Tetrafluorohydrazine

Tetrafluorohydrazine or perfluorohydrazine, N2F4, is a colourless, nonflammable, reactive inorganic gas. It is a fluorinated analog of hydrazine.

Synthesis
Tetrafluorohydrazine was originally prepared from nitrogen trifluoride using an copper as a fluorine atom acceptor:
 * 2NF3 + Cu  ->  N2F4  +  CuF2

A number of F-atom acceptors can be used, including carbon, other metals, and nitric oxide. These reactions exploit the relatively weak N-F bond in NF3.

Properties
Tetrafluorohydrazine is in equilibrium with its radical monomer nitrogen difluoride.


 * N2F4 ⇌ 2 •NF2

At room temperature N2F4 is mostly associated with only 0.7% in the form of NF2 at 5mm Hg pressure. When the temperature rises to 225 °C, it mostly dissociates with 99% in the form of NF2.

The energy needed to break the N−N bond in N2F4 is 20.8 kcal/mol, with an entropy change of 38.6 eu. For comparison, the dissociation energy of the N−N bond is 14.6 kcal/mol in N2O4, 10.2 kcal/mol in N2O2, and 60 kcal/mol in N2H4. The enthalpy of formation of N2F4 (ΔfH°) is 34.421 kJ/mol.

Uses
Tetrafluorohydrazine is used in organic synthesis and some rocket propellant formulations. It adds across double bonds to give vicinal di(difluoroamine)s. In chemical syntheses, as a precursor or a catalyst. It was considered for use as a high-energy liquid oxidizer in some never-flown rocket fuel formulas in 1959.

Safety
Tetrafluorohydrazine is a highly hazardous chemical that explodes in the presence of organic materials.

It is a toxic chemical which irritates skin, eyes and lungs. It is a neurotoxin and may cause methemoglobinemia. May be fatal if inhaled or absorbed through skin. Vapors may be irritating and corrosive. It is a strong oxidizing agent. Contact with this chemical may cause burns and severe injury. Fire produces irritating, corrosive and toxic gases. Vapors from liquefied gas are initially heavier than air and spread across the ground.

Tetrafluorohydrazine explodes or ignites on contact with reducing agents at room temperature, including hydrogen, hydrocarbons, alcohols, thiols, amines, ammonia, hydrazines, dicyanogen, nitroalkanes, alkylberylliums, silanes, boranes or powdered metals. Prolonged exposure of the container of tetrafluorohydrazine to high heat may cause it to rupture violently and rocket. Tetrafluorohydrazine itself can explode at high temperatures or with shock or blast when under pressure. When heated to decomposition in air, it emits highly toxic fumes of fluorine and oxides of nitrogen.

There is a fatal case in which during opening of valves to check the pressure, the cylinder exploded, killing one man and injuring another.