Answer:
Benzoyl Chloride
Explanation:
Friedel-Craft Acylation is reaction utilized to add electrophiles (particularly carbonyl group) across double bonds of aromatic compounds.
In given case benzophenone is synthesized using benzene and benzoyl chloride.
Mechanism:
Step 1: In first step benzoyl chloride is treated with lewis acid to generate an electrophile i.e. oxo(phenyl)methylium.
Step 2: In the second step benzene undergoes electrophilic substitution reaction and adds the electrophile.
Step 3: In last step the aromaticity of benzene is restored with the elimination of proton.
