Organic Compounds Containing Oxygen: Chemistry | JEE Main
Suitable reaction condition for preparation of Methyl phenyl ether is
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Step-by-step solutionView
Correct answer
Methyl phenyl ether (anisole) is synthesized by reacting sodium phenoxide with methyl bromide via an SN2 substitution.
Option analysis
Why each option works or fails
A · Ph−Br,MeO−Na+
Assuming that bromobenzene readily undergoes nucleophilic aromatic substitution with sodium methoxide under standard conditions. Aryl halides do not undergo SN2 displacement because of partial double bond character from resonance and steric hindrance of the aromatic ring; instead, pair the phenoxide nucleophile with an alkyl halide.
B · PhO−Na+,MeOH
Believing that an alcohol can act as an alkylating electrophile for a phenoxide ion without activation. Methanol has hydroxide as a very poor leaving group; an alkyl halide such as methyl bromide is required to supply a good leaving group for nucleophilic attack.
C · PhO−Na+,MeBr
Correct choice. Phenoxide is a strong nucleophile and methyl bromide is an unhindered primary alkyl halide with a good leaving group, enabling rapid SN2 substitution to form methyl phenyl ether.
D · Benzene,MeBr
Confusing Friedel-Crafts alkylation with ether synthesis. Reacting benzene with methyl bromide requires a Lewis acid catalyst and produces toluene (a C-C bond), not an ether (C-O-C bond).
Reviewed route
Solution
StepWorking
01identify
Preparation of methyl phenyl ether (anisole, Ph−O−Me) using Williamson ether synthesis, which proceeds via an SN2 pathway between an alkoxide/phenoxide nucleophile and an alkyl halide.
02mechanism
In Williamson ether synthesis of alkyl aryl ethers, the halide must be an alkyl halide (primary/methyl) because aryl halides (like Ph−Br) do not undergo SN2 substitution due to partial double bond character from resonance and steric hindrance. Therefore, phenoxide ion (PhO−) acts as the nucleophile attacking methyl bromide (MeBr).
03product
PhO−Na++MeBr⟶Ph−O−Me+NaBr. This smoothly yields methyl phenyl ether.
✓verify
Option (0) fails because bromobenzene is inert to SN2. Option (1) lacks an alkylating electrophile (methanol is not an alkylating agent under these conditions). Option (3) is Friedel-Crafts alkylation which produces toluene, not an ether. Hence, option (2) is correct.
Aryl halides cannot undergo SN2 substitution. The C-Br bond has partial double-bond character due to resonance with the benzene ring. Also, backside attack is blocked by the aromatic ring.