Etard Reaction

Overall Reaction:
$$\text{C}_6\text{H}_5\text{--CH}_3 + 2\text{CrO}_2\text{Cl}_2 \xrightarrow{\text{CS}_2 \text{ or } \text{CCl}_4} [\text{C}_6\text{H}_5\text{--CH(OCrOHCl}_2)_2] \xrightarrow{\text{H}_3\text{O}^+} \text{C}_6\text{H}_5\text{--CHO} + 2\text{Cr(OH)}_2\text{Cl}_2$$

Reagents & Conditions:
$$\text{Oxidizing Agent: Chromyl Chloride } (\text{CrO}_2\text{Cl}_2)$$
$$\text{Solvent: Non-polar, inert solvents like}$$  $$\text{CS}_2$$ or $$\text{CCl}_4$$
$$\text{Hydrolysis Step: Mild acidic aqueous conditions } (\text{H}_3\text{O}^+)$$

Intermediate Complex:
$$\text{Brown Chromium Complex Intermediate: } \text{C}_6\text{H}_5\text{--CH(OCrOHCl}_2)_2$$

Concept: Selective partial oxidation of an aromatic methyl side chain to a benzaldehyde compound. The reaction isolates an intermediate chromium complex state, preventing the molecule from auto-oxidizing all the way into benzoic acid.

Notation:

• $$\text{CrO}_2\text{Cl}_2$$
• = Chromyl chloride;
• $$\text{CS}_2$$
• = Non-polar solvent environment.