What is the purpose of ZnCl2 (catalyst) in the preparation of alkyl halides from alcohols?
HCl is less reactive with alcohols since the bond between H and Cl is stronger than HBr and HI due to small size of HCl. Hence its reaction with alcohols needs a catalyst ZnCl2, that helps in providing a Cl- ion for substitution.
The reaction between alcohols and HCl is a substitution reaction in which the chlorine replaces the hydroxyl group. The zinc ion complexes with the hydroxyl group by accepting a lone pair of electron from O of -OH, which makes it a better leaving group. The chloride ion then attacks the remaining carbonium ion to form an alkyl halide.
The reaction between alcohols and HCl is a substitution reaction in which the chlorine replaces the hydroxyl group. The zinc ion complexes with the hydroxyl group by accepting a lone pair of electron from O of -OH, which makes it a better leaving group. The chloride ion then attacks the remaining carbonium ion to form an alkyl halide.