Transcript Aromatic Chemistry

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STRUCTURE OF BENZENE
Benzene = C6H6
Its structure was a mystery for many years
- until Kekule’s dream.
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.
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STRUCTURE OF BENZENE
H
H
C
H
C
C
C
C
H
C
H
H
STRUCTURE OF BENZENE
http://www.isis.stfc.ac.uk/
HYDROGENATION OF BENZENE
Energy
(kJ/mol)
152
-360
-240
-208
-120
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NAMING AROMATIC COMPOUNDS
CH3
methylbenzene
(toluene)
Cl
chlorobenzene
NO2
nitrobenzene
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COOH
benzenecarboxylic acid
(benzoic acid)
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NAMING AROMATIC COMPOUNDS
CH3
CH3
1,3-dimethylbenzene
(m-xylene)
CH3
Cl
COOH
4-methyl-1-chlorobenzene
COOH
OH
O2N
2-hydroxybenzenecarboxylic
acid
NO2
3,5-dinitrobenzenecarboxylic
acid
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NAMING AROMATIC COMPOUNDS
CH3
NH2
CH2
CH2
CH3
phenylamine
(aniline)
2-phenylbutane
O
CH
CH2
phenylethene
CH3
C
phenylethanone
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NAMING AROMATIC COMPOUNDS
O
O
C
O
O
C
CH3
phenylethanoate
CH3
methyl benzenecarboxylate
(methyl benzoate)
O
NH
C
CH3
N-phenylethanamide
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NAMING AROMATIC COMPOUNDS
OH
OH
OH
phenol
OH
OH
Cl
benzene-1,2-diol
Cl
NO2
2-nitrophenol
2,4,6-trichlorophenol
(TCP)
Cl
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NITRATION
NO2
+
+
HNO3
H2O
nitrobenzene
Conditions
conc HNO3
conc H2SO4 catalyst
50ºC
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NITRATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile
+
HNO3 + 2 H2SO4
NO2
+ 2 HSO4- + H3O+
nitronium ion
Reaction of electrophile with aromatic compound
+
NO2
+
NO2
H
+
-H
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NO2
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NITRATION
CH3
CH3
NO2
Equation (name product)
Conditions
Mechanism
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NITRATION
CH3
CH3
NO2
+
HNO3
+
H2O
2-methylnitrobenzene
Conditions
conc HNO3
conc H2SO4 catalyst
50ºC
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NITRATION
Uses of nitro compounds:
1) as explosives
2) to make aromatic amines (used to make dyes)
CH3
O2N
NO2
NO2
1,3,5-trinitrotoluene
TNT
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FRIEDEL-CRAFTS ACYLATION
R
O
C
O
+
R
C
Cl
+
R
HCl
O
C
O
+
R
C
O
O
C
O
R
+
R
C
OH
aromatic
ketone
Conditions
AlCl3 catalyst
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FRIEDEL-CRAFTS ACYLATION
WARNING! - do not mix
Friedel-Crafts acylation
&
other acylations
(needs AlCl3)
H
H
H
N
R
H
O
R
Swap H on benzene ring
Swap H on O/N
for acyl group
for acyl group
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FRIEDEL-CRAFTS ACYLATION
WARNING! - Classic question to test this
NH2
NHCOCH3
CH3COCl
H replaced is on N not benzene ring.
This is NOT Friedel-Crafts acylation!
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FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile
AlCl3
O
AlCl4–
+ RCOCl
+
R
C
+
acylium ion
OR
O
O
AlCl3 + R-C-O-C-R
O
O
–
R-C-O-AlCl3
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+
R
C
+
acylium ion
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FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Reaction of electrophile with aromatic compound
O
O
C
R
C
+
+
R
H
O
+
C
-H
R
Regeneration of catalyst
AlCl4–
+
H+
AlCl3 + HCl
O
O
–
R-C-O-AlCl3
+
H+
or
R-C-OH + AlCl3
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FRIEDEL-CRAFTS ACYLATION
CH3
CH3
C
O
CH2CH3
Equation
Conditions
Mechanism
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FRIEDEL-CRAFTS ACYLATION
CH3
CH3
O
+
CH3CH2
C
+
Cl
HCl
C
O
Conditions
CH2CH3
AlCl3 catalyst
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