| Cyclopropene | |
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| IUPAC name |
Cyclopropene
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| Identifiers | |
| CAS number | 2781-85-3 |
| PubChem | 123173 |
| Properties | |
| Molecular formula | C3H4 |
| Molar mass | 40.0646 g/mol |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Cyclopropene is an organic compound with the formula C3H4. It is the simplest isolable cycloalkene. It has a triangular structure. Because the ring is highly strained, cyclopropene is both difficult to prepare and interesting to study.[1]
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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 320-330 °C under a CO2 atmosphere. This reaction produces mainly trimethylamine and dimethylcyclopropyl amine, together with about 5% of cyclopropene. Cyclopropene can also be obtained in about 1% yield by thermolysis of the adduct of cycloheptatriene and dimethyl acetylenedicarboxylate.
Modern syntheses from allyl chlorides
Allyl chloride undergoes dehydrohalogenation upon treatment with the base sodium amide at 80 °C to produce cyclopropene in ~10% yield.[2]
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- CH2=CHCH2Cl + NaNH2 → C3H4 (cyclopropene) + NaCl + NH3
The major byproduct of the reaction is allyl amine. Adding allyl chloride to sodium bis(trimethylsilyl)amide in boiling toluene over a period of 45-60 min. produces the targeted compound in about 40% yield with an improvement in purity:[3]
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- CH2=CHCH2Cl + NaN(TMS)2 → C3H4 (cyclopropene) + NaCl + NH(TMS)2
1-Methylcyclopropene is synthesized similarly but at room temperature from methallylchloride using phenyllithium as the base:[4]
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- CH2=C(CH3)CH2Cl + LiC6H5 → CH3C3H3 (1-methylcylopropene) + LiCl + 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 sulfate catalyst, ethyl diazoacetate reacts with acetylenes to give cyclopropenes. 1,2-Dimethylcyclopropene-3-carboxylate arises via this method from 2-butyne. Copper has proved to be useful as a catalyst in a variety of cyclopropene syntheses. Copper sulfate and copper dust are among the more popular forms of copper used.
Reactions of cyclopropene
Studies on cyclopropene mainly focus on the consequences of its high ring strain. At 425 °C, cyclopropene isomerizes to methylacetylene.
- C3H4 → H3CC≡CH
Attempted fractional distillation of cyclopropene at -36 °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[3.2.1.02,4]oct-6-ene. This reaction is commonly used to check for the presence of cyclopropene, following its synthesis.[3]
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.[5]
- borirenes, phosphirenes, and silirenes are boron-, phosphorus-, and silicon-substituted cyclopropenes, with the formula RBC2R'2, RPC2R'2, and R2SiC2R'2.
External links
References
- ^ Carter, F. L.; Frampton, V. L. "Review of the Chemistry of Cyclopropene Compounds." Chemical Reviews; 1964; Vol 64, 497-525.
- ^ Closs, G.L.; Krantz, K.D. "A Simple Synthesis of Cyclopropene." Journal of Organic Chemistry; 1966; Volume 31; 638.
- ^ a b Binger, P.; Wedermann, P.; Brinker, U. H. "Cyclopropene: A New Simple Synthesis and Its Diels-Alder reaction with Cyclopentadiene." Organic Syntheses; 2000; Vol 77; 254.
- ^ Clarke, T. C.; Duncan, C. D.; Magid, R. M. "An Efficient and Convenient Synthesis of 1-Methylcyclopropene." J. Org. Chem; 1971; Vol 39; 1320.
- ^ Beaudry, R.; Watkins, C. "Use of 1-MCP on Apples" Perishable Handling Quarterly; 2001;Issue 108; 12.
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