Propylene oxide

Propylene oxide
IUPAC name Epoxypropane
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
Identifiers
CAS number	75-56-9 Y
EC number	200-879-2
KEGG	C15508 N
Jmol-3D images	Image 1
SMILES CC1CO1
Properties
Molecular formula	C3H6O
Molar mass	58.08 g mol−1
Appearance	Colorless liquid
Density	0.830
Melting point	−112 °C
Boiling point	34 °C
Solubility in water	Appreciable
Hazards
MSDS	Oxford MSDS
NFPA 704	4 3 2
Flash point	−37 °C (−35 °F)
Autoignition temperature	747 °C (1,377 °F)
Explosive limits	2.1-37%
N oxide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 chiral epoxide, although it 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.

Production

Industrial production of propylene oxide starts from propylene. Two general approaches are employed, one involving hydrochlorination and the other involving oxidation.^[1] 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

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

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

Lime is often used as a chlorine absorber.

Co-oxidation of propylene

The other general route to propylene oxide involves co-oxidation of the organic chemicals isobutene 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 ban of MTBE, propylene/isobutene was one of the most important production process.

Oxidation of propylene

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.^[2] 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.^[3] 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.^[4]

Uses

Between 60 and 70% of all propylene oxide is converted to polyether polyols for the production of polyurethane plastics.^[5] 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

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.

Fumigant

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 incident in the United States. Pistachio nuts can also be subjected to propylene oxide to control Salmonella. It is a method approved by the FDA.^[6][7]

Microscopy

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.

Safety

Propylene oxide is a probable human carcinogen,^[8] and listed as an IARC Group 2B carcinogen.

References

1. ^ 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
2. ^ "Summary of Sumitomo process from Nexant Reports". http://nexant.ecnext.com/coms2/gi_0255-227/Developments-in-Propylene-Oxide-Technology.html. Retrieved 2007-09-18. 
3. ^ "New BASF and Dow HPPO Plant in Antwerp Completes Start-Up Phase". http://www.basf.com/group/pressrelease/P-09-154. Retrieved 2009-03-05. 
4. ^ Alex Tullo (2004). Dow, BASF to build Propylene Oxide. 82. pp. 15. http://pubs.acs.org/cen/news/8236/8236notw9.html. 
5. ^ "Usage of proplyene oxide, from Dow Chemical". http://www.dow.com/propyleneoxide/app/index.htm. Retrieved 2007-09-10. 
6. ^ See The FDA Guidance Document For More Info
7. ^ 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 on 2007-09-28. http://web.archive.org/web/20070928050927/http://www.almondboard.com/files/Rule.pdf. Retrieved 2007-08-22. 
8. ^ "Safety data for propylene oxide". http://ptcl.chem.ox.ac.uk/MSDS/PR/propylene_oxide.html. 

External links

• WebBook page for C3H6O
• Propylene oxide at the United States Environmental Protection Agency
• Propylene oxide - chemical product info: properties, production, applications.
• Propylene oxide at the Technology Transfer Network Air Toxics Web Site