The key difference between pyrrole pyridine and piperidine is their basicity. Pyrrole is the least basic and pyridine is moderately basic, whereas piperidine is the most basic.
Pyrrole, pyridine and piperidine are organic compounds having nitrogen atoms in their chemical structures. These compounds are basic compounds (opposite to acidic).
What is Pyrrole?
Pyrrole is an organic compound having a five-membered ring structure with the chemical formula C4H4NH. This is a heterocyclic compound having a nitrogen atom contributing to the formation of the ring structure, along with four other carbon atoms. Pyrrole is a volatile and colourless liquid at room temperature. Upon exposure to normal air, the liquid of pyrrole readily darkens, which cause the need to purify it before using. We can do the purification via distillation immediately before use. Furthermore, this liquid has a nutty odour.
Unlike some other five-membered heterocyclic rings such as furan and thiophene, this compound has a dipole in which the positive side of the ring is at the heteroatom (-NH group bears the positive charge). Furthermore, it is a weakly basic compound.
Pyrrole exists in nature as derivatives of pyrrole. For example, vitamin B12, bile pigments such as bilirubin, porphyrins, etc., are pyrrole derivatives. However, this compound is slightly toxic. In the industrial scale, we can synthesize pyrrole via the treatment of furan with ammonia. But this reaction requires a solid catalyst as well.
What is Pyridine?
Pyridine is an organic compound having the chemical formula C5H5N. It is a heterocyclic compound. The structure of pyridine resembles the structure of benzene, where one methyl group is replaced by a nitrogen atom. Moreover, pyridine is a weak alkaline compound, and it exists in the liquid state where it occurs as a viscous liquid. Apart from that, pyridine is colourless and has a distinctive fish-like odour. Moreover, this liquid is water-soluble and is highly flammable.
Pyridine is a diamagnetic substance. The structure of the pyridine molecule is a hexagon. In this molecule, the C-N bond is shorter than C-C bonds. Pyridine crystallizes in the orthorhombic crystal system. However, the pyridine molecule is an electron-deficient structure due to the presence of a more electronegative nitrogen atom. Therefore, it tends to undergo electrophilic aromatic substitution reactions. Another reason for this ability is the presence of a lone electron pair on the nitrogen atom.
Concerning the applications of pyridine, it is mainly useful as a component in pesticide, as a polar-basic solvent, as the Karl Fischer reagent in organic synthesis, etc.
What is Piperidine?
Piperidine is an organic compound having the chemical formula (CH2)5NH. This compound occurs as a six-membered cyclic structure which is heterocyclic. In this structure, there is a nitrogen atom as a member of the cyclic structure in addition to the five carbon atoms. Therefore, it is a heterocyclic amine. Piperidine appears as a colourless liquid and has an amine-like odour. Furthermore, piperidine is miscible with water, and its aqueous solution has high acidity.
The older method of producing piperidine was the reaction between piperine and nitric acid. However, we can produce it in industrial-scale via the hydrogenation reaction of pyridine. This process is usually done over a molybdenum disulfide catalyst. In addition, we can obtain piperidine by reducing pyridine via modified Birch reduction process using sodium in ethanol. However, we can directly obtain piperidine via extracting it from black pepper.
When considering the chemical structure of piperidine, it has a chair conformation similar to cyclohexane. There are two different chair conformations of this compound. One has the N-H bond in the axial position while the other confirmation has it in the equatorial position.
Piperidine is a secondary amine. It is widely used to convert ketones into enamines. These enamines can be used for Stork enamine alkylation reaction. Furthermore, piperidine is useful as a solvent and as a base. In industries, piperidine is useful for the production of dipiperidinyl dithiuram tetrasulfide (an accelerator for sulfur vulcanization of rubber).
What is the Difference Between Pyrrole Pyridine and Piperidine?
Pyrrole, pyridine and piperidine are organic compounds. The key difference between pyrrole pyridine and piperidine is that pyrrole is the least basic and pyridine is moderately basic, whereas piperidine is the most basic.
The following infographic summarizes the differences between pyrrole pyridine and piperidine in tabular form.
Summary – Pyrrole vs Pyridine vs Piperidine
Pyrrole, pyridine and piperidine are organic compounds having nitrogen atoms in their chemical structures. These compounds are basic compounds. The key difference between pyrrole, pyridine and piperidine is that pyrrole is the least basic, and pyridine is moderately basic, whereas piperidine is the most basic.
1. “Piperidine – Major Uses.” U.S. National Library of Medicine, National Institutes of Health, Available here.
3. “Piperidin” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia