Water → Sulfanilic acid

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47.8 parts of 2-amino-5-hydroxynaphthalene-7-sulfonic acid are stirred into 500 parts of water at 25° C. and are dissolved by the addition of 22 parts of a 30% by weight solution of sodium hydroxide. To this solution is added 26.8 parts of 2,4,6-trifluoropyrimidine dropwise over a 30 minute period. At the same time a 20% of sodium carbonate solution is added to this mixture continuously in order to maintain the pH of the mixture at 4-5. The reaction temperature is increased to 40-45° C. The end point of the reaction is determined using chromatographic techniques. The resultant suspension is cooled to 20-25° C. and poured onto a diazonium salt solution which is formed of 34.6 parts of 4-aminobenzene-sulfonic acid and 50 parts by volume of 4 N sodium nitrite solution at 0-5° C. and a pH of 1. During the coupling reaction the pH is maintained at 6-7 by continuously adding 20% sodium carbonate solution. The monoazo compound thus formed is salted-out using conventional methods, filtered and dried at 60° C. under vacuum. The product has the formula ##STR8##

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