Fluoroform

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Fluoroform
Fluoroform.svg Fluoroform-3D-vdW.png
Identifiers
CAS number 75-46-7 YesY
PubChem 6373
ChemSpider 21106179 YesY
UNII ZJ51L9A260 YesY
EC number 200-872-4
ChEBI CHEBI:24073 N
RTECS number PB6900000
Jmol-3D images Image 1
Properties
Molecular 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 (117.95 K)
Boiling point -82.1°C (191.05 K)
Solubility in water 1 g/l
Solubility in organic solvents Soluble
Vapor pressure 4.38 MPa at 20 °C
kH 0.013 mol.kg-1.bar-1
Acidity (pKa) 25 - 28
Hazards
S-phrases S38
Main hazards Nervous system depression
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/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[edit]

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[edit]

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[edit]

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

Greenhouse gas[edit]

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[edit]

  1. ^ Kirschner, E., Chemical and Engineering News 1994, 8.
  2. ^ Meslans M. M. (1894). "Recherches sur quelques fluorures organiques de la série grasse". Annales de chimie et de physique 7 (1): 346–423. 
  3. ^ a b Henne A. L. (1937). "Fluoroform". Journal of the American Chemical Society 59 (7): 1200–1202. doi:10.1021/ja01286a012. 
  4. ^ Rozen, S.; Hagooly, A. "Fluoroform" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi: 10.1002/047084289
  5. ^ a b 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 and 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". 
  6. ^ http://unfccc.int/di/FlexibleQueries.do
  7. ^ http://ozone.unep.org/Data_Reporting/Data_Access/
  8. ^ Profits on Carbon Credits Drive Output of a Harmful Gas August 8, 2012 New York Times
  9. ^ Subsidies for a Global Warming Gas

Literature[edit]

External links[edit]

Additional physical properties[edit]

Property Value
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 moment 1.649 D
Critical pressure (pc) 4.816 MPa (48.16 bar)
Critical temperature (Tc) 25.7 °C (299 K)
Critical densityc) 7.52 mol/l
Compressibility factor (Z) 0.9913
Acentric factor (ω) 0.26414
Viscosity (η) at 25 °C 14.4 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