Propylene oxide
Structural formula
Ball-and-stick model of the propylene oxide molecule
Preferred IUPAC name
Other names
Propylene oxide
Propylene epoxide
1,2-Propylene oxide
Methyl oxirane
Propene oxide
Methyl ethylene oxide
Methylethylene oxide
3D model (JSmol)
ECHA InfoCard 100.000.800 Edit this at Wikidata
EC Number
  • 200-879-2
  • InChI=1S/C3H6O/c1-3-2-4-3/h3H,2H2,1H3
  • CC1CO1
Molar mass 58.080 g·mol−1
Appearance Colourless liquid
Odor benzene-like[1]
Density 0.859 g/cm3[2]
Melting point −111.9 °C (−169.4 °F; 161.2 K)[2]
Boiling point 35 °C (95 °F; 308 K)[2]
41% (20 °C)[1]
Vapor pressure 445 mmHg (20 °C)[1]
−4.25×10−5 cm3/mol[3]
120.4 J·(K·mol)−1
196.5 J·(K·mol)−1
−123.0 kJ·mol−1[4]
Occupational safety and health (OHS/OSH):
Main hazards
Extremely flammable[5][6]
GHS labelling:
GHS02: FlammableGHS08: Health hazardGHS07: Exclamation mark
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 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 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
Flash point −37 °C (−35 °F; 236 K)
747 °C (1,377 °F; 1,020 K)
Explosive limits 2.3–36%[1]
Lethal dose or concentration (LD, LC):
660 mg/kg (guinea pig, oral)
380 mg/kg (rat, oral)
440 mg/kg (mouse, oral)
1140 mg/kg (rat, oral)
690 mg/kg (guinea pig, oral)[7]
1740 ppm (mouse, 4 h)
4000 ppm (rat, 4 h)[7]
2005 ppm (dog, 4 h)
4000 ppm (guinea pig, 4 h)[7]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 100 ppm (240 mg/m3)[1]
REL (Recommended)
IDLH (Immediate danger)
Ca [400 ppm][1]
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 ?)

Propylene oxide is an acutely toxic and carcinogenic organic compound with the molecular formula CH3CHCH2O. This colourless volatile liquid with an odour similar to ether, is produced on a large scale industrially. Its major application is its use for the production of polyether polyols for use in making polyurethane plastics. It is a chiral epoxide, although it is commonly used as a racemic mixture.

This compound is sometimes called 1,2-propylene oxide to distinguish it from its isomer 1,3-propylene oxide, better known as oxetane.


Industrial production of propylene oxide starts from propylene.[8] Two general approaches are employed, one involving hydrochlorination and the other involving oxidation.[9] In 2005, about half of the world production was through chlorohydrin technology and one half via oxidation routes. The latter approach is growing in importance.[10]

Hydrochlorination route

The traditional route proceeds via the conversion of propene to propylene chlorohydrin according to the following simplified scheme:

The mixture of 1-chloro-2-propanol and 2-chloro-1-propanol is then dehydrochlorinated. For example:

Lime (calcium hydroxide) is often used to absorb the HCl.

Oxidation of propylene

The other general route to propylene oxide involves oxidation of propylene with an organic peroxide. The reaction follows this stoichiometry:


The process is practiced with four hydroperoxides:[10]

In principle, this process produces only water as a side product. In practice, some ring-opened derivatives of PO are generated.[12]


Like other epoxides, PO undergoes ring-opening reactions. With water, propylene glycol is produced. With alcohols, reactions, called hydroxylpropylation, analogous to ethoxylation occur. Grignard reagents add to propylene oxide to give secondary alcohols.

Some other reactions of propylene oxide include:[13]


Between 60 and 70% of all propylene oxide is converted to polyether polyols by the process called alkoxylation.[14] These polyols are building blocks in the production of polyurethane plastics.[15] About 20% of propylene oxide is hydrolyzed into propylene glycol, via a process which is accelerated by acid or base catalysis. Other major products are polypropylene glycol, propylene glycol ethers, and propylene carbonate.

Niche uses


The United States Food and Drug Administration has approved the use of propylene oxide to pasteurize raw almonds beginning on September 1, 2007, in response to two incidents of contamination by Salmonella in commercial orchards, one incident occurring in Canada and one in the United States.[16][17] Pistachio nuts can also be subjected to propylene oxide to control Salmonella.


Propylene oxide is commonly used in the preparation of biological samples for electron microscopy, to remove residual ethanol previously used for dehydration. In a typical procedure, the sample is first immersed in a mixture of equal volumes of ethanol and propylene oxide for 5 minutes, and then four times in pure oxide, 10 minutes each.


