4. HETEROCYCLIC COMPOUNDS
• Have five or six membered carbon ring with
atleast one hetero atom as a member of ring.
• The common hetero atoms present in the
carbon ring are oxygen (O), nitrogen (N) and
sulphur (S), which are:
– Relatively stable
– Show aromatic character
– Contain conjugated double and single bonds
• There are a number of heterocyclic rings
which are easily opened and do not easily
possess any aromatic properties e.g. ethylene
oxide, - and -lactones etc. These are not
considered to be heterocyclic compounds.
• The importance of heterocyclic compounds is apparent
from variety of compounds that occur naturally or
they’re prepared on a commercial state by the dye or
• They are important building blocks for new materials
possessing interesting electronic, mechanical or
• Many of these compounds fulfill important
physiological functions in plants and animals thus the
carbohydrates may be classified as o-heterocycles
whereas nucleic acids and some amino acids, peptides
and proteins possess nitrogen containing ring system.
• Oxygen as hetero atom.
• All ring atoms in furan (4C + 1O) are sp2
• Possesses resonance.
• Less aromatic than benzene.
12. Physical Properties
• Most reactive among five membered heterocyclic
• Highly volatile liquid
• Boiling point is 31.40C
• Odour of chloroform
• Less dense than water
• Insoluble in water
• Soluble in most organic solvents such as alcohol, ether
and chloroform etc
18. Applications / Uses
• Nitrofurazone (Furacin) - anti-bacterial agent
• Nitrofurnatoin - anti-biotic in urinary tract
• In anti-pyretic drugs.
• It forms many derivatives like furfural and
• Nitrogen as hetero atom
• All ring atoms in furan (4C + 1N) are sp2
• Possesses resonance
• It has less aromaticity than thiophene and is
more reactive than furan
21. Physical Properties
• It is a colorless, volatile liquid that darkens on the
exposure to air
• Weakly basic
• Boiling point is 1310C
• It is sparingly soluble in water but fairly soluble in
ethanol and ether
• Burning pungent taste
• Its smell resembles to chloroform
• It occurs in coal-tar and bone oil
26. Applications / Uses
• Pyrrole is a constituent of anti-inflammatory drug
• It is present in drugs like (anti-depression) and Mirapex
(treatment against Parkinson’s disease).
• It is also used in anti-bacterial and anti-psychoticdrugs.
• It is used in drugs for the treatment of dyslipidimia and
in prevention of cardiac diseases.
• It is precursor of many biological molecules such as
porphyrin, hemoglobin, chlorophyll-A and vitamin B12.
29. Physical Properties
• Colorless liquid
• Boiling point 840C
• Odour is similar to that of benzene
• Insoluble in water but soluble in organic solvent
• More reactive than benzene
• Occurs in coal-tar and shale oils (rock)
• Boiling point is close to that of benzene so it is
difficult to separate it from the benzene fraction
obtained from coal-tar
• It can be obtained by heating disodium
succinate with phosphorous trisulphide.
• It can be prepared by the high temperature
reaction of sulphur with butane.
31. • Thiophene may be prepared by passing a
mixture of acetylene and hydrogen sulphide
through a tube containing alumina at 4000C.
2C2H2 + H2S → C4H4S + H2
32. Chemical Properties
Catalytic reduction of thiophene with Ni catalyst
results in the removal of sulphur to form n-
Thiophene + H2 + Ni (Catalyst) → CH3 (CH2)2CH3 + NiS
On reduction with sodium amalgam and ethanol,
it is converted into tetrahydro-thiophene.
• Derivatives of thiophene may be prepared
by heating 1, 4-diketone with phosphorous
• Condensed Structures:
• A number of condensed thiophene
systems are known e.g.
35. Applications / Uses
• Thiophenes are important heterocyclic
compounds that are widely used as building
blocks in many agrochemicals and
• The benzene ring of a biologically active
compound may often be replaced by a
thiophene without loss of activity. This is seen
in examples such as NSAID lornoxicam, the
thiophene analogue of piroxicam.
• Pyridine has nitrogen as hetero atom
• All ring atoms in thiophene are sp2 hybridized.
