Etard Reaction

The name “Etard” was inspired by French scientist Alexandre Léon Etard (1852 – 1910), who spent most of his career at Wurtz Laboratory. Using Etard reagent, also known as chromyl chloride, he found the partial oxidation of aromatic rings bearing methyl groups (CrO2Cl2).

The Etard reaction uses Chromyl Chloride to partially oxidise aromatic ring-like Benzene. Because Chromyl Chloride is a poor oxidising agent, it is used with a non-polar solvent such as Carbon Tetrachloride.

Toluene interacts with Chromyl Chloride (CrO2Cl2) in the presence of Carbon Disulphide (CS2) and Carbon Tetrachloride to generate Benzaldehyde (CCl4). Toluene reacts to generate the complex molecule C7 H6 O, which is also known as an intermediate in this reaction. It is hydrolyzed once more to produce the desired chemical, C7 H6 O -Benzaldehyde.

Etard reaction

The Etard reaction, named after French chemist Alexandre Leon Etard, is a reaction that can be used to create Benzaldehyde from Toluene. When Toluene is combined with Chromyl Chloride in a nonpolar solvent and subsequently hydrolyzed, it produces Benzaldehyde, which is known as the Etard reaction. Benzaldehyde is a significant chemical molecule having a benzene ring and a formyl substituent that is utilised for aroma in cosmetics and perfume.

The Etard response is divided into two steps:

• A brown complex that is unstable forms.
• Hydrolysis yields the final product.

Mechanism of etard reaction

Consider the example of methyl benzene to better understand the process of the etard reaction (toluene).

Toluene undergoes a parietal oxidation process in the presence of chromyl chloride and carbon tetrachloride, resulting in the production of Benzaldehyde.

The mechanism of the etard reaction can be broken down into five processes.

Step 1: Homolytic breakdown of toluene bonds

Toluene undergoes homolytic breakage of four bonds when it reacts with Chromyl chloride. A homolytic cleavage occurs between two C-H (Carbon-Hydrogen) bonds in the methyl group bonded to the benzene. Two Cr-O (Chromium-Oxygen) bonds in chromyl chloride are also cleaved homolytically.

Step 2: The etard complex intermediate is produced.

The creation of the etard complex occurs after the bonds are broken. The hydrogens liberated from the methyl group as a result of homolytic cleavage form bonds with the oxygens of chromyl chloride. Two OCr(OH)Cl2 molecules are formed as a result of this bond formation. These OCr(OH)Cl2 attach to the carbon atom of the methyl group in toluene through second oxygen. It signifies that OCr(OH)Cl2 has replaced the hydrogens that have been homolytically cleaved. Therefore, OCr(OH)Cl2molecules occupy the two hydrogens removed from the methyl group via homolytic cleavage. This unstable product is known as the etard complex intermediate.

Step 3: Etard complex hydrolysis

The sodium sulfite utilised in the procedure serves to protect the etard complex from further oxidation. The hydrolysis of the unstable etard complex results in the production of two OCr(OH)Cl2 groups.

Step 4: Benzaldehyde formation

The OCr(OH)Cl2 groups attached to the aromatic ring dissociate, leaving the aldehyde product, benzaldehyde, behind.

Step 5: Benzaldehyde Purification

The etard complex is very combustible. To avoid being oxidised, it undergoes a breakdown process in the presence of a reducing environment. The etard complex is degraded through a pericyclic process known as [2,3] Sigmatropic Rearrangement. Filtering using various solvents is used to preserve the product from degradation. This solution is purified to produce a high-quality final product, namely pure benzaldehyde.

Applications

• Benzaldehyde (a byproduct of this process) is used as a basis in the production of fragrances.
• In the food industry, benzaldehyde is also used as a replacement for the almond taste.
• Phentermine is synthesised using benzaldehyde. 

Limitations

The Etard reaction is a synthetic technique for synthesising amines from alkyl halides and ammonia. There are several limits to the Etard response, including:

1. The Etard reaction is limited to alkyl halides containing a tertiary carbon atom.
2. The Etard reaction is inefficient and frequently results in a combination of products.
3. The Etard reaction frequently creates difficult-to-purify byproducts.
4. The Etard reaction is not highly selective and can generate a wide spectrum of amines.

Conclusion

The Etard reaction, named after French chemist Alexandre Leon Etard, is a reaction that can be used to create Benzaldehyde from Toluene. When Toluene is combined with Chromyl Chloride in a nonpolar solvent and subsequently hydrolyzed, it produces Benzaldehyde, which is known as the Etard reaction. Toluene undergoes a parietal oxidation process in the presence of chromyl chloride and carbon tetrachloride, resulting in the production of Benzaldehyde. The Etard reaction is limited to alkyl halides containing a tertiary carbon atom. Toluene is required for the Etard reaction to be successful since any other reagent will not produce Benzaldehyde.