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Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C and its boiling point is 49 °C. Cyclopentane is in the class of cycloalkanes, being alkanes that have one or more rings of carbon atoms.

Skeletal formula
Space-filling model
IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.005.470
EC Number 206-016-6
RTECS number GY2390000
Molar mass 70.1 g/mol
Appearance clear, colorless liquid
Odor mild, sweet
Density 0.751 g/cm3
Melting point −93.9 °C (−137.0 °F; 179.2 K)
Boiling point 49.2 °C (120.6 °F; 322.3 K)
156 mg·l−1 (25 °C)[1]
Solubility soluble in ethanol, acetone, ether
Vapor pressure 400 mmHg (31 °C)[2]
Acidity (pKa) ~45
-59.18·10−6 cm3/mol
Main hazards Flammable[2]
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasolineHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point −37.2 °C (−35.0 °F; 236.0 K)
361 °C (682 °F; 634 K)
Explosive limits 1.1%-8.7%[2]
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 600 ppm (1720 mg/m3)[2]
IDLH (Immediate danger)
Related compounds
Related compounds
cyclopropane, cyclobutane, cyclohexane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
The typical structure of cyclopentane is the "envelope" conformation.

It is formed by cracking cyclohexane in the presence of alumina at a high temperature and pressure.

It was first prepared in 1893 by the German chemist Johannes Wislicenus.[3]


Industrial usageEdit

Cyclopentane is used in the manufacture of synthetic resins and rubber adhesives and also as a blowing agent in the manufacture of polyurethane insulating foam, as found in many domestic appliances such as refrigerators and freezers, replacing environmentally damaging alternatives such as CFC-11 and HCFC-141b[4]

Multiply alkylated cyclopentane (MAC) lubricants have low volatility and are used in some specialty applications.[5]

The United States produces more than half a million kilograms of this chemical per year.

Formulation of cycloalkanesEdit

Cycloalkanes can be formulated via a process known as catalytic reforming.

For example, 2-methylbutane can be reformed into cyclopentane, by use of a platinum catalyst. This is particularly well known in automobiles, as branched alkanes will burn much more readily.

Half-chair conformation of lower-energy state chemical structure of cyclopentane.


  1. ^ Record of cyclopentane in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 28 February 2015.
  2. ^ a b c d e f "NIOSH Pocket Guide to Chemical Hazards #0171". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ J. Wislicenus and W. Hentschel (1893) "Der Pentamethenylalkohol und seine Derivate" (Cyclopentanol and its derivatives), Annalen der Chemie, 275 : 322-330; see especially pages 327-330. Wislicenus prepared cyclopentane from cyclopentanone ("Ketopentamethen"), which is prepared by heating calcium adipate.
  4. ^ Greenpeace - Appliance Insulation Archived 2008-10-30 at the Wayback Machine.
  5. ^ Pennzane - lubrication technology

External linksEdit