4-Nitronaphthalene-2,7-disulfonic acid

Sulfurous acid and its salts are inexpensive reducing agents which are, however, usable only in special cases. These reagents frequently give sulfonation simultaneously with reduction (cf. the preparation of l-naphthylamine-2,4-disulfonic acid from 1-nitronaphthalene, and of l-amino-2-naphthol-4-sulfonic acid from nitroso- -naphthol, pages 178 and 201). Also, in the reduction of diazobenzene to phenylhydrazine, a N-sulfonic acid is formed first and this must be split by vigorous treatment with hydrochloric acid (see pages 96 and 128). 

A mixture of 35.0 g a-nitronaphthalene (0.2 mol), 200 mL 52 N NaHS03 (75% excess), and 250 mL H2O was heated under a return condenser until the mixture was completely homogeneous. The contents of the flask were evaporated to 300 mL and treated with 50 mL 12 iV HCI to give a heavy white precipitate, which was filtered from the cooled solution. This mixture was warmed with 300 mL water, which dissolved the salts present, leaving the naphthionic acid (solubility of0.024 g in 100 mL water) 13.5 g aminosulfonic acid was thus obtained, in a yield of 29%. The combined filtrates were saturated with NaCl, and the precipitate produced was filtered off. It was nearly free from inorganic salts. When dry, it weighed 31 g, which, on the basis of a monosodium salt of a naphthylamine disulfonic acid is equivalent to a yield of 66%. 

The core scaffold of three of the previously identified inhibitors, VI, SI, and S5 (31), is 4,5-dihydroxynaphthalene-2,7-disulfonate—structure A in Durrant et al. (47). Similarity searches were performed using three structures similar to this core scaffold naphthalene-2-sulfonic acid, 2-naphthoic acid, and 2-nitronaphthalene—structures B, C, and D in Fig. 1 of Durrant et al. (47), respectively. 

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