Chlorine trifluoride

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Chlorine trifluoride
Skeletal formula of chlorine trifluoride with some measurements Chlorine-trifluoride.png
Skeletal formula of chlorine trifluoride with some measurements
Spacefill model of chlorine trifluoride Chlorine-trifluoride-3D-vdW.png
Spacefill model of chlorine trifluoride
Systematic IUPAC name
Trifluoro-λ3-chlorane [1] (substitutive)
Other names
3D model (JSmol)
ECHA InfoCard 100.029.301 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 232-230-4
MeSH chlorine+trifluoride
PubChem CID
RTECS number
  • FO2800000
UN number 1749
  • InChI=1S/ClF3/c2-1(3)4 Yes check.svgY
  • InChI=1/ClF3/c2-1(3)4
  • F[Cl](F)F
  • [F-].[F-].F[Cl++]
Molar mass 92.45 g·mol−1
AppearanceColorless gas or greenish-yellow liquid
Odor sweet, pungent, irritating, suffocating [2] [3]
Density 3.779 g/L [4]
Melting point −76.34 °C (−105.41 °F; 196.81 K) [4]
Boiling point 11.75 °C (53.15 °F; 284.90 K) [4] (decomposes at 180 °C (356 °F; 453 K))
Reacts with water [5]
Solubility Reacts with benzene, toluene, ether, alcohol, acetic acid, hexane. [5] Soluble in CCl4 but can be explosive in high concentrations.
Vapor pressure 175 kPa
−26.5×10−6 cm3/mol [6]
Viscosity 91.82 μPa s
Thermochemistry [7]
63.9 J K−1 mol−1
281.6 J K−1 mol−1
−163.2 kJ mol−1
−123.0 kJ mol−1
Occupational safety and health (OHS/OSH):
Main hazards
Very toxic, very corrosive, powerful oxidizer, violent hydrolysis [3]
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg
NFPA 704 (fire diamond)
Flash point noncombustible [3]
Lethal dose or concentration (LD, LC):
95 ppm (rat, 4 hr)
178 ppm (mouse, 1 hr)
230 ppm (monkey, 1 hr)
299 ppm (rat, 1 hr)
NIOSH (US health exposure limits):
PEL (Permissible)
C 0.1 ppm (0.4 mg/m3) [3]
REL (Recommended)
C 0.1 ppm (0.4 mg/m3) [3]
IDLH (Immediate danger)
20 ppm [3]
Safety data sheet (SDS)
Related compounds
Related compounds
Chlorine pentafluoride

Chlorine monofluoride
Bromine trifluoride
Iodine trifluoride


Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

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 temperature). The compound is primarily of interest in plasmaless cleaning and etching operations in the semiconductor industry, [9] [10] in nuclear reactor fuel processing, [11] as a component in rocket fuels, and other industrial operations. [12]

Preparation, structure, and properties

It was first reported in 1930 by Ruff and Krug who prepared it by fluorination of chlorine; this also produced ClF (chlorine monofluoride) and the mixture was separated by distillation. [13]

3 F2 + Cl2 → 2 ClF3

The molecular geometry of ClF3 is approximately T-shaped, with one short bond (1.598  Å) and two long bonds (1.698 Å). [14] This structure agrees with the prediction of VSEPR theory, which predicts lone pairs of electrons as occupying two equatorial positions of a hypothetic trigonal bipyramid. The elongated Cl-F axial bonds are consistent with hypervalent bonding.

Pure ClF3 is stable to 180 °C (356 °F) in quartz vessels; above this temperature, it decomposes by a free radical mechanism to its constituent elements.[ citation needed ]


Reactions with many metals give chlorides and fluorides. With phosphorus, it yields phosphorus trichloride (PCl3) and phosphorus pentafluoride (PF5), while sulfur yields sulfur dichloride (SCl2) and sulfur tetrafluoride (SF4). ClF3 also reacts with water to give hydrogen fluoride and hydrogen chloride, along with oxygen and oxygen difluoride (OF2):

ClF3 + H2O HF + HCl + OF2
ClF3 + 2H2O 3HF + HCl + O2

It will also convert many metal oxides to metal halides and oxygen or oxygen difluoride.

