CHEM267 Chapter Notes - Chapter 19: Electrophilic Aromatic Substitution, Nucleophilic Aromatic Substitution, Nitro Compound
5 Mar 2013
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When benzene undergoes an addition reaction with br2, no reaction occurs (too stable: however, when iron (fe) is introduced into the mixture, a reaction takes place. Instead of an addition reaction, an electrophilic aromatic substitution occurs: one aromatic proton is replaced by an electrophile. Fe enhances the electrophilicity of the bromine (br) atom. Note: no additional products would occur! (it is already stable/aromatic) When benzene is treated with fuming sulphuring acid (fuming h2so4), sulfonic acid is obtained: fuming sulphuric acid is a mixture of h2so4 and so3 gas (so3 = very strong electrophile!) Reaction mechanism is the same as all electrophilic aromatic substitution reactions (but with an extra proton transfer at the end to protonate the electronegative oxygen atom) Note: the reaction between benzene and fuming h2so4 is reversible! When benzene is treated with a mixture of nitric acid and sulfuric acid, a nitrobenzene is formed. Reaction proceeds via an electrophilic aromatic substitution (eas) with a nitronium ion (no2.
