Nitrogen triiodide

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Nitrogen triiodide
Image:Nitrogen triiodide.gif
Molecular formula	NI₃
Molar mass	394.77 g/mol
CAS number	[13444-85-4]
Density	? g/cm³
Solubility (water)	Decomposes
Melting point	Decomposes
Related halides	Nitrogen trifluoride Nitrogen trichloride Nitrogen tribromide
Related iodides	Phosphorus triiodide Arsenic triiodide
Disclaimer and references

Nitrogen triiodide, also called ammonium triiodide or nitrogen iodide, is a highly explosive compound of nitrogen and iodine, NI₃. It is a contact explosive, and small quantities explode with a gunpowder-like snap when touched by even a feather, releasing a volatile cloud of iodine vapor. The decomposition of nitrogen triiodide occurs via the following reaction:

2NI_{3 (s)} → N_{2 (g)} + 3I_{2 (g)}

Pure nitrogen triiodide is a dark red compound, first prepared in 1990 by reaction of boron nitride with iodine monofluoride in trichlorofluoromethane at -30°C.

The compound usually referred to as nitrogen triiodide is an ammonia adduct, NI₃·NH₃, synthesized by reacting iodine with ammonia. It was first prepared by Bernard Courtois in 1812, and its formula was finally determined unequivocally in 1905 by Silberrad.Template:Ref Its solid state structure consists of zig-zag chains of corner-sharing NI₄ tetrahedra, with ammonia molecules between the chains.

Small amounts of nitrogen triiodide are sometimes synthesized as a demonstration to high school chemistry students. However, because the compound is so unstable, it has not been used in blasting caps or primers for explosives. While still wet, nitrogen triiodide is safer to handle than the dry compound, but is still prone to spontaneous explosion. NI₃·NH₃ explosions leave orange-to-purple iodine stains that are difficult to wash. However, they can be easily removed by sodium thiosulfate solution.

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Preparation

Nitrogen triiodide can be made by reacting 15 ml of ammonia with 3 g of solid iodine, and leaving the mixture in a well ventilated area for no more than 10 minutes, but no less than 5 minutes. After this time the excess liquid should be decanted off and the brown solid divided into 3 or 4 piles and left to dry. The more pure the ammonia, the more sensitive the explosive becomes, however it has very little blasting power in small amounts, and is relatively harmless as a demonstration. However care should be taken not to get any of the dust produced in your eyes, as this could be very harmful. When dry, it is important not to store the powder in a large heap, because it can sometimes explode under its own weight or even from acoustic vibrations. The better way to store it is to pour it with ethanol. Once the ethanol evaporates nitrogen triiodide regains its reactivity, still the solution should not be considered safe. Any attempt to store it is highly discouraged, rather only a small quantity for immediate use should be prepared.

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