Question

Which of the following statements regarding electrophilic aromatic substitution is wrong?
A.Sulfonation of toluene is reversible.
B.Friedel-crafts alkylation of benzene can be reversible.
C.Friedel-crafts alkylation with primary alkyl chloride may involve rearrangement
D.Friedel-crafts acylation of nitrobenzene readily gives a meta substitution

Answer 1

To solve this question, we must first understand the meaning of aromatic electrophilic substitution and then study the options given to us. We must observe if the substituents given are electrophilic in nature, and if they are, we must find if they cause substitution reactions or any other types of reactions.

Complete Step-by-Step Answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
Electrophilic aromatic substitution reactions can be understood as those chemical reactions which involve the breaking of the $C-H$ bond and formation of a $C-E$ bond, where E is any electrophilic substituent and it causes the substitution of H atoms from the aromatic compound. Let us now discuss the options given to us:
A.Sulfonation of toluene is reversible.
Most aromatic electrophilic reactions are not reversible. But sulphonation is a reversible process. This reaction produces benzene sulphonic acid by the addition of fuming ${H_2}S{O_4}$ and sulphur trioxide.
B.Friedel-crafts alkylation of benzene can be reversible.
In Friedel Crafts alkylation of benzene, the alkyl group is attached to the benzene molecule on the basis of electrophilic aromatic substitution. These reactions can be reversible in nature if the Halo acid is formed in excessive quantities.
C.Friedel-crafts alkylation with primary alkyl chloride may involve rearrangement.
Friedel-crafts alkylation with primary alkyl chloride reactions involves the electrophilic substitution of the H atom from the aromatic ring. These reactions involve the rearrangement of the functional group positions because the alkyl group will get attached at the place of the primary carbon atom.
D.Friedel-crafts acylation of nitrobenzene readily gives a meta substitution.
Nitro group is a deactivating substituent. Because of this, it activates only the ortho and para positions on the benzene rings. Friedel-Crafts acylation of nitrobenzene does not take place under any conditions. However, the presence of a second strongly - activating substituent group permits acylation; the site of reaction is favoured by both substituents.

Hence, Option D is the correct option

Note: Friedel – Crafts reactions involve aromatic electrophilic substitution that is used for linking the given aromatic molecule with other chemical substituents. There are two main types of Friedel – Crafts reactions, viz. Alkylation and Acylation reactions. Aluminium trichloride is often used as a catalyst in Friedel-Crafts reactions since it acts as a Lewis acid and coordinates with the halogens, generating an electrophile in the process.