Structural determination of unknown subsidiary colors in commercial food red Nos. 2 and 102.

Major subsidiary colors A (Sub A) and B (Sub B) in commercial Food Red No. 102, and colors C (Sub C) and D (Sub D) in commercial Food Red No.2 were isolated. These structures were characterized by physicochemical evidence. The structures of Sub A, B, and C are trisodium salt of 7-hydroxy-8-(6-sulfonaphthyl-2-azo)-1,3-naphthalenedisulfonic++ + acid, disodium salt of 4-amino-3-(4-sulfonaphthyl-1-azo)-1-naphthalenesulfonic acid and trisodium salt of 3-hydroxy-4-(6-sulfonaphthyl-2-azo)-2,7-naphthalenedisulfonic++ + acid, respectively. Sub D was identified as Sub B.