Propylene oxide

Propylene oxide is a highly toxic flammable chemical compound. It is an epoxide having a molecular formula C3H6O.

Propylene oxide has a single chiral center, and thus exists as a pair of enantiomers. The material commonly available, and all industrial material, is an equal mixture of the two enantiomers, and is thus a racemic mixture.

Its major industrial application is as a monomer for the production of polyether polyols for use in making polyurethane plastics.

Production
Industrial production of propylene oxide is mainly from co-oxidation of propylene with other chemicals.


 * Propylene + Chlorine + Lime(chlorine absorber) → Propylene oxide + Calcium Chloride
 * Propylene + isobutene → Propylene oxide + t-butyl alcohol
 * Propylene + ethylbenzene → Propylene oxide + styrene

On 2005, about half of the world production is through chlorohydrin technology (the first one of the above), one third from PO/SM technology (the third one), and the other from PO/TBA technology (the second one). The above technologies create additional side products.

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. This is a variant of the POSM process (third above) that uses cumene instead of ethylbenzene and recycles the coproducts via dehydration and hydrogenation back to cumene.

In the new HPPO-Process recently developed by BASF and Dow Chemical propylene is oxidized with hydrogen peroxide:

C3H6 + H2O2 → C3H6O + H2O

In this process no side products besides of water are created. The first technical plant is currently being built in Antwerp and due to begin production in 2008.

Properties
Propylene oxide degrades into propylene glycol in the presence of water, a process which is accelerated by the presence of acid or base. Propylene oxide is often confused with ethylene oxide due to their similar structures, however ethylene oxide is a known carcinogen while propylene oxide has not been shown to be so.

Chirality
Propylene oxide is a chiral compound due to presence of asymmetrical carbon atom in oxirane cycle. Industrial propylene oxide is a racemic mixture.

Uses
Between 60 and 70% of all propylene oxide is consumed making polyether polyols for use in making polyurethane plastics. Propylene oxide is also used in the production of propylene glycol (using about 20% of propylene oxide), polypropylene glycol], propylene glycols ethers and [[propylene carbonate.

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.

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.