Polynuclear Hydrocarbons
Classification of Polynuclear Hydrocarbons Polynuclear Hydrocarbons may be divided into two groups,
Polynuclear Hydrocarbons
Benzenoid
Isolated
Non- Benzenoid
Fused rings
Linear
Azulene
Angular
Biphenyl
Naphthalene
Phenanthrene
I. I.
Isolated Isolated Ring Ring Polynuclear Polynuclear Hydrocarbons Hydrocarbons
Biphenyl Biphenyl (diphenyl): (diphenyl):
Preparation of Biphenyl a) Fittig reaction 2Ph-Br + 2Na
ether soln
Ph-Ph + 2NaBr
b) From benzene diazonium sulphate N=N HSO4
Cu EtOH
+ N2 + CuHSO4 Biphenyl
c) From benzidine H2N
NH2
Benzidine H3PO4
Biphenyl
NaNO2 HCl
Cl N=N
N=N Cl
d) Ulmann diaryl synthesis 2 Ph-I
2 Cu
2 H3C
I
Ph-Ph + 2CuI 2 Cu
H3C
sealed tube
CH3
4,4'- Dimethyl-biphenyl NO2
NO2
2
I
2 Cu
sealed tube O2N
2,2'- Dinitro-biphenyl
e) By using Arylmagnesium halide C OC l PhMgBr + PhBr
2
Ph-Ph + MgBr2
Reactions of biphenyl Biphenyl undergoes substitution reactions,
• In biphenyl one ring act as electron donating group and the other act as electron withdrawing group
Resonance shows that O- and P- are the most reactive positions towards electrophilic substitution. The electrophilic substitution occurs in 4- position (major) and 2- position (minor) due to steric effect of other benzene ring. The 2nd substitution occurs in the empty ring in 2 or 4- position. e.g. NO2 conc HNO3 conc H2SO4
+ 2-Nitro-biphenyl
NO2 4-Nitro-biphenyl conc HNO3 conc H2SO4
NO2 O2N
NO2 + 4,4'-Dinitro-biphenyl
NO2 NO2 +
2,4'-Dinitro-biphenyl
O2N 2,2'-Dinitro-biphenyl
Problem: Explain the products formed when biphenyl is mononitrated and .when it is dinitrated
Biphenyl derivatives (1) Benzidine (4, 4`-diaminobiphenyl) H2N
(2) Diphenic acid
NH2
COOH COOH
(3) Diphenyl methane CH2
(1) Benzidine (4, 4' diaminobiphenyl) Methods of preparation
From dihydrazo benzene NH-NH Hydrazano-benzene
HCl
H2N
NH2 Benzidine
Q. Show how could you prepare benzidine from benzene?  Answer I
I conc. HNO3
I2
conc. H2SO4
HNO3
NO2
I Cu
2
O 2N
NO2
NO2
H2N
NH2 Benzidine
Zn/HCl
Uses of Benzidine  preparation of Congo red H2N
NH2 NH2
2
NaNO2/HCl
Cl N N
N N Cl
NH2
NH2 NN
SO3H
N N
SO3H
SO3H Congo Red
Diphenic acid) 2(
Methods of preparation
From anthranilic acid NH2
COOH COOH
COOH
COOH NaNO2 HCl
N N
∆ Cu
biphenyl- 2,2'- dicarboxylic acid (Diphenic acid)
Ulmann diaryl synthesis COOEt COOEt
COOEt 2
I
∆ Cu
COOH COOH HCl
biphenyl- 2,2'- dicarboxylic acid (Diphenic acid)
oxidation of Phenanthrene or phenanthraquinone COOH 50% H2O2 AcOH, ∆
phenanthrene
COOH
Diphenic acid
O K2Cr2O7 H2SO4
O
phenanthraquinone
Chemical Reactions
with acetic anhydride. 1 O COOH
Ac2O
O
COOH O Diphenic acid
Diphenic anhydride
2. Conversion of diphenic acid to dflourenone COOH COOH Diphenic acid
Ca(OH)2
O C O C O O Ca diphenate
Ca
∆ 80-200°C -CaCO3
O
9- fluorenone
3. with conc. H2SO4 COOH COOH
Diphenic acid
Free rotation
O
O OH
conc. H2SO4 HOOC OH
