Why does only one $\ce{Br+}$ ion get generated in a non-polar solvent (such as $\ce{CS2}$), while more $\ce{Br+}$ ions are generated in aqueous or polar solvent (such as $\ce{H2O}$)?

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The reaction of phenol with bromine is known as bromination of phenol. Solvent has great influence on the reaction. In different solvents, different products are obtained. The action of bromine on phenol can be explained as:

Reaction with bromine in water:—-

Reaction with bromine in water

Phenol reacts with bromine water to give 2,4,6-tribromophenol.

In water, ionisation is facilitated. Phenol gets ionised to form phenoxide ion, which is even better ortho,para-directing. Bromine also gets ionised to a larger extent to form a large number of bromonium ions. And Bromine ions are highly stabilized in ionic solvents. So the formation of strong o,p-directing group and stabilization of $\ce{Br+}$ enhances the formation of tribromophenol.

Reaction with bromine in $\ce{CS2}$:—-

Reaction with bromine in non-polar organic solvents

Phenol reacts with bromine in a presence of Carbon disulphide to form a mixture of o-bromophenol and p-bromophenol. Among which p-bromophenol predominates. In $\ce{CS2}$ ionisation is not facilitated that much. As it is a non-polar solvent it doesn't the $\ce{Br+}$ on. Also $\ce{-OH}$ group is moderately o,p-directing. So as usual para-product is more formed.

  • $\begingroup$ sorry may I ask why is brominum ion produced form Br2 in aqueous solution? I know Br+ is more electrophilic, hence even more encouraging multiple halogenation. But isn't Br- bromide ion formed instead? $\endgroup$
    – 234ff
    Aug 7 '20 at 6:39

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