Several procedures for obtaining titte compound have been reported: In one method the acylation of 1 naphthylamine 4,6,8-trisulfonic acid trisodium salt (I) with 4 methyl-3-nitrobenzoyt chloride (II) yields the correspond ing amide (III), which is reduced with Fe in acetic acid to the amine (IV). Acylation of (IV) with 3-nitrobenzoyl chloride (V) affords the nitro diamide (VI), which is reduced with Fe and acetic acid before to the amine (VII). Finally, this compound is condensed with phosgene.