Propylene oxide

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Propylene oxide
Propylene oxide.svg
IUPAC name
Other names
Propylene oxide; Epoxypropane; Propylene epoxide; 1,2-Propylene oxide; Methyl oxirane; 1,2-Epoxypropane; Propene oxide; Methyl ethylene oxide; Methylethylene oxide: PPO; PO
75-56-9 YesY
EC Number 200-879-2
Jmol interactive 3D Image
KEGG C15508 N
Molar mass 58.08 g·mol−1
Appearance Colorless liquid
Odor benzene-like[1]
Density 0.830 g/cm3
Melting point −112 °C (−170 °F; 161 K)
Boiling point 34 °C (93 °F; 307 K)
41% (20°C)[1]
Vapor pressure 445 mmHg (20°C)[1]
Main hazards Extremely flammable
Safety data sheet Oxford MSDS
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER!
R-phrases R45, R46, R12, R20/21/22, R36/37/38
S-phrases S53, S45
NFPA 704
Flammability code 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., propane Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored diamond
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)[2]
1740 ppm (mouse, 4 hr)
4000 ppm (rat, 4 hr)[2]
2005 ppm (dog, 4 hr)
4000 ppm (guinea pig, 4 hr)[2]
US health exposure limits (NIOSH):
TWA 100 ppm (240 mg/m3)[1]
Ca [400 ppm][1]
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

Propylene oxide is an organic compound with the molecular formula CH3CHCH2O. This colourless volatile liquid is produced on a large scale industrially, its major application being 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. Two general approaches are employed, one involving hydrochlorination and the other involving oxidation.[5] 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.

Hydrochlorination route[edit]

The traditional route proceeds via the conversion of propylene to chloropropanols:

Propylenoxid Darstellung 1.svg

The reaction produces a mixture of 1-chloro-2-propanol and 2-chloro-1-propanol, which is then dehydrochlorinated. For example:

Propylenoxid Darstellung 2.svg

Lime is often used as a chlorine absorber.

Co-oxidation of propylene[edit]

The other general route to propylene oxide involves co-oxidation of the organic chemicals isobutane or ethylbenzene. In the present of catalyst, air oxidation occurs as follows:

CH3CH=CH2 + Ph-CH2CH3 + O2 → CH3CHCH2O + Ph-CH=CH2 + H2O

The coproducts of these reactions, t-butyl alcohol or styrene, are useful feedstock for other products. For example, t-butyl alcohol reacts with methanol to give MTBE, an additive for gasoline. Before the current US ban of MTBE, propylene/isobutane was one of the most important production process.

Oxidation of propylene[edit]

In April 2003, Sumitomo Chemical commercialized the first PO-only plant in Japan, which produces propylene oxide from oxidation of cumene without significant production of other products.[6] This method is a variant of the POSM process (co-oxidation) that uses cumene hydroperoxide instead of ethylbenzene hydroperoxide and recycles the coproduct (alpha-hydroxycumene) via dehydration and hydrogenation back to cumene.

In March 2009, BASF and Dow Chemical started up their new HPPO plant in Antwerp.[7] In the HPPO-Process, propylene is oxidized with hydrogen peroxide:

CH3CH=CH2 + H2O2 → CH3CHCH2O + H2O

In this process no side products other than water are generated.[8]


Between 60 and 70% of all propylene oxide is converted to polyether polyols for the production of polyurethane plastics.[9] 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.

Historic and niche uses[edit]

Propylene oxide was once used as a racing fuel, but that usage is now prohibited under the US NHRA rules for safety reasons. It has also been used in glow fuel for model aircraft and surface vehicles, typically combined in small percentages of around 2% as an additive to the typical methanol, nitromethane, and oil mix. It is also used in thermobaric weapons, and microbial fumigation.


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.[10][11] 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 a probable human carcinogen,[12] and listed as an IARC Group 2B carcinogen.[13]


  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 "Propylene oxide". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  3. ^
  4. ^
  5. ^ Dietmar Kahlich, Uwe Wiechern, Jörg Lindner “Propylene Oxide” in Ullmann's Encyclopedia of Industrial Chemistry, 2002 by Wiley-VCH, Weinheim. doi:10.1002/14356007.a22_239Article Online Posting Date: June 15, 2000
  6. ^ "Summary of Sumitomo process from Nexant Reports". Retrieved 2007-09-18. 
  7. ^ "New BASF and Dow HPPO Plant in Antwerp Completes Start-Up Phase". Retrieved 2009-03-05. 
  8. ^ Alex Tullo (2004). "Dow, BASF to build Propylene Oxide" 82 (36): 15. 
  9. ^ "Usage of proplyene oxide, from Dow Chemical". Retrieved 2007-09-10. 
  10. ^ See The FDA Guidance Document For More Info
  11. ^ 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 2007-09-28. Retrieved 2007-08-22. 
  12. ^ "Safety data for propylene oxide". 
  13. ^ Grana, R; Benowitz, N; Glantz, SA (13 May 2014). "E-cigarettes: a scientific review.". Circulation 129 (19): 1972–86. doi:10.1161/circulationaha.114.007667. PMC 4018182. PMID 24821826. 

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