Grade 12Organic Chemistry

why is anhydrous zncl2 is used in lucas reagent?

tejaswini tiwale

12 Years agoGrade 12

5 Answers

Akshay Amol Revankar

12 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

10 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

9 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

9 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

5 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