It occurs as a ligand in the complex CsF(ClF
. [15]

One of the main uses of ClF3 is to produce uranium hexafluoride, UF6, as part of nuclear fuel processing and reprocessing, by the fluorination of uranium metal:

U + 3 ClF3 → UF6 + 3 ClF

The compound can also dissociate under the scheme:

ClF3 → ClF + F2


Semiconductor industry

In the semiconductor industry, chlorine trifluoride is used to clean chemical vapour deposition chambers. [16] It has the advantage that it can be used to remove semiconductor material from the chamber walls without the need to dismantle the chamber. [16] Unlike most of the alternative chemicals used in this role, it does not need to be activated by the use of plasma since the heat of the chamber is sufficient to make it decompose and react with the semiconductor material. [16]

Rocket propellant

Chlorine trifluoride has been investigated as a high-performance storable oxidizer in rocket propellant systems. Handling concerns, however, severely limit its use. John Drury Clark summarized the difficulties:

It is, of course, extremely toxic, but that's the least of the problem. It is 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 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. [17]

Chlorine pentafluoride (ClF5) has also been investigated as a potential rocket oxidizer. It offered improved specific impulse over chlorine trifluoride, but with all of the same difficulties in handling. Neither compound has been used in any operational rocket propulsion system.

Proposed military applications

Under the code name N-Stoff ("substance N"), chlorine trifluoride was investigated for military applications by the Kaiser Wilhelm Institute in Nazi Germany not long before the start of World War II. Tests were made against mock-ups of the Maginot Line fortifications, and it was found to be an extremely effective incendiary weapon and poison gas. From 1938, construction commenced on a partly bunkered, partly subterranean 14,000 m2 (150,000 sq ft) munitions factory, the Falkenhagen industrial complex, which was intended to produce 90 tonnes of N-Stoff per month, plus sarin (a deadly nerve agent). However, by the time it was captured by the advancing Red Army in 1945, the factory had produced only about 30 to 50 tonnes, at a cost of over 100 German Reichsmark per kilogram. a N-Stoff was never used in war. [18] [19]


ClF3 is a very strong oxidizer and fluorinating agent. It is extremely reactive with most inorganic and organic materials, and will combust many otherwise non-flammable materials without any ignition source. These reactions are often violent, and in some cases explosive, especially with flammable materials. Steel, copper, and nickel are not consumed because a passivation layer of insoluble metal fluoride will form which prevents further corrosion, but molybdenum, tungsten, and titanium are unsuitable as the fluorides that they form are volatile. Any equipment that comes into contact with ClF3 must be meticulously cleaned and then passivated, because any contamination left may burn through the unfluorinated material faster than it can re-form. ClF3 will quickly corrode even noble metals like iridium, platinum, or gold, oxidizing them to chlorides and fluorides.

This oxidizing power, surpassing that of oxygen, causes ClF3 to react vigorously with many other materials often thought of as incombustible and refractory. It is known to ignite sand, asbestos, glass, and even ashes of substances that have already burned in oxygen. In one particular industrial accident, a spill of 900 kg of ClF3 burned through 30 cm of concrete and 90 cm of gravel beneath. [20] [17] There is exactly one known fire control/suppression method capable of dealing with ClF3 – the use of nitrogen and noble gases: the surrounding area must be flooded with nitrogen or argon. Barring that, the area must simply be kept cool until the reaction ceases. [21] The compound reacts with water-based suppressors and CO2, rendering them ineffective. [22]

Exposure to larger amounts of ClF3, as a liquid or as a gas, ignites living tissue, resulting in severe chemical and thermal burns. ClF3 reacts violently with water and exposure to the reaction also results in burns. The products of hydrolysis are mainly hydrofluoric acid and hydrochloric acid, which are usually released as steam or vapor due to the highly exothermic nature of the reaction.

See also


^a Using data from Economic History Services and The Inflation Calculator, we can calculate that 100 Reichsmark in 1941 is approximately equivalent to $4,652.50 USD in 2021. Reichsmark exchange rate values from 1942 to 1944 are fragmentary.

Related Research Articles

<span class="mw-page-title-main">Chlorine</span> Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine. On several scales other than the revised Pauling scale, nitrogen's electronegativity is also listed as greater than chlorine's, such as on the Allen, Allred-Rochow, Martynov-Batsanov, Mulliken-Jaffe, Nagle, and Noorizadeh-Shakerzadeh electronegativity scales.

In chemistry, an interhalogen compound is a molecule which contains two or more different halogen atoms and no atoms of elements from any other group.

<span class="mw-page-title-main">Oxygen difluoride</span> Chemical compound

Oxygen difluoride is a chemical compound with the formula OF2. As predicted by VSEPR theory, the molecule adopts a "bent" molecular geometry similar to that of water. However, it has very different properties, being a strong oxidizer.

