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 With tertiary alcohols, the reaction is conducted by simply shaking the
alcohol with concentrated HCl at room temperature