Chemistry - Extending Carbon Chains

Ways of extending a carbon chain

Formation of Nitriles
Friedel Crafts Alkylation
Friedel Crafts Acylation

Formation of Nitriles

1. KCN in Ethanol is heated under reflux with a haloalkane (Nucleophilic Substitution of CN- and Halogen)

2. HCN Can be added to carbonyls to form nitriles (nucleophilic addition). CN- reduces C=O to C-O-, H+ bonds to O- & CN bonds to Carbon

Hydrolysis of Nitriles

1. With Dilute Acid: Forms Carboxylic Acid + Ammonium Salt

2. With Dilute Alkali: Forms Sodium Carboxylate Salt + Ammonia, acidify to turn carboxylate ion to carboxylic acid

Reduction of Nitriles

-CN can be reduced to -NH2 forming primary amines
Nitrile vapour + H2(g) can be passed over Ni Catalyst OR LiAlH4 in dry ether can be used

Friedel Crafts Reactions

Arenes are often unreactive, hence to make them more reactive we can add alkyl/acyl groups to change their structure and increase their reactivity via electrophilic substitution reactions

Friedel Crafts Alkylation

Substitution of Alkyl group
Benzene is reacted with a choloroalkane in presence of AlCl3
Generation of Electrophile: CH3CH2Cl + AlCl3 → CH3CH2+ + [AlCl4]-
CH3CH2+ substitutes a H
Regeneration of Catalyst: H+ + [AlCl4]- → HCl + AlCl3

Friedel Crafts Acylation

Acyl group is substituted onto benzene using an Acyl chloride in presence of AlCl3
Generation of Electrophile: CH3COCl + AlCl3 → CH3C+O + [AlCl4]-
CH3C+O substitutes H on benzene
Regeneration of Catalyst: H+ + [AlCl4]- → AlCl3 + HCl