Sulphamide, SO₂(NH₂)₂

Sulphamide, SO₂(NH₂)₂, the amide of sulphuric acid, may be obtained by the action of dry ammonia upon a cooled solution of sulphuryl chloride in either ethylene chloride or chloroform solution:

4NH₃ + SO₂Cl₂ = SO₂(NH₂)₂ + 2NH₄Cl.

It is better prepared by saturating a solution of sulphuryl chloride in 15 to 20 times its volume of chloroform with ammonia and shaking the product with water until the precipitate has dissolved. The aqueous solution, after boiling with lead oxide or silver oxide to remove chlorine and filtering, yields a viscid, hygroscopic liquid on evaporation.

Another method of preparation for pure sulphamide is to dissolve the product of the reaction between sulphuryl chloride and liquid ammonia in a small quantity of water and acidify the solution in order to cause hydrolysis. After two or three days, when hydrolysis is complete, the mixture is evaporated to dryness in vacuo and the residue extracted with ethyl acetate. The sulphamide is dissolved out and on evaporating off the ethyl acetate, pure sulphamide is obtained.

Sulphamide forms large, colourless, tabular crystals, which melt between 91-5° and 93° C. It is tasteless, only sparingly soluble in water or dilute alcohol, and neutral in reaction. On heating to 100° C. it begins to lose ammonia, with formation of imidodisulphamide, NH₂. SO₂.NH.SO₂.NH₂, and at 250° C. it decomposes completely, with loss of sulphur dioxide. With ammoniacal silver nitrate a precipitate is produced, which on heating to a temperature of 170° to 180° C. (preferably with a little ammonium chloride) until evolution of ammonia ceases, deposits the silver salt of sulphimide, SO₂NAg. On heating, this compound yields metallic silver mixed with a little silver sulphate. Sulphamide dissolves readily in cold concentrated nitric acid without nitration. On the addition of concentrated sulphuric acid, nitrosulphamide, NH₂.SO₂.NH.NO₂, is precipitated. This, on reduction with zinc dust and dilute sulphuric acid, yields first, hydrazine sulphon- amide, NH₂.SO₂.NH.NH₂, and ultimately, amidosulphonic acid and hydrazine sulphonic acid or their zinc salts.

Sulphamide absorbs

1.4 molecular proportions of dry ammonia at	+ 20° C.
3.0 molecular proportions of dry ammonia at	0 ° C.
5.4 molecular proportions of dry ammonia at	-20° C.

In the pure state, sulphamide is a non-electrolyte, indicating the weakness of its acidic tendencies. With the alkalis it forms salts, but not more than two atoms of hydrogen are displaceable by the metal.

From a consideration of the electrical conductivities of its solutions it has been suggested that sulphamide may also exist in an aci form, thus:

⇔ ,

just as in the case of carbamide.