Exams › JEE Advanced › Chemistry
In the Reimer-Tiemann reaction (phenol + CHCl3 + NaOH, heated), which intermediate is formed on the pathway to salicylaldehyde?
- o-quinone methide intermediate with a -CCl2H side chain
- phenoxide intermediate bearing a -CHCl2 side chain
- phenoxide intermediate bearing a -CCl3 side chain
- o-quinone methide intermediate with a -CHCl side chain
Correct answer: phenoxide intermediate bearing a -CCl3 side chain
Solution
Mechanism: (1) CHCl3 + NaOH ->:CCl2 (dichlorocarbene) + NaCl + H2O. (2) Phenoxide ion attacks:CCl2 at ortho position to form an adduct - the ring carbon bears the -CCl3 group after proton shift (the o-position C gains CCl3 group, with the O- still on phenoxide). This is the phenoxide intermediate with -CCl3 on the ring. (3) Hydrolysis of -CCl3 and rearrangement gives -CHO. The key intermediate is the phenoxide (or cyclohexadienyl anion) with a -CCl3 substituent at ortho position.
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