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Electrophilic substitution is a reaction which involves an electrophile reacting with a molecule with high electron density such as benzene. Benzene and its derivatives are commonly used in electrophilic substitution as benzene has 6 delocalised electrons forming its electron ring (also termed aromatic ring), therefore giving it a high electron density. This can also be visualised as 3 alkene bonds, both methods of visualisation illustrate how electrons are delocalised around the benzene ring. 

A good example of electrophilic substitution reaction is the Friedel-Crafts acylation whereby an acyl group is added to an aromatic ring such as benzene. Here AlCl₃ is required to form the reactive acyl intermediate (electrophile) to allow the electrophilic substitution to occur. To learn more about why AlCl₃ is required and its role in the reaction see the chemBAM page; Is that a catalyst – Friedel-Crafts acylation.

A similar reaction is the Friedel-Crafts alkylation which involves adding an alkyl group to an aromatic ring such as benzene. This reaction was used commonly in the production of shampoos and surfactants.

Task;

Using what you know, calculate how many tonnes of AlCl₃ are required to react 10 000 tonnes of benzene to form methyl-benzene (aka toluene) if 1.05 moles of AlCl₃ are required in the reaction?

Bonus task;

If you treat AlCl₃ as a reagent in the reaction, can you calculate the atom economy and E factor of the reaction? Can you use this to justify why other “catalysts” were developed for this reaction?

For a recap on atom economy and E factor see the chemBAM page. 

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