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Cyclopropane

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Cyclopropane[1]
Cyclopropane - displayed formula
Cyclopropane - displayed formula
Cyclopropane - skeletal formula
Cyclopropane - skeletal formula
Names
IUPAC name
Cyclopropane
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.000.771 Edit this at Wikidata
  • InChI=1/C3H6/c1-2-3-1/h1-3H2
    Key: LVZWSLJZHVFIQJ-UHFFFAOYAL
  • C1CC1
Properties
C3H6
Molar mass 42.08 g/mol
Density 1.879 g/L (1 atm, 0 °C)
Melting point −128 °C (−198 °F; 145 K)
Boiling point −33 °C (−27 °F; 240 K)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Highly flammable
Asphyxiant
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
4
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms. Cyclopropane and propene have the same empirical formula but have different structures, making them structural isomers.

The bonds between the carbon atoms are considerably weaker than in a typical carbon-carbon bond, yielding reactivity similar to or greater than alkenes. Baeyer strain theory explains why: the angle strain from the 60° angle between the carbon atoms (less than the normal angle of 109.5° for bonds between atoms with sp3 hybridised orbitals) reduces the compound's carbon-carbon bond energy, making it more reactive than other cycloalkanes such as cyclohexane and cyclopentane. The molecule also has torsional strain due to the eclipsed conformation of its hydrogen atoms. It is somewhat stabilized by some pi character in its carbon-carbon bonds, indicated by the Walsh orbital description whereas it is modeled as a three-center-bonded orbital combination of methylene carbenes [citation needed]. Bent bonds also describe the bonding in cyclopropane.

The smallest polycyclic compounds contain multiple fused cyclopropane rings. Tetrahedrane contains four fused cyclopropane rings which form the faces of a tetrahedron. [1.1.1]Propellane contains three cyclopropane rings which share a single central carbon-carbon bond.

Cyclopropane is an anaesthetic when inhaled. In modern anaesthetic practice, it has been superseded by other agents, due to its extreme reactivity under normal conditions: when the gas is mixed with oxygen there is a significant risk of explosion.

History

Cyclopropane was discovered in 1881 by August Freund, who also proposed the right structure for the new substance in his first paper. Freund reacted 1,3-dibromopropane with sodium, the reaction is an intramolecular Wurtz reaction leading directly to cyclopropane.[2][3] The yield of the reaction can be improved by the use of zinc instead of sodium.[4] Cyclopropane had no commercial application until Henderson and Lucas discovered its anaesthetic properties in 1929;[5] industrial production had begun by 1936.[6]

Safety

Because of the strain in the carbon-carbon bonds of cyclopropane, the molecule has an enormous amount of potential energy. In pure form, it will break down to form linear hydrocarbons, including "normal", non-cyclic propene. This decomposition is potentially explosive, especially if the cyclopropane is liquified, pressurized, or contained within tanks. Explosions of cyclopropane and oxygen are even more powerful, because the energy released by the formation of propene is compounded by the energy released via the oxidation of the carbon and hydrogen present.

At room temperature, sufficient volumes of liquified cyclopropane will self-detonate. To guard against this, the liquid is shipped in cylinders filled with tungsten wool, which prevents high-speed collisions between molecules and vastly improves stability. Pipes to carry cyclopropane must likewise be of small diameter, or else filled with unreactive metal or glass wool, to prevent explosions. Even if these precautions are followed, cyclopropane is dangerous to handle and manufacture, and is no longer used for anaesthesia.

Cyclopropanes

Cyclopropanes are a class of organic compounds sharing the common cyclopropane ring, in which one or more hydrogens may be substituted. These compounds are found in biomolecules; for instance, the pyrethrum insecticides (found in certain Chrysanthemum species) contain a cyclopropane ring.

Organic synthesis

Cyclopropanes can be prepared in the laboratory by organic synthesis in various ways and many methods are simply called cyclopropanation.

By coupling

Cyclopropanes can be obtained by an intramolecular coupling reaction in the addition of sodium to 1,3-dibromopropane in the Freund reaction (1881)[2][3][6] or zinc to 1,3-dichloropropane in the Gustavson reaction(1887)[4][7] or by intramolecular Wurtz coupling for example in the synthesis of bicyclo[1.1.0]butane[8]

From alkenes

The addition to an alkene of a zinc carbenoid takes place in the Simmons-Smith reaction (1958) for example to cinnamyl alcohol.[9] In one adaptation[10] an amide is reacted with two equivalents of dichloromethane aided by titanium tetrachloride and magnesium:

Amide cyclopropanation
a possible reaction mechanism for this cyclopropanation was proposed[11]:
Amide cyclopropanation Mechanism

The carbene can also be a regular carbene such as dibromocarbene in the synthesis of propellane[12] or carbene precursor methyl diazoacetate[13]

The addition of a carbene to an alkene is a form of cheletropic reaction.

