Why is phenol more reactive in electrophilic aromatic substitutions?

1 Answer
anor277
Jan 22, 2017

The phenyl ring is activated by delocalization of the lone pairs of oxygen around the ring........

Explanation:

Benzene normally requires Lewis acid activation for electrophilic aromatic substitution; for instance, bromination of the #C_6H_6# ring requires the bromine (obviously), and some Lewis acid catalysis. (Typically aluminum or iron metal which is oxidized up to #MBr_3#, and this acts as a bromine transfer reagent).

By constrast, when phenol is treated with bromine, presumably because of the donation of #pi# electrons to the ring by oxygen, bromination is facile. And 2,4,5-substitution of bromine (with respect to the #OH# group) may be observed, sometimes even in the absence of Lewis acid catalysis.

At any rate, there is nothing I can say here that you won't learn better than from your organic chemistry text. Read the chapters on electrophilic aromatic substitution, and digest their account.

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