Question

Give test to differentiate 1, 1 - dichloroethane and 1, 2 - dichloroethane :

• A. 2, 4 - DNP then aq. KOH
• B. aq. KOH then 2, 4 - DNP
• C. $NaHS{O}_3$
• D. Lucas reagent

Answer 1

The correct option is B aq. KOH then 2, 4 - DNP

$C{H}_3-\underset{|}{CH}-Cl\stackrel{aq.KOH}{\to }C{H}_3-CHO\stackrel{2,4-DNP}{\to }$ positive test

$Cl$
$\underset{|}{C}{H}_2-\underset{|}{C}{H}_2\stackrel{aq.KOH}{\to }\underset{|}{C}{H}_2-\underset{|}{C}{H}_2\stackrel{2,4-DNP}{\to }$ negative test

$Cl$ $Cl$ $OH$ $OH$

As $2,4$ $DNP$ test is positive for aldehyde not for alcohol. Thus the best reagent to differentiate is aqueous $KOH$ & then $2,4-DNP$ .