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
Identifiers
CAS number	75-56-9 Y
EC number	200-897-2
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
Autoignition temperature	747 °C
Explosive limits	2.1 - 37%
Y (what is this?)  (verify) 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 additives 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 commercialised 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 a HPPO-Process developed by BASF and Dow Chemical, propylene is oxidized with hydrogen peroxide:

CH₃CH=CH₂ + H₂O₂ → CH₃CHCH₂O + H₂O

In this process no side products other than water are generated. Production is expected to start in Antwerp in 2008.^[3]

Uses

Between 60 and 70% of all propylene oxide is converted to polyether polyols for the production of polyurethane plastics.^[4] 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 glycols ethers, and propylene carbonate.

Historic and niche uses

It was once used as a racing fuel, but that usage is now prohibited under the US NHRA rules for safety reasons. It is also used in thermobaric weapons, and microbial fumigation.

Fumigant

The United States Food & Drug Administration has approved its use to pasteurize raw almonds beginning on September 1, 2007 in response to several incidences of contamination by salmonella in commercial orchards.^[5]

Safety

Propylene oxide is a probable human carcinogen.^[6]

References

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