THIS PRESENTATION COVER INTRODUCTION, STRUCTURE, AROMATICITY, RESONANCE, BASICITY, PHYSICAL PROPERTIES, SYNTHESIS, CHEMICAL PROPERTIES AND MEDICAL USES OF PYRIDINE AND PYRIMIDINE

1. 6th MEMBERED HETEROCYCLIC
COMPOUNDS CONTAINING ONE
AND TWO HETERO ATOM
BY- VISHAL SINGH SOLANKI
IDEAL INSTITUTE OF PHARMACY, POSHERI, WADA, M.H.

2. INDEX
• PYRIDINE
• PYRIMIDINE

3. PYRIDINE

4. INTRODUCTION
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.
It is a highly flammable, weakly alkaline, water-miscible liquid
with a distinctive, unpleasant fish-like smell.
Pyridine is colourless, but older or impure samples can appear
yellow.
The pyridine ring occurs in many important compounds,
including agrochemicals, pharmaceuticals, and vitamins.
Historically, pyridine was produced from coal tar.

5. Structure of pyridine

6. AROMATICITY
• PYRIDINE FOLLOW HUCKLE RULE (4n+2πe)
• PYRIDINE HAVE 6 πe
• PYRIDINE HAVE SP2 HYBRIDIzED ORBITAL IN EACH ATOM
OF THE RING
• CYCLIC STRUCTURE

7. BASICITY OF PYRIDINE

8. RESONANCE
• The bond length and stability of Pyridine can be explained by the resonating
structures. Electronegative atom N produces the deficiency of electron density
in pyridine and ring carbon acquires increased electron density. Thus nitrogen
atom in pyridine causes deactivation of the ring, contrary to pyrrole.

9. PHYSICAL PROPERTIES OF PYRIDINE
Chemical formula C5H5N
Molar mass 79.102 g·mol
−1
Appearance Colourless liquid
Odour Nauseating, fish-like
Density 0.9819 g/ml
Melting point −41.6 °C (−42.9 °F; 231.6 K)
Boiling point 115.2 °C (239.4 °F; 388.3 K)
Solubility in water Miscible
Preferred IUPAC name Pyridine
Other names Azine, Azinine, 1-Azacyclohexa-1,3,5-diene

10. SYNTHESIS OF PYRIDINE

11. 1. Hantzsch synthesis
• The Hantzsch synthesis is a four-component reaction between an
aldehyde, two equivalents of a β-ketoester and ammonia, followed by
oxidation to give a pyridine-3,5-dicarboxylate.
• Subsequent decarboxylation gives the corresponding pyridines.

13. MECHANISM

14. CONTI…

15. CONTI……..

16. CONTI…

17. CONTI…

18. 2. USING I,5 DIKETONE COMPOUNDS

19. CHEMICAL PROPERTIES OF
PYRIDINE

30. APPLICATION OF PYRIDINE
• Pyridine is widely used as a versatile solvent.
• It is important in industrial organic chemistry, both as a fundamental building block and as a
solvent and reagent in organic synthesis.
• It is used as a solvent in Knoevenagel condensations.
• Pyridine-borane, C5H5NBH3 (m.p. 10–11°C), is a mild reducing agent with improved stability
compared to sodium borohydride (NaBH4) in protic solvents and improved solubility in aprotic
organic solvents.
• Pyridine-sulphur trioxide, C5H5NSO3 (mp-175 °C), is a sulfonation agent used to convert alcohols
to sulfonates, which in turn undergo C-O bond scission (break-up) upon reduction with hydride
agents.
• It is a starting material in the synthesis of compounds used as intermediates in making insecticides,
herbicides, pharmaceuticals, food flavorings, dyes, rubber chemicals, adhesives, paints, explosives,
and disinfectants.
• It is used as a denaturant for antifreeze mixtures.
• It is sometimes used as a ligand in coordination chemistry.

