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Polynuclear Aromatics
Phenanthrene
AnthraceneNaphthalene
12
3
45
6
78
9
10
Napthalene
Naphthalene: nomenclature:
Mono substituted: α- 1-β- 2-
Special names:
NO2
2-nitronaphthalene -nitronaphthalene
OH NH2 SO3H
-naphthol -naphthylamine -naphthalenesulfonic acid
also
flat, sp2 4i + 2 = 10 e- aromatic
Heat of hydrogenation is –61 Kcal/mole lower than predicted (resonance stabilization energy).
Benzene is –36 Kcal/mole lower than predicted.
- 61 = - 36 - 25 the second aromatic ring is less stable.
Naphthalene, reactions:
1) oxidation:
O
O
O
O
O
CrO3
HOAc, 25o
O2, V2O5
460-480o
1,4-naphthoquinone
phthalic anhydride
Note: Because naphthalene is sensitive to oxidation, you cannot make naphthoic acids via oxidation of a side chain.
[oxid.]CH3 CH3
O
O
CCH3
O
NaOICOOH
2. Reduction:
Na, EtOH
78o
Na, i-PeOH
132o
(xs) H2, Pt
heat, pressure
1,4-dihydronaphthalene
tetrahydronaphthalene(tetralin)
decalin
3. Electrophilic Aromatic Substitution:
a) nitrationHNO3
NO2
b) sulfonationH2SO4
H2SO4
80o
1600
SO3H
SO3H
c) halogenationBr2
CCl4
Br
nocatalyst required
Electrophilic aromatic substitution (cont.)
d) Friedel-Crafts alkylation
e) Friedel-Crafts acylation
polyalkylation!
CH3COCl, AlCl3
non-polar solvent
CH3COCl, AlCl3
nitrobenzene
C
C
O CH3
CH3
O
Why is EAS in naphthalene mostly to the alpha-position?
EAS in syntheses of substituted naphthalenes:
Alpha-substitution via halogenation or nitration.
Br MgBr
NO2NH2
Br2
CCl4
HNO3
Mg
H2/Ni
Beta-substitution via high temp sulfonation or Friedel-Crafts acylation in nitrobenzene.
SO3H ONa
OHNH2
CCH3
O
COOH
CNH2
ONH2
OH-, 3000
H+
NH3
heat,pressure
OI- SOCl2; then NH3
OBr-
EAS in substituted naphthalenes:
a) With an activating group to EAS
in the alpha position 4- plus a little 2-
in the beta position 1-
b) With a deactivating group to EAS
the other ring, usually alpha ( 5- & 8- )
G
G
G
+ a little 2-
OH OH
OH
NO2
NO2
N
N2
N
+
HNO3
azo dye
polynitration
OH OH
NO2 NO2
NO2
NO2NO2
HNO3
N2
NN
+
+
Haworth Synthesis of naphthalene
O
O
O
O
HO2C
AlCl3+
Zn(Hg)
HClHO2C
HF orPPA
O
Zn(Hg)
HCl
Pd
CO2, heat
Substituted naphthalenes via Haworth synthesis:
CH3
O
O
O
+ AlCl3
CH3
CO
COOH
CH3
beta-
O
+ RMgX
OHR
H+
Pd, CO2
heat
a) use a substituted benzene G = -R, -X, -OCH3
b) Grignard
RR
alpha-
O
HO2C
R'OH, H+
O
R'O2C
RMgX H2OR OH
R'O2C
H+, heat
R
HO2C
R
alpha-
2
34
1
10
9
56
78
anthracene
Heat of hydrogenation is-84 Kcal lower than expected.2 x -36 = -72-86 - (-72) = -12 Kcal/mole toremove the middle ring'saromaticity.
3
21
4
109
8
76
5
3
2
1
4
1098
7
6 5
Phenanthrene
14 pi e-, totalof five resonacestructures
Heat of hydrogenation is -92 Kcal/mole lower thanpredicted.2 x -36 = -72-92 -(-72) = -20 Kcal/mole to remove the aromaticityof the middle ring.
K2Cr2O7
H+
K2Cr2O7
H+
O
O
OO
9,10-antraquinone
9,10-penanthrone
Oxidation:
Na, heat
EtOH
Na,heat
i-PeOH
9,10-dihyroanthracene
9,10-dihydrophenanthrene
Reduction:
EAS in anthracene or phenanthrene yields mixtures and is not generally useful. For example, in sulfonation:
13%
8%
18%
18%0%
Bromination is an exception:
Br2
FeBr3
Br2, CCl4
Br
BrBr
H
Br
Br
H
Br
9-bromoanthracene
OH- or heat
Br2, CCl4
Haworth synthesis of anthracene
O
O
HO2C
O
O
O
O
+AlCl3
H2SO4
Zn(Hg)
HCl
Pd, CO2, heat
phthalic anhydride
Haworth synthesis of phenanthrene
O
O
COOH O
HOOC
+
O
O
+AlCl3
succinic anhydride Zn(Hg), HCl
COOH
HOOC
+HF
O
O
+
Pd, CO2, heatZn(Hg),HCl
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