Dimethyl 2,5-bis{(4-chlorophenyl)amino}cyclohexa-1,4-diene-1,4-dicarboxylate (4.47 gm, 10 mmol), the sodium salt of 3-nitrobenzenesulphonic acid (2.3 gm; 10 mmol), ethanol (70 ml) and 1.0M sodium hydroxide (40 ml) were heated to reflux overnight under a nitrogen atmosphere. The bright yellow solution was allowed to cool and water (120 ml) was added. The mixture was acidified with conc. hydrochloric acid when a red solid precipitated out. This material was filtered off, washed with water and dried under vacuum over phosphorous pentoxide to give 4.0 gm (96%) of 2,5-bis{(4-chlorophenyl)amino}terephthalic acid.
