The reactions of arenes

Arenes are compounds that contain the benzene ring. In this experiment we look at the typical reactions of arenes, and also investigate the effect that the side chain has on the reactivity of the ring. Look at the videos showing the experiments with methylbenzene. Make notes of any changes you see and check your observations using the theory link. Repeat this procedure for the reactions of methoxybenzene. In this case try to write equations for any of the reactions you see. You may want to check out the typical reactions of the benzene ring. Try to explain any difference in reactivity between the methylbenzene and methoxybenzene.


methylbenzene	methoxybenzene

Procedure for methylbenzene

1 Combustion

What type of flame does methylbenzene burn with, and what is it about the structure of the molecule that results in this flame type?

Video - combustion of methylbenzene

2 Oxidation

We use acidified potassium manganate(VII) solution in this experiment. Is there any sign of reaction and how does the reactivity compare to that of the alkenes?

Video - oxidation of methylbenzene

Video - oxidation of cyclohexene

3 Action of bromine

Look for signs of reaction in the video and contrast the reactivity with that of the alkenes.

Video - bromination of methylbenzene

Video - bromination of cyclohexene

4 Action of sulfuric acid

We use concentrated sulfuric acid in this experiment. Does this mix with the methylbenzene? Were there any signs of reaction? Again compare the reactivity to that of the alkenes.

Video - the reaction of methylbenzene and concentrated sulfuric acid

Video - the reaction of cyclohexene and concentrated sulfuric acid

Theory - the reactions of methylbenzene

Procedure for methoxybenzene

1 Bromination

How does the reactivity of methoxybenzene towards bromine compare with that of methylbenzene? Try to suggest why there is a difference. What are the fumes which are given off? Write an equation for the reaction assuming that only one mole of bromine reacts with one mole of methoxybenzene.

Video - the bromination of methoxybenzene

2 Sulfonation

Describe the changes seen in this reaction with concentrated sulfuric acid. Write an equation for the reaction assuming that one mole of sulfuric acid reacts with one mole of methoxybenzene.

Video - the sulfonation of methoxybenzene

3 The Friedel-Crafts reaction

This is a very important reaction in organic synthesis. The aluminium chloride is the catalyst, and care needs to be taken with it as it is a very reactive substance. You will see copious fumes given off which you should be able to identify from the test shown. Again, try to write an equation for the reaction assuming a 1:1 reaction between the methylbenzene and the 2-chloro-2-methylpropane.

Video - the Friedel-Crafts reaction

4 Nitration

A mixture of concentrated nitric acid and water is used in this experiment. Make a note of any signs of reaction in this case and try to write down an equation for the reaction, again assuming a 1:1 reacting ratio.

Video - the nitration of methoxybenzene

Theory - the reactions of methoxybenzene