How benzene is converted into benzene sulphonic acid? Give its mechanism. Or Explain the mechanism of sulphonation of benzene.
Sulphonation of benzene is carried out by the action of benzene with fuming sulphuric acid or oleum.
Mechanism: It involves the following steps:
(i) Generation of sulphur trioxide (electrophile). The attacking electrophile sulphur trioxide, SO3 (neutral but electron deficient) is present as such in oleum (H2SO4 + SO3) or can be formed by the dissociation of the sulphuric acid.
The sulphur atom in sulphur trioxide has the only sextet of electrons. Thus the molecule is electron deficient in nature.
(ii) Formation of the carbocation. The electrophile (SO3) attacks the benzene ring to form intermediate carbocation which is resonance stabilised. It is a slow step.
The resonance hybrid structure of the above resonating form can be represented as
(iii) Transfer of proton from the carbocation to form benzene sulphonate ion.
(iv) The reaction between benzene sulphonate ion and hydronium ion to form benzene sulphonic acid.
524 Views
Advertisement
Hydrocarbons
Hope you found this question and answer to be good. Find many more questions on Hydrocarbons with answers for your assignments and practice.
Chemistry Part II
Browse through more topics from Chemistry Part II for questions and snapshot.
