Alcohols Phenols and Ethers - Result Question 4

####4. Which of the following reaction (s) can be used for the preparation of alkyl halides? [2015 RS]

(I) CH3CH2OH+HCl

 anh. ZnCl2

(II) CH3CH2OH+HCl

(III) (CH3)3COH+HCl

(IV) (CH3)2CHOH+HCl anh. ZnCl2

(a) (I), (III) and (IV) only

(b) (I) and (II) only

(c) (IV) only

(d) (III) and (IV) only

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Solution:

  1. (a)

CH3CH2OH+ZnCl2ROZnCl2(R=CH3CH2)HH (I) 

ROZnCl2HR+[HOZnCl2]

(I)

Carbocation is formed as intermediate in the SN1 mechanism which these reaction undergoes. (III) Tertiary carbocation easily formed due to the stability.

CH3CCH3CH3+H2O

(IV) In the presence of ZnCl2,2 carbocation is formed from (CH3)2CHOH i.e., CH3CHCH3

ZnCl2 is a lewis acid and interact with alcohol. In the absence of ZnCl2 formation of primary carbocation is difficult.



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