-H2O
O
9- fluorenone- 4carboxylic acid
4. Oxidation of KMnO4 COOH COOH Diphenic acid
KMnO4
COOH COOH pthalic acid
5. with sodalime COOH
Sodalime
COOH Diphenic acid
biphenyl
Atropisomers of biphenyl  Optical isomers produced due to restricted rotation is called atropisomers  Restricted rotation produce when 0position contains two different bulky groups and hence molecule is optically active.. for example
CO2H NO2
NO2 A
Mirror
CO2H
NO2 CO2H
CO2H NO2
Optically active
NO2
Cl
H
H
Cl
Mirror
H
Cl
H2N
H
B
CO2H Cl
CO2H CO2H Optically active no plane of symmetry
Optically active
NO2
CO2H NO 2 Optically active no plane of symmetry
 When o- position contains two similar groups, the molecule is optically inactive due to presence of plane of symmetry .. for example HO2C
CO2H
H3OC
CO2H
H3OC
NO2
Plane of symmetry
O 2N
CO2H
Optically inactive due to presence of plane of symmetry
COOH
O2 N
HO2C
NO2
Optically active free rotation is possible
NO2
F Optically active F is a small atom so permit by free rotation
(3) Diphenyl methane
Methods of preparation
1. Friedel- Crafte CH2Cl +
AlCl3
Benzyl chloride
2
+
CH2
Diphenyl methane
CH2Cl2
AlCl3
CH2
Diphenyl methane
From benzophenone. 2 O HI/ P ∆ or Zn Hg/ HCl or NH2NH2/ NaOEt Benzophenone
CH2
Diphenyl methane
Chemical Reactions
1. Nitration CH2
conc. HNO2 conc. H2SO4
Diphenyl methane
conc. HNO2 conc. H2SO4
CH2
NO2
1-benzyl-4-nitrobenzene
O2 N
CH2
bis(4- nitrophenyl)methane
NO2
2. Halogenation Br CH2 Diphenyl methane
Br2 hv
C H Diphenylmethylbromide
3. Oxidation O CH2 Diphenyl methane
[O] K2Cr2O7 H2SO4
C benzophenone
II. Fused System
a) Naphthalene OH
α
α
8
1
β
7
2
β
β
6
3
β
4
5 α
α
1-Naphthol or α-Naphthol Br
OH
2-Naphthol or β -Naphthol Br
HO3S
1,8- Dibromo-naphthalene
SO3H
Naphthalene-2,7- disulfonic acid
Structure elucidation of naphthalene 1- Molecular Formula: C10H8 COOH
2- Naphthalene
O COOH
Phthalic acid C
So naphthalene contain the skeleton C
NO2 COOH
3-
Naphthalene
nitration
Nitronaphthalene
O COOH
Nitrophthalic acid
So nitro group is present in benzene ring
Naphthalene nitration
4-
Nitronaphthalene
redn.
aminonaphthalene
O COOH
COOH
Phthalic acid
The benzene ring in phthalic acid produced by oxidation of aminonaphthalene is not the same ring is that obtained by oxidation of nitronaphthalene.
i.e. Naphthalene contains two benzene rings and we can explain this by this equation A
B
HNO3 NH2
NO2
NO2
COOH
HOOC B HOOC
O
A
B
redn.
A
B
O
A COOH
The structure of naphthalene is confirmed by method of its analysis
1- Howarth method O
O
+
O
AlCl3
Zn-Hg/HCl
HO
R
R
Zn-Hg/HCl
R
R
O
O
O
O Succinic anhydride
conc.H2SO4 -H2O
HO
R
Se ∆
R
Other way of cyclization O
O
+
O
SOCl2
AlCl3 HO
R
R
Zn-Hg/HCl
intramoluclar Friedel Craft R
R O
O
O
O Succinic anhydride
AlCl3
Cl
R
Se ∆
R
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 β -substituted naphthalene.
