Question
Explain (1) Kolbe’s reaction (2) Reimer-Tiemann reaction.
✓
Answer
(1) Kolbe’s reaction : When phenol reacts with sodium hydroxide, sodium phenoxide is obtained. Phenoxide ion being more reactive than phenol towards electrophilic substitution. Phenoxide undergoes electrophilic substitution with carbon dioxide at 398 K under pressure of 6 atm (a weak electrophile) forms salicylic acid as major product.
(2) Reimer-Tiemann reaction : Phenol is heated with chloroform along with aqueous NaOH, this is followed by acidification with dil. HC1 when salicyladehyde (2-hydroxy benzaldehyde) is formed as the major product, which can be separated from p-isomer by steam distillation. The stability of o-isomer is due to intramolecular hydrogen bonding.
(2) Reimer-Tiemann reaction : Phenol is heated with chloroform along with aqueous NaOH, this is followed by acidification with dil. HC1 when salicyladehyde (2-hydroxy benzaldehyde) is formed as the major product, which can be separated from p-isomer by steam distillation. The stability of o-isomer is due to intramolecular hydrogen bonding.
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