Chemistry:Hydrofluorocarbon
Hydrofluorocarbons (HFCs) are man-made organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air conditioning and as refrigerants; R-134a (1,1,1,2-tetrafluoroethane) is one of the most commonly used HFC refrigerants. In order to aid the recovery of the stratospheric ozone layer, HFCs were adopted to replace the more potent chlorofluorocarbons (CFCs), which were phased out from use by the Montreal Protocol, and hydrochlorofluorocarbons (HCFCs) which are presently being phased out.[1] HFCs replaced older chlorofluorocarbons such as R-12 and hydrochlorofluorocarbons such as R-21.[2] HFCs are also used in insulating foams, aerosol propellants, as solvents and for fire protection.
They may not harm the ozone layer as much as the compounds they replace, but they still contribute to global warming --- with some like trifluoromethane having 11,700 times the warming potential of carbon dioxide.[3] Their atmospheric concentrations and contribution to anthropogenic greenhouse gas emissions are rapidly increasing[quantify], causing international concern about their radiative forcing.
Chemistry
Fluorocarbons with few C–F bonds behave similarly to the parent hydrocarbons, but their reactivity can be altered significantly. For example, both uracil and 5-fluorouracil are colourless, high-melting crystalline solids, but the latter is a potent anti-cancer drug. The use of the C-F bond in pharmaceuticals is predicated on this altered reactivity.[4] Several drugs and agrochemicals contain only one fluorine center or one trifluoromethyl group.
Environmental regulation
Unlike other greenhouse gases in the Paris Agreement, hydrofluorocarbons are included in other international negotiations.[5]
In September 2016, the New York Declaration on Forests urged a global reduction in the use of HFCs.[6] On 15 October 2016, due to these chemicals' contribution to climate change, negotiators from 197 nations meeting at a summit of the United Nations Environment Programme in Kigali, Rwanda reached a legally-binding accord (the Kigali Amendment) to phase down hydrofluorocarbons (HFCs) in an amendment to the Montreal Protocol.[7][8][9] As of February 2020, 16 U.S. states ban or are phasing down HFCs.[10]
COVID-19 relief legislation, which included a measure that would require chemical manufacturers to phase down the production and use of HFCs, was passed by the United States House of Representatives and United States Senate on December 21, 2020.[11] The U.S. Environmental Protection Agency signed a final rule phasing down HFCs on 23 September, 2021.[12]
See also
- Greenhouse gas § Sources - comparative chart
References
- ↑ Zaelke, Durwood; Borgford-Parnell, Nathan; Andersen., Stephen (11 January 2018). Primer on HFCs. Kristin Campbell, Xiaopu Sun, Dennis Clare,Claire Phillips, Stela Herschmann, Yuzhe PengLing, Alex Milgroom, Nancy J. Sherman.. Institute for Governance & Sustainable Development (IGSD). pp. 5. http://www.igsd.org/wp-content/uploads/2018/01/HFC-Primer-v11Jan18.pdf.
- ↑ Milman, Oliver (22 September 2016). "100 countries push to phase out potentially disastrous greenhouse gas". The Guardian (London, UK). https://www.theguardian.com/environment/2016/sep/22/100-countries-phase-out-hydrofluorocarbons-greenhouse-gas.
- ↑ 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. https://www.sciencedirect.com/science/article/abs/pii/S0022113912001315.
- ↑ G. Siegemund, W. Schwertfeger, A. Feiring, B. Smart, F. Behr, H. Vogel, B. McKusick "Fluorine Compounds, Organic" in "Ullmann's Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_349
- ↑ Davenport, Carol (23 July 2016). "A Sequel to the Paris Climate Accord Takes Shape in Vienna". New York Times. https://www.nytimes.com/2016/07/24/world/europe/vienna-sequel-paris-climate-accord.html.
- ↑ "The New York Declaration of the Coalition to Secure an Ambitious HFC Amendment". Washington, DC: US Department of State. 22 September 2016. https://2009-2017.state.gov/e/oes/rls/pr/2016/262236.htm.
- ↑ Johnston, Chris; Milman, Oliver; Vidal, John (15 October 2016). "Climate change: global deal reached to limit use of hydrofluorocarbons". https://www.theguardian.com/environment/2016/oct/15/climate-change-environmentalists-hail-deal-to-limit-use-of-hydrofluorocarbons.
- ↑ "Climate change: 'Monumental' deal to cut HFCs, fastest growing greenhouse gases". BBC News. 15 October 2016. https://www.bbc.co.uk/news/science-environment-37665529.
- ↑ "Nations, Fighting Powerful Refrigerant That Warms Planet, Reach Landmark Deal". New York Times. 15 October 2016. https://www.nytimes.com/2016/10/15/world/africa/kigali-deal-hfc-air-conditioners.html.
- ↑ Baker Administration Planning Rule To Ban Hydrofluorocarbons
- ↑ Davenport, Coral (2020-12-22). "Congress included climate change legislation in its coronavirus relief deal." (in en-US). The New York Times. ISSN 0362-4331. https://www.nytimes.com/2020/12/22/us/congress-included-climate-change-legislation-in-its-coronavirus-relief-deal.html.
- ↑ Volcovici, Valerie (2021-09-23). "Biden administration takes aim at climate warming gas". Yahoo! News. https://news.yahoo.com/biden-administration-takes-aim-climate-092027109.html.
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