Mechanism of Electrophilic Substitution

In the procedure of electrophilic substitution, an electrophile replaces the functional group attached to a molecule. The functional displacement group is usually a hydrogen atom. Electrophilic aliphatic substitution is one type of electrophilic substitution. The synthesis of a carbocation as an intermediate and the removal of a proton from the solution are both required to produce an electrophile.

The electrophilic substitution processes of benzene include alkylation, acylation, halogenation, nitration, sulphonation, and other electrophilic substitution processes.

Electrophilic Substitution Reaction Mechanism

The electrophilic substitution reaction mechanism involves three steps.

1. Generation of Electrophiles: Chlorination, alkylation, and acylation of an aromatic ring using anhydrous chloride helps form electrophiles. Electrophiles are formed when Cl+, R+, and RC+ O anhydrous aluminium chloride iss combined with the attacking reagents.

2.Formation of Carbocation: The electrophile creates an arenium ion and a sigma complex after attacking the aromatic ring. A few carbons within the sigma complex sp3 are hybridised. The arenium ion, instead of the sigma complex, obtains stabilisation in the resonance structure in the second of the electrophilic substitution cycle. The aromatic property of the sigma complex is eliminated because electron delocalisation stops at the sp3 hybridised carbon.

3.Removal of Protons: Another step is essential to reestablish the aromatic characteristic because a proton is emitted from sp3 hybridised carbon whenever AlCl4 attacks the sigma complex or even the arenium ion. The electrophile in the benzene ring replaces the hydrogen in the third stage.

Reaction of Amines

Amines are organic ammonia (NH3) variants wherein the hydrogen is substituted by alkyl, cycloalkyl, or aromatic groups to connect to the nitrogen atom. The most basic element of aromatic amine is aniline, which has amine-type nitrogen linked to an aromatic ring.

The following are some instances of amine reactions:

• When amine reacts with acid as a base, a salt is formed.

• Whenever an amine functions as a nucleophile and combines with only an alkyl halide, the SN2 substitution process induces alkylation.

• While KMNO4 oxidises basic aliphatic amines, ethanol can be produced.

Types of Electrophilic Substitution Reactions of Anilines

Aniline is an organic molecule with the chemical formula C6H5NH2 that has a phenyl group linked to an amino group. Because aniline is an electron-donating type group, the functional group (NH2) is particularly active in electrophilic substitution reactions. The aniline’s electrophilic substitution process targets both the o and p sites of a benzene ring because para position sites have more negative charge electrons than meta location. The following electrophilic substitution processes can be carried out with aniline:

Nitration of Aniline 

The aniline molecule is protonated in an acidic media to generate an anilion ion. A meta isomer is detected along with para in the nitration of aniline process. Despite the fact that the NH2 group is an o and p indication, it creates meta-nitroaniline whenever it reacts with acid.

Sulphonation of Aniline

Aniline reacts strongly with sulphuric acid to generate anilinium hydrogen sulphate, which, when heated, produces 4-amino benzene sulphonic acid that has a resonant structure with zwitterion. This reaction is known as the  sulphonation of aniline.

Halogenation of Aniline

A white precipitate termed as 2, 4, 6 – tribromoaniline occurs whenever aniline is handled by bromine water at room temperature. It also happens because a bromine molecule develops polarity, but bromine needs to behave as an electrophile because of its slightly positive charge. It goes after the aniline’s electron-dense ortho and para positions.

Conclusion

The three primary processes in the electrophilic substitution reaction are the synthesis of an electrophile, the creation of a carbocation as an intermediate, and the elimination of a proton from the medium.