Electrophilic Aromatic Substitution Test - 3

Attack by an electrophilic reagent on benzene ring is a rate determining step in electrophilic substitution reaction. It is also the slowest step of the reaction.

Conc. H₂SO₄ act as a catalysis in the nitration of benzene. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at a temperature not exceeding 50°C.

Fuming sulphuric acid is the solution of 7% SO₃ in conc. H₂SO₄. It is also called Oleum which is produced in the contact process, where sulphur is oxidized to sulphur trioxide which is subsequently dissolved in concentrated sulphuric acid.

The necessary condition for desulphonation is to Use dilute acid, high concentration of water and remove volatile hydrocarbon by steam distillation.

Halonium ion act as electrophile in halogenation. Nitronium ion is used in nitration. Sulphonium ion is used in sulphonation. Acylium ion is used in acylation.

Aromatic bromination catalyzed by the Lewis acid thalium acetate gives only para isomer. It is not Ortho and meta directing.

The reaction in which benzene reacts with alkyl halide in the presence of a lewis acid as a catalyst to produce alkylbenzene is known as Friedel-Crafts Alkylation. With anhydrous ferric chloride as a catalyst, the alkyl group attaches at the former site of the chloride ion.

p-xylene is not a product of reaction of benzene with CH₃Cl and AlCl₃. Toulene, isopropyl benzene and O-xylene are the products of such reaction.

The product of Friedel-Crafts Acylation reactions are Arylketone. The acylated products may easily be converted to the corresponding alkanes via Clemmensen Reduction or Wolff-Kishner Reduction.

Friedel-Crafts Acylation followed by clemmensen reduction of ketone will give n-propyl benzene. Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid.