Reaction of Benzene and Methyl Chloride with Anhydrous AlCl₃

Toluene (methyl benzene) is given as the product when benzene reacts methyl chloride in presence of anhydrous Aluminium chloride (AlCl₃). This reaction is defined as an electrophilic substitution reaction. AlCl₃ catalysis the reaction and HCl molecules are formed as by-products during the reaction mechanism.

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Preparation of methylbenzene by benzene

If excess methyl chloride is available, reaction continues. That means, given product by toluene reacts with more methyl chloride molecules and form more products. We will discuss those reactions later in this tutorial.

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Friedel craft alkylation reaction

This is an example reaction to friedel craft alkylation. In a Friedel craft alkylation reaction, an alkyl chloride compound and a benzene or benzene substituted compound are involed in the presence of lewis acid catalyst.

Benzene + Methyl Chloride + Anhydrous AlCl₃ → methylbenzene

C₆H₆ + CH₃Cl + AlCl₃ → C₆HCH₃ + HCl + AlCl₃

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Catalyst behavior of anhydrous AlCl₃

Aluminium chloride is a lewis acid. As well, anhydrous aluminium chloride (AlCl₃) is a catalyst and it increases the reaction rate. Therefore added AlCl₃ do not change with reaction. As a by-product, HCl is given in the reaction.

Toluene has more names, methylbenzene, Phenylmethane. This reaction can be used to prepare benzoic acid as an initial step.

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Mechanism of benzene and methyl chloride reaction

• As first step, ⁺CH₃ carbocation is generated. This cation is an electrophile and can attack parts which has higher electron density.
• ⁺CH₃ carbocation attacks the benzene ring and form an intermediate product as the below figure and that intermediate product also is a carbocation.
• This carbocation get a stability by sharing its positive charge through the benzene ring.
• Finally, hydrogen atom which is connected together with newly bonded -CH₃ group is eliminated to give the desired final product.

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Toluene (Methylbenzene) reacts methyl chloride in presence of AlCl₃

Now, we are going to discuss, what will be happened if excess AlCl₃ is there at the beginning of the reaction. First, toluene is prepared as described earlier.

Toluene reacts with more easily than benzene with methyl chloride in presence of AlCl₃. This reaction will give two products 1,2-Dimethylbenzene and 1,4-Dimethylbenzene because toluene is a ortho-para activator.

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What is correct about following statements?

1. For benzene alkylation, benzene reacts with methyl chloride.
2. For benzene alkylation, benzene reacts with AlCl₃.
3. For benzene alkylation, benzene reacts with methyl chloride and anhydrous AlCl₃.
4. For benzene alkylation, benzene reacts with benzoyl chloride in presence of anhydrous AlCl₃.

Statement 3 is correct.

In the statement 4, benzene reacts with benzoyl chloride in presence of anhydrous AlCl₃. We call it acylation.

benzene react with benzoyl chloride in presence of anhydrous alcl₃

Benzoyl chloride is an aromatic carboxylic acid chloride compound. As other aliphatic carboxylic acid chloride, benzoyl chloride reacts with benzene in presence of anhydrous AlCl₃ and give Benzophenone (diphenylmethanone).

Why AlCl₃ is used in the reaction of benzene and methyl chloride?

AlCl₃ is a catalyst which reduces activation energy of the reaction of benzene and methyl chloride.

Will benzene + methyl chloride in presence of anhydrous AlCl₃ give toxic compounds?

Reactants (benzene, methyl chloride) and given product methyl benzene are toxic compounds. Benzene was identified as a compound which can causes cancer in humans. When a man is exposed to benzene vapor, following signs and symptoms within minutes to several hours

• Drowsiness
• Dizziness
• Rapid or irregular heartbeat
• Headaches

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