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Pyridine - Syntheis, Reactions and Medicinal uses
- 1. Heterocyclic Compounds Pyridine Synthesis,Reactions&MedicinalUses Prof.Dr.P.Venkatesh Chem Eazy N
- 2. Synthesis of Pyridine 1. By passing a mixture of acetylene and hydrogen cyanide through a red hot tube. 2. From Glutaconaldehyde and ammonia. HC HC HC HC CH N N pyridine O OH Glutaconaldehyde + NH3 -2H2O N pyridine Chem Eazy
- 3. 3. From Pentamethylenediamine hydrochloride. 4. Oxidation of 3-methyl pyridine (β-picoline) H2N NH2.HCl HCl. -NH4Cl, HCl N H piperidine H2SO4 300 °C N pyridine Pentamethylenediamine hydrochloride N CH3 3- methylpyridine K2Cr2O7 H2SO4 N COOH Nicotinic acid CaO N pyridine + CO2 Chem Eazy
- 4. Characteristic Reactions of Pyridine Chem Eazy 3 2 4 N 1 5 6
- 5. 1. Electrophilic substitution Reactions Pyridine is much lesser reactive than benzene towards electrophilic reagents. Because, the electronegativity of nitrogen lowers the electron density around the ring carbons & the usual electrophiles can coordinate with the lone pair of electrons on nitrogen to form resonance stabilized pyridinium ion. The formation of pyridinium ion deactivates the ring and thus further substitution occurs with difficulty and at position 3. N N + E + E + Pyridinium ion Chem Eazy
- 6. Electrophilic attack at position-2 Electrophilic attack at position-4 Resonance forms A & B which result from attack at position 2 & 4 respectively are energetically unfavourable and may be ignored. Because, the nitrogen atom in these forms has only six electrons. The intermediates arising from attack at position 2 & 4 have two resonance forms each. N + E + N E H + N E H + N E H + [A] -H+ N E N + E + N H E + N H E + [B] N H E + -H+ N E Chem Eazy
- 7. So, the product with a substituent at position-3 predominates. Electrophilic attack at position-3 [If position-3 is already blocked, substitution will occur at the other available β-position, i.e., at position-5] Pyridine may be substituted by electrophilic reagents only under vigorous conditions. N + E + N E H + N E H + N E H + -H+ N E Chem Eazy
- 8. a. Nitration: With nitric acid in the presence of sulfuric acid at 300°C b. Sulphonation: With fuming sulfuric acid in the presence of mercuric sulphate at 230°C N + HNO 3 H2SO4 300 °C N NO2 pyridine 3-nitropyridine N pyridine N SO3H pyridine-3-sulfonic acid H2SO4 HgSO4, 230 °C Chem Eazy
- 9. c. Bromination: Brominated by passing the vapours of pyridine and bromine over charcoal at 300°C. When temperature of 500°C is used, a mixture of 2-bromopyridine and 2,6-dibromopyridine is obtained. N pyridine N Br + 3-bromopyridine N Br Br 3,5-dibromopyridine Br2 300 °C N pyridine N Br + N Br Br Br2 500 °C 2-bromopyridine 2,6-dibromopyridine Chem Eazy
- 10. d. Friedel-Crafts Acylation and Alkylation Pyridine doesn’t undergo Friedel-Crafts reaction. Because Lewis acid which are used as catalysts in these reactions coordinate with the lone pair of electrons on nitrogen. e. Mercuration: Pyridine can be mercurated with mercuric acetate N + AlCl 3 pyridine N AlCl 3 + Pyridine-Aluminium complex N pyridine + Hg(OCOCH 3)2 Mercuric acetate N HgOCOCH 3 3- pyridylmercuric acetate Chem Eazy
- 11. Presence of electron donating substituents Presence of electron-donating substituents will make electrophilic aromatic substitution easier and will direct substitution to the less sterically hindered ortho or para position. N NHCH 3 3-(methylamino)pyridine HNO3 H2SO4 N NHCH 3 NO2 3-Methylamino- 2-nitropyridine N NH2 HNO3 H2SO4 N NH2 O2N 2-aminopyridine 2-amino- 5-nitropyridine Chem Eazy
