Tetraazidomethane: Chemistry With A Bang

The chemistry of compounds containing multiple azide groups (N₃) has entered a renaissance in recent years. Inorganic and organic versions of polyazides are of interest as high-energy-density materials (explosives, propellants, or fireworks) and have potential uses in the fabrication of electronic devices. Klaus Banert and his coworkers at Chemnitz University of Technology, in Germany, now report the latest addition to the polyazide family: tetraazidomethane (shown, top), a carbon atom with four azide groups attached (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200603960).

The tetraazide was previously proposed as an energetic material, and its structure had been calculated, the researchers note. In addition, a search of the literature turned up a case of a lab explosion that might have been caused by the compound's unplanned formation. But "amazingly," the synthesis of C(N₃)₄ has not been published previously, Banert says.

The team attempted a number of approaches to make C(N₃)₄ before finding two routes that work. The most straightforward synthesis is to react commercially available and stable trichloroacetonitrile (Cl₃CCN) with sodium azide (NaN₃). The second route is to prepare and react the triazido salt (N₃)₃CSbCl₆ with NaN₃. Though this second route has higher yield, the triazido starting material is explosive and more expensive.

The researchers isolated C(N₃)₄ as a high-boiling-point liquid that is dangerous to handle. The tetraazide hydrolyzes very rapidly, and the researchers found that it can be trapped by the double bond of norbornene (shown, bottom) or the triple bond of cyclooctyne to form diverse new compounds. It also adds to phosphines to form phosphazenes.

Synthesis of tetraazidomethane "is a great breakthrough," comments Thomas M. Klapötke of Ludwig Maximilians University, Munich, Germany. "This new binary C-N compound???s extremely high instability might preclude it from being used as an energetic material in the real world, but its controlled decomposition could form interesting carbon nitride species," Klapötke says.