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Fluoroform
Verifiedfieldschanged
Watchedfieldschanged
Verifiedrevid461102015
IupacnameTrifluoromethane
OthernamesFluoroform, carbon trifluoride,[citation needed] methyl trifluoride, Fluoryl, Freon 23, Arcton 1

Fluoroform, or trifluoromethane, is the chemical compound with the formula CHF3. It is a hydrofluorocarbon as well as being a part of the haloforms, a class of compounds with the formula CHX3 (X = halogen) with C3v symmetry. Fluoroform is used in diverse applications in organic synthesis. It is not an ozone depleter but is a greenhouse gas.[1]

Synthesis

About 20 million kg per year are produced industrially as both a by-product of and precursor to the manufacture of Teflon.[1] It is produced by reaction of chloroform with HF:[2]

CHCl3 + 3 HF → CHF3 + 3 HCl

It is also generated biologically in small amounts apparently by decarboxylation of trifluoroacetic acid.[3]

Historical

Fluoroform was first obtained by Maurice Meslans in the violent reaction of iodoform with dry silver fluoride in 1894.[4] The reaction was improved by Otto Ruff by substitution of silver fluoride by a mixture of mercury fluoride and calcium fluoride.[5] 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 bromodifluoromethane in the reaction of antimony trifluoride with bromoform and finishing the reaction with mercury fluoride the first efficient synthesis method was found by Henne.[5]

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 was 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

Fluoroform is weakly acidic with a pKa = 25–28 and quite inert. Attempted deprotonation results in defluorination to generate F− and difluorocarbene (CF2). Some organocopper and organocadmium compounds have been developed as trifluoromethylation reagents.[6]

Fluoroform is a precursor of the Ruppert-Prakash reagent CF3Si(CH3)3, which is a source of the nucleophilic CF3− anion.[7][8]

Greenhouse gas

CHF3 is a potent greenhouse gas. A ton of HFC-23 in the atmosphere has the same effect as 11,700 tons of carbon dioxide. This equivalency, also called a 100-yr global warming potential, is slightly larger at 14,800 for HFC-23.[9] The atmospheric lifetime is 270 years.[9]

HFC-23 was the most abundant HFC in the global atmosphere until around 2001, 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).

Substantial decreases in HFC-23 emissions by developed countries were reported from the 1990s to the 2000s: from 6-8 Gg/yr in the 1990s to 2.8 Gg/yr in 2007.[10]

However, research in 2024 strongly indicates that the HFC-23 emission decrease is much less than has been reported and does not meet the internationally agreed Kigali Amendment of 2020.[11][12]

The UNFCCC Clean Development Mechanism provided funding and facilitated the destruction of HFC-23.

Developing countries have become the largest producers of HCFC-23 in recent years according to data compiled by the Ozone Secretariat of the World Meteorological Organization.[13][14][15] 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.[16]

Additional physical properties

PropertyValue
Density (ρ) at -100 °C (liquid)1.52 g/cm3
Density (ρ) at -82.1 °C (liquid)1.431 g/cm3
Density (ρ) at -82.1 °C (gas)4.57 kg/m3
Density (ρ) at 0 °C (gas)2.86 kg/m3
Density (ρ) at 15 °C (gas)2.99 kg/m3
Dipole moment1.649 D
Critical pressure (pc)4.816 MPa (48.16 bar)
Critical temperature (Tc)25.7 °C (299 K)
Critical density (ρc)7.52 mol/l
Compressibility factor (Z)0.9913
Acentric factor (ω)0.26414
Viscosity (η) at 25 °C14.4 μPa.s (0.0144 cP)
Molar specific heat at constant volume (CV)51.577 J.mol−1.K−1
Latent heat of vaporization (lb)257.91 kJ.kg−1

References

  1. ^ ShivaKumar Kyasa (2015). "Fluoroform (CHF3)". Synlett. 26 (13): 1911–1912. doi:10.1055/s-0034-1380924
  2. ^
  3. ^ Kirschner, E., Chemical and Engineering News 1994, 8.
  4. ^ Meslans M. M. (1894). "Recherches sur quelques fluorures organiques de la série grasse". Annales de chimie et de physique. 7 (1): 346–423.
  5. ^ Henne A. L. (1937). "Fluoroform". Journal of the American Chemical Society. 59 (7): 1200–1202. Bibcode:1937JAChS..59.1200H. doi:10.1021/ja01286a012
  6. ^ Zanardi, Alessandro; Novikov, Maxim A.; Martin, Eddy; Benet-Buchholz, Jordi; Grushin, Vladimir V. (2011-12-28). "Direct Cupration of Fluoroform". Journal of the American Chemical Society. 133 (51): 20901–20913. Bibcode:2011JAChS.13320901Z. doi:10.1021/ja2081026. ISSN 0002-7863. PMID 22136628
  7. ^ Rozen, S.; Hagooly, A. "Fluoroform" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.rn00522
  8. ^ Prakash, G. K. Surya; Jog, Parag V.; Batamack, Patrice T. D.; Olah, George A. (2012-12-07). "Taming of Fluoroform: Direct Nucleophilic Trifluoromethylation of Si, B, S, and C Centers". Science. 338 (6112): 1324–1327. Bibcode:2012Sci...338.1324P. doi:10.1126/science.1227859. ISSN 0036-8075. PMID 23224551. S2CID 206544170
  9. ^ Forster, P.; V. Ramaswamy; P. Artaxo; T. Berntsen; R. Betts; D.W. Fahey; J. Haywood; J. Lean; D.C. Lowe; G. Myhre; J. Nganga; R. Prinn; G. Raga; M. Schulz; & R. Van Dorland (2007). Changes in Atmospheric Constituents and in Radiative Forcing.. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.
  10. ^ Montzka, S. A.; Kuijpers, L.; Battle, M. O.; Aydin, M.; Verhulst, K. R.; Saltzman, E. S.; Fahey, D. W. (2010). "Recent increases in global HFC-23 emissions". Geophysical Research Letters. 37 (2): n/a. Bibcode:2010GeoRL..37.2808M. doi:10.1029/2009GL041195. S2CID 13583576
  11. ^ Cuff, Madeleine (3 Jan 2025). "Global treaty is failing to curb ultra-potent greenhouse gas emissions". New Scientist. Retrieved 2025-01-03.
  12. ^ Adam, Ben; Western, Luke M.; Mühle, Jens; Choi, Haklim; Krummel, Paul B.; O’Doherty, Simon; Young, Dickon; Stanley, Kieran M.; Fraser, Paul J.; Harth, Christina M.; Salameh, Peter K.; Weiss, Ray F.; Prinn, Ronald G.; Kim, Jooil; Park, Hyeri (2024-12-21). "Emissions of HFC-23 do not reflect commitments made under the Kigali Amendment". Communications Earth & Environment. 5 (1): 1–8. Bibcode:2024ComEE...5..783A. doi:10.1038/s43247-024-01946-y. ISSN 2662-4435. PMC 11663144. PMID 39717369
  13. ^ "Data Access Centre". Archived from the original on 2011-07-21. Retrieved 2010-04-03.
  14. ^ Profits on Carbon Credits Drive Output of a Harmful Gas August 8, 2012 New York Times
  15. ^ Subsidies for a Global Warming Gas
  16. ^ Han, Wenfeng; Li, Ying; Tang, Haodong; Liu, Huazhang (2012). "Treatment of the potent greenhouse gas, CHF3. An overview". Journal of Fluorine Chemistry. 140: 7–16. doi:10.1016/j.jfluchem.2012.04.012

Literature