I - AMINO-2-NAPHTHOL-4-SULFONIC ACID

A mixture of 145 cc. of nitric acid (sp. gr. 1.42) and 400 cc. of water in a 2-1. beaker is cooled to 30° in a slush of ice and water, and 350 g. (1.46 moles) of pure, anhydrous i-amino-2-naphthol-4-sulfonic acid (Note 1) is weighed into a separate 2-1. beaker. The beaker is removed from the bath a 10-g. portion of the i-amino-2-naphthol-4-sulfonic acid is stirred into the solution, and the liquid is then allowed to become entirely motionless. Generally, oxidation starts during this addition if not, 2 cc. of... 

If technical i-amino-2-naphthol-4-sulfonic acid is used, the yield of ammonium i,2-naphthoquinone-4-sulfonate is 313 g. (84 per cent) of a rust-colored product. If the technical material... 

Salts of 1,2-naphthoquinone-4-sulfonate have been prepared by the oxidation of 2-amino-i-naphthol-4-sulfonic acid with nitric acid,2 or by the oxidation of the more readily available i-amino-2-naphthol-4-sulfonic acid with the same reagent.3,4 5... 

Nitrophthalic acid has usually been prepared by nitration of phthalic add or phthalic anhydride, followed by separation from the accompanying 3-nitrophthalic acid. It has also been prepared from 6-nitro-2-naphthol-4-sidfonic acid (obtained from the technical diazo-anhydride of 6-nitro-i-amino-2-naphthol-4-sulfonic acid). The present procedure is more convenient than any of the earlier methods. 

Technical I-amino-2-naphthol-4-sulfonic acid (du Pont Co., Dyes and Chemicals Div. Allied Chem. Corp., National Aniline Division) is rendered suitable for use in the next step by washing with warm ethanol and then with ether. 

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