adminlower 6 organic13 Organicnowt crest  
nowtarenephenolsaldehydesketonesacidspolymersnowt
nowt12345678910nowt
 

Sulphonation of  Benzene

sulfonation of arenes

Reaction type: Electrophilic Aromatic Substitution

Summary.

  • Overall transformation :  Ar-H to Ar-SO3H, a sulphonic acid.
  • Reagent : for benzene, H2SO4 / heat or SO3 / H2SO4 / heat (=  fuming sulphuric acid)
  • Electrophilic species :  SO3 which can be formed by the loss of water from the sulfuric acid
  • Unlike the other electrophilic aromatic substitution reactions, sulphonation is reversible.
  • Removal of water from the system favours the formation of the sulphonation product.
  • Heating a sulphonic acid with aqueous sulphuric acid can result be the reverse reaction, desulphonation.
  • Sulphonation with fuming sulphuric acid strongly favours formation of the product the sulphonic acid.
MECHANISM FOR SULPHONATION OF BENZENE
Step 1:
The p electrons of the aromatic C=C act as a nucleophile, attacking the electrophilic S, pushing charge out onto an electronegative O atom. This destroys the aromaticity giving the cyclohexadienyl cation intermediate.



Step 2:
Loss of the proton from the sp3 C bearing the sulfonyl- group reforms the C=C and the aromatic system.




Step 3:
Protonation of the conjugate base of the sulphonic acid by sulphuric acid produces the sulphonic acid.
 
sulfonation of arenes
 

© LEV