<P> Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published . </P> <P> The hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer . Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted . Later alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even shorter lifetimes in the lower atmosphere . One of these compounds, HFC - 134a, is now used in place of CFC - 12 in automobile air conditioners . Hydrocarbon refrigerants (a propane / isobutane blend) are also used extensively in mobile air conditioning systems in Australia, the USA and many other countries, as they have excellent thermodynamic properties and perform particularly well in high ambient temperatures . </P> <P> One of the natural refrigerants (along with ammonia and carbon dioxide), hydrocarbons have negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are becoming available in new split system air conditioners . Various other solvents and methods have replaced the use of CFCs in laboratory analytics . </P> <Table> <Tr> <Th_colspan="3"> Applications and replacements for CFCs </Th> </Tr> <Tr> <Th> Application </Th> <Th> Previously used CFC </Th> <Th> Replacement </Th> </Tr> <Tr> <Td> Refrigeration & air - conditioning </Td> <Td> CFC - 12 (CCl F); CFC - 11 (CCl F); CFC - 13 (CClF); HCFC - 22 (CHClF); CFC - 113 (Cl FCCClF); CFC - 114 (CClF CClF); CFC - 115 (CF CClF); </Td> <Td> HFC - 23 (CHF); HFC - 134a (CF CFH); HFC - 507 (a 1: 1 azeotropic mixture of HFC 125 (CF CHF2) and HFC - 143a (CF CH)); HFC 410 (a 1: 1 azeotropic mixture of HFC - 32 (CF H) and HFC - 125 (CF CF H)) </Td> </Tr> <Tr> <Td> Propellants in medicinal aerosols </Td> <Td> CFC - 114 (CClF CClF) </Td> <Td> HFC - 134a (CF CFH); HFC - 227ea (CF CHFCF) </Td> </Tr> <Tr> <Td> Blowing agents for foams </Td> <Td> CFC - 11 (CCl F); CFC 113 (Cl FCCClF); HCFC - 141b (CCl FCH) </Td> <Td> HFC - 245fa (CF CH CHF); HFC - 365 mfc (CF CH CF CH) </Td> </Tr> <Tr> <Td> Solvents, degreasing agents, cleaning agents </Td> <Td> CFC - 11 (CCl F); CFC - 113 (CCl FCClF) </Td> <Td> None </Td> </Tr> </Table>

What chemical reaction is used to create a cfc from an alkane