Introduction and classification of Polynuclear aromatic Hydrocarbons, Preparation, Properties and uses of Naphthalene, Phenanthrene and Anthracene

1. POLYNUCLEAR
HYDROCARBONS
Presented by
Ms. V. Pushpalatha
M. Pharm
Assistant Professor
Dept. of Pharmaceutical Chemistry
School of Pharmacy
Sri Balaji Vidyapeeth University.

2. INTRODUCTION
Polynuclear hydrocarbons are compounds which contain two or more aromatic rings.
Also known as Polycyclic aromatic hydrocarbons.
Polynuclear hydrocarbons are non polar and lipophilic in nature
E.g.
Naphthalene Diphenylmethane

3. Classification of Polynuclear aromatic Hydrocarbons

4. Naphthalene:
 The simple and most important fused ring system is naphthalene.
 Molecular formula – C10H8
 It is the largest single constituent of coal-tar.
 Erlenmeyer (1866) proposed the symmetrical formula for naphthalene and Graebe
(1869) proved that it contains two benzene rings fused together in the ortho position.
1
2
3
4
5
6
7
8

5. Resonance structures of Naphthalene

6. Synthesis of Naphthalene
I. Haworth synthesis:
+
O
O
O
O
O
OH
Benzene Succinic Anhydride
AlCl3
3- Benzoyl propanoic acid
O
O
OH
Zn(Hg)/HCl
3- Benzoyl propanoic acid
O
OH
3 Benzyl Propanoic acid

7. O
OH
3 Benzyl Propanoic acid
Ring closure
Conc. H2SO4
O
Tetralone
O
Tetralone
Zn(Hg)/HCl
Tetralin

8. II. Synthesis of naphthalene from 4 phenylbut-1 ene
Aromatisation
Pd
Naphthalene
Tetralin
C
H2
+ H2
4- Phenylbut 1-ene Naphthalene
Hot CaO

9. Physical properties:
 Naphthalene is a colorless solid which forms shining flaked crystals.
 The Molecular weight of Naphthalene is 128.18 g/mol.
 It is insoluble in water and soluble in organic solvents.
 It is very volatile and slowly sublimates at room temperature.
 Its melting point is 80.2℃ and boiling point is 217.9 ℃
 It has an aromatic odour.

10. Chemical Properties
+ Conc.HNO3
N
+ O
–
O
1. Nitration:
2. Sulphonation:
S
O O
OH
S
O
O
OH
Conc.H2SO4
3. Halogenation:
+ Cl Cl
Cl
Conc. H2SO
CCl4 + Cl
H

11. 4. Friedal craft acylation:
O CH3
5. Friedal craft alkylation:
CH3COCl
AlCl3
+ C
H3
Cl AlCl3 CH3
+ Cl
H

12. 6. Oxidation:
O
O
O
O
O
Naphthalene
Naphthoquinone
Phthalic anhydride
CrO3
V2O5
7. Reduction :
Na, C5H11OH
Tetralin

13. Uses of Naphthalene:
 It is used for the commercial production of Phthalic anhydride.
 It is used for making Insecticide.
 Used as a mouth repellant.
 Used for the manufacture of dyes and synthetic resins

14. References:
Organic chemistry By Morison and Boyd, Page number : 967 – 982.
Organic chemistry, Volume I, The Fundamental Principles by I.L Finar,
Page Number : 697 – 722.

15. Thank You …