Prepn. of 2-amino-4-nitrophenol-6-sulphonic acid in improved yield and purity useful for prepn. of azo dyes - by partial redn. of 2,4-di:nitro phenol-6-sulphonic acid in the presence of magnesium sulphate

摘要

Prepn. of 2-amino-4-nitrophenol-6-sulphonic acid comprises (i) partial redn. of 2,4-dinitro phenol-6-sulphonic acid with alkali sulphides and/or hydrogen sulphides or polysulphides in the presence of magnesium sulphate; and (ii) isolating the solid end prod. (without intermediate isolation) by: (a) reducing reaction mixt. pH to less than 0.5 by adding mineral acid; (b) bubbling inert gas through the reaction mixt. to remove hydrogen sulphide and sulphur dioxide; (c) bubbling air through the reaction mixt. at raised temp. to remove sulphur, decompose any thiosulphate formed and separate impurities insol. in acid; and (d) cooling the reaction mixt. and separating the pptd. prod. USE/ADVANTAGE - ANS is useful for the prepn. of azo dyes for the textile and leather industry. ANS is obtd. in improved yield and purity.