Synthesis of 1-alkyl naphthalene O
O
+
AlCl3
O
Zn-Hg/HCl
COOH O benzene Succinic anhydride
4-oxo-4-phenylbutanic acid
COOH
4-phenylbutanoic acid
1) RMgX 2) HOH
conc. H2SO4 -H2O O
1-tetralone
HO
R
R
1- Alkyl naphthalene
2- From β -benzylidene – propenoic acid conc. H2SO4 -H2O
OH O
β-Benzylidene-3-propenpoic acid Zn -ZnO naphthalene
O
OH
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
Naphthalene
CHO Phthaldehyde O
O2 V2O3
O O Phthalic anhydride COOH
KMnO4 H
COOH Phthalic acid
3. Addition of Cl2 Cl Cl2
Cl 1,4- dichloro- 1,4- dihydronaphthalene
Naphthalene Cl excess
Cl
Cl2
Cl Cl 1,2,3,4- tetrachloro- 1,2,3,4-tetrahydronaphthalene
4. Electrophilic substitution reaction Q:
Naphthalene udergoes electrophilic substitution at position 1 not 2. Explain
At position 1; carbocation intermediate stabilize by two resonance E
E E 1 Naphthalene
E
E
Naphthalene
one resonance structure
So carbocation is more stable position 1 than 2
Examples of electrophilic substitution
NO2 conc. HNO3 conc. H2SO4
1- nitronaphthalene SO3H
Cl2 conc. H2SO4 40째C
naphthalene-1- sulfonic acid SO3H
conc. H2SO4 180째C
naphthalene-2- sulfonic acid Cl
Naphthalene Cl2
FeCl3
1- chloronaphthalene COCH3 CH3COCl AlCl3 CS2
1- Acetylnaphthalene CH3COCl AlCl3 PhNO2
COCH3
2- Acetylnaphthalene
Substituted naphthalene  Activating groups direct the electrophile to the same ring, while deactivating groups direct it to the other ring. Elctrodonating group (EDG): NH2, OH, OR, alkyl
Electrowithdrawing group (EWG): NO2, CO, COOH, CN, SO3H
Homonuclear attack Minor EDG
E
E EDG
E
Major
Heteronuclear attack E
E EWG EWG
E
Major
E
Major
Examples:
OH
OH
OH
NO2 conc. HNO3
+
conc. H2SO4
NO2 OH
NO2 Major
OH
conc. HNO3 conc. H2SO4
NO2
NO2 conc. HNO3
NO2
NO2
+
conc. H2SO4
NO2 Minor
Major
NO2
NO2
conc. HNO3
+
conc. H2SO4
O2N NO2
NO2
Naphthalene derivatives
1. Nitronaphthalene 1. naphthalene is prepared by direct nitration NO2 conc. HNO3 conc. H2SO4
Naphthalene
1- nitronaphthalene
2. naphthalene is prepared by indirect method N=N
NH2 NaNO2 HBF4
2- Aminonaphthalene
BF4 CuNO2 ∆ -N2
NO2
2. Naphthols Preparation: OH
SO3H conc. H2SO4 40°C
NaOH 300°C
Naphthalene-1- sulfonic acid
Naphthalene
conc. H2SO4 180°C
1- Naphthol
OH
SO3H
NaOH 300°C
Naphthalene-2- sulfonic acid
2- Naphthol
Properties: 1- Reaction of α and β- naphthols with aryl diazonium salt OH
O
H
N
Ph
O
N
H
N
Ph
N
Ph-N=N-Cl NaOH
2- phenylazo-1- Naphthol Azo form
Ph
Ph
N
N
N OH Ph-N=N-Cl
hydrazo form stable by intermol. H.B
H O
NaOH
2- phenylazo-2- Naphthol
N
H O
2- Reaction of α and β- naphthols with nitrous acid OH
OH
O
2- nitroso-1- naphthol
[1,2]naphthoquinone-2-oxime
O N
N OH
O N
O OH
H
N
HONO
1- Naphthol
O
H O
HONO
2- Naphthol
2- nitroso-2- naphthol
[1,2]naphthoquinone-1-oxime
3- Conversion of α and β- naphthols to naphthyl ether OR RI
OH
NaOH
OR 1- Naphthol
ROH conc. H2SO4
RI
OR
NaOH
OH
1- Naphthol
OR ROH conc. H2SO4
3. Naphthylamine
 Preparation: 1- Naphthylamine NO2
NH2 Zn/HCl
conc. HNO3 conc. H2SO4
1- Nitronaphthalene
1- aminonaphthalene
Preparation: 2- Naphthylamine Bucherer reaction
