Question

‘A’ in the below reaction is:
$ {C_6}{H_6} + CO + HCl\xrightarrow{{'A'}}{C_6}{H_5}CHO + HCl $
(A) Anhydrous $ AlC{l_3} $
(B) $ {V_2}{O_5}/{450^ \circ }C $
(C) Solid $ KOH $
(D) Anhydrous $ ZnC{l_2} $

Answer 1

Hint: $ {C_6}{H_6} $ is called Benzene. The benzene molecule is made up of six carbon atoms arranged in a planar ring, each with one hydrogen atom. Benzene is classified as a hydrocarbon since it only has carbon and hydrogen atoms.

Complete answer:
The Gattermann reaction, (also known as the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formulated by hydrogen cyanide in the presence of a Friedel-Craft catalyst (e.g. AlCl3).
 $ {C_6}{H_6} + CO + HCl\xrightarrow{{AlC{l_3}(Catalyst)}}{C_6}{H_5}CHO + HCl $
This is an electrophilic substitution reaction (modified Friedel-Crafts reaction), where the most likely electrophile is acylium ion.
 $ CO + HCl + AlC{l_3} \to HC{O^ + }(Acylium\_ion) + AlC{l_4}^ - $
 $ {C_6}{H_5}^ - + HC{O^ + } \to {C_6}{H_5}CHO $
The aromatic ring undergoes an electrophilic aromatic substitution. The formal cation receives an electron pair from the aromatic ring, which serves as a nucleophile. The loss of aromaticity is easily restored when a proton is ejected.
As a result of the Gatterman – Koch reaction, the formal group is bound to the aromatic ring. Benzaldehyde is formed when benzene is treated with carbon monoxide and hydrochloric acid in the presence of aluminium chloride, as seen in the above mechanism.
The provided reaction is the Gattermann–Koch reaction, which is used in the development of benzaldehyde in industry.
As a result, the correct answer is (A) Anhydrous $ AlC{l_3} $ .

Additional Information:
The Gattermann–Koch reaction does not work with phenol or phenol ether as a substrate. Since copper(I) chloride acts as a co-catalyst when zinc chloride is used as a catalyst in the Gattermann – Koch reaction, traces of copper(I) chloride are frequently required.

Note:
The electrophilic replacement of benzene occurs when an electrophile replaces the hydrogen atom of the molecule. These reactions are extremely random in nature since the aromaticity of benzene is not disrupted during the reaction.