Flag Organic Chemistry> organic-reagent...
question mark

why is anhydrous zncl2 is used in lucas reagent?

tejaswini tiwale , 11 Years ago
Grade 12
anser 5 Answers
Akshay Amol Revankar

Last Activity: 11 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

Last Activity: 9 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

Last Activity: 8 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

Last Activity: 8 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

Last Activity: 4 Years 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

Provide a better Answer & Earn Cool Goodies

star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments


Ask a Doubt

Get your questions answered by the expert for free