OH NH3
NH2
NH4HSO3
β- Naphthol
β- naphthylamine
Mechanism H OH
OH
O
H
H
SO3NH4
SO3NH4
NH4HSO3
β- Naphthol NH
NH2
NH3
NH2
-NH4HSO3
H
H
SO3NH4
SO3NH4
β- naphthylamine
4. Halogenated naphthalene  A) Preparation of 1- halogented naphthalene
Br Br2 FeBr3
1- bromonaphthalene
B) Preparation of 2- halogenated naphthalene via Sandemeyer
NH2 NaNO2 HCl 0°C
2- Naphthylamine
N
Cl
N CuBr ∆, -N2
Br
Questions: Convert 2- naphthol to:
A) 2- bromonaphthol b) Naphthalene -2- carboxylic acid C) 1,2- naphthaquinone-1- oxime D) Ethyl β–naphthyl ether
5. Alkyl naphthalene  Synthesis of 1- alkyl naphthalene O
O + Benzene
O
O Succinic anhydride
Zn-Hg/ HCl
COOH
AlCl3
4- oxo-4-phenylbutanoic acid
COOH
4-phenylbutanoic acid
Synthesis of 2- alkyl naphthalene O
O +
Zn-Hg/HCl
AlCl3
O
H3C
H3C Toluene
O Succinic anhydride
HO
O
Zn-Hg/HCl
conc. H2SO4 -H2O
H3 C
H3C
HO
H3C O
O
Se ∆
H3C 2- methyl naphthalene
6. Naphthaquinones  There are six possible naphthaquinones, but only common are 1,2; 1,4; 2,6- naphthaquinones O
O O
O
1,2- Naphthaquinone
O 1,4- Naphthaquinone
O 2,6- Naphthaquinone
Preparation of naphthaquinones
:Naphthaquinone- 1,4 O CrO3 AcOH
O Naphthalene
1,4- Naphthaquinone
:Naphthaquinone- 1,2 NH2
O OH
O
K2Cr2O7 H2SO4 or PbO2
1- Amino- 2-naphthol
1,2- Naphthaquinone
:Naphthaquinone- 2,6 OH
O PbO2
HO 2,6- dihydroxynaphthalenel
benzene
O 2,6- Naphthaquinone
7. Naphthoic acid COOH
1- Naphthoic acid or α- Naphthoic acid
COOH
2- Naphthoic acid or β- Naphthoic acid
Preparation of 1-naphthoic acid
From bromonaphthalene Br Mg dry ether 1- bromonaphthalene
COOH
MgBr 1) CO2 2) H
1- naphthyl magnesium bromide
1- Naphthoic acid
From 1- naphthylamine Cl
NH2
N NaNO2
CN CuCN
HCl
1- Naphthylamine
N
COOH
H2O H
1- Naphthoic acid
1- naphthonitrile
From 1- acetylacetophenone COOH
COCH3 I2/NaOH
1- Acetylacetophenone
1- Naphthoic acid
2- Naphthoic acid can be prepared by the same above methods
Anthracene 1
9
8
2
7
3
6 4
10
5
 Anthracene has 4 isomers:
I
II
Resonance I, II are more stable, contain 2 benzene rings.
Synthesis of anthracene  1. Friedl Crafts CH2Cl + ClH2C Benzyl chloride
AlCl3
-2H
Anthracene
 2. Elbe reaction
O Pyrolysis
CH3 o- Methyl- benzenophenone or o- Benzoyl- toluene
Anthracene
 3. From 1,4- Naphthoquinone O
O +
O 1,4- Naphthaquinone
1,3- Butadiene
O
O CrO3 AcOH
Zn
O 9,10- anthraquinone
Anthracene
The above method shows presence of naphthalene in anthracene
 4. From benzene and phthalic anhydride O +
O
O AlCl3 HOOC
O Phthalic anhydride O H2SO4
Zn
-H2O
O anthraquinone
Anthracene
Chemical reactions
 1) Diels Alder
O +
Anthracene
O O Maleic anhydride
O ∆
O O Endo- anthracene- maleic anhydride adduct
 2) Addition of one molecule of O2
+
Anthracene
O2
O O
Anthracene epoxide
 3) Halogenation of anthracene
X
X X2
-HX
X= Cl or Br
Anthracene
X
 4) Oxidation of anthracene
O Dil HNO3
O Anthracene
9, 10- Anthraquinone
In using dil. HNO3 only to obtain 9,10- anthraquinone
 4) Reduction of anthracene
Na isopropanol
Anthracene
9, 10- Dihydroanthracene
Anthraquinone O
O
Preparation
O Dil HNO3 K2Cr2O7
