Dimethyl 2,5-bis{(4-methoxyphenyl)amino}cyclohexa-1,4-diene-1,4-dicarboxylate (6.58 gm, 15 mmol), the sodium salt of 3-nitrobenzenesulphonic acid (3.6 gm; 16 mmol), ethanol (90 ml) and 1.0M sodium hydroxide (50 ml) were heated to reflux overnight under a nitrogen atmosphere. The orange solution was allowed to cool and water (120 ml) was added. The mixture was acidified with conc. hydrochloric acid when a purple solid precipitated out. This material was filtered off, washed with water, then 25% ethanol/water and dried under vacuum over phosphorous pentoxide to give 6.0 gm (98%) of 2,5-bis{(4-methoxyphenyl)amino}terephthalic acid.
