Preparation of Methyl Benzene

The preparation of Methyl Benzene can be done by reacting Benzene with Bromo-Methane in the presence of Anhydrous AlCl3. This reaction is also known as Friedel-Crafts alkylation.

Reaction

CH3Br + C6H6 → CH3C6H5 + HBr

Mechanism

- The reaction takes place in the presence of Lewis Acid Catalyst, Anhydrous AlCl3.
- The Lewis Acid Catalyst AlCl3 accepts an electron pair from the Bromine atom in Bromo-Methane.
- The Bromine atom becomes positively charged and attacks the Benzene ring to form an intermediate carbocation.
- The intermediate carbocation is stabilized by the resonance of the Benzene ring.
- A Chloride ion from AlCl3 removes a proton from the intermediate carbocation to form Methyl Benzene.
- The Chloride ion from AlCl3 also regenerates the Lewis Acid Catalyst for further reaction.

Advantages

- This method is a simple and economical way of preparing Methyl Benzene.
- Anhydrous AlCl3 is a cheap catalyst and can be easily obtained.
- This method is useful for preparing Methyl Benzene in large quantities.

Disadvantages

- This method is not useful for preparing Methyl Benzene in small quantities as the reaction is highly exothermic and can lead to explosions.
- The use of Anhydrous AlCl3 can lead to the formation of toxic fumes which can be harmful to the environment and human health.
- This method is not useful for preparing Methyl Benzene with other substituents on the Benzene ring as the reaction can lead to the formation of unwanted by-products.