1,2-Difluoroethane

1,2-Difluoroethane is a saturated hydrofluorocarbon containing an atom of fluorine attached to each of two carbons atoms. The formula can be written CH2FCH2F. It is an isomer of 1,1-Difluoroethane. It has a HFC name of HFC-152 with no letter suffix.[3] When cooled to cryogenic temperatures it can have different conformers, gauche and trans.[4] In the liquid form these are about equally abundant and easily interconvert. As a gas it is mostly the gauche form.[5]

1,2-Difluoroethane
Names
IUPAC name
1,2-difluoroethane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.259.147
EC Number
  • 200-866-1
UNII
Properties
C2H4F2
Molar mass 66.051 g·mol−1
Appearance colourless liquid
Density 0.913
Melting point −104 °C; −155 °F; 169 K [2]
Boiling point 30.7 °C (87.3 °F; 303.8 K)
2.31 g/L
Solubility ether, benzene, chloroform
log P 1.21
1.28 (liquid)
Structure
monoclinic
C2/c
a = 7.775, b = 4.4973, c = 9.024
α = 90°, β = 101.73°, γ = 90°
density 1.420
308.9
4
Structure
Orthorhombic
P212121
a = 8.047, b = 4.5086, c = 8.279
α = 90°, β = 101.73°, γ = 90°
density 1.461
300.4
4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is YN ?)
Infobox references

In the HFC-152 designation, 2 means two fluorine atoms, 5 means 5-1 or four hydrogen atoms, and 1 means 1+1 or two carbon atoms.[6]

Formation

Ethylene reacts explosively with fluorine yielding a mixture of 1,2-difluoroethane and vinyl fluoride. With solid fluorine it will react when triggered by near-infrared radiation.[7]

Properties
The F-C-C-F dihedral angle in 1,2-difluoroethane is 68° in the crystal structure.[8]

Critical temperature is 107.5 °C.[2]

If a C-H bond is over excited with too much vibration, the intramolecular vibrational relaxation takes 490 picoseconds.[9]

The F-C-C-F dihedral angle is about 72°.[10] Natural bond orbital deletion bond calculations show that 1,2-difluoroethane prefers the gauche conformation due to hyperconjugation effects. The cis C-H bonds and the C-F σ* interactions are significant. The dihedral angle of about 72ᵒ is a result of decreasing hyper conjugative stability and decreasing steric destabilization.[11]

Reactions

CH2FCH2F reacts with chlorine when treated with light. Two products are formed CH2FCCl2F and CHClFCHClF. The proportions of each depends on the solvent.[3]

Uses

1,2-Difluoroethane is primarily used in Refrigerants, 39%; foam blowing agents, 17%; solvents, 14%; fluoropolymers, 14%; sterilant gas, 2%; aerosol propellants, 2%; food freezant, 1%; other, 8%; exports, 3%.[12]

Safety

1,2-Difluoroethane is toxic when inhaled or when it comes into direct contact with the skin. Fluorocarbons are 4 to 5 times heavier than air, so it tends to concentrate in low-lying areas. This increases the risk of inhalation. 1,2-difluoroethane is toxic to humans through several mechanisms. First, because it has a high density, it can displace oxygen in the lungs causing suffocation. In addition, inhaled fluorocarbons causes the myocardium to become more sensitive to catecholamines, which results in deadly cardiac arrhythmias.[13]

When inhaled by rats, 1,2-difluoroethane is converted to fluoroacetate using cytochrome P450 and then to fluorocitrate both toxic. 100 parts per million in the atmosphere was sufficient to poison rats in 30 minutes and to kill them in four hours. 1,2-Difluoroethane is likely to be similarly toxic to humans.[14]

Environmental fate

1,2-Difluoroethane can enter the environment various ways. One way is through volatilization from rivers and lakes. Henry’s Law estimates that the volatilization half life from a model river is about 2.4 hours and 3.2 days from a model lake.[12] When 1,2-difluoroethane is released to the environment, it will end up in the atmosphere. Here it is degraded by reaction with hydroxyl radicals and oxygen.[15]

CH2FCH2F + OH → CH2FCHF + H2O

CH2FCHF + O2 → CH2FCHFO2 peroxy radical

CH2FCHFO2 + NO → CH2FCHFO alkoxy radical

When catalysed by chlorine atoms and oxidised by nitrogen oxides the end product is HCOF which can decompose further to HF and CO.[15]

The halflife in air is between 140 and 180 days.[12]

Control

1,2-Difluoroethane is a greenhouse gas when released to the atmosphere. It has a warming equivalent to 140 times that of carbon dioxide. As such it may be controlled by government regulation. The Australian government classifies 1,2-difluoroethane as an exotic synthetic greenhouse gas.[16]

