Preparation and Reactions of Pyridine

Preparation and Reactions of Pyridine | Chemical Properties of Pyridine

Preparation and Reactions of Pyridine

Pyridine is six membered nitrogen containing aromatic 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.

Preparation of Pyridine

Preparation of Pyridine from acroline

Pyridine can be prepared by the reaction of acroline(Acrylaldehyde) and ammonia according to following reaction steps.
Preparation of Pyridine from acroline

Preparation of Pyridine From Pyrrole

Pyrrole when heated with methylene chloride in presence of sodium ethoxide, pyridine is formed.
Preparation of Pyridine From Pyrrole

Preparation of Pyridine From Picoline

Beta-picoline on oxidation with potassium dichromate and sulphuric acid gives nicotinic acid, which on decarboxylation with calcium oxide gives pyridine.
Preparation of Pyridine From Picoline

Industrial Method for the Preparation of Pyridine

Pyridine is prepared by heating the acetylene, ammonia and formaldehyde dimethylacetal in the presence of alumina at 500°C.
Industrial Method for the Preparation of Pyridine

Hantzsch Pyridine Synthesis

Condensation of two moles of β keto esters with one molecule of an aldehyde in the presence of ammonia is known as the Hantzsch pyridine synthesis. Pyridine derivatives can easily be prepared by this method. Hantzsch Pyridine Synthesis

Physical Properties of Pyridine

Pyridine is a colourless liquid. Its boiling point is 115.5° C. It has a characteristic unpleasant odor. It is soluble in water and most organic solvents.

Chemical Properties of Furan/Reactions of Pyridine

Resonance in Pyridine

Resonance of Pyridine

Basic Character of Pyridine

Pyridine behaves as a base and forms fairly stable salts with acids. The lone of nitrogen is not involved in the formation of delocalized π molecular orbital, so is available for the formation of a new N-H bond with proton.
Pyridine is a stronger base than pyrrole because the lone pair of nitrogen in pyrrole is involved in the formation of the delocalized π molecular orbital, so not available for the formation of a new N-H bond with proton or simply you can say the basicity decreases due to delocalization of nitrogen lone pair of electron.

Electrophylic Substitution Reactions in Pyridine

Pyridine is an aromatic compound and is less aromatic than benzene and pyrrole. It highly deactivated aromatic nucleus towards electrophilic substitution reactions. So, highly vigorous reaction conditions should be used for these reactions to take place. The low reactivity of pyridine towards the electrophilic substitution reactions is due to the higher electro negativity of nitrogen atom reduces electron density on the ring, thus deactivate the ring and also it is highly sensitive to acidic medium, it readily forms pyridinium cation with a positive charge on nitrogen atom. Similarly, electrophile itself may also react with pyridine to form corresponding pyridinium ion. This positive charge on nitrogen atom decreases electron density on nitrogen atom, consequently, the electron density on ring also decreases.
Pyridine undergoes electrophilic substitution reaction at position C-3. However, attack of electrophile at position C-2 or C-4, more electronegative nitrogen bears a +ve charge in one the resonating structures and makes it unstable. Because of the unstable nature of one of the resonating structure of the intermediate ion formed during the attack of electrophile at position C-2 or C-4, the electrophilic substitution in pyridine at position C-3 is always favoured.
Electrophilic Attack in Pyridine

Nitration of Pyridine

Pyridine undergoes nitration with potassium nitrate in the presence of sulphuric acid at 300°C to yield 3-nitropyridine.
Nitration of Pyridine

Sulphonation of Pyridine

Pyridine undergoes sulphonation with fuming sulphuric acid in the presence of Hg+2 at 230°C to give pyridine-3-sulphonic acid.
Sulphonation of Pyridine

Bromination of Pyridine

Pyridine reacts with Bromine at 300°C to give 3-Bromopyridine and 3,5-dibromopyridine. At 500°C, 2-bromopyridine and 2,6-dibromopyridine is obtained.
Halogenation of Pyridine

Reaction of Pyridine with Sodamide(Chichibabin Reaction)

Pyridine reacts with sodamide in liquid ammonia at about 100°C to form 2-Aminopyridine.
Reaction of Pyridine with Sodamide(Chichibabin Reaction)

Reaction of Pyridine with Sodium Hydroxide

Pyridine reacts with NaOH at 300°C gives an equimolar mixture of 2-hydroxypyridine and 2-pyridone.
Reaction of Pyridine with Sodium Hydroxide

Reaction of Pyridine with n-Butyl Lithium

Pyridine reacts with n-butyllithium at 100°C to give 2-n-butylpyridine.
Reaction of Pyridine with n-Butyl Lithium

Reaction of Pyridine with Alkyl halide

Pyridine reacts with alkyl halides to form N-alkylpyridinium halides.
Reaction  of Pyridine with Alkyl halide

Reduction of Pyridine

Pyridine undergoes reduction with LiAlH4 or H2-Ni to form piperidine.
Reduction  of Pyridine

Oxidation of Pyridine

Pyridine may be oxidized by peracitic acid to give pyridine-N-oxide.
Oxidation of Pyridine