This is a standard method for introducing carbon groups to benzene rings using alkyl halides, alkenes and alcohols. Conventionally a catalyst like aluminium chloride is used, but this method generates a lot of waste, and the catalyst is destroyed in product recovery.

For more details of Friedel-Crafts reactions see the catalysis site

Carrying out the reaction in scCO₂ allows the use of a solid, re-usable catalyst, and results in a narrower range of products, simplifying product separation. Products more difficult to obtain may also be made. The product mixture is very easily obtained as the scCO₂ simply vaporises when pressure is released.