of chlorodifluoromethane or bromodifluoromethane using alkoxides or alkyllithium also produces difluorocarbene: A variant of this reaction is using ethylene oxide in conjunction with a catalytic amount of quaternary ammonium halide at elevated temperature. In equilibrium a small amount of β-haloalkoxide is present that acts as a base. This avoids an excess concentration of base that will destroy the carbene just formed. Thermolysis of hexafluoropropylenoxide at 190 °C gives difluorocarbene and trifluoroacetyl fluoride. This is an attractive method for the synthesis of difluorocyclopropanes as hexafluoropropylenoxide is inexpensive and the byproduct trifluoroacetyl fluoride is a gas. Application The thermolysis of chlorodifluomethane between 600 and 800 °C gives 1,1,2,2-tetrafluoroethylene (TFE). The required is generated by fluorination of chloroform. TFE, tetrafluoroethylene , is also produced by dehalogenation of bromofluoro-, or iodofluoroalkanes with zinc and alcohol, by dehydrohalogenation of hydrogen-containing haloalkenes with alcoholic alkali, or by heating. The industrial annual production of PTFE, generated by polymerization of tetrafluoroethylene (TFE), in 1991 was 9000 tons. Difluorocarbene is used to generate geminal difluorocyclopropanes. See also Dichlorocarbene References Fluorine compounds Carbenes