- 12. 2. Nucleophilic substitution Reactions The electron deficient nature of the 2 and 4 positions of pyridine makes these positions very reactive towards nucleophilic reagents. N Br N NH2 2-bromopyridine 2-aminopyridine NH3 180 - 200 °C N Cl N NH2 4-chloropyridine 4-aminopyridine NH3 180 - 200 °C Chem Eazy
- 13. Typical nucleophilic reactions of Pyridine i. [Chichibabin Reaction] ii. iii. N NaNH2 100 °C N NH2 2-aminopyridine N C6H5NHNa Toluene, 100 °C N NHC 6H5 N-phenylpyridin-2-amine N C6H5Li - C6H5CH3 100 °C N C6H5 2-phenylpyridine Chem Eazy
- 14. iv. v. vi. 4-chloropyridine reacts with sodium methoxide to form 4-methoxypyridine, but 3- chloropyridine does not react with sodium methoxide. N N CH2CH2CH2CH3 2-butylpyridine CH3CH2CH2CH2Li 100 °C N C6H5CH2MgCl N CH2C6H5 N CH2C6H5 + 2-benzylpyridine 4-benzylpyridine N Cl 4-chloropyridine CH3ONa N OCH 3 4-methoxypyridine Chem Eazy
- 15. 3. Oxidation Due to low electron-density about its carbon atoms, pyridine is more resistant than benzene to most of the oxidizing agents, such as boiling nitric acid or chromic acid. It is evident by the oxidation of 2-phenylpyridine to pyridine-2-carboxylic acid. However, pyridine is oxidised by perbenzoic acid, peracetic acid or hydrogen peroxide in acetic acid to pyridine-1-oxide. N C6H5 2-phenylpyridine N COOH pyridine-2-carboxylic acid N C6H5CO3H N O + Pyridine- 1-oxide Chem Eazy
- 16. 4. Reduction Due to lower electron density about the carbon atoms the pyridine ring is more easily reduced than benzene. Raney nickel reduces pyridine to piperidine even at atmospheric pressure. If reduction is effected by means of hydriodic acid at 300°C, the piperidine ring also reduced with the opening of the ring. N pyridine + 3H2 N H piperidine Raney Ni HI 300 °C CH3CH2CH2CH2CH3 + NH3 n-pentane Chem Eazy
- 17. Sodium in liquid ammonia reduces pyridine to 1,4-dihydropyridine. Pyridine can also be reduced using sodium and alcohol (or) lithium aluminium hydride. N pyridine Na - Liq.NH3 N H 1,4-dihydropyridine N Na/ROH (or) LiAlH4 N H Tetrahydropyridine Chem Eazy
- 18. Medicinal Uses of Pyridine Chem Eazy N
- 19. Pyridoxine Pyridoxine is used to treat or prevent vitamin B6 deficiency. It is also used to treat a certain type of anemia (lack of red blood cells). Pyridoxine injection is also used to treat some types of seizure in babies. N CH2OH CH2OH HO H3C Pyridoxine Chem Eazy
- 20. Nicotine Nicotine is a stimulatory alkaloid found in tobacco products that is often used for the relief of nicotine withdrawal symptoms and as an aid to smoking cessation. N N CH3 Nicotine Chem Eazy
- 21. Pantoprazole Pantoprazole is a proton pump inhibitor used to treat erosive esophagitis, gastric acid hypersecretion, and to promote healing of tissue damage caused by gastric acid. N OCH 3 OCH 3 CH2 N HN O F F S O Pantoprazole Chem Eazy
- 22. Amlodipine Amlodipine is a calcium channel blocker used to treat hypertension and angina. N H Cl COOCH 2CH3 CH2OCH 2CH2NH2 H3C H3COOC Amlodipine Chem Eazy
- 23. Ethionamide Ethionamide is a second line antitubercular agent used to treat tuberculosis when other treatments have failed. N NH2 S H3CH2C Ethionamide Chem Eazy
- 24. Isoniazid Isoniazid is an antibiotic used to treat mycobacterial infections; most commonly used in combination with other antimycobacterial agents for the treatment of active or latent tuberculosis. N NH-NH 2 O Isoniazid Chem Eazy
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