[3] Phenols | Electrophilic Substitution of phenol | Naming reaction with mechanism | BSc 2nd Year

Electrophilic aromatic substitution reactions are the reactions where an electrophile replaces one or more hydrogen atoms attached to the aromatic ring. Phenols are highly prone to electrophilic substitution reactions due to rich electron density.

The hydroxyl group attached to the aromatic ring in phenol facilitates the effective delocalization of the charge in the aromatic ring. Thus, it stabilizes the arenium ion through resonance. The hydroxyl group also acts as ortho para directors. Hence, we acknowledge most of these substitutions at ortho and para positions only.

. Nitration of Phenols

Phenols upon treatment with dilute nitric acid undergo nitration at low temperature (298 K) to give a mixture of ortho and para nitrophenols. The mixture formed is further separated into ortho and para nitrophenols by steam distillation on the basis of their volatility.

Due to intramolecular and intermolecular hydrogen bonding, ortho nitrophenols are lesser volatile in comparison to para nitrophenols which involves only intermolecular hydrogen bonding.

Halogenation of Phenols
Due to a highly activating effect of the hydroxyl group in phenols, they undergo halogenation even in the absence of Lewis acids. When phenols are treated with bromine in the presence of a solvent of low polarity like CHCl3 at low temperatures, monobromophenols are formed.

Reimer-Tiemann Reaction

When phenol is treated with chloroform in the presence of sodium hydroxide, an aldehyde group is formed at the ortho position of the benzene ring. This reaction is popularly known as the Reimer-Tiemann reaction.

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   • [1] Phenols | Method of formation | N...  
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   • [2] Phenols | Chemical Properties of ...  
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Time stamp
00:00- Electrophile substitution at phenol ring
12:45- Halogenation of phenol ring
19:00- Nitration of phenol ring
22:37- Sulphonation of phenol ring
24:38- Friedel craft Alkylation
26:27- Gattermann synthesis
37:45- Hauben - Hoesch Reaction
42:55- special reaction of phenol
48:46- Reimer Tiemann Reaction

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#Halogenationofphenolring #Sulphonationofphenolring#FriedelcraftAlkylation #Gattermannsynthesis #Haubenhoeschreaction #specialreactionofphenolring #ReimerTiemannreaction