Reactions of benzene

Conditions: catalyst (Fe/FeBr3 for bromination, AlCl3 for chlorination), heat.

1) Br-Br + FeBr3 --> Br+ + (FeBr4)-   (for bromination)

Cl-Cl+ AlCl3 --> Cl+ + (AlCl4)-   (for chlorination

2)+ Br+ -->+ H+   (bromination)

+ Cl+ --> + H+ (chlorination)

3) H+ + (FeBr4)- --> FeBr3 + HBr

H+ + (AlCl4)- --> AlCl3 + HCl

Conditions: catalyst (like AlCl3) and heat under reflux.

Alkylation: the addition of an alkyl group. In this example, an ethyl group is added to benzene

1) CH3CH3Cl + AlCl3 --> (CH3CH2)+ + (AlCl4)-

2) + (CH3CH2)+ --> + H+

3) H+ + (AlCl4)-  --> AlCl3 + HCl

Acylation of benzene: when an acyl chloride reacts with benzene to form a ketone

1)+ AlCl3 --> (CH3CH2CO)+ + (AlCl4)-

2) + (CH3CH2CO)+ --> propanoylbenzene + H+

3) H+ + (AlCl4)- --> AlCl3 + HCl

• Useful intermediates in organic synthesis- halobenzenes for example
• Acylation and alkylation reactions build up the carbon side-chains on benzene rings
• Sulfonic acid derivatives can be converted to a sulfonate, which increases solubilty
• Allows benzene derivatives to act as dyes
• Allows benzene derivatives to act as chromaphores- increased region of delocalisation