Cyclopentadiene
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Names | |||
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Preferred IUPAC name
Cyclopenta-1,3-diene | |||
Other names | |||
Identifiers | |||
3D model (
JSmol ) |
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Abbreviations | CPD, HCp | ||
471171 | |||
ChEBI | |||
ChemSpider | |||
ECHA InfoCard
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100.008.033 | ||
EC Number |
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1311 | |||
MeSH | 1,3-cyclopentadiene | ||
PubChem CID
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RTECS number
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UNII | |||
CompTox Dashboard (EPA)
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Properties | |||
C5H6 | |||
Molar mass | 66.103 g·mol−1 | ||
Appearance | Colourless liquid | ||
Odor | irritating, terpene-like[1] | ||
Density | 0.802 g cm−3 | ||
Melting point | −90 °C; −130 °F; 183 K | ||
Boiling point | 39 to 43 °C; 102 to 109 °F; 312 to 316 K | ||
insoluble[1] | |||
Vapor pressure | 400 mmHg (53 kPa)[1] | ||
Acidity (pKa) | 16 | ||
Conjugate base
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Cyclopentadienyl anion | ||
−44.5×10−6 cm3 mol−1 | |||
Refractive index (nD)
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1.44 (at 20 °C)[3] | ||
Structure | |||
Planar[4] | |||
0.419 D[3] | |||
Thermochemistry | |||
Heat capacity (C)
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115.3 J·mol−1·K−1 | ||
Std molar
entropy (S⦵298) |
182.7 J·mol−1·K−1 | ||
Std enthalpy of (ΔfH⦵298)formation |
105.9 kJ·mol−1[3] | ||
Hazards | |||
NFPA 704 (fire diamond) | |||
Flash point | 25 °C (77 °F; 298 K) | ||
640 °C (1,184 °F; 913 K) | |||
Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration)
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14,182 ppm (rat, 2 hr) 5091 ppm (mouse, 2 hr)[5] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 75 ppm (200 mg/m3)[1] | ||
REL (Recommended)
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TWA 75 ppm (200 mg/m3)[1] | ||
IDLH (Immediate danger) |
750 ppm[1] | ||
Related compounds | |||
Related hydrocarbons
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Benzene Cyclobutadiene Cyclopentene | ||
Related compounds
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Dicyclopentadiene | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cyclopentadiene is an organic compound with the formula C5H6.[6] It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−.
This colorless liquid has a strong and
The compound is mainly used for the production of cyclopentene and its derivatives. It is popularly used as a precursor to the cyclopentadienyl anion (Cp−), an important ligand in cyclopentadienyl complexes in organometallic chemistry.[7]
Production and reactions
Cyclopentadiene production is usually not distinguished from dicyclopentadiene since they interconvert. They are obtained from coal tar (about 10–20 g/tonne) and by steam cracking of naphtha (about 14 kg/tonne).[8] To obtain cyclopentadiene monomer, commercial dicyclopentadiene is cracked by heating to around 180 °C. The monomer is collected by distillation, and used soon thereafter.[9] It advisable to use some form of fractionating column when doing this, to remove refluxing uncracked dimer.
Sigmatropic rearrangement
The hydrogen atoms in cyclopentadiene undergo rapid [1,5]-sigmatropic shifts. The hydride shift is however sufficiently slow at 0 °C to allow alkylated derivatives to be manipulated selectively.[10]
Even more fluxional are the derivatives C5H5E(CH3)3 (E = Si, Ge, Sn), wherein the heavier element migrates from carbon to carbon with a low activation barrier.
Diels–Alder reactions
Cyclopentadiene is a highly reactive diene in the Diels–Alder reaction because minimal distortion of the diene is required to achieve the envelope geometry of the transition state compared to other dienes.[11] Famously, cyclopentadiene dimerizes. The conversion occurs in hours at room temperature, but the monomer can be stored for days at −20 °C.[8]
Deprotonation
The compound is unusually
Metallocene derivatives
Metallocenes and related cyclopentadienyl derivatives have been heavily investigated and represent a cornerstone of organometallic chemistry owing to their high stability. The first metallocene characterised, ferrocene, was prepared the way many other metallocenes are prepared: by combining alkali metal derivatives of the form MC5H5 with dihalides of the transition metals:[12] As typical example, nickelocene forms upon treating nickel(II) chloride with sodium cyclopentadienide in THF.[13]
- NiCl2 + 2 NaC5H5 → Ni(C5H5)2 + 2 NaCl
Organometallic complexes that include both the cyclopentadienyl anion and cyclopentadiene itself are known, one example of which is the rhodocene derivative produced from the rhodocene monomer in protic solvents.[14]
Organic synthesis
It was the starting material in Leo Paquette's 1982 synthesis of dodecahedrane.[15] The first step involved reductive dimerization of the molecule to give dihydrofulvalene, not simple addition to give dicyclopentadiene.
Uses
Aside from serving as a precursor to cyclopentadienyl-based catalysts, the main commercial application of cyclopentadiene is as a precursor to comonomers. Semi-hydrogenation gives cyclopentene. Diels–Alder reaction with butadiene gives ethylidene norbornene, a comonomer in the production of EPDM rubbers.
Derivatives
Cyclopentadiene can substitute one or more hydrogens, forming derivatives having covalent bonds:
- Bulky cyclopentadienes
- Calicene
- Cyclopentadienone
- Di-tert-butylcyclopentadiene
- Methylcyclopentadiene
- Pentamethylcyclopentadiene
- Pentacyanocyclopentadiene
Most of these substituted cyclopentadienes can also form
See also
References
- ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0170". National Institute for Occupational Safety and Health (NIOSH).
- ISBN 978-1498754286.
- ^ OCLC 930681942.
- doi:10.1039/b005247g.
- ^ "Cyclopentadiene". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ISBN 978-1-891389-53-5.
- ^ ISBN 978-3527306732.
- ^ Moffett, Robert Bruce (1962). "Cyclopentadiene and 3-Chlorocyclopentene". Organic Syntheses; Collected Volumes, vol. 4, p. 238.
- PMID 5808505.
- PMID 25741891.
- ISBN 0-935702-48-2.
- ISBN 0-13-879932-6.
- .
- .
- S2CID 105376454.