Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It has 5 carbon atoms and 1 nitrogen atom arranged in a six-membered aromatic ring. Pyridine can be obtained from coal tar or synthesized by passing acetylene and hydrogen cyanide over a hot tube. It undergoes electrophilic aromatic substitution preferably at the carbon-3 position due to stabilization of the intermediate carbocation. Nucleophilic substitution also occurs, preferentially at the carbon-2 position. Pyridine is used as a solvent, in organic reactions, to denature alcohol, and in preparing certain drugs that contain a pyridine ring system.

1. PYRIDINE
BY
MRS. NEELAM S. BHAGDEWANI
ASST.PROFESSOR
SGMSPM’S DNYANVILAS COLLEGE OF PHARMACY,
DUDULGAON, PUNE
C6H5N
M.P 38οC
B.P 115 οC

2. INTRODUCTION
• Pyridine is a six membered heterocyclic ring system containing
nitrogen as a heteroatom.
• Pyridine is a basic heterocyclic organic compound with the
chemical formula C5H5N. It is structurally related to benzene,
with one methine group (=CH-) replaced by a nitrogen atom.
Pyridine have 5 carbon atoms and one nitrogen atom.
• The numbering of pyridine is as follows:
Source: the credit for the discovery of the pyridine goes to
Anderson who first obtained it from bone oil. It occurs in coal
tar as well.

3. Coal tar (0.1%), bone oil, petroleum.

4. SYNTHETIC METHODS OF PYRIDINE
1. Pyridine is present in light oil fraction of coal tar distillation. The light oil
fraction is treated with dil. Sulphuric acid. This dissolves basic substances
including pyridine. The acid layer is isolated, neutralized and fractionated
several times to get a pure pyridine.
2. Pyridine is prepared by passing a mixture of acetylene and HCN through a
red hot tube.
Passed over red hot
tube
3. By heating the hydrochloride of pentamethylenediamine and oxidizing the
product piperidine with conc. Sulphuric acid at 300◦C or by catalytic
dehydrogenation.

5. 4. Hantzsch Synthesis: one important method is the hantzsch synthesis a β-
dicarbonyl compound is condensed with one molecule of aldehyde and one
molecule of ammonia, the dihydropyridine is formed and this give the pyridine
derivative on oxidation with nitric acid.

6. 5. From pyrrole:

7. CHEMICAL PROPERTIES OF PYRIDINE
• Pyridine is colorless liquid bp 115οC and freezing point -42 οC.
• Pyridine is completely soluble in water and most organic solvents its solubility
in water is due to presence of excellent H-bonding present between pridine and
water.
• Pyridine has a characteristic pleasant odor.
• Basicity: Pyridine is basic in nature reacts with acids to form salts. The
basicity of pyridine is due to the availability of lone pair of electrons of nitrogen
atom. Pyridine is much weaker base than alkyl amines because the lone pair of
electrons of nitrogen are present in the sp2 hybrid orbital instead of sp3 hybrid
orbital. Consequently the lone pair is more tightly held and is less available for
protonation.
• Pyridine have 5 carbon atoms and one nitrogen atom. All are sp²
hybridized. The porbital of nitrogen and all carbon atoms lie in the same
plane. Overlapping of p-orbitals result in delocalization of six π-electrons
in the cyclic ring, following Hückel rule, imparts aromatic chaeacter

8. 1. ELECTROPHILIC AROMATIC SUBSTITUTION REACTION OF PYRIDINE
Electrophilic aromatic substitution reactions of pyridine is preffered at carbon-3 than at
carbon-2 and carbon-4 due to high stability of carbocation formed by the attack of
electrophile at carbon-3. the low reactivity of pyridine is due to the presence of non-
bonding electrons of nitrogen in perpendicular to the π system hence cannot stabilise
intermediate carbocation. Further the heteroatom cannot donate electrons to the
carbocation instead it withdraws electrons by electron withdrawing inductive effect and
resonance effect.pyridine is therefore less reactive than benzene and nitrobenzene towards
electrophilic aromatic substitution.
Mechanism: Electrophilic aromatic substitution of pyridine involves through the
intermediate formation of carbocation. It involves following steps:

10. REACTIONS OF ELECTROPHILIC AROMATIC SUBSTITUTION

11. 2. NUCLEOPHILIC SUBSTITUTION REACTIONS OF PYRIDINE
Pyridine undergoes nucleophilic substitution reaction. The electron density at the carbon
atoms of pyridine ring is decreased due to electron withdrawal by nitrogen.substitution
usually takes place at the 2- and 4 position but position 2 is more preffetred than
position 4.
Mechanism: the nucleophilic substitution at position 2 is preffered than the position 4
due to the more stabilised intermediate anion.

12. REACTIONS OF NUCLEOPHILIC SUBSTITUTION
1. Tischtischibabin reaction: when pyridine is heated with sodamide in
toluene sodio salt of 2-aminopyridine is formed. This on hydrolysis gives
amine. When excess of sodamide is used 2, 6- diaminopyridine is obtained.
2. Hydroxylation: when pyridine is heated with solid potasium
hydroxide at 400οC, 2-Hydroxypyridine is formed.

13. 3. Alkylation by alkyl lithium: when pyridine is heated with n-butyl lithium, 2-
butyllithium is formed.

14. 3. Oxidation: the pyridine is being deactivated. It is very resistant towards
oxidation on treatment with peracids.however pyridine is forms pyridine-1-
oxide.

15. 4. Reduction:

16. REACTIONS ON SIDE CHAIN OF PYRIDINE HOMOLOGUES

19. Uses of pyridine: pyridine is used
1. As a solvent
2. As a catalyst in many organic reactions.
3. For denaturing alcohol
4. In the preparation of certain drugs
Medicinal compounds: the following medicinal compounds possess pyridine
heterocyclic ring system.

21. THANK YOU