• It is Iso-electronic and analogous to benzene
• It is a resonance hybrid
38. Physical Properties
• Discovered by Anderson in 1851
• Boiling point is 1150C
• Occurs in coal-tar (0.1%) and in bone oil
• Disagreeable smell
• Miscible with water
• Basic liquid
• Crystallizes in orthorhombic system
40. Chemical Properties
• Electrophilic Substitution Reaction
• Nucleophilic Substitution Reaction
• Formation of Salts
Pyridine is stable and it is not easily oxidized at
carbon. It undergoes substitution rather than
addition. It shows negative inductive (electron
withdrawn) and negative mesomeric effect.
44. Applications / Uses
• It is used in formation of Pyridium
(structure) that is a pain reliever
and is given in urinary tract infection.
• It is used in formation of Imidazole [1, 2-a]
pyridine (anti-inflammatory) and Nexium
(used in acid reflex problem).
• It acts as a catalyst in the formation of
Grignard reagent and solvent in the
estimation of active hydrogen.
• Boiling point 1240C
• Among diazines, it is most important closely
related to pyridine and certain characteristic
properties increase in it.
• Two electron withdrawing nitrogen in 1, 3-
relationship is present.
• Ring carbon atoms are more deactivated
towards electrophilic attack than pyridine.
• Its nucleus occurs in purines, nucleic acid
synthesis and barbiturates.
• Bicyclic heterocyclic compound having a
benzene ring fused with a pyridine ring at 2, 3-
• It could be considered as naphthalene in
which one CH in 2-position has been replaced
• The official name of quinoline is 1-
51. Physical Properties
• Hygroscopic liquid
• Boiling point is 2380C
• Present in coal-tar, bone oil, petroleum and shale
• First isolated in 1834 and was first obtained from
alkaloid quinine by alkaline decomposition
• Disagreeable, pyridine-like odor
• It is soluble in water and completely miscible with
alcohol, ether and acetone
• Skraups Synthesis:
A mixture of aniline, glycerol and sulphuric acid is
heated in the presence if a mild oxidizing such as
nitrobenzene. The reaction being exothermic tends to
be violent and FeSO4 is used asmoderator.
• Friedlander’s Synthesis:
o-Amino benzaldehyde is condensed with
acetaldehyde in aq. NaOH.
• From Indole:
When methyl-lithium is added to Indole in methylene
dichloride solution, quinoline is produced by ring
expansion via the addition of chloromethylene.
57. • It is also used as a highly boiling basic solvent
in organic reactions.
• It is used in manufacture of dyes and
• It is used as solvent for resins and terpenes,
food colors, lake colors and salt free dyes.
• Over exposure to quinoline can cause injury to
cornea, retina and optic nerve.
• It is bicyclic heterocyclic compound having a
benzene ring fused with a pyridine isomer to
name of quinoline is 2-
• The official
60. Physical Properties
• It is a colorless, oily solid or liquid.
• Its melting point is 230C and boiling point is
• It is weakly basic and hygroscopic.
• It is penetrating and has unpleasant odour.
• It is insoluble in water and soluble in organic
62. Chemical Properties
• Electrophilic at position 5 or 8 nucleophilic
substitution reactions at position 1 (like
• Protonate to form salts upon treatment with
strong acid such as HCl
• While it shows oxidation as:
63. Applications / Uses
• Paparerine HCl (USP) which acts as
spasmolytic (relax / bronchodilator) on
• The Isoquinoline ring in natural components
derives from the amino acid tyrosine.
• It is used as viscosity adjustor and
intermediate in various chemical reactions.
• It was first isolated by Baeyer in 1866 from
degradation products of Indigo (C16H10O2N2).
• It occurs in coal-tar, jasmine flower and
• It is also present in human feces and has
intense fecal color.
66. Physical Properties
• Colorless solid
• Melting point 52.50C
• Strong fecal odour
• In dilute solutions, it has flowery odour
• It is soluble in hot water, alcohol and ether.
• Indole is widely distributed in the natural
environment and can be produced by a variety
• Indole can be prepared from aniline.
68. • Fischer-Indole Synthesis (1866):
When phenyl-hydrazone of Pyruvic acid is
heated with zinc chloride catalyst it yields
indole-2-carboxylic acid which decarboxylates
69. Chemical Properties
• Chemically, it resembles pyrrole.
• It shows usual substitution reactions at
position 3 due to greater stabilization of
intermediate carbonium ion as compared to
that in 2-position.
• If both 2 and 6 positions are occupied,
substitution occurs at 6-position.
71. Uses / Applications
• It is used in preparation of Indomethacin (anti-
• It is used in perfumery for the preparing
jasmine and orange blends.