31. PYRIMIDINE

32. INTRODUCTION TO PYRIMIDINE
• Pyrimidine is a simple aromatic ring composed of two nitrogen atoms
and four carbon atoms, with hydrogen atoms attached to each carbon a
six-membered ring.
• The carbon and nitrogen atoms are connected via alternating double
and single bonds. This bond structure allows for resonance, or
aromaticity, causing the ring to be very stable.
• The term pyrimidine is also used to refer to pyrimidine derivatives,
most notably the three nitrogenous bases that, along with the two
purines, are the building blocks of both deoxyribonucleic acid (DNA)
and ribonucleic acid (RNA).

33. Structure of pyrimidine

34. PHYSICAL PROPERTIES OF PYRIMMIDINE
Chemical formula C4H4N2
Molar mass 80.088 g mol
−1
Density 1.016 g cm
−3
Melting point 20 to 22 °C (68 to 72 °F; 293 to
295 K)
Boiling point 123 to 124 °C (253 to 255 °F;
396 to 397 K)
Solubility in water Miscible (25°C)
Other names 1,3-Diazine, m-Diazine
1,3-Diazacyclohexa-1,3,5-triene
state solid

35. AROMATICITY
• PYRIDIMINE FOLLOW HUCKLE RULE (4n+2πe)
• PYRIMIDINE HAVE 6 πe
• PYRIMIDINE HAVE SP2 HYBRIDIZED ORBITAL IN EACH
ATOM OF THE RING
• CYCLIC STRUCTURE

36. RESONANCE
• Pyrimidine shows aromatic properties because the resulting molecular orbital satisfies the Hackle’s
rule (4n+2 rule).
• The nitrogen lone pair is not released into the aromatic system because it is perpendicular to the
system.
• The nitrogen withdraws electrons by resonance, resulting in an electron-deficient ring system.

37. BASIC CHARACTER
• Pyrimidine is a weaker base than pyridine, because of electron
withdrawing effect of the second nitrogen atom present in
pyrimidine.
• Pyrimidine gets protonated in acidic medium.
• Presence of electron donating groups like alkyl, alkoxy enhance
the basicity.

38. SYNTHESIS OF PYRIMIDINE

39. 1. BY USING 1,3 DICARBONYL COMPOUND
COMBINING OF 1,3 DICARBONYL COMPOUND WITH N-C-N FRAGMENT SUCH
AS AN UREA, AN AMIDINE OR A GUANIDINE.

40. EG.

41. 2. FROM ALKYL PYRIMIDINE

42. 3. FROM CHLORO PYRIMIDINE

44. CHEMICAL PROPERTIES OF
PYRIMIDINE

45. ELECTROPHILIC ADDITION TO N

46. NUCLEOPHILIC SUBSTITUTION
REACTIONS
Pyrimidine easily undergoes
nucleophilic substitution.
Nucleophilic attack takes place at
2, 4 or 6th positions.
Grignard & oregano lithium add to
4 position at reaction Metal –
Halogen Exchange: Lithio -
diazines are also accessible via
halogen exchange with alkyl -
lithiums, but very low
temperatures must be used in
order to avoid nucleophilic
addition to the ring.

47. ELECTROPHILIC SUBSTITUTION
REACTIONS
Pyrimidine is less reactive than
pyridine due to two electron
withdrawing groups towards
electrophilic substitution.
However presence of electron
donating groups on ring,
electrophilic substitution is
possible at 5th position (the least
electron-deficient).
Nitration, Sulphonation,
Bromination, Formylation and azo
coupling have been observed
with substituted pyrimidines.

48. MEDICAL USES

49. CONTI…

50. CONTI…

51. REFERENCE
1. H. G. O. Alvim, E. N. da Silva Júnior and B. A. D.
Neto, ORGANIC CHEMISTRY, RSC Adv., 2014, 4, 54282–
54299.
2. https://en.wikipedia.org/wiki/Pyrimidine#Synthesis
3. https://www.slideshare.net/surajKumarGupta9/synthesis-of-
pyrimidine-and-its-medical-application?qid=5f7091d1-a45b-4855-
bd4e-aad69ebf4aed&v=&b=&from_search=28
4. https://www.slideshare.net/AZCPh/heterocyclic-compounds-
organic-chemistry-b-pharm

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