Pyrrol
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| Names | |||
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Preferred IUPAC name
1H-Pyrrole
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| Other names
Azole
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| Identifiers | |||
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3D model (JSmol)
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| 1159 | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.003.387 | ||
| EC Number | 203-724-7 | ||
| 1705 | |||
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PubChem CID
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| RTECS number | UX9275000 | ||
| UNII | |||
| UN number | 1992, 1993 | ||
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| Properties | |||
| C4H5N | |||
| Molar mass | 67.09 g·mol−1 | ||
| Density | 0.967 g cm−3 | ||
| Melting point | −23 °C (−9 °F; 250 K) | ||
| Boiling point | 129 to 131 °C (264 to 268 °F; 402 to 404 K) | ||
| Vapor pressure | 7 mmHg at 23 °C | ||
| Acidity (pKa) | 16.5 (for the N-H proton) | ||
| Basicity (pKb) | 13.6 (pKa 0.4 for C.A.) | ||
| -47.6·10−6 cm3/mol | |||
| Viscosity | 0.001225 Pa s | ||
| Thermochemistry | |||
| 1.903 J K−1 mol−1 | |||
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Std enthalpy of
formation (ΔfH |
108.2 kJ mol−1 (gas) | ||
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Std enthalpy of
combustion (ΔcH |
2242 kJ mol−1 | ||
| Hazards | |||
| Safety data sheet | Chemical Safety Data | ||
| NFPA 704 | |||
| Flash point | 33.33 °C (91.99 °F; 306.48 K) | ||
| 550 °C (1,022 °F; 823 K) | |||
| Explosive limits | 3.1–14.8% | ||
| Related compounds | |||
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Related compounds
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Phosphole, arsole, bismole, stibole | ||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |||
Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3. Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme.
Pyrroles are components of more complex macrocycles, including the porphyrins of heme, the chlorins, bacteriochlorins, chlorophyll, and porphyrinogens.
Pyrrole is a colorless volatile liquid that darkens readily upon exposure to air, and is usually purified by distillation immediately before use. Pyrrole has a nutty odor. Pyrrole is a 5-membered aromatic heterocycle, like furan and thiophene. Unlike furan and thiophene, it has a dipole in which the positive end lies on the side of the heteroatom, with a dipole moment of 1.58 D. In CDCl3, it has chemical shifts at 6.68 (H2, H5) and 6.22 (H3, H4). Pyrrole is weakly basic, with a conjugate acid pKa of −3.8. The most thermodynamically stable pyrrolium cation (C4H6N+) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pKa of +3.7. Pyrrole is also weakly acidic at the N–H position, with a pKa of 17.5.
Pyrrole was first detected by F. F. Runge in 1834, as a constituent of coal tar. In 1857, it was isolated from the pyrolysate of bone. Its name comes from the Greek pyrrhos (πυρρός, “reddish, fiery”), from the reaction used to detect it—the red color that it imparts to wood when moistened with hydrochloric acid.
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