1. Benzene Reactions Dr AKM Shafiqul Islam School of Bioprocess Engineering University Malaysia Perlis

2. Electrophilic Aromatic Substitution Aromatic ring systems react with electrophiles differently than alkenes. We obtain a substitution rather than an addition product.

4. Mechanism First, we get a carbocation intermediate. At the carbon that adds the electrophile, rehybridization (sp 2  sp 3 ) takes place. Molecule loses aromatic character.

5. The electron-rich part of the reagent can act either as nucleophile in an addition reaction or as a base to remove a proton. Nonaromatic comp Aromatic comp

6. Mechanism Carbocation is resonance stabilized.

7. Aromatic Halogenation 1 st step is generating an electrophile: FeBr 3 is a Lewis acid that coordinates with Br 2 and polarizes it, generating an electrophilic Br +

8. Aromatic Nitration 1 st step is generating an electrophile, the nitronium ion:

9. Aromatic Nitration 2 nd step: The highly electrophilic nitronium ion attacks the aromatic ring.

10. Aromatic Sulfonation Generating of the electrophile

11. Aromatic Aromatic Sulfonation Reaction of electrophile with aromatic ring

12. Friedel-Crafts Alkylation of Benzene Places an alkyl group on a benzene ring The electrophile, i.e., carbocation, is formed from the reaction of alkyl halide with AlCl 3

13. Friedel-Crafts Alkylation of Benzene Electrophilic Aromatic Substitution

14. Friedel–Crafts Alkylation

15. Friedel-Crafts alkylation Benzene with 1-chlorobutane will give primarily 2-phenylbutane

16. Mechanism The carbocation will rearrange if rearrangement leads to a more stable carbocation

17. The Friedel-Crafts alkylation Benzene with 1-chloro-2,2-dimethylpropane gives 2-methyl-2-phenylbutane

18. Mechanism Rearrangement of a primary carbocation to yield a tertiary carbocation The primary carbocation undergoes a 1,2-methyl shift to yield a tertiary carbocation

19. Alkylation of Benzene by Alcohol Benzene reacts with 2-propanol to form isopropylbenzene Benzene can react with carbocations generated from the reaction of an alcohol with an acid

20. A straight-chain alkyl group can be placed on a benzene ring by means of a Friedel-Crafts acylation reaction, followed by reduction of the carbonyl group to a methylene group Benzene with propanoyl chloride yields propyl phenyl ketone, which is reduced to butylbenzene

21. Reaction with Substituent of Benzene N-Bromosuccinimide (NBS) will selectively brominate at the benzylic carbon Reaction of propylbenzene with NBS yields 1- bromo-1-phenylpropane

22. Reactions of benzyl bromide

23. Reaction with Substituent of Benzene Oxidation of toluene to benzoic acid

24. Reaction with Substituent of Benzene Any alkyl group, except tertiary alkyl groups, on the benzene is oxidized to a carboxylic acid 1-Butylisopropylbenzene is oxidized to isophthalic acid

25. Exercise

26. Exercise