Useful for UG Students of all Universities

1. POLYNUCLEAR
HYDROCARBONS
Dr. Nilesh R Thakare

2. Polynuclear Aromatics
Phenanthrene
Anthracene
Naphthalene

3. 1
2
3
4
5
6
7
8
9
10
Napthalene

4. Naphthalene: nomenclature:
Mono substituted: α- 1-
β- 2-
Special names:
NO2
2-nitronaphthalene
-nitronaphthalene

OH NH2 SO3H
-naphthol -naphthylamine -naphthalenesulfonic acid
  
also 

5. 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.

6. Naphthalene, reactions:
1) oxidation:
O
O
O
O
O
CrO3
HOAc, 25o
O2, V2O5
460-480o
1,4-naphthoquinone
phthalic anhydride

7. 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
NaOI
COOH

8. 2. Reduction:
Na, EtOH
78o
Na, i-PeOH
132o
(xs) H2, Pt
heat, pressure
1,4-dihydronaphthalene
tetrahydronaphthalene
(tetralin)
decalin

9. 3. Electrophilic Aromatic Substitution:
a) nitration
HNO3
NO2
b) sulfonation
H2SO4
H2SO4
80o
1600
SO3H
SO3H
c) halogenation
Br2
CCl4
Br
nocatalyst required

10. 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

11. Why is EAS in naphthalene mostly to the alpha-position?



12. EAS in syntheses of substituted naphthalenes:
Alpha-substitution via halogenation or nitration.
Br MgBr
NO2
NH2
Br2
CCl4
HNO3
Mg
H2/Ni

13. Beta-substitution via high temp sulfonation or Friedel-Crafts
acylation in nitrobenzene.
SO3H ONa
OH
NH2
C
CH3
O
COOH
C
NH2
O
NH2
OH-
, 3000
H+
NH3
heat,pressure
OI- SOCl2; then NH3
OBr-

14. 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-

15. OH OH
OH
NO2
NO2
N
N2
N
+
HNO3
azo dye
polynitration

16. OH OH
NO2 NO2
NO2
NO2
NO2
HNO3
N2
N
N
+
+

17. Haworth Synthesis of naphthalene
O
O
O
O
HO2C
AlCl3
+
Zn(Hg)
HCl
HO2C
HF or
PPA
O
Zn(Hg)
HCl
Pd
CO2, heat

18. Substituted naphthalenes via Haworth synthesis:
CH3
O
O
O
+
AlCl3
CH3
C
O
COOH
CH3
beta-
O
+ RMgX
OH
R
H+
Pd, CO2
heat
a) use a substituted benzene G = -R, -X, -OCH3
b) Grignard
R
R
alpha-

19. O
HO2C
R'OH, H+
O
R'O2C
RMgX H2O
R OH
R'O2C
H+, heat
R
HO2C
R
alpha-

20. 2
3
4
1
10
9
5
6
7
8
anthracene
Heat of hydrogenation is
-84 Kcal lower than expected.
2 x -36 = -72
-86 - (-72) = -12 Kcal/mole to
remove the middle ring's
aromaticity.

21. 3
2
1
4
10
9
8
7
6
5
3
2
1
4
10
9
8
7
6 5
Phenanthrene
14 pi e-
, total
of five resonace
structures
Heat of hydrogenation is -92 Kcal/mole lower than
predicted.
2 x -36 = -72
-92 -(-72) = -20 Kcal/mole to remove the aromaticity
of the middle ring.

22. K2Cr2O7
H+
K2Cr2O7
H+
O
O
O
O
9,10-antraquinone
9,10-penanthrone
Oxidation:

23. Na, heat
EtOH
Na,heat
i-PeOH
9,10-dihyroanthracene
9,10-dihydrophenanthrene
Reduction:

24. 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
Br
Br

25. H
Br
Br
H
Br
9-bromoanthracene
OH- or heat
Br2, CCl4

26. Haworth synthesis of anthracene
O
O
HO2C
O
O
O
O
+
AlCl3
H2SO4
Zn(Hg)
HCl
Pd, CO2, heat
phthalic anhydride

27. Haworth synthesis of phenanthrene
O
O
COOH O
HOOC
+
O
O
+
AlCl3
succinic anhydride Zn(Hg), HCl
COOH
HOOC
+
HF
O
O
+
Pd, CO2, heat
Zn(Hg),HCl