Fluoroform, or trifluoromethane, is the chemical compound with the formula . It is a hydrofluorocarbon as well as being a part of the haloforms, a class of compounds with the formula (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]
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:
It is also generated biologically in small amounts apparently by decarboxylation of trifluoroacetic acid.[2]
Fluoroform was first obtained by Maurice 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 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.[4]
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. 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.
Fluoroform is weakly acidic with a pKa = 25–28 and quite inert. Attempted deprotonation results in defluorination to generate and difluorocarbene . Some organocopper and organocadmium compounds have been developed as trifluoromethylation reagents.[5]
Fluoroform is a precursor of the Ruppert-Prakash reagent , which is a source of the nucleophilic anion.[6] [7]
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.[8] The atmospheric lifetime is 270 years.[8]
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.[9]
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.[10] [11] [12] Emissions of all HFCs are included in the UNFCCCs Kyoto Protocol. To mitigate its impact, can be destroyed with electric plasma arc technologies or by high temperature incineration.[13]
| 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 |