The reversibility of sulfonation allows it to be used to protect activated positions of benzene. Let's see an example:

protection for 01

To obtain o-bromotoluene, we perform the following steps:

1. Friedel-Crafts alkylation.
2. Stop position protection, activated by methyl
3. Bromation of the ortho position. Only activated after protection
4. Position checkout for.
protection for 02