Chlorine pentafluoride is an interhalogen compound with formula ClF₅. This colourless gas is a strong oxidant that was once a candidate oxidizer for rockets. The molecule adopts a Square pyramidal molecular geometry, square pyramidal structure with C_4v Molecular symmetry, symmetry, as confirmed by its Fluorine-19 NMR, high-resolution ¹⁹F NMR spectrum. It was first synthesized in 1963.

Preparation

Some of the earliest research on the preparation was classified. It was first prepared by fluorination of chlorine trifluoride at high temperatures and high pressures: :ClF₃ + F₂ → ClF₅ :ClF + 2F₂ → ClF₅ :Cl₂ + 5F₂ → 2ClF₅ :CsClF₄ + F₂ → CsF + ClF₅ Nickel(II) fluoride, NiF₂ catalyzes this reaction. Certain metal fluorides, MClF₄ (i.e. KClF₄, RbClF₄, CsClF₄), react with F₂ to produce ClF₅ and the corresponding alkali metal fluoride.

Reactions

In a highly exothermic reaction, ClF₅ reacts with water to produce chloryl fluoride and hydrogen fluoride: : + 2 → + 4 It is also a strong fluorinating agent. At room temperature it reacts readily with all elements (including otherwise "inert" elements like platinum and gold) except noble gases, nitrogen, oxygen and fluorine.

Uses

Rocket propellant

Chlorine pentafluoride was once considered for use as an oxidizer for rockets. As a propellant, it has a higher maximum specific impulse than Chlorine trifluoride, ClF₃, but with the same difficulties in handling. Due to the hazardous nature of chlorine pentafluoride, it has yet to be used in a large scale rocket propulsion system. John Drury Clark summarized the difficulties of handling ClF₃:

It is, of course, extremely toxic, but that's the least of the problem. It is Hypergolic propellant, hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the passivation (chemistry), formation of a thin film of insoluble metal fluoride that protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

References

External links

National Pollutant Inventory - Fluoride and compounds fact sheetNew Jersey Hazardous Substance Fact SheetWebBook page for ClF5
{{DEFAULTSORT:Chlorine Pentafluoride Fluorides Inorganic chlorine compounds Interhalogen compounds Rocket oxidizers Fluorinating agents Oxidizing agents Chlorine(V) compounds Substances discovered in the 1960s