Question -The thionyl chloride method is preferred over hydrogen chloride or phosphorous chloride method for the preparation of haloalkanes because both the by-products (SO2 and HCl) in this case are gases and escape leaving behind pure chloroalkane. This reaction takes place in the presence of
Options:
A .  Conc. sulphuric acid
B .  Phosphoric acid
C .  Anhydrous zinc chloride
D .  Pyridine
Answer: Option D : D Pyridine molecule act as a catalyst which is used to neutralise HCl formed.Pyridine also acts as a nucleophile because in the reaction proton is added to alcoholic O due to strong electronegative SOCl2 group and proton is removed by pyridine and reforms S=O and Cl- is removed from SOCl2.This Cl- ion reacts with electrophilic C atom of alcohol and displaces SO2 and another releases another Cl- Ion which makes alkyl chloride.
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