By nucleophilic displacement

In nucleophilic displacement a leaving group is displaced by a carbon nucleophile in a 1,3 relationship, for example the synthesis of cyclopropylacetylene from 5-chloro-1-pentyne.[14] Another example can be found in the Bingel reaction. An asymmetric reaction creating three stereocenters is demonstrated in a reaction of cyclohexenone with bromonitromethane assisted by trans-2,5-dimethylpiperazine as a base and a pyrrolidine based tetrazole organocatalyst[15][16]:

Asymmetric nitrocyclopropanation Hansen 2006

Rearrangements

Rearrangement reaction of certain cyclobutane compounds can result in cyclopropanes for instance the conversion of 1,2-cyclobutanediol to cyclopropanecarboxaldehyde[17], the di-pi-methane rearrangement is a photochemical rearrangement reaction of 1,4-dienes to vinylcyclopropanes [18]

Other

In the Kulinkovich reaction esters react with Grignards in presence of a titanium alkoxide. Extrusion of nitrogen takes place in certain pyrazolines in the so called Kishner cyclopropane synthesis [19][20]

Organic reactions

Although cyclopropanes are formally cycloalkanes, they are very reactive due to considerable strain energy and due to double bond character.

Electrophilic addition

Cyclopropanes react with mineral acids such as HX in electrophilic addition (very much like a double bond) to linear alkyl halides with ring-opening. Substituted cyclopropanes follow Markovnikov's rule.[21]

Electrophilic addition of HBr to cyclopropane

Cycloadditions

Cyclopropyl groups participate in cycloaddition reactions such as the formal [5+2]cycloaddition shown below:

Cyclopropane Cycloaddition

This asymmetric synthesis is catalyzed by a rhodium BINAP system with 96% enantiomeric excess[22]. Also see the vinylcyclopropane rearrangement.

Rearrangements

Cyclopropyl groups also engage in many rearrangement reactions. An extreme example is found in the compound bullvalene. A cyclopropane ring is an intermediate in the Favorskii rearrangement. Certain methylenecyclopropanes are found to convert to cyclobutenes[23]:

Methylene cyclopropane isomerization

This reaction is catalyzed by platinum(II) chloride in a carbon monoxide environment. The proposed reaction mechanism is supported by deuterium labeling[24].

In another version of the same reaction[25] the catalyst is PdBr2 is prepared in situ from palladium(II) acetate and copper(II) bromide and the solvent is toluene.

Molecular orbitals

Bonding between the carbon centers in cyclopropane is generally described by invoking bent bonds.[26]

