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bromination of phenol (and benzene)

on addition of bromine to phenol, some of the products have substituted only one, bromine. Some have 2 and some have 3. (occurs with benzene too). Why does this happen?

Reply 1

username986184

Rate of reaction and stoichiometry.

Reply 2

______10______

Original post by TeachChemistry

Rate of reaction and stoichiometry.

Can you please elaborate?

Reply 3

Infraspecies

Original post by ______10______

Can you please elaborate?

If the ratio of Br₂ : C₆H₅OH is

1:1 you'll have monosubstituted phenol (largely)
2:1 you'll have disubstituted phenol (largely)
3:1 you'll have trisubstituted phenol (largely)

Bromine is a deactivating group, on a phenyl ring. This has the consequence of making mono-, di- and tri- bromophenol sequential less reactive towards further bromination. Hence, in a 1:1 mix, it is more likely that all the bromine will react with separate phenol molecules, rather than several bromines adding to one, and leaving some unreacted. The argument continues the same for the other cases.