Pyrrolidine

Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula (CH₂)₄NH. It is a cyclic secondary amine, also classified as a saturated heterocycle. It is a colourless liquid that is miscible with water and most organic solvents. It has a characteristic odor that has been described as "ammoniacal, fishy, shellfish-like".^[4] In addition to pyrrolidine itself, many substituted pyrrolidines are known.

Pyrrolidine

Names
Preferred IUPAC name Pyrrolidine[1]
Other names Azolidine Azacyclopentane Tetrahydropyrrole Prolamine Azolane
Identifiers
CAS Number	123-75-1 Y
3D model (JSmol)	Interactive image
Beilstein Reference	102395
ChEBI	CHEBI:33135 Y
ChEMBL	ChEMBL22830 Y
ChemSpider	29008 Y
ECHA InfoCard	100.004.227
EC Number	204-648-7
Gmelin Reference	1704
PubChem CID	31268
RTECS number	UX9650000
UNII	LJU5627FYV Y
UN number	1922
CompTox Dashboard (EPA)	DTXSID3059559
InChI InChI=1S/C4H9N/c1-2-4-5-3-1/h5H,1-4H2 Y Key: RWRDLPDLKQPQOW-UHFFFAOYSA-N Y InChI=1/C4H9N/c1-2-4-5-3-1/h5H,1-4H2 Key: RWRDLPDLKQPQOW-UHFFFAOYAX
SMILES C1CCNC1
Properties
Chemical formula	C4H9N
Molar mass	71.123 g·mol−1
Appearance	Clear colorless liquid
Density	0.866 g/cm3
Melting point	−63 °C (−81 °F; 210 K)
Boiling point	87 °C (189 °F; 360 K)
Solubility in water	Miscible
Acidity (pKa)	11.27 (pKa of conjugate acid in water),[2] 19.56 (pKa of conjugate acid in acetonitrile)[3]
Magnetic susceptibility (χ)	-54.8·10−6 cm3/mol
Refractive index (nD)	1.4402 at 28°C
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly flammable, harmful, corrosive, possible mutagen
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H302, H314, H332
Precautionary statements	P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P330, P363, P370+P378, P403+P235, P405, P501
NFPA 704 (fire diamond)	3 3 1
Flash point	3 °C (37 °F; 276 K)
Autoignition temperature	345 °C (653 °F; 618 K)
Safety data sheet (SDS)	MSDS
Related compounds
Related nitrogen heterocyclic compounds	Pyrrole (aromatic with two double bonds) Pyrroline (one double bond) Pyrrolizidine (two pentagonal rings)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Production and synthesis

Industrial production

Pyrrolidine is prepared industrially by the reaction of 1,4-butanediol and ammonia at a temperature of 165–200 °C and a pressure of 17–21 MPa in the presence of a cobalt- and nickel oxide catalyst, which is supported on alumina.^[5]

The reaction is carried out in the liquid phase in a continuous tube- or tube bundle reactor, which is operated in the cycle gas method. The catalyst is arranged as a fixed-bed and the conversion is carried out in the downflow mode. The product is obtained after multistage purification and separation by extractive and azeotropic distillation.^[5]

Laboratory synthesis

In the laboratory, pyrrolidine was usually synthesised by treating 4-chlorobutan-1-amine with a strong base:

Furthermore, 5-membered N-heterocyclic ring of the pyrrolidine derivatives can be synthesized via cascade reactions.^[6]

Occurrence

Many modifications of pyrrolidine are found in natural and synthetic drugs and drug candidates.^[6] The pyrrolidine ring structure is present in numerous natural alkaloids i.a. nicotine and hygrine. It is found in many drugs such as procyclidine and bepridil. It also forms the basis for the racetam compounds (e.g. piracetam, aniracetam). The amino acids proline and hydroxyproline are, in a structural sense, derivatives of pyrrolidine.

Nicotine contains an N-methylpyrrolidine ring linked to a pyridine ring.

Reactions

Pyrrolidine is a base. Its basicity is typical of other dialkyl amines.^[7] Relative to many secondary amines, pyrrolidine is distinctive because of its compactness, a consequence of its cyclic structure.

Pyrrolidine is used as a building block in the synthesis of more complex organic compounds. It is used to activate ketones and aldehydes toward nucleophilic addition by formation of enamines (e.g. used in the Stork enamine alkylation):^[8]

References

1. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 142. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
2. Hall, H. K. (1957). "Correlation of the Base Strengths of Amines". Journal of the American Chemical Society. 79 (20): 5441–5444. doi:10.1021/ja01577a030.
3. Kaljurand, I.; Kütt, A.; Sooväli, L.; Rodima, T.; Mäemets, V.; Leito, I.; Koppel, I. A. (2005). "Extension of the Self-Consistent Spectrophotometric Basicity Scale in Acetonitrile to a Full Span of 28 pKa Units: Unification of Different Basicity Scales". The Journal of Organic Chemistry. 70 (3): 1019–1028. doi:10.1021/jo048252w. PMID 15675863.
4. Pyrrolidine Archived 2017-11-21 at the Wayback Machine, The Good Scents Company
5. Bou Chedid, Roland; Melder, Johann-Peter; Dostalek, Roman; Pastre, Jörg; Tan, Aik Meam. "Process for the preparation of pyrrolidine". Google Patents. BASF SE. Archived from the original on 5 July 2019. Retrieved 5 July 2019.
6. Łowicki, Daniel; Przybylski, Piotr (2022). "Tandem construction of biological relevant aliphatic 5-membered N-heterocycles". European Journal of Medicinal Chemistry. 235: 114303. doi:10.1016/j.ejmech.2022.114303. PMID 35344904. S2CID 247580048.
7. H. K. Hall Jr. (1957). "Correlation of the Base Strengths of Amines". J. Am. Chem. Soc. 79 (20): 5441. doi:10.1021/ja01577a030.
8. R. B. Woodward, I. J. Pachter, and M. L. Scheinbaum (1974). "2,2-(Trimethylenedithio)cyclohexanone". Organic Syntheses. 54: 39{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 6, p. 1014.

External links

• Media related to Pyrrolidine at Wikimedia Commons