Step-by-step explanation:
Pthalic anhydride on reacts with AlCl₃ forms a complex which on reaction with m-xylene gives 2-(2,4-dimethylbenzoyl) benzoic acid.
The mechanism the reaction follows is:
(a) Image 1.
The mechanism shows the formation of the complex of pthalic anhydride with aluminum chloride. AlCl₃ acts as Lewis base which gets attached to the nucleophilic oxygen of pthalic anhydride.
(b) Image 2.
The attack of the double of m-xylene to the oxygen bearing positive charge of pthalic acid which on protonation gives 2-(2,4-dimethylbenzoyl) benzoic acid.