(I) From alkanes by free radical halogenation
Free radical chlorination or bromination of alkanes gives a complex
mixture of isomeric mono- and polyhaloalkanes, which is difficult to
The hydroxyl group of an alcohol is replaced by halogen on reaction with
concentrated halogen acids, phosphorus halides or thionyl chloride Thionyl chloride is preferred because in this reaction alkyl halide is formed
along with gases SO2 and HCl The two gaseous products are escapable,
hence, the reaction gives pure alkyl halides The reactions of primary and
secondary alcohols with HCl require the presence of a catalyst, ZnCl2