Fluoroform

Fluoroform

Names
IUPAC name Trifluoromethane
Other names Fluoroform, Carbon trifluoride, Methyl trifluoride, Fluoryl, Freon 23, Arcton 1, HFC 23, R-23, FE-13, UN 1984
Identifiers
CAS Registry Number	75-46-7 Y
ChEBI	CHEBI:24073 N
ChemSpider	21106179 Y
EC number	200-872-4
InChI InChI=1S/CHF3/c2-1(3)4/h1H Y Key: XPDWGBQVDMORPB-UHFFFAOYSA-N Y InChI=1/CHF3/c2-1(3)4/h1H Key: XPDWGBQVDMORPB-UHFFFAOYAM
Jmol-3D images	Image
PubChem	6373
RTECS number	PB6900000
SMILES FC(F)F
UNII	ZJ51L9A260 Y
Properties
Chemical formula	CHF3
Molar mass	70.01 g/mol
Appearance	Colorless gas
Density	2.946 kg·m−3 (gas, 1 bar, 15 °C)
Melting point	−155.2 °C (−247.4 °F; 118.0 K)
Boiling point	−82.1 °C (−115.8 °F; 191.1 K)
Solubility in water	1 g/l
Solubility in organic solvents	Soluble
Vapor pressure	4.38 MPa at 20 °C
Henry's law constant (kH)	0.013 mol.kg−1.bar−1
Acidity (pKa)	25 - 28
Structure
Molecular shape	Tetrahedral
Hazards
Main hazards	Nervous system depression
S-phrases	S38
NFPA 704	0 2 0
Flash point	Non-flammable
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
Infobox references

Fluoroform is the chemical compound with the formula CHF₃. It is one of the "haloforms", a class of compounds with the formula CHX₃ (X = halogen). Fluoroform is used in diverse niche applications and is produced as a by-product of the manufacture of Teflon. It is also generated biologically in small amounts apparently by decarboxylation of trifluoroacetic acid.^[1]

Synthesis

Fluoroform was first obtained by Maurice Meslans in the violent reaction of iodoform with dry silver fluoride in 1894.^[2] The reaction was improved by Otto Ruff by substitution of silver fluoride by a mixture of mercury fluoride and calcium fluoride.^[3] The exchange reaction works with iodoform and bromoform, and the exchange of the first two halogen atoms by fluorine is vigorous. By changing to a two step process, first forming a bromodifluoro methane in the reaction of antimony trifluoride with bromoform and finishing the reaction with mercury fluoride the first efficient synthesis method was found by Henne.^[3]

Industrial applications

CHF₃ is used in the semiconductor industry in plasma etching of silicon oxide and silicon nitride. Known as R-23 or HFC-23, it is also a useful refrigerant, sometimes as a replacement for chlorotrifluoromethane (cfc-13) and is a byproduct of its manufacture.

When used as a fire suppressant, the fluoroform carries the DuPont trade name, FE-13. CHF₃ is recommended for this application because of its low toxicity, its low reactivity, and its high density. HFC-23 has been used in the past as a replacement for Halon 1301[cfc-13b1] in fire suppression systems as a total flooding gaseous fire suppression agent.

Organic chemistry

CHF₃ is a reagent to generate sources of "CF₃⁻" by deprotonation. The molecule is weakly acidic with a pK_a = 25–28. It is a precursor to CF₃Si(CH₃)₃^[4]

Greenhouse gas

CHF₃ is a potent greenhouse gas. The secretariat of the Clean Development Mechanism estimates that a ton of HFC-23 in the atmosphere has the same effect as 11,700 tons of carbon dioxide. More recent work (IPCC, 2007) suggests that this equivalency, also called a 100-yr global warming potential, is slightly larger at 14,800 for HFC-23.^[5] The atmospheric lifetime is 270 years.^[5]

According to the 2007 IPCC climate report, HFC-23 was the most abundant HFC in the global atmosphere until around 2001, which is when the global mean concentration of HFC-134a (1,1,1,2-tetrafluoroethane), the chemical now used extensively in automobile air conditioners, surpassed those of HFC-23. Global emissions of HFC-23 have in the past been dominated by the inadvertent production and release during the manufacture of the refrigerant HCFC-22 (chlorodifluoromethane).

Data reported to the United Nations Framework Convention on Climate Change (UNFCCC) greenhouse gas emissions databases ^[6] indicate substantial decreases in developed or Annex 1 countries HFC-23 emissions from the 1990s to the 2000s (UNFCCC greenhouse gas emissions databases). The UNFCCC Clean Development Mechanism projects have provided funding and facilitated the destruction of HFC-23 co-produced from a portion of HCFC-22 produced in developing or non-Annex 1 countries since 2003. Developing countries have become the largest producers of HCFC-22 in recent years according to data compiled by the Ozone Secretariat of the World Meteorological Organization.^[7][8][9] Emissions of all HFCs are included in the UNFCCCs Kyoto Protocol. To mitigate its impact, CHF₃ can be destroyed with electric plasma arc technologies or by high temperature incineration.

References

Literature

• McBee E. T. (1947). "Fluorine Chemistry". Industrial & Engineering Chemistry 39 (3): 236–237. doi:10.1021/ie50447a002. 
• Oram D. E., Sturges W. T., Penkett S. A., McCulloch A., Fraser P. J. (1998). "Growth of fluoroform (CHF₃, HFC-23) in the background atmosphere". Geophysical Research Letters 25 (1): 236–237. Bibcode:1998GeoRL..25...35O. doi:10.1029/97GL03483. 
• McCulloch A. (2003). "Fluorocarbons in the global environment: a review of the important interactions with atmospheric chemistry and physics". Journal of Fluorine Chemistry 123 (1): 21–29. doi:10.1016/S0022-1139(03)00105-2. 

External links

• International Chemical Safety Card 0577
• MSDS at Oxford University
• MSDS at mathesontrigas.com
• Coupling of fluoroform with aldehydes using an electrogenerated base

Additional physical properties