Oxidation of a benzylic methyl group (–CH₃ attached to benzene) to an aldehyde (–CHO) using
Chromyl chloride in a non-aqueous solvent (like CCl₄).

Mechanism (Stepwise)

Formation of Etard Complex

• Chromyl chloride attacks benzylic hydrogen
• Forms a brown complex (Etard complex)

$$Ar-CH_3 \rightarrow Ar-CH(OCrOCl_2)_2$$

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Hydrolysis of Complex

• On hydrolysis (H₂O), the complex breaks
• Gives aldehyde

$$Ar-CH(OCrOCl_2)_2 \xrightarrow{H_2O} Ar-CHO$$