The exact mechanism of this reaction is a little complicated, as it involves the copper ions. However, the process involves the formation of small amounts of bromine in situ. Draw the mechanism of the bromination of 4-tert-butyl phenol with Br2. -g

see picture below

Explanation:

The mechanism is in the following picture.

In the first step, the lone pair of oxygen (from the OH) as it's a strong activating group in the molecule, will go to the ring. This will cause that the double bond of the ring of the ortho position, attacks as nucleophyle to the Br2, causing the breaking of the bond.

In the second step, the bromine ion substract the hydrogen from the ortho position, and then, by resonance, the pair of electrons returns to the oxygen of the phenol.

particle   p is an electron and particle q is a neutron