Polynuclear Hydrocarbons a) Naphthalene

Polynuclear Hydrocarbons
Classification of Polynuclear Hydrocarbons Polynuclear Hydrocarbons may be divided
into two groups, 1) Benzenoid which may be isolated e.g biphenyl or fused in linear
form e.g naphthalene or fused in angular form e.g anthracene or it may be 2) Non
benzenoid e.g azulene
Biphenyl
Naphthalene
a) Naphthalene
Phenanthrene
OH
8
2
6
3
4
Br
HO3S
OH
7
5
Br
1
1-Naphthol or -Naphthol
2-Naphthol or -Naphthol
1,8- Dibromo-naphthalene
SO3H
Naphthalene-2,7- disulfonic acid
Structure elucidation of naphthalene can be explained by such oxidation of naphthalene that give
phathalic acid
COOH
O
Naphthalene
COOH
Phthalic acid
When naphthalene was treated with nitric acid it give nitro naphthalene that when oxidized it give nitro
phathalic acid So nitro group is present in benzene ring
NO2
COOH
Naphthalene
nitration
Nitronaphthalene
O
COOH
Nitrophthalic acid
But when nitro naphthalene was reduced it produce amino naphthalene that when suspected to oxidation
it give phathalic acid this means The benzene ring in phthalic acid produced by oxidation of
aminonaphthalene is not the same ring is that obtained by oxidation of nitronaphthalene.
COOH
Naphthalene nitration
Nitronaphthalene
redn.
aminonaphthalene
O
COOH
Phthalic acid
1
Naphthalene contains two benzene rings and we can explain this by this equation
A
B
HNO3
NH2
NO2
NO2
COOH
HOOC
O
B
A
redn.
B
A
O
B
A
COOH
HOOC
Synthesis :1- Howarth method
O
O
O
+
AlCl3
Zn-Hg/HCl
HO
R
R
O
Succinic anhydride
conc.H2SO4
-H2O
HO
R
O
O
Se
Zn-Hg/HCl

R
R
R
O
2-Other way of cyclization
O
O
+
O
SOCl2
AlCl3
HO
R
R
O
Succinic anhydride
AlCl3
O
Se
Zn-Hg/HCl
intramoluclar
Friedel Craft R
Cl
R
O

R
R
O
The reaction occurs if R is o- or p- directing group such as NH2, NHR, OH, OR, R, halogen.
If R is m- directing group (e.g. NO2, CN, COOH, COCH3, SO3H) no reaction occur.The above
reaction gives  -substituted naphthalene.
2
Chemical Reactions of naphthalene
1.
Reduction
Na
EtOH
1,4- dihydronaphthalene
Na
isoamyl alc.
1,2,3,4-tetrahydronaphthalene
Naphthalene
Tetralene
H2
Ni
decahydronaphthalene
Decalene
2. Oxidation
O
CrO3
AcOH
O
1,4- naphthoquinone
CHO
1) O3
2) H2O/Zn
CHO
Naphthalene
Phthaldehyde
O
O2
V2O3
O
O
Phthalic anhydride
COOH
KMnO4
H
COOH
Phthalic acid
3) Electrophilic substitution reaction
At position 1; carbocation intermediate stabilize by two resonance So carbocation is more stable position
1 than 2
3
NO2
conc. HNO3
conc. H2SO4
1- nitronaphthalene
SO3H
conc. H2SO4
40°C
naphthalene-1- sulfonic acid
SO3H
conc. H2SO4
180°C
naphthalene-2- sulfonic acid
Cl
Naphthalene
Cl2
FeCl3
1- chloronaphthalene
COCH3
CH3COCl
AlCl3
CS2
1- Acetylnaphthalene
COCH3
CH3COCl
AlCl3
PhNO2
2- Acetylnaphthalene
Elctrodonating group
(EDG): NH2, OH, OR,alkyl
Substituted naphthalene
Activating groups direct the electrophile to the same ring, while deactivating groups direct it to the
other ring.
Minor
EDG
Electrowithdrawing group (EWG):
NO2, CO, COOH, CN, SO3H
E
E
EDG
E
Major
4
Examples:
OH
OH
OH
NO2
conc. HNO3
+
conc. H2SO4
NO2
Major
NO2
OH
OH
conc. HNO3
conc. H2SO4
NO2
NO2
conc. HNO3
NO2
NO2
+
conc. H2SO4
NO2
Minor
Major
NO2
NO2
conc. HNO3
+
conc. H2SO4
O2 N
NO2
5
NO2
8
Anthracene
9
1
2
7
3
6
5
10
4
Anthracene has 4 isomers
I
III
II
IV
Synthesis of anthracene
1) Friedl Crafts
CH2Cl
AlCl3
-2H
+
ClH2C
Anthracene
Benzyl chloride
2) Elbe reaction
O
Pyrolysis
CH3
Anthracene
o- Methyl- benzenophenone
or o- Benzoyl- toluene
3) From 1,4- Naphthoquinone
The following method shows presence of naphthalene in anthracene
O
O
O
CrO3
AcOH
+
O
1,4- Naphthaquinone
1,3- Butadiene
O
Zn
O
9,10- anthraquinone
6
Anthracene
4) From benzene and phthalic anhydride
O
+
O
O
O
H2SO4
AlCl3
Zn
-H2O
HOOC
O
Phthalic anhydride
O
anthraquinone
Anthracene
Chemical reactions
X
X
X2
X= Cl or Br
-HX
Halogenation
X
O
Oxidation
Dil HNO3
In using dil. HNO3 only
to obtain 9,10anthraquinone
Anthracene
Anthracene
O
Reduction
9, 10- Anthraquinone
Na
isopropanol
Anthracene
9, 10- Dihydroanthracene
O
Anthraquinone
O
Preparation
O
1) From anthracene
Dil HNO3
K2Cr2O7
O
Anthracene
9, 10- Anthraquinone
7
Phenanthrene
Position of double bond
The most stable
3 benzenoid rings
Preparation of phenanthrene:
1) Howrth method
O
O
COOH
+
Zn-Hg/HCl
AlCl3
O
O
Succinic anhydride
COOH
9-bromo-9,10-dihydro-phenanthrene
Br
Br
Br2
Br
9,10-dibromo-9,10-dihydro-phenanthrene
Biphenyl-2,2'-dicarbaldehyde
CHO
Br2
1) O2
2) H2O
9,10-dihydro-phenanthrene
Na/EtOH
CHO
8
FeBr3
COOH COOH
Diphenic acid
O Zn-Hg/HCl
conc.H2SO4
H2O2
AcOH
Naphthalene
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