Submitted by W. A. Jacobs and M. Heidelberger.
Checked by Roger Adams and L. F. Martin.
1. Procedure
The crude product thus obtained is contaminated with some
arsanilic acid and possibly other products. These are removed during purification. The crude product is suspended in about 400 cc. of water, and, with vigorous stirring, treated carefully with
25 per cent aqueous sodium hydroxide until solution is just complete. At this point the mixture is still acid to litmus, and an excess of
sodium hydroxide is to be avoided to prevent decomposition of the product. About 15 g. of animal charcoal is added, the mixture stirred for five minutes without heating, and filtered. The filtrate is treated during vigorous stirring with
100 cc. of 20 per cent hydrochloric acid, and the pure acid at once separates. After cooling, it is filtered by suction and washed thoroughly with small portions of ice-cold water until the filtrate is practically halogen-free (Note
2).
The acid, without drying, is suspended in about 200 cc. of distilled water and, with vigorous stirring, cautiously (Note
3) treated with
25 per cent sodium hydroxide solution until dissolved and the solution reacts neutral to litmus. The solution is then filtered through
folded filter paper which should be free from soluble calcium salts, otherwise the filtrate will remain clouded by a suspension of the calcium salt. The clear, faintly yellow or colorless filtrate is then vigorously stirred and treated with
1.5 volumes of 95 per cent alcohol. Crystallization is induced by rubbing with a rod, and then an additional volume of alcohol is added. The mixture should be allowed to cool to about 20° and stand for at least two hours to complete the precipitation of the salt, which is then filtered by suction and washed thoroughly with
85 per cent alcohol. The salt is then air-dried. The yield is
73–77 g. (
38–40 per cent of the theoretical amount).
2. Notes
2. If the free acid is desired it may be obtained by drying the product at this stage. The yield of free acid is about
100 g. (
60 per cent of the theoretical amount).
3. If
sodium hydroxide is added too rapidly some solid precipitates which does not redissolve.
3. Discussion
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