Polynuclear Hydrocarbons

Useful for UG Students of all Universities

1. POLYNUCLEAR
HYDROCARBONS
Dr. Nilesh R Thakare

2. Polynuclear AromaticsPhenanthrene
AnthraceneNaphthalene

3. 1
2
3
45
6
7
8
9
10 Napthalene

4. Naphthalene: nomenclature:
Mono substituted:α-1-
β-2-
Special names:NO
2
2-nitronaphthalene
-nitronaphthalene OH NH
2
SO
3H
-naphthol -naphthylamine-naphthalenesulfonic acid  
also

5. flat, sp
2
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
CrO
3
HOAc, 25
o
O
2, V
2O
5
460-480
o
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.]
CH
3 CH
3
O
O
CCH
3
O
NaOI
COOH

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

9. 3. Electrophilic Aromatic Substitution:a) nitration
HNO
3
NO
2
b) sulfonation
H
2SO
4
H
2SO
4
80
o
160
0
SO
3H
SO
3H
c) halogenation
Br
2
CCl
4
Br
nocatalyst required

10. Electrophilic aromatic substitution (cont.)d) Friedel-Crafts alkylation
e) Friedel-Crafts acylation
polyalkylation!
CH
3COCl, AlCl
3
non-polar solvent
CH
3COCl, AlCl
3
nitrobenzene
C
C
OCH
3
CH
3
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
NO
2
NH
2
Br
2
CCl
4
HNO
3
Mg
H
2/Ni

13. Beta-substitution via high temp sulfonation or Friedel-Crafts
acylation in nitrobenzene.SO
3H ONa
OHNH
2
C
CH
3
O
COOH
C
NH
2
O
NH
2
OH
-
, 300
0
H
+
NH
3
heat,pressure
OI
- SOCl
2; then NH
3
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
NO
2
NO
2
N
N
2
N
+
HNO
3
azo dye
polynitration

16. OH OH
NO
2 NO
2
NO
2
NO
2NO
2
HNO
3
N
2
N
N
+
+

17. Haworth Synthesis of naphthaleneO
O
O
O
HO
2C
AlCl
3
+
Zn(Hg)
HCl
HO
2C
HF or
PPA
O
Zn(Hg)
HCl
Pd
CO
2, heat

18. Substituted naphthalenes via Haworth synthesis:CH
3
O
O
O
+
AlCl
3
CH
3
C
O
COOH
CH
3
beta-
O
+ RMgX
OHR
H
+
Pd, CO
2
heat
a) use a substituted benzene G = -R, -X, -OCH
3
b) Grignard
RR
alpha-

19. O
HO
2C
R'OH, H
+
O
R'O
2C
RMgX H
2O
ROH
R'O
2C
H
+
, heat
R
HO
2C
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
109
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. K
2Cr
2O
7
H
+
K
2Cr
2O
7
H
+
O
O
OO
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:
Br
2
FeBr
3
Br
2, CCl
4
Br
BrBr

25. H
Br
Br
H
Br
9-bromoanthracene
OH
-
or heat
Br
2, CCl
4

26. Haworth synthesis of anthraceneO
O
HO
2C
O
O
O
O
+
AlCl
3
H
2SO
4
Zn(Hg)
HCl
Pd, CO
2, heat
phthalic anhydride

27. Haworth synthesis of phenanthreneO
O
COOH O
HOOC
+
O
O
+
AlCl
3
succinic anhydride
Zn(Hg), HCl
COOH
HOOC
+
HF
O
O
+
Pd, CO
2, heat
Zn(Hg),HCl