PYRIDINE
Preparation:
Pyridine may be obtained:
1. By passing a mixture of acetylene and hydrogen cyanide through a red-hot tube.
2. By heating pentamethylene diamine hydrochloride and oxidising the product piperidine with conc. H2SO4 at 300° C.
3. High purity pyridine is obtained commercially by passing acetylene, ammonia, formaldehyde and dimethylacetal over heated alumina at 500°C
4. By heating tetrahydrofurfuryl alcohol with ammonia in the presence of alumina at 500° C (Commercial method).
5.Hantzch pyridine synthesis: By passing a mixture of acetaldehyde, formaldehyde and ammonia over heated CuO –Al2O3 as catalysts
Properties:
Physical: lt is a colourless liquid. freely soluble in water and most organic solvents. it has a characteristic unpleasant odour.
Chemical: Pyridine is basiç in nature. it is much less reactive.
1. Basic character: it behaves as a base. It is much less basic than alkyl amines. However, it is more basic than pyrrole and aniline.less basic nature of pyridine is due to the availability of a lone pair of electrons on nitrogen atom.
2.Addition reactions:
i) Catalytic hydrogenation or reduction with sodiumn in ethyl alcohol yields piperidine (hexahydro pyridine).
3. Electrophilic substitution reactions:
Pyridine shows electrophilic substitution reactions in 3-position under vigorous conditions. It does not undergo Friedel-Crafts reaction. It is considerably less reactive than benzene.
i} Bromination: At 300°C in the presence of á catalyst charcoal, it mixture of 3-bromo pyridine and 3.5-dibromoryridine.when temperature of 500°C is used, a mixture of 2-bromo pyridine and di bromo pyridine is obtained.
ii)Nitration: It undergoes nitration with potassium nitrate in the presence of sulphuric acid at 300°c to yield 3-nitro pyridine.
iii) Sulphonation: Pyridine may be sulphonated by treating it with fuming sulphuric acid in the presence of mercuric sulphate at 230°C to give pyridine-3-sulphonic acid.
iv) Mercuration: It undergoes mercuration with mercuric acetate,(CH3COO)2Hg.
