redn. is carried out at 1-60 (6-15) bar and 40-100 deg.C, using 0.005-1 wt.% noble metal catalyst w.r.t. (II) and a water:(II) wt. ratio of 6.6-12.3:1. The soln. of the di-K salt of (I) is specified for the prodn. of azobenzene-4,4'-dicarboxylic acid (III) and/or its di-K salt by oxidising the soln. with air or gases contg. O2 at 40-110 deg.C. (III) can be obtd. by a very simple process and with min. by-prod. formation from readily available starting materials and using an incombustible solvent. (II) is useful for colouring polyester and polyamide compsns.