Chlorine pentafluoride is an

interhalogen compound In chemistry, an interhalogen compound is a molecule which contains two or more different halogen atoms ( fluorine, chlorine, bromine, iodine, or astatine) and no atoms of elements from any other group. Most interhalogen compounds known are b ...

with formula ClF₅. This colourless gas is a strong oxidant that was once a candidate oxidizer for rockets. The molecule adopts a square pyramidal structure with C_4v symmetry, as confirmed by its 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 In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, ...

chlorine trifluoride Chlorine trifluoride is an interhalogen compound with the formula ClF3. This colorless, poisonous, corrosive, and extremely reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room temp ...

at high temperatures and high pressures: :ClF₃ + F₂ → ClF₅ :ClF + 2F₂ → ClF₅ :Cl₂ + 5F₂ → 2ClF₅ :CsClF₄ + F₂ → CsF + ClF₅ 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 Chloryl fluoride is the chemical compound with the formula ClO2F. It is commonly encountered as side-product in reactions of chlorine fluorides with oxygen sources. It is the acyl fluoride of chloric acid. Preparation ClO2F was first reported by ...

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 Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

and

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...

) except

noble gases The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

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 Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...

than 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 John Drury Clark, Ph.D. (August 15, 1907 – July 6, 1988) was an American rocket fuel developer, chemist, and science fiction writer. He was instrumental in the revival of interest in Robert E. Howard's '' Conan'' stories and influenced the wr ...

summarized the difficulties of handling ClF₃:

It is, of course, extremely toxic, but that's the least of the problem. It is
hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. T ...
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 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