Sulfamic acid from acetoxime

A solution of 50 g. of acetoxime in 50 ml. of water and an excess of liquid sulfur dioxide (about 50 g.) are placed in an autoclave and kept at room temperature under pressure for 5 hours. The excess sulfur dioxide is then allowed to escape slowly, and the product is removed by filtration. It is washed on the filter with alcohol and then with ether. Yield 60 g. (90 per cent). 

Sulfamic acid is a crystalline, nonhygroscopic solid, melting with decomposition at 205°. Its solubility in 100 g. of water varies from 14.689 g.. at 0° to 47.08 g. at 80°. It is not appreciably soluble in organic oxygen-containing solvents, but it does dissolve easily in such nitrogenous solvents as liquid ammonia and formamide. The solubility of sulfamic acid in water is decreased markedly by the addition of sulfuric acid. 

Sulfamic acid is a strong acid and may be titrated with bases by means of indicators whose transition ranges lie within the pH range 4.5 to 9. Because of its unusual physical properties and the ease with which it may be prepared in a state of high purity, it has found application as an acidimetric standard of reference. It has also been suggested for the estimation and detection of nitrates and nitrites in the presence of each other. A comprehensive review of the physical and chemical properties of sulfamic acid and of its inorganic derivatives has recently appeared in Chemical Reviews. ° 

Audrieth, Sveda, Sislbr, and Butler Chem. Revs., 26, 49 (1940). 

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Sulfamic acid, 2 176 from acetoxime, 2 177 from hydroxylammonium sulfate, 2 176... 

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