24 декабря, 2015 
Pokraskin Dehydrothiotoluidinesulfonic acid—N
Dehydrothiotoluidinesulfonic acid—N
A solution of 67.4 grams (0.2 mole) of the pure (100 per cent) ammonium salt of dehydrothiotoluidinesulfonic acid (equivalent to 14
101 Cf. Brunner, Dissertation, Zurich, 1943.
grams of sodium nitrite) in 300 cc. water containing 8.2 grams of pure sodium hydroxide is boiled to expel ammonia. Traces of ammonia interfere with the oxidation. When the odor of ammonia has disappeared (about 1 hour), the solution is made up to 500 cc. and cooled to 20°C., and 10.5 grams of hypochlorous acid in the form of a 5 per cent (approximate) solution of sodium hypochlorite is added. The strength of the ammonium salt as well as of the hypochlorite must be determined titrimetrically. The temperature rises about 4 degrees. After 1 hour, a small test sample is heated in a test tube and salted out. The precipitate should be orange, and starch-iodide paper should give a definite test for hypochlorite. If the test comes out otherwise, more hypochlorite should be added to the reaction mixture. After 5 hours, the mixture is heated to boiling, and the dye is precipitated with salt (15 per cent by volume) and filtered off. The yield is about 75 grams of strong dye.
Naphthamine yellow NN is the most light-fast yellow for cotton and is completely stable to chlorine. Because of these properties, it is widely used, especially in the United States where laundry is always treated with bleaching agents. Naphthamine yellow NN is not as pure a color as chrysophenine and is inferior also with respect to color strength.
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