The key difference between pyrrolidine and piperidine is that pyrrolidine contains a five-membered ring, whereas piperidine contains a six-membered ring.
Pyrrolidine and piperidine are organic compounds that have cyclic structures. Both these compounds are non-aromatic, heterocyclic structures – meaning, these compounds have no delocalized electron clouds (because there are no double bonds) and they have different types of atoms as members of the cyclic structure.
CONTENTS
1. Overview and Key Difference
2. What is Pyrrolidine
3. What is Piperidine
4. Side by Side Comparison – Pyrrolidine vs Piperidine in Tabular Form
5. Summary
What is Pyrrolidine?
Pyrroline is an organic compound having the chemical formula (CH2)4NH. It is also named as tetrahydropyrrole. This compound is a cyclic amine that can be classified as a saturated heterocycle. It occurs as a colorless liquid at room temperature. This liquid is miscible with water and with most organic solvents. There is a characteristic odor which is ammonical and fishy in this compound.
Figure 01: Structure of Pyrroline
In the industrial scale, pyrrolidine is produced via the reaction between 1,4-butanediol and ammonia at a high temperature and pressure. This reaction is carried out in the presence of a nickel oxide catalyst that is supported on alumina. However, in the laboratory, we can easily make this compound from the reaction between 4-chlorobutan1-amine and a strong base. However, pyrrolidine is a naturally occurring compound we can find in different alkaloids such as nicotine.
What is Piperidine?
Piperidine is an organic compound having the chemical formula (CH2)5NH. It forms a six-membered cyclic structure which is heterocyclic. This is because 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. This compound appears as a colorless liquid and has an amine-like odor. Furthermore, piperidine is miscible with water, and it has high acidity.
Figure 02: Structure of Piperidine
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 conformation 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. In addition, piperidine is useful as a solvent and as a base. In the industries, piperidine is useful for the production of dipiperidinyl dithiuram tetrasulfide (an accelerator for sulfur vulcanization of rubber).
What is the Difference Between Pyrrolidine and Piperidine?
Pyrroline is an organic compound having the chemical formula (CH2)4NH while piperidine is an organic compound having the chemical formula (CH2)5NH. Both pyrroline and piperidine contain cyclic structures. The key difference between pyrrolidine and piperidine is that pyrrolidine contains a five-membered ring, whereas piperidine contains a six-membered ring.
Moreover, the pyrrolidine can be produced via the reaction between 1,4-butanediol and ammonia at a high temperature and pressure. Piperidine, on the other hand, is produced via the hydrogenation reaction of pyridine.
Below infographic summarizes the differences between pyrrolidine and piperidine.
Summary – Pyrrolidine vs Piperidine
Both pyrroline and piperidine contain cyclic structures. The key difference between pyrrolidine and piperidine is that pyrrolidine contains a five-membered ring, whereas piperidine contains a six-membered ring.
Reference:
1. “Piperidine.” Wikipedia, Wikimedia Foundation, 11 June 2020, Available here.
Image Courtesy:
1. “Pyrrolidine svg” By Arrowsmaster – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Piperidin” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia