Editing Cyclopropene

{{Short description|Organic ring compound (C3H4)}}
{{Chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 442026875
|ImageFile1 = Cyclopropene 2D skeletal.svg
|ImageSize1 = 100
|ImageName1 = Skeletal formula of cyclopropene
|ImageFileL2 = Cyclopropene.png
|ImageNameL2 = Skeletal formula of cyclopropene with implicit hydrogens shown
|ImageFileR2 = Cyclopropene-3D-balls.png
|ImageNameR2 = Ball and stick model of cyclopropene
|PIN = Cyclopropene<ref>{{Cite web|title = cyclopropene - Compound Summary|url = https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=123173&loc=ec_rcs|work = PubChem Compound|publisher = National Center for Biotechnology Information|accessdate = 9 October 2011|location = USA|date = 27 March 2005|at = Identification and Related Records}}</ref>
|Section1={{Chembox Identifiers
|CASNo_Ref = {{cascite|correct|CAS}}
|CASNo = 2781-85-3
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = 7B8994OHJ0
|PubChem = 123173
|ChemSpiderID = 109788
|ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
|MeSHName = cyclopropene
|SMILES = C1C=C1
|StdInChI = 1S/C3H4/c1-2-3-1/h1-2H,3H2
|StdInChI_Ref = {{stdinchicite|changed|chemspider}}
|StdInChIKey = OOXWYYGXTJLWHA-UHFFFAOYSA-N
|StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
}}
|Section2={{Chembox Properties
|C=3 | H=4 
|BoilingPtC = -36
}}
|Section3={{Chembox Thermochemistry
|DeltaHc = −2032 – −2026 kJ mol<sup>−1</sup>
|HeatCapacity = 51.9–53.9 J K<sup>−1</sup> mol<sup>−1</sup>
}}
}}

'''Cyclopropene''' is an [[organic compound]] with the [[chemical formula|formula]] {{chem2|C3H4}}. It is the simplest [[cycloalkene]]. Because the ring is highly [[Ring strain|strained]], cyclopropene is difficult to prepare and highly reactive.  This colorless gas has been the subject for many fundamental studies of bonding and reactivity.<ref>{{cite journal |author= Carter, F. L. |author2= Frampton, V. L. |title= Review of the Chemistry of Cyclopropene Compounds |journal= Chemical Reviews |year= 1964 |volume= 64 |issue= 5 |pages= 497–525 |doi= 10.1021/cr60231a001}}</ref>  It does not occur naturally, but derivatives are known in some [[fatty acid]]s.  Derivatives of cyclopropene are used commercially to control ripening of some fruit.

==Structure and bonding==
The molecule has a [[triangular]] structure.  The reduced length of the [[alkene|double bond]] compared to a [[alkane|single bond]] causes the angle opposite the double bond to narrow to about 51° from the 60° angle found in [[cyclopropane]].<ref>{{cite journal |title= Structure of 3-cyanocyclopropene by microwave spectroscopy and ab initio molecular orbital calculations. Evidence for substituent-ring double bond interactions |author= Staley, S. W. |author2= Norden, T. D. |author3= Su, C.-F. |author4= Rall, M. |author5= Harmony, M. D. |journal= J. Am. Chem. Soc. |year= 1987 |volume= 109 |issue= 10 |pages= 2880–2884 |doi= 10.1021/ja00244a004 }}</ref> As with cyclopropane, the carbon–carbon bonding in the ring has increased [[atomic orbital|p character]]: the alkene carbon atoms use sp<sup>2.68</sup> [[Orbital hybridisation|hybridization]] for the ring.<ref>{{cite journal |journal= Tetrahedron |volume= 38 |issue= 5 |year= 1982 |pages= 645–655 |doi= 10.1016/0040-4020(82)80206-8 |title= The geometry of small rings: Molecular geometry of cyclopropene and its derivatives |author= Allen, F. H. }}</ref>

==Synthesis of cyclopropene and derivatives==

===Early syntheses===
The first confirmed synthesis of cyclopropene, carried out by Dem'yanov and Doyarenko, involved the [[thermal decomposition]] of trimethylcyclopropylammonium hydroxide over platinized clay at approximately 300&nbsp;°C. <ref>{{Cite book|last1=Hart|first1=Harold|url=https://books.google.com/books?id=qhwSBQAAQBAJ|title=Advances in Alicyclic Chemistry|last2=Karabatsos|first2=G. J.|publisher=Academic Press Inc.|year=1966|volume=1|location=New York and London|page=55|isbn=9781483224206|language=en}} </ref> This reaction produces mainly [[trimethylamine]] and dimethylcyclopropyl amine, together with about 5% of cyclopropene. Later Schlatter improved the pyrolytic reaction conditions using platinized [[asbestos]] as a [[Catalysis|catalyst]] at 320–330 °C and obtained cyclopropene in 45% [[Yield (chemistry)|yield]].<ref>{{Cite journal|last=Schlatter|first=Maurice J.|date=1941-06-01|title=The Preparation of Cyclopropene|url=https://doi.org/10.1021/ja01851a068|journal=Journal of the American Chemical Society|volume=63|issue=6|pages=1733–1737|doi=10.1021/ja01851a068|issn=0002-7863|url-access=subscription}}</ref>

Cyclopropene can also be obtained in about 1% yield by thermolysis of the adduct of [[cycloheptatriene]] and [[dimethyl acetylenedicarboxylate]].<ref>{{Cite book|url=https://books.google.com/books?id=GVeGAwAAQBAJ&dq=alder+jacobs+cyclopropene+1528&pg=PA2713|title=Houben-Weyl. Methods of Organic Chemistry – Cyclopropanes, Authors Index, Compound Index|publisher=George Thieme Verlag|year=1997|isbn=978-3-13-101644-7|editor-last=de Meijere|editor-first=Armin|volume=E 17d|location=Stuttgart, New York|pages=2712–2713|language=en}}</ref>

