Cyclopentadiene

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

<templatestyles src="Chembox/styles.css"/>

Template:Chembox image cellTemplate:Chembox AllOtherNamesTemplate:Chembox headerbarTemplate:Chembox IndexlistTemplate:Chembox JmolTemplate:Chembox ChEMBLTemplate:Chembox ECHATemplate:Chembox E numberTemplate:Chembox IUPHAR ligandTemplate:Chembox UNIITemplate:Chembox CompToxTemplate:Chembox headerbarTemplate:Chembox SolubilityInWaterTemplate:Chembox ConjugateAcidBaseTemplate:Chembox headerbarTemplate:Chembox headerbarTemplate:Chembox headerbarTemplate:Chembox Lethal amounts (set)Template:Chembox setHeaderTemplate:Chembox setDatarowTemplate:Chembox setDatarowTemplate:Chembox setDatarowTemplate:Chembox headerbarTemplate:Chembox Datapage checkTemplate:Chembox Footer
Cyclopentadiene
Template:Chembox image sbs cell
Template:Longitem Template:Unbulleted list
Abbreviations CPD, HCp
Template:Longitem 471171
ChEBI Template:Unbulleted list
ChemSpider Template:Unbulleted list
DrugBank Template:Unbulleted list
EC Number Template:Unbulleted list
Template:Longitem 1311
KEGG Template:Unbulleted list
MeSH 1,3-cyclopentadiene
Template:Longitem Template:Unbulleted list
RTECS number Template:Unbulleted list
Script error: No such module "collapsible list".
Script error: No such module "collapsible list".
Template:Longitem Template:Chembox Elements/molecular formula
Molar mass Template:Chem molar mass
Appearance Colourless liquid
Odor irritating, terpene-like[1]
Density 0.802 g/cm3
Melting point Template:Chembox CalcTemperatures
Boiling point Template:Chembox CalcTemperatures
Vapor pressure Script error: No such module "convert".[1]
Acidity (pKa) 16
Template:Longitem Script error: No such module "val".
Template:Longitem 1.44 (at 20 °C)[3]
Template:Longitem Planar[4]
Template:Longitem 0.419 D[3]
Template:Longitem 115.3 J/(mol·K)
Template:Longitem 182.7 J/(mol·K)
Template:Longitem 105.9 kJ/mol[3]
NFPA 704 (fire diamond) Template:NFPA 704 diamond
Flash point Template:Chembox CalcTemperatures
Template:Longitem Template:Chembox CalcTemperatures
Template:Longitem Benzene
Cyclobutadiene
Cyclopentene
Template:Longitem Dicyclopentadiene

Template:Chembox Footer/trackingScript error: No such module "TemplatePar".Template:Short description

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 unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction. This dimer can be heated to induce thermal cracking and regenerate the monomer through a retro-Diels–Alder reaction

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

File:AW Cyclopentadiene.jpg
Cyclopentadiene monomer in an ice bath

Cyclopentadiene production is usually not distinguished from dicyclopentadiene since they interconvert. They are obtained from coal tar (about 10–20 g/t) and by steam cracking of naphtha (about 14 kg/t).[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]

File:Prostaglandin Diels-Alder Corey (cropped2).png
The methoxy group ends up only on the methylene bridge, because Diels-Alder addition at −55 °C occurs much faster than the sigmatropic shift (excerpted from Corey's total synthesis of prostaglandin F2α)[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

Script error: No such module "Labelled list hatnote". The compound is unusually acidic (pKa = 16) for a hydrocarbon due to the high stability of the aromatic cyclopentadienyl anion, Template:Chem/link. Deprotonation can be achieved with a variety of bases, typically sodium hydride, sodium metal, and butyllithium. Salts of this anion are commercially available, including sodium cyclopentadienide and lithium cyclopentadienide. They are used to prepare cyclopentadienyl complexes.

Metallocene derivatives

Script error: No such module "Labelled list hatnote". 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]

Template:Chem2

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.

File:DodecahedranePrecursorSynthesis.png
The start of Paquette's 1982 dodecahedrane synthesis. Note the dimerisation of cyclopentadiene in step 1 to dihydrofulvalene.

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

File:(t-Bu)3C5H3.png
Structure of t-Bu3C5H3, a prototypical bulky cyclopentadiene[16]

Cyclopentadiene can substitute one or more hydrogens, forming derivatives having covalent bonds:

Most of these substituted cyclopentadienes can also form anions and join cyclopentadienyl complexes.

See also

References

<templatestyles src="Reflist/styles.css" />

  1. ↑ a b c d e f g Script error: No such module "citation/CS1".
  2. ↑ Script error: No such module "citation/CS1".
  3. ↑ a b c Script error: No such module "citation/CS1".
  4. ↑ Script error: No such module "Citation/CS1".
  5. ↑ Template:IDLH
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ Script error: No such module "citation/CS1".
  8. ↑ a b Script error: No such module "Template wrapper".
  9. ↑ Script error: No such module "Citation/CS1".; Script error: No such module "citation/CS1"..
  10. ↑ a b Script error: No such module "Citation/CS1".
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ Script error: No such module "Citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".

Script error: No such module "Check for unknown parameters".

External links

Script error: No such module "Navbox". Template:Annulenes Template:Cyclopentadiene complexes

Retrieved from "http://debianws.lexgopc.com/wiki143/index.php?title=Cyclopentadiene&oldid=9684483"