Cyclopropane

Source: Wikipedia, the free encyclopedia.
Cyclopropane[1]
Cyclopropane - displayed formula
Cyclopropane - displayed formula
Cyclopropane - skeletal formula
Cyclopropane - skeletal formula
Names
Preferred IUPAC name
Cyclopropane[2]
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.000.771 Edit this at Wikidata
KEGG
UNII
UN number 1027
  • InChI=1S/C3H6/c1-2-3-1/h1-3H2 checkY
    Key: LVZWSLJZHVFIQJ-UHFFFAOYSA-N checkY
  • InChI=1/C3H6/c1-2-3-1/h1-3H2
    Key: LVZWSLJZHVFIQJ-UHFFFAOYAL
  • C1CC1
Properties
C3H6
Molar mass 42.08 g/mol
Appearance Colorless gas
Odor Sweet, ethereal
Density 1.879 g/L (1 atm, 0 °C)
680 g/L (liquid)
Melting point −128 °C (−198 °F; 145 K)
Boiling point −32.9 °C (−27.2 °F; 240.2 K)
502 mg/L
Vapor pressure 640 kPa (20 °C)
1350 kPa (50 °C)
Acidity (pKa) ~46
-39.9·10−6 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Highly flammable
Asphyxiant
GHS labelling:
GHS02: FlammableGHS04: Compressed Gas
Danger
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 hazard SA: Simple asphyxiant gas. E.g. nitrogen, helium
1
4
0
SA
495 °C (923 °F; 768 K)
Explosive limits
 2.4 % (lower)
10.4 % (upper)
Safety data sheet (SDS) Air Liquide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a triangular ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself is mainly of theoretical interest but many of its derivatives - cyclopropanes - are of commercial or biological significance.[3]

Cyclopropane was used as a clinical inhalational anesthetic from the 1930s through the 1980s. The substance's high flammability poses a risk of fire and explosions in operating rooms due to its tendency to accumulate in confined spaces, as its density is higher than that of air.

History

Cyclopropane was discovered in 1881 by August Freund, who also proposed the correct structure for the substance in his first paper.[4] Freund treated 1,3-dibromopropane with sodium, causing an intramolecular Wurtz reaction leading directly to cyclopropane.[5] The yield of the reaction was improved by Gustavson in 1887 with the use of zinc instead of sodium.[6] Cyclopropane had no commercial application until Henderson and Lucas discovered its anaesthetic properties in 1929;[7] industrial production had begun by 1936.[8] In modern anaesthetic practice, it has been superseded by other agents.

Anaesthesia

Cyclopropane was introduced into clinical use by the American anaesthetist Ralph Waters who used a closed system with carbon dioxide absorption to conserve this then-costly agent. Cyclopropane is a relatively potent, non-irritating and sweet smelling agent with a

cardiac dysrhythmia: a reaction known as "cyclopropane shock".[10] For this reason, as well as its high cost and its explosive nature,[11]
it was latterly used only for the induction of anaesthesia, and has not been available for clinical use since the mid-1980s. Cylinders and flow meters were colored orange.

Pharmacology

Cyclopropane is inactive at the GABAA and glycine receptors, and instead acts as an NMDA receptor antagonist.[12][13] It also inhibits the AMPA receptor and nicotinic acetylcholine receptors, and activates certain K2P channels.[12][13][14]

Structure and bonding

Further information: Bent bond
Orbital overlap in the bent bonding model of cyclopropane

The triangular structure of cyclopropane requires the

pm versus 153-155 pm.[15][16]

Despite their shortness, the C-C bonds in cyclopropane are weakened by 34 kcal/mol vs ordinary C-C bonds. In addition to ring strain, the molecule also has torsional strain due to the eclipsed conformation of its hydrogen atoms. The C-H bonds in cyclopropane are stronger than ordinary C-H bonds as reflected by NMR coupling constants.

Bonding between the carbon centres is generally described in terms of bent bonds.[17] In this model the carbon-carbon bonds are bent outwards so that the inter-orbital angle is 104°.

The unusual structural properties of cyclopropane have spawned many theoretical discussions. One theory invokes σ-aromaticity: the stabilization afforded by delocalization of the six electrons of cyclopropane's three C-C σ bonds to explain why the strain of cyclopropane is "only" 27.6 kcal/mol as compared to cyclobutane (26.2 kcal/mol) with cyclohexane as reference with Estr=0 kcal/mol,[18][19][20] in contrast to the usual π aromaticity, that, for example, has a highly stabilizing effect in benzene. Other studies do not support the role of σ-aromaticity in cyclopropane and the existence of an induced ring current; such studies provide an alternative explanation for the energetic stabilization and abnormal magnetic behaviour of cyclopropane.[21]

Synthesis

Cyclopropane was first produced via a

cyclised using sodium.[4] The yield of this reaction can be improved by the use of zinc as the dehalogenating agent and sodium iodide as a catalyst.[22]

BrCH2CH2CH2Br + 2 Na → (CH2)3 + 2 NaBr

The preparation of cyclopropane rings is referred to as cyclopropanation.

Reactions

Owing to the increased π-character of its C-C bonds, cyclopropane is often assumed to add bromine to give 1,3-dibromopropane, but this reaction proceeds poorly.

hydrohalic acids gives linear 1-halogenopropanes. Substituted cyclopropanes also react, following Markovnikov's rule.[24]

Electrophilic addition of HBr to cyclopropane

Cyclopropane and its derivatives can

C–C activation
.

Safety

Cyclopropane is highly flammable. However, despite its strain energy it does not exhibit explosive behavior substantially different from other alkanes.

See also

References

  1. ^ Merck Index, 11th Edition, 2755.
  2. ISBN 978-0-85404-182-4
    .
  3. PMID 11433485
    .
  4. ^
    doi:10.1002/prac.18820260125
    .
  5. S2CID 197767176
    .
  6. doi:10.1002/prac.18870360127
    .
  7. PMID 20317448
    .
  8. doi:10.1021/ie50322a013
    .
  9. PMID 4378907
    .
  10. PMID 15426685
    .
  11. PMID 8024925
    .
  12. ^
    ISBN 978-0-323-03707-5
    .
  13. ^
    ISBN 978-1-60761-463-0
    .
  14. S2CID 21160239.[permanent dead link
    ]
  15. doi:10.1039/P298700000S1
    .
  16. ISBN 978-3-319-22824-2
    .
  17. ^ Eric V. Anslyn and Dennis A. Dougherty. Modern Physical Organic Chemistry. 2006. pages 850-852
  18. ^ S. W. Benson, Thermochemical Kinetics, S. 273, J. Wiley & Sons, New York, London, Sydney, Toronto 1976
  19. doi:10.1021/ja00315a036
    .
  20. doi:10.1016/s0040-4020(01)86238-4
    .
  21. PMID 19562784
    .
  22. ISBN 978-3527306732
    .
  23. doi:10.1021/ed044p461
    .
  24. ISBN 0-471-85472-7

External links

Wikimedia Commons has media related to Cyclopropane.