Acylation reaction, Kolbe's reaction, Reimer Tiemann's reaction

Esters of phenols yields phenolic ketones on treatment with anhydrous aluminium chloride.

formation of phenolic ketones

Phenyl ethanoate yields ortho and para hydroxy acetophenones. It involves migration of an acyl groyp from phenolic oxygen to ortho and para positions of the aromatic ring.

Kolbe's reaction
On reaction sodium salt of phenol with carbon dioxide gas, ortho hydroxy benzoic acid is formed as the main product. The temperature is 400 K and a pressure of 4-7 atm is required. Sodium salicylateis formed which an acidification yields salicylic acid (ortho hydroxy benzoic acid).

formation of salicylic acid
Reimer Tiemann's reaction
On treating phenol with chloroform in presence of sodium hydroxide at 340 K, a - CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemenn reaction. This results in the formation of O - hydroxybenzaldehyde (salicylaldehyde) and para-hydroxybenzaldehyde, the ortho isomer being the major product.

formation of salicylaldehyde from phenol

The intermediate substituted benzal chloride is hydrolysed in presence of alkali to produce salicylaldehyde.

Reimer Tiemenn reaction is an electrophilic substitution reaction. The first step is generation of electrophile.

Reimer Tiemenn reaction

Dichlorocarbene contains a sextet of electrons and thus is a strong electrophile.

Dichlorocarbene is a strong electrophile

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