Chlorine trifluoride

Chlorine trifluoride
Skeletal formula of chlorine trifluoride with some measurements	Spacefill model of chlorine trifluoride
Names
	Systematic IUPAC name Trifluoro-λ3-chlorane (substitutive)
	Other names Chlorotrifluoride
Identifiers
CAS Number	7790-91-2 ;
3D model (JSmol)	Interactive image; Interactive image;
ChEBI	CHEBI:30123 ;
ChemSpider	23039 ;
ECHA InfoCard	100.029.301
EC Number	232-230-4;
Gmelin Reference	1439
MeSH	chlorine+trifluoride
PubChem CID	24637;
RTECS number	FO2800000;
UNII	921841L3N0 ;
UN number	1749
CompTox Dashboard (EPA)	DTXSID90893948 ;
	InChI InChI=1S/ClF3/c2-1(3)4 Key: JOHWNGGYGAVMGU-UHFFFAOYSA-N ; InChI=1/ClF3/c2-1(3)4 Key: JOHWNGGYGAVMGU-UHFFFAOYAB;
	SMILES F[Cl](F)F; [F-].[F-].F[Cl++];
Properties
Chemical formula	ClF3
Molar mass	92.45 g·mol−1
Appearance	Colorless gas or greenish-yellow liquid
Odor	Sweet, pungent, irritating, suffocating
Density	3.779 g/L
Melting point	−76.34 °C (−105.41 °F; 196.81 K)
Boiling point	11.75 °C (53.15 °F; 284.90 K) (decomposes at 180 °C, 356 °F, 453 K)
Solubility in water	Reacts with water
Solubility	Soluble in carbon tetrachloride but explosive in high concentrations. Reacts with hydrogen-containing compounds e.g. hydrogen, methane, benzene, ether, ammonia.
Vapor pressure	175 kPa
Magnetic susceptibility (χ)	−26.5×10−6 cm3/mol
Viscosity	91.82 μPa s
Structure
Molecular shape	T-shaped molecular geometry
Thermochemistry
Heat capacity (C)	63.9 J K−1 mol−1
Std molar; entropy (S⦵298)	281.6 J K−1 mol−1
Std enthalpy of; formation (ΔfH⦵298)	−163.2 kJ mol−1
Gibbs free energy (ΔfG⦵)	−123.0 kJ mol−1
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Very toxic, very corrosive, powerful oxidizer, violent hydrolysis
	GHS labelling:
Pictograms
Signal word	Danger
NFPA 704 (fire diamond)	4 0 4 W; OX
Flash point	Noncombustible
	Lethal dose or concentration (LD, LC):
LC50 (median concentration)	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)
REL (Recommended)	C 0.1 ppm (0.4 mg/m3)
IDLH (Immediate danger)	20 ppm
Safety data sheet (SDS)	[1]
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). verify (what is ?) Infobox references

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]

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 ClF₃‍—‍flooding 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.

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.

References

^ ^a ^b ^c "Chlorine trifluoride". PubChem Compound. National Center for Biotechnology Information. 4 July 2023. Retrieved 8 July 2023.
^ ClF₃/Hydrazine Archived 2007-02-02 at the Wayback Machine at the Encyclopedia Astronautica.
^ ^a ^b ^c ^d ^e ^f NIOSH Pocket Guide to Chemical Hazards. "#0117". National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b ^c Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 4.58. ISBN 978-1-4398-5511-9.
^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 4.132. ISBN 978-1-4398-5511-9.
^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 5.8. ISBN 978-1-4398-5511-9.
^ "Chlorine trifluoride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ Habuka, Hitoshi; Sukenobu, Takahiro; Koda, Hideyuki; Takeuchi, Takashi; Aihara, Masahiko (2004). "Silicon Etch Rate Using Chlorine Trifluoride". Journal of the Electrochemical Society. 151 (11): G783–G787. Bibcode:2004JElS..151G.783H. doi:10.1149/1.1806391. Archived from the original on 2022-01-25. Retrieved 2017-04-11.
^ Xi, Ming et al. (1997) U.S. patent 5,849,092 "Process for chlorine trifluoride chamber cleaning"
^ Board on Environmental Studies and Toxicology, (BEST) (2006). Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 5. Washington D.C.: National Academies Press. p. 40. ISBN 978-0-309-10358-9. (available from National Academies Press Archived 2014-11-07 at the Wayback Machine)
^ Boyce, C. Bradford and Belter, Randolph K. (1998) U.S. patent 6,034,016 "Method for regenerating halogenated Lewis acid catalysts"
^ Otto Ruff, H. Krug (1930). "Über ein neues Chlorfluorid-CIF₃" [A New Chlorofluoride, ClF₃]. Zeitschrift für anorganische und allgemeine Chemie. 190 (1): 270–276. doi:10.1002/zaac.19301900127.
^ ^a ^b ^c Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a11_307. ISBN 3-527-30673-0.
^ Smith, D. F. (1953). "The Microwave Spectrum and Structure of Chlorine Trifluoride". The Journal of Chemical Physics. 21 (4): 609–614. Bibcode:1953JChPh..21..609S. doi:10.1063/1.1698976. hdl:2027/mdp.39015095092865.
^ ^a ^b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 828. ISBN 978-0-08-037941-8.
^ Scheibe, Benjamin; Karttunen, Antti J.; Müller, Ulrich; Kraus, Florian (5 October 2020). "Cs[Cl 3 F 10 ]: A Propeller-Shaped [Cl 3 F 10 ] − Anion in a Peculiar A [5] B [5] Structure Type". Angewandte Chemie International Edition. 59 (41): 18116–18119. doi:10.1002/anie.202007019. PMC 7589245. PMID 32608053.
^ ^a ^b Clark, John D. (1972). Ignition! An Informal History of Liquid Rocket Propellants. Rutgers University Press. p. 214. ISBN 978-0-8135-0725-5.
^ Müller, Benno (24 November 2005). "A poisonous present". Nature. Review of: Kampfstoff-Forschung im Nationalsozialismus: Zur Kooperation von Kaiser-Wilhelm-Instituten, Militär und Industrie [Weapons Research in National Socialism] by Florian Schmaltz (Wallstein, 2005, 676 pages). 438 (7067): 427. Bibcode:2005Natur.438..427M. doi:10.1038/438427a.
^ "Germany 2004". www.bunkertours.co.uk. Archived from the original on 2006-06-13. Retrieved 2006-06-13.
^ Safetygram. Air Products
^ "Chlorine Trifluoride Handling Manual". Canoga Park, CA: Rocketdyne. September 1961. p. 24. Archived from the original on 2013-04-08. Retrieved 2012-09-19.
^ Patnaik, Pradyot (2007). A comprehensive guide to the hazardous properties of chemical substances (3rd ed.). Wiley-Interscience. p. 478. ISBN 978-0-471-71458-3.
^ Officer, Lawrence H. (2002), Exchange Rate Between the United States Dollar and Forty Other Countries, 1913–1999, EH.net (Economic History Services), archived from the original on 15 June 2006, retrieved 7 July 2023
^ "The Inflation Calculator". S. Morgan Friedman's 'Webpage': Ceci N'est Pas Une Homepage. Retrieved 7 July 2023.