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References
  1. Change, Intergovernmental Panel on Climate (2005-10-24). Safeguarding the Ozone Layer and the Global Climate System: Special Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. p. 469. ISBN 9780521863360.
  2. Kirk, Raymond E.; Othmer, Donald F.; Grayson, Martin. Kirk-Othmer Encyclopedia of Chemical Technology. 11 (4 ed.). p. 283.
  3. Nappa, Mario J.; Sievert, Allen C. (June 1993). "The chlorination of 1,2-difluoroethane (HFC-152)". Journal of Fluorine Chemistry. 62 (2–3): 111–118. doi:10.1016/S0022-1139(00)80085-8.
  4. Huber-Wälchli, P.; Günthard, Hs.H. (January 1981). "Trapping of unstable conformations from thermal molecular beams in argon matrices: 1,2-difluoroethane and 1,3-butadiene, i.r. spectra and conformer equilibria". Spectrochimica Acta Part A: Molecular Spectroscopy. 37 (5): 285–304. Bibcode:1981AcSpA..37..285H. doi:10.1016/0584-8539(81)80159-6.
  5. Klaboe, Peter; Nielsen, J. Rud (1960). "Infrared and Raman Spectra of Fluorinated Ethanes. XIII. 1,2-Difluoroethane". The Journal of Chemical Physics. 33 (6): 1764. Bibcode:1960JChPh..33.1764K. doi:10.1063/1.1731499.
  6. Kirk, Raymond E.; Othmer, Donald F.; Grayson, Martin. Kirk-Othmer Encyclopedia of Chemical Technology. 11 (4 ed.). p. 282.
  7. Hauge, R. H.; Gransden, S.; Wang, J. L. F.; Margrave, J. L. (November 1979). "Studies of the reactions of molecular fluorine with methane, acetylene, ethylene, allene, and other small hydrocarbons in matrices at low temperatures". Journal of the American Chemical Society. 101 (23): 6950–6954. doi:10.1021/ja00517a027.
  8. Floris Akkerman; Jürgen Buschmann; Dieter Lentz; Peter Luger; Eva Rödel (2003). "Crystal and molecular structure of 1,2-difluoroethane and 1,2-diiodoethane". Journal of Chemical Crystallography. 33 (12): 969–975. doi:10.1023/A:1027494101785. S2CID 94249439.
  9. Bethardy, G.A.; Wang, Xiaouang; Perry, David S. (March 1994). "The role of molecular flexibility in accelerating intramolecular vibrational relaxation". Canadian Journal of Chemistry. 72 (3): 652–659. doi:10.1139/v94-090.
  10. Steven W. Mork; C. Cameron Miller; Laura A. Philips (29 May 1992). "High Resolution Spectroscopy of 1,2-Difluoroethane in a Molecular Beam: A Case Study of Vibrational Mode-Coupling". Office of Naval Research.
  11. Goodman, Lionel; Gu, Hongbing; Pophristic, Vojislava (2005). "Gauche Effect in 1,2-Difluoroethane. Hyperconjugation, Bent Bonds, Steric Repulsion". The Journal of Physical Chemistry A. 109 (6): 1223–1229. Bibcode:2005JPCA..109.1223G. doi:10.1021/jp046290d. PMID 16833433.
  12. "1,2-DIFLUOROETHANE | C2H4F2". pubchem.ncbi.nlm.nih.gov.
  13. https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+6786
  14. KELLER, DOUGLAS A.; ROE, D. CHRISTOPHER; LIEDER, PAUL H. (1996). "Fluoroacetate-Mediated Toxicity of Fluorinated Ethanes" (PDF). Toxicological Sciences. 30 (2): 213–219. doi:10.1093/toxsci/30.2.213. PMID 8812268.
  15. Wallington, Timothy J.; Hurley, Michael D.; Ball, James C.; Ellermann, Thomas; Nielsen, Ole J.; Sehested, Jens (May 1994). "Atmospheric Chemistry of HFC-152: UV Absorption Spectrum of CH2FCFHO2 Radicals, Kinetics of the Reaction CH2FCFHO2 + NO → CH2FCHFO + NO2, and Fate of the Alkoxy Radical CH2FCFHO". The Journal of Physical Chemistry. 98 (21): 5435–5440. Bibcode:1994JPhCh..98.5435W. doi:10.1021/j100072a008.
  16. "Ozone Protection and Synthetic Greenhouse Gas Management Amendment Regulations 2004 (No 1)". 7 September 2004. Retrieved 7 December 2016.
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