1. Chemsheets AS006 (Electron arrangement)
24/04/2017
AROMATIC CHEMISTRY
© A Jul-12

2. STRUCTURE OF BENZENE Benzene = C6H6
Its structure was a mystery for many years - until Kekule’s dream.

4. STRUCTURE OF BENZENE Problems with Kekule’s structure:
1) C-C bonds are all the same length (between C-C and C=C length).
2) Benzene does not undergo addition reactions readily (e.g. with bromine water).
3) H hydrogenation about 152 kJ mol-1 less than expected.
© A Jul-12

5. STRUCTURE OF BENZENE

6. STRUCTURE OF BENZENE

7. HYDROGENATION OF BENZENE
© A Jul-12

8. NAMING AROMATIC COMPOUNDS benzenecarboxylic acid
methylbenzene
(toluene)
chlorobenzene
nitrobenzene
benzenecarboxylic acid
(benzoic acid)
© A Jul-12

9. NAMING AROMATIC COMPOUNDS
1,3-dimethylbenzene
(m-xylene)
4-methyl-1-chlorobenzene
2-hydroxybenzenecarboxylic
acid
3,5-dinitrobenzenecarboxylic
acid
© A Jul-12

10. NAMING AROMATIC COMPOUNDS
phenylamine
(aniline)
2-phenylbutane
phenylethene
phenylethanone
© A Jul-12

11. NAMING AROMATIC COMPOUNDS methyl benzenecarboxylate
phenylethanoate
methyl benzenecarboxylate
(methyl benzoate)
N-phenylethanamide
© A Jul-12

12. NAMING AROMATIC COMPOUNDS
phenol
benzene-1,2-diol
2-nitrophenol
2,4,6-trichlorophenol
(TCP)
© A Jul-12

13. NITRATION Conditions conc HNO3 conc H2SO4 catalyst 50ºC nitrobenzene
© A Jul-12

14. NITRATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile
HNO3
+ 2 H2SO4
+ 2 HSO4-
+ H3O+
NO2 +
nitronium ion
Reaction of electrophile with aromatic compound
NO2 +
NO2 +
NO2 -H H +
© A Jul-12

15. NITRATION Equation (name product) Conditions Mechanism
© A Jul-12

16. NITRATION Conditions conc HNO3 conc H2SO4 catalyst 50ºC
2-methylnitrobenzene
Conditions
conc HNO3
conc H2SO4 catalyst
50ºC
© A Jul-12

17. NITRATION Uses of nitro compounds: 1) as explosives
2) to make aromatic amines (used to make dyes)
1,3,5-trinitrotoluene
TNT
© A Jul-12

18. FRIEDEL-CRAFTS ACYLATION
aromatic
ketone
Conditions
AlCl3 catalyst
© A Jul-12

19. FRIEDEL-CRAFTS ACYLATION
WARNING! - do not mix
Friedel-Crafts acylation & other acylations
(needs AlCl3)
Swap H on benzene ring
for acyl group
Swap H on O/N
for acyl group
© A Jul-12

20. FRIEDEL-CRAFTS ACYLATION
WARNING! - Classic question to test this
H replaced is on N not benzene ring.
This is NOT Friedel-Crafts acylation!
© A Jul-12

21. FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile O
AlCl3
+ RCOCl
AlCl4 – + R C +
acylium ion OR O O O O –
R-C-O-AlCl3 +
AlCl3
+ R-C-O-C-R R C +
acylium ion
© A Jul-12

22. FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Reaction of electrophile with aromatic compound + C O R O O C R + C R -H H +
Regeneration of catalyst
AlCl4 –
+ H+
AlCl3 + HCl or O O –
R-C-O-AlCl3
+ H+
R-C-OH
+ AlCl3
© A Jul-12

23. FRIEDEL-CRAFTS ACYLATION
Equation
Conditions
Mechanism
© A Jul-12

24. FRIEDEL-CRAFTS ACYLATION
Conditions
AlCl3 catalyst
© A Jul-12