Chlorine trifluoride

Last updated
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
Names
Systematic IUPAC name
Trifluoro-λ3-chlorane [1] (substitutive)
Other names
Chlorotrifluoride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.301 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 232-230-4
1439
MeSH chlorine+trifluoride
PubChem CID
RTECS number
  • FO2800000
UNII
UN number 1749
  • InChI=1S/ClF3/c2-1(3)4 Yes check.svgY
    Key: JOHWNGGYGAVMGU-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/ClF3/c2-1(3)4
    Key: JOHWNGGYGAVMGU-UHFFFAOYAB
  • F[Cl](F)F
  • [F-].[F-].F[Cl++]
Properties
ClF3
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 [1]
Solubility Soluble in carbon tetrachloride but explosive in high concentrations. Reacts with hydrogen-containing compounds e.g. hydrogen, methane, benzene, ether, ammonia. [1]
Vapor pressure 175 kPa
−26.5×10−6 cm3/mol [5]
Viscosity 91.82 μPa s
Structure
T-shaped molecular geometry
Thermochemistry [6]
63.9 J K−1 mol−1
Std molar
entropy
(S298)
281.6 J K−1 mol−1
−163.2 kJ mol−1
−123.0 kJ mol−1
Hazards
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
Danger
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazard W+OX: Reacts with water in an unusual or dangerous manner AND is oxidizer
4
0
4
W
OX
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)
[7]
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. It is a colorless, poisonous, corrosive, and extremely reactive gas that condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room temperature). It is famous for its extreme oxidation properties. The compound is primarily of interest in plasmaless cleaning and etching operations in the semiconductor industry, [8] [9] in nuclear reactor fuel processing, [10] historically as a component in rocket fuels, and various other industrial operations owing to its corrosive nature. [11]

Contents

Preparation, structure, and properties

It was first reported in 1930 by Ruff and Krug who prepared it by fluorination of chlorine; this also produced Chlorine monofluoride (ClF) and the mixture was separated by distillation. [12]

3 F2 + Cl2 → 2 ClF3

Several hundred tons are produced annually. [13]

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.

Reactions

ClF3 also reacts explosively with water to give hydrogen fluoride and hydrogen chloride, along with oxygen and oxygen difluoride (OF2): [15]

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

Upon heating, it decomposes: [13]

ClF3 ⇌ ClF + F2

Reactions with many metals and even metal oxides to give fluorides: [15]

NiO + 2/3 ClF3 → NiF2 + 1/2 O2 + 1/3 Cl2
AgCl + ClF3 → AgF2 + ClF + 1/2 Cl2

ClF3 is used to produce uranium hexafluoride:

U + 3 ClF3 → UF6 + 3 ClF

With phosphorus, it yields phosphorus trichloride (PCl3) and phosphorus pentafluoride (PF5), while sulfur yields sulfur dichloride (SCl2) and sulfur tetrafluoride (SF4).

It reacts with caesium fluoride to give a salt containing the anion F(ClF3)3. [16]

Uses

Semiconductor industry

In the semiconductor industry, chlorine trifluoride is used to clean chemical vapour deposition chambers. It can be used to remove semiconductor material from the chamber walls without the need to dismantle the chamber. 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.

Fluorination reagent

ClF3 is used for the fluorination of a variety of compounds. [13]

Military applications (defunct)

Chlorine trifluoride has been investigated as a high-performance storable oxidizer in rocket propellant systems. Handling concerns, however, severely limit its use. The following passage by rocket scientist John D. Clark is widely quoted in descriptions of the substance's extremely hazardous nature:

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 aluminium 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.

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, in addition to 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 Reichsmarks per kilogram. a N-Stoff was never used in war. [18] [19]

Hazards

ClF3 is a very strong oxidizer. 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. Steel, copper, and nickel are not consumed because a passivation layer of metal fluoride will form which prevents further corrosion, but molybdenum, tungsten, and titanium are unsuitable as their fluorides are volatile. 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 ignites 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 ClF3flooding the fire with nitrogen or noble gases such as 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 counterproductive. [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

Explanatory notes

^a Using data from Economic History Services [23] and The Inflation Calculator [24] it can be calculated that the sum of 100 Reichsmarks in 1941 is approximately equivalent to US$4,652.50 in 2021. Reichsmark exchange rate values from 1942 to 1944 are fragmentary.

Related Research Articles

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">Copper(I) chloride</span> Chemical compound

Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear green due to the presence of copper(II) chloride (CuCl2).

<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.

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

Bromine trifluoride is an interhalogen compound with the formula BrF3. At room temperature, it is a straw-coloured liquid with a pungent odor which decomposes violently on contact with water and organic compounds. It is a powerful fluorinating agent and an ionizing inorganic solvent. It is used to produce uranium hexafluoride (UF6) in the processing and reprocessing of nuclear fuel.

<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">Nitrogen trifluoride</span> Chemical compound

Nitrogen trifluoride is an inorganic, colorless, non-flammable, toxic gas with a slightly musty odor. It finds increasing use within the manufacturing of flat-panel displays, photovoltaics, LEDs and other microelectronics. Nitrogen trifluoride is also an extremely strong and long-lived greenhouse gas. Its atmospheric burden exceeded 2 parts per trillion during 2019 and has doubled every five years since the late 20th century.

<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 strong Lewis acid and a component of the superacid fluoroantimonic acid, formed upon mixing liquid HF with liquid SbF5 in 1:1 ratio. It is notable for its strong Lewis acidity and the 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 is an inorganic compound with the formula AlF3. It forms hydrates AlF3·xH2O. Anhydrous AlF3 and its hydrates are all colorless solids. Anhydrous AlF3 is used in the production of aluminium. Several occur as minerals.

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

Selenium tetrafluoride (SeF4) is an inorganic compound. It is a colourless liquid that reacts readily with water. It can be used as a fluorinating reagent in organic syntheses (fluorination of alcohols, carboxylic acids or carbonyl compounds) and has advantages over sulfur tetrafluoride in that milder conditions can be employed and it is a liquid rather than a gas.

Perchloryl fluoride is a reactive gas with the chemical formula ClO
3
F
. 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.

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

Antimony trifluoride is the inorganic compound with the formula SbF3. Sometimes called Swarts' reagent, it 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.

Arsenic trifluoride is a chemical compound of arsenic and fluorine with the chemical formula AsF3. It is a colorless liquid which reacts readily with water.

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">Promethium(III) fluoride</span> Chemical compound

Promethium(III) fluoride or promethium trifluoride is a salt of promethium and fluorine with the formula PmF3.

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

Terbium(IV) fluoride is an inorganic compound with a chemical formula TbF4. It is a white solid that is a strong oxidizer. It is also a strong fluorinating agent, emitting relatively pure atomic fluorine when heated, rather than the mixture of fluoride vapors emitted from cobalt(III) fluoride or cerium(IV) fluoride. It can be produced by the reaction between very pure terbium(III) fluoride and xenon difluoride, chlorine trifluoride or fluorine gas:

References

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Further reading