Nitrogen Iodide, N₂H₃I₃

A very explosive compound of nitrogen and iodine, discovered by Courtois in 1812, was investigated later by Serullas, who prepared it by the action of an alcoholic solution of iodine on aqueous ammonia.

The action of strong ammonia solution on solid iodine also produces the substance as a black powder, which can be filtered off.

Alcoholic solutions of iodine and ammonia produce the same compound.

A convenient method is to add gradually a solution of iodine in potassium iodide to aqueous ammonia, when a black precipitate separates.

The reaction between iodine and ammonia appears to proceed in three stages. Firstly, hypoiodous acid and ammonium iodide are produced:

NH₄OH + I₂ = HOI + NH₄I;

and the hypoiodous acid further combines with ammonia to form ammonium hypoiodite:

NH₄OH + HOI = NH₄IO + H₂O.

Finally, the ammonium hypoiodite decomposes into nitrogen iodide:

3NH₄IO ⇔ N₂H₃I₃ + NH₄OH + 2H₂O.

The last reaction is apparently reversible, as the nitrogen iodide redissolves in strong ammonia.

Ammonium iodide and bleaching-powder solutions also give the explosive nitrogen iodide.

Nitrogen iodide exists in the form of flattened needles which are copper-coloured by reflected light and red by transmitted light, with a density of 3.5. It is one of the most explosive of substances; when dry it will explode spontaneously or by the lightest contact, even that of a feather. Warming or exposure to strong light also causes its explosive decomposition, and in all its reactions it tends to break down into nitrogen and hydrogen iodide.

The composition of nitrogen iodide has been the subject of much investigation, but it seems that the usual product of ammonia and iodine is NI₃.NH₃. Sodium sulphite is oxidised to the sulphate according to the following equation: -

3Na₂SO₃ + N₂H₃I₃ + 3H₂O = 3Na₂SO₄ + 2NH₄I + HI.

The reaction between nitrogen iodide and zinc ethyl confirms the composition N₂H₃I₃:

N₂H₃I₃ + 3Zn(C₂H₅)₂ = 3ZnC₂H₅I + NH₃ + N(C₂H₅)₃.

A black explosive compound is obtained when silver nitrate is added to nitrogen iodide suspended in water, which has the composition NI₃.AgNH₂.

The hydrolysis of nitrogen iodide by water proceeds according to the equation

N₂H₃I₃ + 3H₂O ⇔ 2NH₄IO + HIO.

Many substances are readily oxidised by nitrogen iodide: hydrogen iodide liberates iodine, hydrogen chloride forms iodine chloride, hydrogen cyanide gives iodine cyanide, ICN, and alkalies form a mixture of iodide and iodate.

At low temperatures a number of addition compounds of nitrogen iodide can be produced, such as NI₃.2NH₃, NI₃.3NH₃, and NI₃.12NH₃.