Perhalogen-2-azapropenes such as perfluoro-2-azapropene and the novel compounds monofluorodichlormethyl isocyanide dichloride and difluoromonochloromethyl isocyanide dichloride are prepared by reacting trichloromethyl isocyanide dichloride with sodium fluoride in an organic solvent at a temperature of from 80* to 220*C. At least 5 moles of sodium fluoride are used to produce the perfluoro compound and no more than 5 moles are used to produce the novel isocyanide dichloride compounds.