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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. Fluoroform is also generated biologically in small amounts apparently by decarboxylation of trifluoroacetic acid.[1]
Additional physical properties
[編輯]| 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 density (ρc) | 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 |
Industrial applications
[編輯]CHF3 is used in the semiconductor industry in plasma etching of silicon oxide and silicon nitride.
As a refrigerant, CHF3 is known as R-23 or HFC-23.
HFC-23 is also used as a replacement for Halon 1301[cfc-13b1] in fire suppression systems as a total flooding gaseous fire suppression agent. It is also used as a low temperature refrigerant (replacement for Chlorotrifluoromethane (cfc-13). It is a byproduct of its manufacture. When used as a fire suppressant, the chemical 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.
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. The atmospheric lifetime is 260 years.[2] According to researchers, it is the most abundant of hydrofluorocarbons (HFCs). Its usage has been regulated since December 1997 at Kyoto climate conference.
Chemistry
[編輯]It was first obtained by Meslans in the violent reaction of iodoform with dry silver fluoride in 1894. [3] The reaction was improved by Otto Ruff by substitution of silver fluoride by a mixture of mercury fluoride and calcium fluoride.[4] 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.[5]
Organic chemistry
[編輯]CHF3 is a reagent to generate CF3- reagents by deprotonation. The molecule is weakly acidic with a pKa = 25–28. It is a precursor to CF3Si(CH3)3[6]
See also
[編輯]- Haloalkane
- Halomethane
- Trihalomethane
- Fluoromethane
- Difluoromethane
- Tetrafluoromethane
- Chloroform
- Bromoform
- Iodoform
References
[編輯]- ^ Kirschner, E., Chemical and Engineering News 1994, 8.
- ^ Refrigerant Data Summary. Engineered Systems. 2001, 18: 74–88.
- ^ Meslans M. M. Recherches sur quelques fluorures organiques de la série grasse. Annales de chimie et de physique. 1894, 7 (1): 346–423.
- ^ Henne A. L. Fluoroform. Journal of the American Chemical Society. 1937, 59 (7): 1200–1202. doi:10.1021/ja01286a012.
- ^ Henne A. L. Fluoroform. Journal of the American Chemical Society. 1937, 59 (7): 1200–1202. doi:10.1021/ja01286a012.
- ^ 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
- McBee E. T. Fluorine Chemistry. Industrial & Engineering Chemistry. 1947, 39 (3): 236–237. doi:10.1021/ie50447a002.
- Oram D. E., Sturges W. T., Penkett S. A., McCulloch A., Fraser P. J. Growth of fluoroform (CHF3, HFC-23) in the background atmosphere. Geophysical Research Letters. 1998, 25 (1): 236–237. doi:10.1029/97GL03483.
- McCulloch A. Fluorocarbons in the global environment: a review of the important interactions with atmospheric chemistry and physics. Journal of Fluorine Chemistry. 2003, 123 (1): 21–29. doi:10.1016/S0022-1139(03)00105-2.