Propylene oxide is sometimes used in thermobaric munitions as the fuel in fuel–air explosives. In addition to the explosive damage from the blast wave, unexploded propylene oxide can cause additional effects from direct toxicity.[18]


Propylene oxide is both acutely toxic and carcinogenic. Acute exposure causes respiratory tract irritation, eventually leading to death [19]. Signs of toxicity after acute exposure include salivation, lacrimation, nasal discharge, gasping, lethargy and hypoactivity, weakness, and incoordination. Propylene oxide is also neurotoxic in rats, and presumably in humans [20]

Propylene oxide alkylates DNA.[21] As such, it is known animal carcinogen[22] and a potential human carcinogen, and is included into the List of IARC Group 2B carcinogens.[23]

Natural occurrence

In 2016 it was reported that propylene oxide was detected in Sagittarius B2, a cloud of gas in the Milky Way weighing three million solar masses. It is the first chiral molecule to be detected in space, albeit with no enantiomeric excess.[24]


  1. ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0538". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ a b c d Haynes 2011, p. 3.384
  3. ^ Haynes 2011, p. 3.577
  4. ^ Haynes 2011, p. 5.24
  5. ^ "NFPA DIAMOND".
  6. ^ GOV, NOAA Office of Response and Restoration, US. "PROPYLENE OXIDE | CAMEO Chemicals | NOAA".
  7. ^ a b c "Propylene oxide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  8. ^ Nijhuis TA, Makkee M, Moulijn JA, Weckhuysen BM (2006). "The Production of Propene Oxide: Catalytic Processes and Recent Developments". Industrial & Engineering Chemistry Research. 45 (10): 3447–3459. doi:10.1021/ie0513090. hdl:1874/20149.
  9. ^ Kahlich D, Wiechern U, Lindner J. "Propylene Oxide". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_239.
  10. ^ a b Nijhuis TA, Makkee M, Moulijn JA, Weckhuysen BM (2006). "The Production of Propene Oxide: Catalytic Processes and Recent Developments". Industrial & Engineering Chemistry Research. 45 (10): 3447. doi:10.1021/ie0513090. hdl:1874/20149.
  11. ^ "Summary of Sumitomo process from Nexant Reports". Archived from the original on 2006-01-17. Retrieved 2007-09-18.
  12. ^ Russo V, Tesser R, Santacesaria E, Di Serio M (2013). "Chemical and Technical Aspects of Propene Oxide Production via Hydrogen Peroxide (HPPO Process)". Industrial & Engineering Chemistry Research. 52 (3): 1168–1178. doi:10.1021/ie3023862.
  13. ^ Heilbron I, ed. (1953). Dictionary of Organic Compounds. Vol. 4. Oxford University Press. p. 249.
  14. ^ Adam N, Avar G, Blankenheim H, Friedrichs W, Giersig M, Weigang E, et al. "Polyurethanes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a21_665.pub2.
  15. ^ "Usage of proplyene oxide". Dow Chemical. Archived from the original on 2007-09-15. Retrieved 2007-09-10.
  16. ^ "Guidance for Industry: Measures to Address the Risk for Contamination by Salmonella Species in Food Containing a Pistachio-Derived Product As An Ingredient; Draft Guidance". June 2009. Archived from the original on 2011-02-09.
  17. ^ Agricultural Marketing Service, USDA (30 March 2007). "Almonds Grown in California; Outgoing Quality Control Requirements" (PDF). Federal Register. 72 (61): 15, 021–15, 036. Archived from the original (PDF) on 28 September 2007. Retrieved 2007-08-22.
  18. ^ "Backgrounder on Russian Fuel Air Explosives ("Vacuum Bombs") | Human Rights Watch". February 1, 2000. Archived from the original on February 10, 2013. Retrieved April 23, 2013.
  19. ^ National Research Council (US) Committee on Acute Exposure Guideline Levels (2010). Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 9. National Academies Press.
  20. ^ Ohnishi A, Murai Y (February 1993). "Polyneuropathy due to ethylene oxide, propylene oxide, and butylene oxide". Environmental Research. 60 (2): 242–247. doi:10.1006/enrs.1993.1032. PMID 8472653.
  21. ^ Lawley PD, Jarman M (February 1972). "Alkylation by propylene oxide of deoxyribonucleic acid, adenine, guanosine and deoxyguanylic acid". The Biochemical Journal. 126 (4): 893–900. doi:10.1042/bj1260893. PMC 1178497. PMID 5073240.
  22. ^ Ringo DL, Brennan EF, Cota-Robles EH (September 1982). "Epoxy resins are mutagenic: implications for electron microscopists". Journal of Ultrastructure Research. 80 (3): 280–287. doi:10.1016/s0022-5320(82)80041-5. PMID 6752439.
  23. ^ Grana R, Benowitz N, Glantz SA (May 2014). "E-cigarettes: a scientific review". Circulation. 129 (19): 1972–1986. doi:10.1161/circulationaha.114.007667. PMC 4018182. PMID 24821826.
  24. ^ "Scientists just detected this life-forming molecule in interstellar space for the first time". Science Alert. 2016-06-15.

Cited sources