|Molar mass||85.15 g·mol−1|
|Density||0.862 g/mL, liquid|
|Melting point||−7 °C (19 °F; 266 K)|
|Boiling point||106 °C (223 °F; 379 K)|
|Viscosity||1.573 cP at 25 °C|
|EU classification||Flammable (F)
|R-phrases||R11, R23/24, R34|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Piperidine (Azinane after the Hantzsch–Widman nomenclature) is an organic compound with the molecular formula (CH2)5NH. This heterocyclic amine consists of a six-membered ring containing five methylene bridges (-CH
2-) and one amine bridge (-NH-). It is a colorless fuming liquid with an odor described as ammoniacal or pepper-like; the name comes from the genus name Piper, which is the Latin word for pepper. Piperidine is a widely used building block and chemical reagent in the synthesis of organic compounds, including pharmaceuticals.
- C5H5N + 3 H2 → C5H10NH
Natural occurrence of piperidine and derivatives
The piperidine structural motif is present in numerous natural alkaloids. These include piperine, which gives black pepper its spicy taste. This gave the compound its name. Other examples are the fire ant toxin solenopsin, the nicotine analog anabasine of the Tree Tobacco (Nicotiana glauca), lobeline of the Indian tobacco, and the toxic alkaloid coniine from poison hemlock, which was used to put Socrates to death.
Piperidine prefers a chair conformation, similar to cyclohexane. Unlike cyclohexane, piperidine has two distinguishable chair conformations: one with the N–H bond in an axial position, and the other in an equatorial position. After much controversy during the 1950s–1970s, the equatorial conformation was found to be more stable by 0.72 kcal/mol in the gas phase. In nonpolar solvents, a range between 0.2 and 0.6 kcal/mol has been estimated, but in polar solvents the axial conformer may be more stable. The two conformers interconvert rapidly through nitrogen inversion; the free energy activation barrier for this process, estimated at 6.1 kcal/mol, is substantially lower than the 10.4 kcal/mol for ring inversion. In the case of N-methylpiperidine, the equatorial conformation is preferred by 3.16 kcal/mol, which is much larger than the preference in methylcyclohexane, 1.74 kcal/mol.
NMR chemical shifts
13C NMR = (CDCl3, ppm) 47.5, 27.2, 25.2
1H NMR = (CDCl3, ppm) 2.79, 2.19, 1.51
Piperidine is used as a solvent and as a base. The same is true for certain derivatives: N-formylpiperidine is a polar aprotic solvent with better hydrocarbon solubility than other amide solvents, and 2,2,6,6-tetramethylpiperidine is a highly sterically hindered base, useful because of its low nucleophilicity and high solubility in organic solvents.
List of piperidine medications
Piperidine and its derivatives are ubiquitous building blocks in the synthesis of pharmaceuticals and fine chemicals. The piperidine structure is e.g. found in the pharmaceuticals:
- SSRI (Selective Serotonin Reuptake Inhibitors)
- Analeptics/Nootropics (Stimulants)
- SERM (Selective Estrogen Receptor Modulators)
- Neuroleptics (Antipsychotics)
- Other agents
- Psychochemical compounds
Piperidine is also commonly used in chemical degradation reactions, such as the sequencing of DNA in the cleavage of particular modified nucleotides. Piperidine is also commonly used as a base for the deprotection of Fmoc-amino acids used in solid-phase peptide synthesis.
Piperidine is listed as a Table II precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances due to its use (peaking in the 1970s) in the clandestine manufacture of PCP (also known as angel dust, sherms, wet, etc.).
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