<span class="mw-page-title-main">Oxygen fluoride</span> Any binary compound of oxygen and fluorine

Oxygen fluorides are compounds of elements oxygen and fluorine with the general formula OnF2, where n = 1 to 6. Many different oxygen fluorides are known:

<span class="mw-page-title-main">Chlorine pentafluoride</span> Chemical compound

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 structure with C4v symmetry, as confirmed by its high-resolution 19F NMR spectrum. It was first synthesized in 1963.

<span class="mw-page-title-main">Nickel(II) fluoride</span> Chemical compound

Nickel(II) fluoride is the chemical compound with the formula NiF2. It is an ionic compound of nickel and fluorine and forms yellowish to green tetragonal crystals. Unlike many fluorides, NiF2 is stable in air.

Dioxygen difluoride is a compound of fluorine and oxygen with the molecular formula O2F2. It can exist as an orange-colored solid which melts into a red liquid at −163 °C (110 K). It is an extremely strong oxidant and decomposes into oxygen and fluorine even at −160 °C (113 K) at a rate of 4% per dayits lifetime at room temperature is thus extremely short. Dioxygen difluoride reacts vigorously with nearly every chemical it encounters (including ordinary ice) leading to its onomatopoeic nickname "FOOF" (a play on its chemical structure and its explosive tendencies).

<span class="mw-page-title-main">Bromine pentafluoride</span> Chemical compound

Bromine pentafluoride, BrF5, is an interhalogen compound and a fluoride of bromine. It is a strong fluorinating agent.

<span class="mw-page-title-main">Cobalt(III) fluoride</span> Chemical compound

Cobalt(III) fluoride is the inorganic compound with the formula CoF3. Hydrates are also known. The anhydrous compound is a hygroscopic brown solid. It is used to synthesize organofluorine compounds.

<span class="mw-page-title-main">Silver(II) fluoride</span> Chemical compound

Silver(II) fluoride is a chemical compound with the formula AgF2. It is a rare example of a silver(II) compound. Silver usually exists in its +1 oxidation state. It is used as a fluorinating agent.

Antimony pentafluoride is the inorganic compound with the formula SbF5. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, formed when mixing liquid HF with liquid SbF5 in a 2:1 ratio. It is notable for its Lewis acidity and its ability to react with almost all known compounds.

<span class="mw-page-title-main">Sulfur tetrafluoride</span> Chemical compound

Sulfur tetrafluoride is the chemical compound with the formula SF4. It is a colorless corrosive gas that releases dangerous HF upon exposure to water or moisture. Despite these unwelcome characteristics, this compound is a useful reagent for the preparation of organofluorine compounds, some of which are important in the pharmaceutical and specialty chemical industries.

<span class="mw-page-title-main">Aluminium fluoride</span> Chemical compound

Aluminium fluoride refers to inorganic compounds with the formula AlF3·xH2O. They are all colorless solids. Anhydrous AlF3 is used in the production of aluminium metal. Several occur as minerals.

Perchloryl fluoride is a reactive gas with the chemical formula ClO
. It has a characteristic sweet odor that resembles gasoline and kerosene. It is toxic and is a powerful oxidizing and fluorinating agent. It is the acid fluoride of perchloric acid.

Antimony trifluoride is the inorganic compound with the formula SbF3. Sometimes called Swarts' reagent, is one of two principal fluorides of antimony, the other being SbF5. It appears as a white solid. As well as some industrial applications, it is used as a reagent in inorganic and organofluorine chemistry.

Boron monofluoride or fluoroborylene is a chemical compound with formula BF, one atom of boron and one of fluorine. It was discovered as an unstable gas and only in 2009 found to be a stable ligand combining with transition metals, in the same way as carbon monoxide. It is a subhalide, containing fewer than the normal number of fluorine atoms, compared with boron trifluoride. It can also be called a borylene, as it contains boron with two unshared electrons. BF is isoelectronic with carbon monoxide and dinitrogen; each molecule has 14 electrons.

Chromium pentafluoride is the inorganic compound with the chemical formula CrF5. It is a red volatile solid that melts at 34 °C. It is the highest known chromium fluoride, since the hypothetical chromium hexafluoride has not yet been synthesized.

Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.

<span class="mw-page-title-main">Chlorine trifluoride oxide</span> Chemical compound

Chlorine oxide trifluoride or chlorine trifluoride oxide is a corrosive liquid molecular compound with formula ClOF3. It was developed secretly as a rocket fuel oxidiser.

Tetraoxygen difluoride is an inorganic chemical compound of oxygen, belonging to the family of oxygen fluorides. It consists of two O2F units bound together with a weak O-O bond, and is the dimer of the O2F radical.


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Further reading