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Propylene oxide

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Propylene oxide
Names
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
3D model (JSmol)
ECHA InfoCard 100.000.800 Edit this at Wikidata
EC Number
  • 200-897-2
  • CC1CO1
Properties
C3H6O
Molar mass 58.08 g mol−1
Appearance colorless liquid
Density 0.830
Melting point −112 °C
Boiling point 34 °C
appreciable
Hazards
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
3
4
2
Flash point −37 °C
Explosive limits 2.1 - 37%
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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]

Clearing Agent

PO is commonly used for the preparation of biological samples for electron microscopy. It's applied for clearing the sample of alcohol used for dehydration. The process can be broken down into two stages; first, equal volumes of ethanol and PO are added for 5 minutes, then, pure PO is applied 4 times, lasting for 10 minutes each.

Safety

Propylene oxide is a probable human carcinogen.[6]

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". Retrieved 2007-09-18.
  3. ^ Alex Tullo (2004). "Dow, BASF to build Propylene Oxide". 82 (36): 15. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ "Usage of proplyene oxide, from Dow Chemical". Retrieved 2007-09-10.
  5. ^ Agricultural Marketing Service, USDA (30 March 2007). "Almonds Grown in California; Outgoing Quality Control Requirements" (PDF). Federal Register. 72 (61): 15, 021–15, 036. Retrieved 2007-08-22.
  6. ^ "Safety data for propylene oxide".
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