1. TY 2002 Organic Mechanism 4 Nitration of Benzene

2. TY 2002 production of the electrophile the benzene ring is a centre of high electron density which makes it susceptible to electrophilic attack the nitryl cation, NO 2 +, is the electrophile in this reaction it is produced by the reaction of concentrated nitric acid with concentrated sulphuric acid

3. TY 2002 the initial reaction HNO 3 + H 2 SO 4 HSO 4 - + NO 2 + + H 2 O the sulphuric acid acts as a catalyst in this reaction it is regenerated later in the reaction mechanism

4. TY 2002 mechanism the benzene molecule has 6 delocalised electrons in a molecular orbital the NO 2 + electrophile is attracted to this centre of high electron density situated above and below the ring an electron pair move from the delocalised ring system to the NO 2 + forming a new covalent bond

5. TY 2002 electrons move from the benzene ring towards the electrophile electrophilic attack

6. TY 2002 the intermediate formed is very unstable

7. TY 2002 mechanism the stable delocalised ring system is reformed as the unstable intermediate breaks down the covalent bond between the hydrogen and the carbon atom in the benzene ring breaks heterolytically the delocalised benzene ring system is reformed

8. TY 2002 the hydrogen - carbon bond breaks the delocalised molecular orbital reforms

9. TY 2002 the products the H + reacts with HSO 4 - to regenerate sulphuric acid

10. TY 2002 mechanism the product of this reaction is nitrobenzene this is an electrophilic substitution reaction the halogens e.g.chlorine will undergo a similar reaction with benzene in the presence of a catalyst such as aluminium chloride producing chlorobenzene CARE!!benzene and chlorine undergo an addition reaction in the presence of UV light the product is 1,2,3,4,5,6-hexachlorocyclohexane