Question

Benzene and alkyl-substituted benzenes can be hydroxylated by reaction with ${\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}$in the presence of an acidic catalyst. What is the structure of the reactive electrophile? Propose a mechanism for the reaction.

Short answer

The proposed mechanism is shown below

Step-by-step solution

Reaction of hydrogen peroxide in presence of an acid catalyst

When the reaction of hydrogen peroxide in the presence of an acid catalyst leads to the formation of $\mathrm{HO}-\stackrel{+}{\mathrm{O}}{\mathrm{H}}_2$ , carbocation acts as an electrophile in reaction with the benzene.

Reaction of benzene with an electrophile

When the dichloro carbocation reacts with benzene, one of the double bonds of the aromatic ring breaks and the addition of $\mathrm{HO}-\stackrel{+}{\mathrm{O}}{\mathrm{H}}_2$occurs at the ring, followed by hydrolysis which protonates the hydrogen and the ring regains its aromaticity and the formation of phenol occurs.

Mechanism

Mechanism for the formation of electrophiles:

1. Addition of electrophile to a benzene ring.
2. Hydrolysis for deprotonation of hydrogen.

3.Formation of phenol occurs as shown below

Formation of electrophile

Mechanism