O Anthracene
9, 10- Anthraquinone
O +
O
O
AlCl3 HOOC
O Phthalic anhydride O H2SO4 -H2O
O anthraquinone
Chemical Reactions
Zn/ ∆ Distillation or Zn/H/150°C
Anthracene
O
O Sn/HCl/AcOH
O
9- Anthrone OH Zn/ NaOH
OH Anthraquinol
 Nitration O
O
O
NO2
O
HNO3
HNO3
H2SO4
H2SO4
O 1- nitro-9,10- anthraquinone
Major NO2
NO2
O
1,5- dinitroanthraquinone +
NO2
O
NO2
O 1,8- dinitroanthraquinone
Sulphonation O
O
O
SO3H
SO3H
Oleum
+
160°C
O
O
O
Anthraquinone-2-sulfonic acid
small
Major
Anthraquinone does not undergo Friedl Craft reaction •Preparation of 2-amino-anthraquinone O
O
NH2
SO3H NH3
∆
O Anthraquinone-2-sulfonic acid
O 2- amino-anthraquinone
Alizarin O
OH OH
O
1,2-dihydroxyanthraquinone Alizarine
Preparation O
O SO3H Oleum, H2SO4 160°C
O Anthraquinone
O 9,10- anthraquinone-2- sulfonic acid 1)NaOH, ∆ 2) [O]
O
OH OH
O Alizarine
Preparation of Alizarine Blue O
OH
O OH
OH OH
1) conc. HNO3 conc. H2SO4 2) [H]
NH2
O Alizarine
O O
OH OH
1) Glycerol/ H2SO4 2) PhNO2
N O Alizarine Blue
Alizarine blue is used for dyeing wool by blue color
Phenanthrene 6 5
1
10
9
4
2 3 7 11
1
10
9
8
6
2 5
14
13
7
8
3 12
14 13
4
11
12
Position of double bond
The most stable 3 benzenoid rings
Preparation of phenanthrene  1) Howrth method O O COOH +
Naphthalene
O
AlCl3
Zn-Hg/HCl
O Succinic anhydride
COOH conc.H2SO4
O Zn-Hg/HCl
Preparation of 1- alkyl phenanthrene: R O 1) RMgX
OH
R Se
2) HOH
Preparation of 2- alkyl phenanthrene: O
R
O COOH
R +
O
Naphthalene R
R
COOH
O Zn-Hg/HCl
conc.H2SO4
R
Se
Zn-Hg/HCl
AlCl3
O
R
2) Posher synthesis COOH
CH2COONa
CHO NO2
+
Ac2O
Zn-Hg/HCl
NO2 COOH
COOH
NaNO2/H2SO4
NH2
N2HSO4
Cu
Phenanthrene
Chemical Reactions
Na/EtOH
9,10-dihydro-phenanthrene
1) O2 2) H2O
CHO CHO
Biphenyl-2,2'-dicarbaldehyde
Br2
Br
Br 9,10-dibromo-9,10-dihydro-phenanthrene
Br Br2 FeBr3
9-bromo-9,10-dihydro-phenanthrene
H2O2 AcOH
COOH COOH
Diphenic acid
Benzil-Benzilic rearrangement COONa Ph C O
NaOH
Ph C O
Ph
C
OH
Ph Benzilic acid salt
Benzil
Mechanism Ph C O Ph C O
OH HO
OH
Ph C O
C O
Ph C O
Ph C O Ph
O Proton transfer
C O Ph C OH Ph
COOH
O
NaOH
OH
H
O
9-hydroxy-9H-flourene-9-carboxylic acid
Phenanthraquinone
Mechanism O
OH HO
O
O
O
COO Proton transfer
OH
COOH O
Phenanthraquinone  Preparation
O K2Cr2O7 H2SO4
Phenanthrene
O
Phenanthraquinone
Condition necessary for aromaticity Any compound to be aromatic, it must be; 1. Cyclic 2. Planner 3. All atoms must be SP2 4. All double bonds must be conjugated 5. Obey Huckle rule which state that any aromatic compound must contain 4n+2 pi electrons where n 0,1,2,3,…
Examples
n=1 6 π electron
n=2 10 π electron
n=3 14 π electron
Examples of non- benzenoid aromatic cmpound
All are aromatic( cyclic, planner,1, and agree with Huckle rule: 4n+2= 6 (n=1)
Examples of non- aromatic
Not aromatic; both contain Sp3
Not aromatic
Not aromatic
Aromatic; cyclic, planner,
Does not obey Huckel rule
Does not obey Huckel rule
obey Huckel rule
4n+2=8; n=1.5
4n+2=4; n=0.5
4n+2=2; n=0
Aromatic
Not Aromatic
Aromatic
4n+2=10; n=2
8 pi electrons
4n+2=14; n=3
Aromatic
Aromatic
4n+2=10; n=2
4n+2=10; n=2