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Synthesis, Reactions and Medicinal Uses of Pyridine and Basicity of Pyridine

Acetaldehyde and formaldehyde are combined with ammonia to make pyridine.

Pyridine

Synthesis

Acetaldehyde and formaldehyde are combined with ammonia to make pyridine.



Hantzsch synthesis - A tricarbonyl compound, an aldehyde, and ammonia are combined in an efficient reaction.

A 1,3-dicarbonyl compound can be converted into unsymmetrically substituted pyridine through a reaction between a 1,3-dicarbonyl compound and 3-amino acrylate.


Guareschi Thorpe synthesis - Aldehydes are condensed into substituted pyridine when they combine with keto ester.


Krohnke pyridine synthesis - 2, 4, 6-trisubstituted pyridines, consisting of 2, 4, 6-pyridinium methyl ketone salts, occur as a result of the reaction between α-pyridinium methyl ketone salts and α, β-unsaturated carbonyl compounds.


Reactions

The pyridine molecule is electron deficient due to its electronegative nitrogen. This makes it different from benzene.

There is no easy way to electrophilically substitute pyridine with aromatic compounds.

A pyridine ring can be metalated by strong organometallic bases at positions 2 and 4 and is more prone to nucleophilic substitutions at those positions

N - protonation takes place in pyridine, and pyridine becomes N-oxide through oxidation.

N – protonation - Because of its nitrogen atom, pyridine is capable of forming extra bonds. Upon reaction of pyridines with acids, metal ions or acyl, sulfonyl, and anhydrides, they form quaternary salts.

A hygroscopic salt of pyridine, crystalline and containing most protic acids.


The compounds of aluminum, boron, beryllium, etc. with the basic pyridine are metal ion complexes.


As acylating and sulfonating agents, acyl, sulfonyl, and anhydride quaternary salts form readily with pyridine.


Salts of quaternary pyridinium can be formed from alkyl halides and sulfates reacting with pyridines readily.


Oxidation - In contrast to this, the N-atom in its pyridine ring is highly electron-rich, which makes it easily susceptible to oxidation by hydrogen peroxide or other peracids.


Reduction - Nucleophilic reducing agents can reduce pyridine since it easily reacts with nucleophiles.


Medicinal Uses

In addition to sulfapyridine, tripelenamine and mepyramine (antihistaminics), niacin, pyridoxine, and isoniazid (anti-TB), it is found as part of the structural skeleton of pyridine.

Basicity of Pyridine

With a chemical formula of C5H5N, pyridine is a colourless to yellow liquid heterocyclic compound. Atoms of nitrogen possess a single pair of electrons, which contributes to the basicity of amines. It is benzene in which one nitrogen atom replaces a CH- or methane group. Pyridine is the hydrogen derivative of this ring. There is no lone electron in pyridine, which is a cyclic aromatic compound without resonance. Therefore, a lone pair of electrons does not delocalize, rather they are localized. It is possible to form a new bond with a proton or Lewis acid using this lone electron pair. Pyridines' nitrogen lone pairs are delocalized, so they are more basic than dimethylamines.
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