Freons (CFC)

Chlorofluoro derivatives of methane and ethane are called Freons (chlorofluorocarbons, CFCs), named Freon-cba where c = (number of carbon atoms - 1), b = (number of hydrogen atoms + 1), a = total number of fluorine atoms, e.g. CFCl3 (c=0, b=1, a=1) is Freon-11; CF2Cl2 (c=0, b=1, a=2) is Freon-12; C2F2Cl4 (c=1, b=1, a=2) is Freon-112; C2F3Cl3 (c=1, b=1, a=3) is Freon-113. Freon-12 is manufactured by treating carbon tetrachloride with hydrogen fluoride over a catalytic amount of antimony pentachloride (SbCl5): CCl4 + 2 HF gives CCl2F2 + 2 HCl -- this halogen-exchange step is itself called the Swarts reaction (the same named reaction as section 14.3.3, applied here to CCl4 rather than a simple haloalkane). Physical properties: Freons are highly stable, unreactive, non-corrosive, non-toxic, easily liquefiable gases. Uses: (i) as refrigerants in refriger …