Cyclopentane

Production, occurrence and use

Cycloalkanes are formed by catalytic reforming. For example, when passed over a hot platinum surface, 2-methylbutane converts into cyclopentane.

Cyclopentane is principally used as a blowing agent in the manufacture of polyurethane insulating foam, replacing ozone-depleting agents such as CFC-11 and HCFC-141b. While cyclopentane is not typically used as a refrigerant, it is common for domestic appliances that are insulated with cyclopentane-based foam, such as refrigerators and freezers, to be marked with cyclopentane warning labels due to its flammability. Cyclopentane is also used in the manufacture of synthetic resins and rubber adhesives.

Cyclopentane is a minor component of automobile fuel, with its share in US gasoline varying between 0.2 and 1.6% in early 1990s and 0.1 to 1.7% in 2011. Its research and motor octane numbers are reported as 101 or 103 and 85 or 86 respectively.

Multiple alkylated cyclopentane (MAC) lubricants, such as 1,3,4-tri-(2-octyldodecyl) cyclopentane, have low volatility and are used by NASA in space applications.

Cyclopentane requires safety precautions to prevent leakage and ignition as it is both highly flammable and can also cause respiratory arrest when inhaled.

Cyclopentane can be fluorinated to give compounds ranging from to perfluorocyclopentane . Such species are conceivable refrigerants and specialty solvents.

The cyclopentane ring is pervasive in natural products including many useful drugs. Examples include most steroids, prostaglandins, and some lipids.

Conformations

In a regular pentagon, the angles at the vertices are all 108°, slightly less than the bond angle in perfectly tetrahedrally bonded carbon, which is about 109.47°. However, cyclopentane is not planar in its normal conformations. It puckers in order to increase the distances between the hydrogen atoms (something which does not happen in the planar cyclopentadienyl anion because it doesn't have as many hydrogen atoms). This means that the average C-C-C angle is less than 108°. There are two conformations that give local minima of the energy, the "envelope" and the "half-chair" (occurring in two enantiomorphs). The envelope has mirror symmetry (C), while the half chair has two-fold rotational symmetry (C). In both cases the symmetry implies that there are two pairs of equal C-C-C angles and one C-C-C angle that has no pair. In fact for cyclopentane, unlike for cyclohexane (C6H12, see cyclohexane conformation) and higher cycloalkanes, it is not possible geometrically for all the angles and bond lengths to be equal except if it is in the form of a flat regular pentagon.

File:Cyclopentane envelope conformation.svg|Envelope File:Cyclopentane3D.png|3D envelope File:Cyclopentane halfchair.svg|Half-chair

References

References

1. {{GESTIS
2. "ICSC 0353 - CYCLOPENTANE".
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4. (1981). "Comparative Study of C-Pentane and N-Pentane Transformations on Ni and Pt Catalysts". Studies in Surface Science and Catalysis.
5. (January 1893). "III. Der Pentamethenylalkohol und seine Derivate (Cyclopentanol and its derivatives)". Justus Liebigs Annalen der Chemie.
6. (May 2000). "Appliance Rigid Foams Blown with Cyclopentane and Cyclopentane/Isopentane Blends". Journal of Cellular Plastics.
7. [http://archive.greenpeace.org/ozone/excuse/20excuse.html Greenpeace - Appliance Insulation] {{webarchive. link. (2008-10-30)
8. (November 1992). "Source Fingerprints for Volatile Non-Methane Hydrocarbons". Journal of the Air & Waste Management Association.
9. (2011). "Hydrocarbon Composition of Gasoline Vapor Emissions from Enclosed Fuel Tanks". United States Environmental Protection Agency.
10. Scherzer, Julius. (1990-08-31). "Octane-Enhancing Zeolitic FCC Catalysts: Scientific and Technical Aspects". CRC Press.
11. (2020). "A kinetic investigation on the synergistic low-temperature reactivity, antagonistic RON blending of high-octane fuels: Diisobutylene and cyclopentane". Combustion and Flame.
12. (1 September 1999). "Life of Pennzane and 815Z-Lubricated Instrument Bearings Cleaned with Non-CFC Solvents". National Aeronautics and Space Administration.
13. (12 April 2004). "Pennzoil Products: High Tech Products".
14. Robert W. Virtue, M.D.. (May 1949). "Observations on Cyclopentane as an Anesthetic Agent". Anesthesiology.
15. Tatlow, John Colin. (1995). "Cyclic and bicyclic polyfluoro-alkanes and -alkenes". Journal of Fluorine Chemistry.
16. (January 2016). "Synthesis of 1,1,2,2,3,3,4-heptafluorocyclopentane as a new generation of green solvent". Journal of Fluorine Chemistry.