[Chemistry Class Notes] Etard Reaction Pdf for Exam

Etard reaction is one of the important name reactions of CBSE Class XII Chemistry. It is named after French Chemist Alexandre Leon Etard. Benzaldehyde can be prepared using toluene by etard reaction. Benzaldehyde is an important organic compound that is highly used in the food industry in place of almonds due to its almond-like flavor. In this reaction partial oxidation of the methyl group bonded to an aromatic ring takes place. To formaldehyde, we require partial oxidation, and this is the reason we use chromyl chloride in non-polar solvent as it’s a weak oxidizing agent. If we use potassium permanganate which is a strong oxidizing agent in place of chromyl chloride, then due to complete oxidation we get carboxylic acid as a product. 

 

The reaction in which the methyl group attached to an aromatic ring undergoes partial oxidation using chromyl chloride and non-polar solvent (such as carbon tetrachloride, carbon disulphide, etc.) to give aldehyde is called Etard Reaction. The reaction is given below –

 

Etard Reaction –      

 

     

 

The above reaction can also be written in detail as follows –

 

 

 

Reaction Mechanism of Etard’s Oxidation

In the Etard reaction first weak oxidizing agent chromyl chloride reacts with toluene in presence of non-polar solvent carbon tetrachloride. During this reaction homolytic cleavage of – bonds of chromyl, chloride takes place. In the same way, homolytic cleavage of C-H bonds of methyl group also takes place. It leads to the formation of the Etard complex or chromyl complex. The reaction is given below (By dotted arrows we are showing which atom is bonding with which atom to form Etard complex for your better understanding) –

 

 

Now hydrolysis of the etard complex takes place which leads to the removal of two molecules of  Cr(OH)₂Cl₂ and hence the formation of benzaldehyde (Aldehyde). The reaction is given below –

 

 

Thus, the formation of aldehyde from the methyl group attached to the aromatic ring takes place by direct partial oxidation. 

Applications of Etard Reaction 

Conversion of toluene into benzaldehyde by oxidation is very useful as benzaldehyde is quite useful in the food industry due to its almond-like flavor. It is used as a precursor for the formation of dyes, perfumes, and many pharma compounds. Aldehydes are more reactive and take part in aldol condensation. 

 

Dyes, perfumes, and many other compounds are found by this reaction as a precursor. Benzaldehyde is very useful in the synthesis of many compounds such as phentermine. 

Limitations of Etard Reaction 

Although etard reaction is an easy and direct method for conversion of toluene into benzaldehyde. But it has some limitations as well. Obtaining specific aldehyde products by etard reaction using other reagents than toluene is difficult. If we use strong oxidizing agents in the reaction, then they give rise to more stable carboxylic acids. 

 

So, this was all about Etard Reaction for class 11, where we went through the detailed explanation of the mechanism, including Mechanism, Applications, and Limitations. Going through this page will help you clear your concept on the reaction mechanism of Etard’s Oxidation.