1-naphthol-4,7-disulfonic acid

1-Hydroxynaphthalene-4,7-disulfonic acid [6361-37-1]. (4-hydroxynaphthalene-1,6- disulfonic acid), D(Dahl’s)acid, C10H8O7S2, Mr 304.3: its alkali-metal salts are readily soluble in water. Boiling with 65 % sulfuric acid results in desulfonation and formation of 1-hydroxynaphthalene-7-sulfonic acid. Diazo coupling and nitrosation take place in the 2-position.

1-Aminonaphthalene-4,7-disulfonic acid is heated with sodium bisulfite under conditions similar to those described for the production of 1-hydroxynaphthalene-4-sulfonic acid from sodium naphthionate. High yields of 1-Aminonaphthalene-4,7-disulfonic acid have been claimed via sulfonation of 1-(dichlorophosphinyloxy)naphthalene (1-naphthol+ POCl3).