Hydrocarbons Question 328
Question: Alcoholic solution of KOH is used for [CPMT 1982, 86; IIT-JEE 1990]
Options:
A) Dehydration
B) Dehydrogenation
C) Dehydrohalogenation
D) Dehalogenation
Show Answer
Answer:
Correct Answer: C
Solution:
$ CH_3-CH_2-Br+\underset{alk}{\mathop{KOH}}\xrightarrow{Dehydrohalogenation} $
$ CH_2=CH_2+KBr+H_2O $
In alcoholic KOH alkoxide ions $ (R{O^{-}}) $ are present which a strong base is.
They abstract proton from b-carbon of alkyl halide and favours elimination reaction
$ \underset{Alcohol}{\mathop{ROH}}+KOH\to \underset{\text{Potassium alkoxide}}{\mathop{ROK+H_2O}} $
$ ROK\to \underset{\text{Alkoxide ion}}{\mathop{R{O^{-}}}}+{K^{+}} $
$ R{O^{-}}+H-\overset{\beta }{\mathop{CH_2}}-\overset{\alpha }{\mathop{CH_2}}-Br\to ROH+CH_2=CH_2+Br $
BETA