===Modern syntheses from allyl chlorides===
[[Allyl chloride]] undergoes [[dehydrohalogenation]] upon treatment with the base [[sodium amide]] at 80&nbsp;°C to produce cyclopropene in about 10% yield.<ref>{{cite journal |author= Closs, G.L. |author2= Krantz, K.D. |title= A Simple Synthesis of Cyclopropene |journal= Journal of Organic Chemistry |year= 1966 |volume= 31 |issue= 2 |pages= 638 |doi= 10.1021/jo01340a534 }}</ref>
:{{chem2 | CH2\dCHCH2Cl  +  NaNH2 -> C3H4 + NaCl + NH3 }}

The major byproduct of the reaction is [[allylamine]]. Adding allyl chloride to [[sodium bis(trimethylsilyl)amide]] in boiling [[toluene]] over a period of 45–60&nbsp;minutes produces the targeted compound in about 40% yield with an improvement in purity:<ref name=Binger>{{OrgSynth |author= Binger, P. |author2= Wedermann, P. |author3= Brinker, U. H. |year= 2000 |title= Cyclopropene: A New Simple Synthesis and Its Diels-Alder reaction with Cyclopentadiene |volume= 77 |pages= 254 |collvol= 10 |collvolpages= 231 |prep=v77p0254}}</ref>
:{{chem2 | CH2\dCHCH2Cl + NaN(TMS)2 -> C3H4 + NaCl + NH(TMS)2 }}
[[1-Methylcyclopropene]] is synthesized similarly but at room temperature from methallylchloride using [[phenyllithium]] as the base:<ref>{{cite journal |author= Clarke, T. C. |author2= Duncan, C. D. |author3= Magid, R. M. |title= An Efficient and Convenient Synthesis of 1-Methylcyclopropene |journal= J. Org. Chem. |year= 1971 |volume= 36 |issue= 9 |pages= 1320–1321 |doi= 10.1021/jo00808a041 }}</ref>
:{{chem2 | CH2\dC(CH3)CH2Cl + LiC6H5 ->}} {{chem2|CH3\sC3H3|link=1-Methylcyclopropene}} + LiCl + {{chem2|C6H6}}

===Syntheses of derivatives===
Treatment of nitrocyclopropanes with [[sodium methoxide]] eliminates the nitrite, giving the respective cyclopropene derivative. The synthesis of purely aliphatic cyclopropenes was first illustrated by the copper-catalyzed additions of carbenes to alkynes. In the presence of a copper catalyst, [[ethyl diazoacetate]] reacts with acetylenes to give cyclopropenes. 1,2-Dimethylcyclopropene-3-carboxylate arises via this method from [[2-butyne]]. Copper, as copper sulfate and copper dust, are among the more popular forms of copper used to promote such reactions.  [[Rhodium acetate]] has also been used.  

==Reactions of cyclopropene==
Studies on cyclopropene mainly focus on the consequences of its high ring strain. At 425&nbsp;°C, cyclopropene isomerizes to [[methylacetylene]] (propyne).
:{{chem2 | C3H4 -> H3CC\tCH }}

Attempted fractional distillation of cyclopropene at –36&nbsp;°C (its predicted boiling point) results in polymerization.   The mechanism is assumed to be a free-radical chain reaction, and the product, based on NMR spectra, is thought to be polycyclopropane.

Cyclopropene undergoes the [[Diels–Alder reaction]] with [[cyclopentadiene]] to give endo-tricyclo[3.2.1.0<sup>2,4</sup>]oct-6-ene. This reaction is commonly used to check for the presence of cyclopropene, following its synthesis.<ref name=Binger/>
:[[Image:CyclopropeneDielsAlder.PNG|350px|left]]{{clear-left}}

==Related compounds==
*[[Malvalic acid]] is a toxic cyclopropene fatty acid that occurs in cottonseed oil.
*[[1-Methylcyclopropene]] (1-MCP) is used to slow the ripening in fruits.<ref>{{ cite journal |author= Beaudry, R. |author2= Watkins, C. |title= Use of 1-MCP on Apples |journal= Perishable Handling Quarterly |year= 2001 |issue= 108 |pages= 12|publisher= [[University of California]] }}</ref><ref>{{cite journal |journal= Postharvest Biology and Technology |volume= 32 |issue= 2 |date=May 2004 |pages= 193–204 |doi= 10.1016/j.postharvbio.2003.11.009 |title=Inhibition of ethylene action by 1-methylcyclopropene extends postharvest life of "Bartlett" pears |author= Trinchero, G. D. |author2= Sozzi, G. O. |author3= Covatta, F. |author4= Fraschina, A. A. }}</ref>
*[[Borirene]]s, [[phosphirene]]s, and [[silirene]]s are boron-, phosphorus-, and silicon-substituted cyclopropenes, with the formula {{chem2|RBC2R'2, RPC2R'2}}, and {{chem2|R2SiC2R'2}}.
* [[Cyclopropane fatty acid#Cyclopropene fatty acids|Cyclopropene fatty acids]] a class of naturally occurring cyclopropenes.

==References==
{{Reflist}}

==External links==
*{{Commonscatinline|Cyclopropene}}

{{cycloalkenes}}
{{Annulenes}}
{{Authority control}}

[[Category:Cyclopropenes| ]]
[[Category:Cycloalkenes]]
[[Category:Gases]]
[[Category:Annulenes]]