Preparations and Reactions of Pyrrole
Preparation of Pyrrole
Preparation of Pyrrole from Acetylene
By passing a mixture of acetylene and ammonia through a red hot tube, pyrrole is obtained.Preparation of Pyrrole from Succinamide
Pyrrole is obtained when succinamide is heated with zinc dust.Preparation of Pyrrole from Furan (Commercial Method)
When mixture of furan, ammonia and steam is passes over aluminium oxide catalyst at 480-500° C, pyrrole is obtained.Preparation of Pyrrole from Succinic dialdehyde
When succinic dialdehyde heated with ammonia, pyrrole is obtained.Physical Properties of Pyrrole
Pyrrole is a colorless liquid, Boiling Point is 131° C, Readily turns into brown color on air exposure, Sparingly soluble in water but dissolve in ethanol and ether. Its odour is similiar to chloroform.Chemical Properties of Pyrrole/Reactions of Pyrrole
Resonance of Pyrrole
Basic Character of Pyrrole
Pyrrole is a weak base. It reacts with dilute hydrochloric acid to give a crystalline hydrochloride. The lone pair of electron on nitrogen involved in the formation of the delocalized π-molecular orbital and not available for the formation of a new bond with proton. If a proton is added to the nitrogen atom by reaction with an acid, the resulting structure losses their aromaticity and the resonance energy is lost. This makes pyrrol cation very unstable in comparision to the free pyrrole and shows why pyrrole is very weak base.Acidic Character of Pyrrole
Pyrrole is a very weak acid. This is shown by its reaction with solid KOH. The acidic character of pyrrole is due to the electron pair of nitrogen delocalized and makes it positively charged and increases the possibility of proton abstraction giving pyrrole anion. Pyrrole anion is stabilized by delocalization of negatively charged over the ring.Electrophylic Substitution Reactions
Pyrrole undergoes electrophylic substitution reactions at carbon-2 and gives 2-substituted product however, at carbon-3 gives 3-substituted product which is less stable as only two resonating structures are possible.Nitration of Pyrrole
Pyrrole is nitrated by cold solution of nitric acid in acetic anhydride to give 2-nitropyrrole.Sulphonation of Pyrrole
Pyrrole is sulphonated with sulphur trioxide in pyridine at about 100°C to yield pyrrole-2-sulphonic acid.Halogenation of Pyrrole
Chlorination is carried out with sulphuryl chloride in ether at 0°C.Bromination with bromine in ethanol at 0°C.
Iodination with iodine in an aqueous solution of potassium iodide.
All these halogenation gives tetrahalogen pyrrole.
Friedel-Craft Acylation of Pyrrole
Pyrrole is acetylated with acetic anhydride at 250°C to give 2-acetylpyrrole.Kolbe-Schmitt Carboxylation of Pyrrole
Pyrrole reacts with aqueous potassium carbonate at 100°C to give pyrrole-2-carboxylic acid.Reimer-Tiemann Reaction of Pyrrole
Pyrrole reacts with chloroform in the presence of alkali to yield 2-formyl pyrrole (pyrrole 2-aldehyde) and 3-chloropyridine.Diazo-Coupling of Pyrrole
Pyrrol couples with benzenediazoniumchloride in a weakly acidic solution to give 2-phenylazopyrrole.Oxidation of Pyrrole
Pyrrole is oxidized to maleic imide by chromium trioxide in acetic acid.Reduction of Pyrrole
Zn/AcOH reduce pyrrole to 3-pyroline (i.e. 2,5-dihydropyrrole) while catalytic reduction completely hydrogenates the ring system to form pyrrolidine.
