JEE Challenger
More from Alcohols, Phenols and Ethers
ChemMedAdv 2007 • Paper 2

Structure of Dichloromethyl Phenolate Intermediate

Comprehension Passage

Reimer-Tiemann reaction introduces an aldehyde group onto the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below:

p-cresol→reagentintermediate (I)→aq. HCl2-hydroxy-5-methylbenzaldehyde\text{p-cresol} \xrightarrow{\text{reagent}} \text{intermediate (I)} \xrightarrow{\text{aq. HCl}} \text{2-hydroxy-5-methylbenzaldehyde}

The structure of the intermediate I\mathbf{I} is

Options

A
Option A Diagram 1
B
Option B Diagram 1
Correct
C
Option C Diagram 1
D
Option D Diagram 1

Topics & Concepts

Alcohols, Phenols and EthersReimer-Tiemann ReactionReaction IntermediatePhenols

Step-by-Step Solution

Electrophilic attack of dichlorocarbene (:CCl2:\text{CCl}_2) occurs at the activated ortho position of the phenoxide ion derived from pp-cresol.

Aromatization via proton transfer yields a benzal chloride derivative having an −O−Na+-\text{O}^-\text{Na}^+ group, a −CH3-\text{CH}_3 group at the para position, and a −CHCl2-\text{CHCl}_2 group at the ortho position.

Subsequent hydrolysis of this gem-dichloride intermediate during the acidic workup generates the target aldehyde (−CHO-\text{CHO}).

Thus, intermediate I\mathbf{I} is the sodium phenolate bearing −CHCl2-\text{CHCl}_2 at C-2 and −CH3-\text{CH}_3 at C-4, which corresponds exactly to Option B.

Correct Answer: B

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