I have searched, and searched, and nowhere can I find a synthesis to cyclopentadiene except from dicyclopentadiene (which is just a dimer).BromicAcid - 21-11-2005 at 21:32
Humm... couldn't find much. Hawley's states that it is made from "Coal tar and cracked petrolium". Searcing the ACS archives
there is a hit for methods to make cyclopentadiene from 1,3-Pentadiene:
Formation of Cyclopentadiene from 1,3-Pentadiene
R. M. Kennedy, S. J. Hetzel;
Ind. Eng. Chem.; 1950; 42(3); 547-552.
But it requires high temperatures and low pressures, as you mentioned there are methods to convert the dimer to the cyclopentadiene desired:
Determination of Cyclopentadiene and Dicyclopentadiene
Karl Uhrig, Eleanor Lynch, H.C. Becker;
Ind. Eng. Chem. Anal. Ed. ; 1946; 18(9); 550-553.
Gives a good method for making "Pure" cyclopentadiene from the dimer, however it is a cracking process and somewhat difficult, however the
paper does give colorometric methods for the determination of cyclopentadiene.
Just off the top of my head you might be able to do something along the lines of brominating cyclopentane then heating with NaOH to do an elimination
reaction and form your double bonds that way, but that seems like a hassle.Sandmeyer - 22-11-2005 at 09:32
It dimerizes at room temperature on standing since two monomers have higher entopy than one dimer molecule. On heating dimer
undergoes a retro-Diels-Alder to give monomer, it should be enough for you to simply distill it right before use, monomer has a much lower boiling
point than dimer.
[Edited on 22-11-2005 by Sandmeyer]vulture - 22-11-2005 at 14:20
Cyclopentadiene would be anti-aromatic and thus highly reactive. It's only stable for appreciable time in a matrix at solid CO2 temp.stygian - 22-11-2005 at 14:32
What im wanting to know is how it might be synthesized. Not from distilling petroleum, and not from a chem supplier. Surely there is *some* way to
synthesize it?BromicAcid - 22-11-2005 at 15:02
Cyclobutadiene is the quintessential antiaromatic compound stable (or maybe not) under the conditions you describe Vulture, cyclopentadiene has a sp3
hybridized carbon in the ring so it's not fully conjugated so it doesn't fall into the antiaromatic category, it's just unstable due to
the double bonds which like Sandmeyer said can undergo Diels Alder reactions and form dimers and such. From the paper I cited I thought it might be
necessary to crack the resulting product from the distillation of the dimer, hower I am no expert in the field afterall. Realistically though making
this at home would be difficult unless you can get something close to it (like the dimer).
Too bad we can't just order from fisher or something, 2.5L of dicyclopentadiene is only $27.50
[Edited on 11/22/2005 by BromicAcid]stygian - 22-11-2005 at 15:24
Dry distillation of calcium adipate gives cyclopentanone. Another reaction, called Pauson-Khand, which may or may not be feasible for a mad scientist,
give cyclopentenone. Ive read that reduction (I think) of polychlorinated derivatives is also somehow applicable. Besides the dimer, these are
probably as close as one could get. Adipate distillation seems like the best first step if there were a way to go from the ketone to the diene.Sandmeyer - 23-11-2005 at 00:59
Quote:
Originally posted by stygian
What im wanting to know is how it might be synthesized. Not from distilling petroleum, and not from a chem supplier. Surely there is *some* way to
synthesize it?
Sorry, I missunderstood you question, I couldn't belive that someone actually wanted to synthesise this cheap and comercially avilable substance.
Of course there are ways, none of them is practical for laboratory, litterature mostly describe industrial processes.
Here a couple of Sun Oil Corporation patents, strating from more expenisve 1,3-pentadiene:
US 2438402; 1947.
US 2438403; 1947.
US 2438400; 1947.
US 2438401; 1947.
US 2438398; 1947.
US 2438399; 1947.
I haven't forced myself to check them out, they probably involve high pressures and special equipment...
From more expeniive cyklopentane:
Rice; Murphy; J. Am. Chem. Soc.; 64; 1942; 896, 899.
[Edited on 23-11-2005 by Sandmeyer]guy - 7-2-2007 at 13:49
Would this work?
Cross Aldol condensation of acetone and glyoxal to form cyclopendienone. Wolf-Kishner reduction to form clycopentadiene.garage chemist - 7-2-2007 at 16:05
A doable synthesis would indeed start from cyclopentanone.
Reduce to cyclopentanol (with NaBH4, or catalytic hydrogenation) and dehydrate to cyclopentene (this occurs quite easily, look up the preparation of
cyclohexene from cyclohexanol).
Then add bromine to give 1,2- dibromocyclopentane.
Dehydrohalogenation with KOH in Glycol will then yield cyclopentadiene (distills off).
A (french) reference for the last reaction has been posted in the german forum.
