An alkyl halide (X) on reaction with sodium in dry ether gives 2,3-Dimethylbutane. X on reaction with sodium and chlorobenzene in dry ether gives Z as the major product. What is Z?
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Whenever a Wurtz reaction produces 2,3-dimethylbutane, think of coupling of two isopropyl groups. In a Wurtz-Fittig reaction, replace one of those isopropyl groups by a phenyl group to obtain cumene (isopropyl benzene).
Concept:
This question involves Wurtz reaction and Wurtz-Fittig reaction.
• In Wurtz reaction:
\[
2R-X + 2Na \rightarrow R-R + 2NaX
\]
Two alkyl halide molecules combine together.
• In Wurtz-Fittig reaction:
\[
Ar-X + R-X + 2Na \rightarrow Ar-R + 2NaX
\]
An aryl halide combines with an alkyl halide.
Step 1: Identify the alkyl halide X from the Wurtz reaction product.
Given product:
\[
2,3\text{-Dimethylbutane}
\]
Structure:
\[
CH_3-CH(CH_3)-CH(CH_3)-CH_3
\]
This compound is formed by coupling two identical
isopropyl groups.
Therefore,
\[
X=(CH_3)_2CH-X
\]
i.e. X is an isopropyl halide (such as isopropyl chloride or bromide).
\[
2(CH_3)_2CHX
\xrightarrow[\text{dry ether}]{2Na}
(CH_3)_2CH-CH(CH_3)_2
\]
which is 2,3-dimethylbutane.
Step 2: Apply Wurtz-Fittig reaction with chlorobenzene.
Now isopropyl halide reacts with chlorobenzene:
\[
C_6H_5Cl + (CH_3)_2CHX
\xrightarrow[\text{dry ether}]{2Na}
C_6H_5CH(CH_3)_2
\]
The product formed is
\[
\text{Isopropyl benzene}
\]
which is commonly known as
\[
\boxed{\text{Cumene}}
\]
Step 3: Match with the given options.
Among the given structures, the structure corresponding to
\[
C_6H_5CH(CH_3)_2
\]
is Option (3).
\[
\boxed{\text{Z = Isopropyl benzene (Cumene)}}
\]
Hence, the correct answer is
\[
\boxed{\text{(3) Isopropyl benzene (Cumene)}}
\]
