Propylene oxide

December 05, 2022
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Propylene oxide (PO), formally 2-methyloxirane, is low-boiling liquid that is useful for making many commercial materials. It was known as long ago as 1866, when Eduard Linnemann at the University of Lemberg (Germany) described the conversion of PO to acetone.

The initial method for producing PO was the chlorination of propylene in water to give a mixture of chlorohydrins, followed by dehydrochlorinaton with potassium hydroxide. A process developed subsequently was the direct oxidation of propylene with an organic hydroperoxide. Both processes are in use today.

About two-thirds of worldwide PO production (≈13 million t/year) is used to make polyether polyols, which play an important role in the manufacture of the versatile polyurethane foam. Another ≈20% is hydrolyzed to propylene glycol. As an industrial epoxide, PO is second in importance only to ethylene oxide. PO is a chiral molecule, but almost all of it is produced as the racemic mixture.

As shown in the hazard information table, exposure to PO can cause a wide range of health and environmental problems, some severe. It must be handled with extreme care. .

Propylene oxide hazard information

Hazard class**GHS code and hazard statement
Flammable liquids, category 1H224—Extremely flammable liquid and vaporChemical Safety Warning
Acute toxicity, oral, category 4H302—Harmful if swallowedChemical Safety Warning
Acute toxicity, dermal, category 3H311—Toxic in contact with skinChemical Safety Warning
Skin corrosion/irritation, category 2H315—Causes skin irritationChemical Safety Warning
Sensitization, skin, category 1H317—May cause an allergic skin reactionChemical Safety Warning
Serious eye damage/eye irritation, category 2AH319—Causes serious eye irritationChemical Safety Warning
Acute toxicity, inhalation, category 3H331—Toxic if inhaledChemical Safety Warning
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3H335—May cause respiratory irritationChemical Safety Warning
Specific target organ toxicity, single exposure, narcotic effects, category 3H336—May cause drowsiness or dizzinessChemical Safety Warning
Germ cell mutagenicity, category 1BH340—May cause genetic defectsChemical Safety Warning
Carcinogenicity, category 1BH350—May cause cancerChemical Safety Warning
Germ cell mutagenicity, category 1BH361—Suspected of damaging fertility or the unborn childChemical Safety Warning
Short-term (acute) aquatic hazard, category 3H402—Harmful to aquatic life

*Compilation of multiple safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.

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Propylene oxide fast facts

CAS Reg. No.75-56-9
SciFinder nomenclatureOxirane, 2-methyl-
Molar mass58.08 g/mol
AppearanceColorless liquid
Melting point34 °C
Water solubility425 g/L (20 °C)

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1. CAS Reg. No. 3081-61-6.
2. CAS Reg. No. 81-14-1.
3. CAS Reg. Nos. 81-15-2, 10403-00-6, 1222-05-5, and 141773-73-1, respectively.

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