References

  1. ^ Merck Index, 11th Edition, 2755.
  2. ^ a b August Freund (1881). "Über Trimethylen". Journal für Praktische Chemie. 26 (1): 625–635. doi:10.1002/prac.18820260125.
  3. ^ a b August Freund (1882). "Über Trimethylen". Monatshefte für Chemie. 3 (1): 625–635. doi:10.1007/BF01516828.
  4. ^ a b G. Gustavson (1887). "Ueber eine neue Darstellungsmethode des Trimethylens". J. Prakt. Chem. 36: 300–305. doi:10.1002/prac.18870360127.
  5. ^ G. H. W. Lucas and V. E. Henderson (1 August 1929). "A New Anæsthetic: Cyclopropane". Can Med Assoc J. 21 (2): 173–5. PMC 1710967.
  6. ^ a b H. B. Hass, E. T. McBee, and G. E. Hinds (1936). "Synthesis of Cyclopropane". Industrial & Engineering Chemistry. 28 (10): 1178–81. doi:10.1021/ie50322a013.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Freund Reaction
  8. ^ Bicyclo[1.1.0]butane Gary M. Lampman and James C. Aumiller Organic Syntheses, Coll. Vol. 6, p.133 (1988); Vol. 51, p.55 (1971) Link.
  9. ^ Cyclopropanemethanol, 2-phenyl-, (1S-trans)- André B. Charette and Hélène Lebel Organic Syntheses, Coll. Vol. 10, p.613 (2004); Vol. 76, p.86 (1999)Link
  10. ^ Unusual Ambiphilic Carbenoid Equivalent in Amide Cyclopropanation Kuo-Wei Lin, Shiuan Yan, I-Lin Hsieh, and Tu-Hsin Yan Org. Lett.; 2006; 8(11) pp 2265 - 2267; Abstract
  11. ^ Reaction mechanism: Magnesium reacts with titanium tetrachloride 1 to Grignard reagent 2 in equilibrium with divalent Titanium(II) chloride 3 which adds to dichloromethane to adduct 4. Another insertion of magnesium and loss of magnesium dichloride gives the Schrock carbene 6 which reacts with the carbonyl group in amide 7. Loss of titanium oxychloride gives the enamine 9 which continuous to react with another carbene and finally to the cyclopropane. Notes: Instead of chloride, titanium can also be coordinated to solvent. In equally plausible mechanisms the intermediates are Simmons-Smith like
  12. ^ [1.1.1]propellane Kathleen R. Mondanaro and William P. Dailey Organic Syntheses, Coll. Vol. 10, p.658 (2004); Vol. 75, p.98 (1998) Link
  13. ^ Butanoic acid, 3,3-dimethyl-4-oxo-, methyl ester Hans-Ulrich Reissig, Ingrid Reichelt, and Thomas Kunz Organic Syntheses, Coll. Vol. 9, p.573 (1998); Vol. 71, p.189 (1993). Link
  14. ^ Cyclopropylaetylene Edward G. Corley, Andrew S. Thompson, Martha Huntington Organic Syntheses, Coll. Vol. 10, p.456 (2004); Vol. 77, p.231 (2000) Link.
  15. ^ A new asymmetric organocatalytic nitrocyclopropanation reaction Henriette M. Hansen, Deborah A. Longbottom and Steven V. Ley Chem. Commun., 2006, 4838 - 4840, doi:10.1039/b612436b
  16. ^ The initial reaction is a Michael addition. Solvent dichloromethane, 64% enantiomeric excess
  17. ^ J. P. Barnier, J. Champion, and J. M. Conia Organic Syntheses, Coll. Vol. 7, p.129 (1990); Vol. 60, p.25 (1981) Link.
  18. ^ IUPAC Gold book definition
  19. ^ N. M. Kishner, A. Zavadovskii, J. Russ. Phys. Chem. Soc. 43, 1132 (1911).
  20. ^ For an example see: phenylcyclopropane in Organic Syntheses, Coll. Vol. 5, p.929 (1973); Vol. 47, p.98 (1967). http://orgsynth.org/orgsyn/pdfs/CV5P0929.pdf
  21. ^ Advanced organic Chemistry, Reactions, mechanisms and structure 3ed. Jerry March ISBN 0-471-85472-7
  22. ^ Asymmetric Catalysis of the [5 + 2] Cycloaddition Reaction of Vinylcyclopropanes and -Systems Paul A. Wender, Lars O. Haustedt, Jaehong Lim, Jennifer A. Love, Travis J. Williams, and Joo-Yong Yoon J. Am. Chem. Soc.; 2006; 128(19) pp 6302 – 6303; Abstract
  23. ^ PtCl2-Catalyzed Rearrangement of Methylenecyclopropanes Alois Fürstner and Christophe Aïssa J. Am. Chem. Soc.; 2006; 128(19) pp 6306 -6307; Abstract
  24. ^ Reaction mechanism: The starting compound contains one deuterium atom (D), in the first step PtCl2 coordinates to the double bond in 1a. The next step is oxidative addition to 1b which is a non-classical ion. This intermediate rearranges to the cyclobutane carbocation 1c which has also some carbene character through one of its resonance structures. The next step is a deuterium migration to the more stable benzylic carbocation after which the cyclobutene is liberated.
  25. ^ Palladium-Catalyzed Ring Enlargement of Aryl-Substituted Methylenecyclopropanes to Cyclobutenes Min Shi, Le-Ping Liu, and Jie Tang J. Am. Chem. Soc.; 2006; 128(23) pp 7430 - 7431; doi:10.1021/ja061749y
  26. ^ Eric V. Anslyn and Dennis A. Dougherty. Modern Physical Organic Chemistry. 2006. pages 850-852
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