Question

In the following reaction, compound Z Is:

$A.\;\,\,Benzoic{\text{ }}acid$
$B.\;\,\,Benzaldehyde$
$C.\,\,Acetophenone$
$D.\,\,benzene$

Answer 1

It is a type of an Etard’s reaction which involves the conversion of alkyl benzene or compounds having alkyl group attached to a heterocyclic ring into aromatic aldehydes in presence of chromyl chloride. In this case, we have toluene which reacts with chromyl chloride in the presence of carbon disulfide as a medium forms Etard complex then acidic hydrolysis takes place to form benzaldehyde. This reaction is an Etard reaction.

Complete step-by-step answer: The Etard reaction is one type of reaction in which the direct oxidation of an aromatic or heterocyclic bound alkyl group takes place. In this reaction mechanism, via ene-reaction, the further reaction takes place with the chromyl chloride that forms a precipitate i.e., an Etard complex. The Etard complex which was formed will further decompose by sigma-tropic rearrangement under reducing conditions which prevent the further oxidation to a carboxylic acid. The main reducing condition is provided by a saturated solution of aqueous sodium sulfite $\left( {N{a_2}S{O_3}} \right)$ which prevents further decomposition.
In the aforesaid reaction, the toluene $({C_6}{H_5}C{H_3})$ reacts with chromyl chloride in the presence of carbon disulfide as a medium form the Etard complex. This complex gets reduced to in the presence of acidic medium (where acidic hydrolysis takes place) to form benzaldehyde.
In this reaction,to chromyl chloride $\;\left( {Cr{O_2}C{l_2}} \right)$ attacks on the methyl group connected to the benzene ring to form an intermediate which further undergoes $2-3\,sigmatropic$ rearrangement reaction to form a chromium complex, and this complex undergoes hydrolyses so easily to benzaldehyde as a product.
The reaction goes like;

The toluene $({C_6}{H_5}C{H_3})$ reacts with chromyl chloride $\;\left( {Cr{O_2}C{l_2}} \right)$ in the presence of carbon disulfide $\;\left( {C{S_2}} \right)$ as a medium forms Etard complex which is further reacted with the hydronium ion $\;\left( {{H_3}{O^ + }} \right)$ and form benzaldehyde $({C_6}{H_5}CHO)$. This reaction is an Etard reaction.
Toluene $({C_6}{H_5}C{H_3})$ is oxidized with alkaline potassium permanganate $(KMn{O_4})$ followed by acidification to form benzoic acid which on further heating with soda-lime that results in the formation of benzene. The oxidation of toluene to benzoic acid $({C_6}{H_5}COOH)$ and then converted to benzoyl chloride $({C_6}{H_5}COCl)$ by treating with thionyl chloride $\left( {SOC{l_2}} \right)$ and then treated with methyl lithium $\left( {C{H_3}Li} \right)$ to form Acetophenone $({C_6}{H_5}COC{H_3})$ .
So, the correct answer for this question is benzaldehyde formation is taking place.

Therefore, the option B.\;\,\,Benzaldehyde$$$$({C_6}{H_5}CHO) is the correct answer.

Note: The chromyl chloride $\;\left( {Cr{O_2}C{l_2}} \right)$ is used to form an organic complex Etard Complex which can undergo hydrolysis to form the desired compound. Benzaldehyde $({C_6}{H_5}CHO)$ can be reduced to toluene $({C_6}{H_5}C{H_3})$ by Clemmenson reduction reaction.