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why is anhydrous zncl2 is used in lucas reagent?

why is anhydrous zncl2 is used in lucas reagent?

Grade:12

5 Answers

Akshay Amol Revankar
35 Points
7 years ago

HCl is less reactive with alcohols since the bond between H and Cl is a bit stronger than HBr and HI. Hence its reaction with alcohols need a catalyst ZnCl2, which helps in breaking the bond between H and Cl. Sometimes, as with primary alcohols, heating is required to achieve this along with ZnCl2.

Ranjan
11 Points
5 years ago
Why is anhydrous ZnCl2 used in reaction of alcohols with HCl?
The reaction of alcohol with HCl involves a nucleophilic substitution reaction, which results in the formation of chloroalkans. The Cl- is not a good nucleophile and in alcohol —OH- acts a poor leaving group. Reaction with HC1 is thus, carried out in presence of ZnCl2 (Lewis acid). ZnCl2 forms a complex with oxygen of alcohol and converts the      -OH to a much better leaving group thereby giving way to a rapid formation of chioroalkane.
Shubham Gupta
11 Points
4 years ago
So it starts like this.We have to replace -OH group from alcohol by Cl-. That is a type of nucleophilic substitution reaction. Cl- has to replace -OH group.But -OH is a poor leaving group due to the high electronegativity of oxygen & Cl- is a moderate ( not so good ) nucleophile . So, it is slightly difficult.So, we use Lucas Reagent ( ZnCl2 + HCl) . ZnCl2 is a lewis base due to the empty d orbitals of Zn. Oxygen of -OH forms coordinate bond with Zn or in other words complexes with Zinc . Oxygen acquires a positive charge & Zn acquires a negative charge.So , basically what happens is that a poor leaving group -OH has now been converted into a good leaving group as oxygen now has a positive charge (increased electronegativity).
Ankur Saha
56 Points
4 years ago
Reaction with HCL is thus, carried out in presence of ZnCl2 (Lewis acid). ... Lucas reagent is a solution of anhydrous zinc chloride (Lewis acid) in concentrated hydrochloric acid. It is used as a reagent to test alcohols and classify them in accordance to their reactivity.
Kushagra Madhukar
askIITians Faculty 629 Points
11 months ago
Dear student,
Please find the answer to the question.
 
The reaction of alcohol with HCl involves a nucleophilic substitution reaction, which results in the formation of chloroalkanes.
The Cl- is not a good nucleophile and in alcohol –OH- acts a poor leaving group. Reaction with HCl is thus, carried out in presence of ZnCl2 (Lewis acid).
ZnCl2 forms a complex with oxygen of alcohol and converts the –OH- to a much better leaving group thereby giving a way to the rapid formation of chloroalkane.
 
Thanks and regards,
Kushagra

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