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Devansh Mathur from smt maniba chunilal patel sanskar vidya bhavan bahruch , asked a question
Subject: Chemistry , asked on 23/3/13

why is pyridine used as a catalyst in the prepn of haloalkanes from alcohols by action of thionyl chloride?


Shubhangini Kumari ,Meritnation Expert added an answer
Answered on 25/3/13

Dear student,

The reaction of thionyl chloride with alcohol in presence / absence of pyridine is called as Darzen's reaction.

Here, the pyridine molecule acts as a catalyst which is used to neutralize the HCl -produced in the reaction.

CH3CH2OH + SOCl2  --(pyridine)-→  CH3CH2Cl + SO2 ↑+ HCl ↑

Here, pyridine acts as neucleophiles because, in the reaction a proton is added to the alcoholic oxygen due to the strong electronegative SOCl2 group,and this proton is removed by the pyridine and   reforms the S=O and also the Cl- ion is removed from SOCl2 .

This  Cl- ion reacts with electrophilic carbon of alcohol and displaces SO2 and releases another Cl- ion which makes the alkyl chloride.

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Priya , From Swami Harsewanand Public School , added an answer
Answered on 23/3/13

 because pyridine helps in creating nucleophile and the reaction of prepn of haloalkanes froms alcohols in nucleophilic substitution reaction.