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 1 H224—Extremely flammable liquid and vapor Chemical Safety Warning
Acute toxicity, oral, category 4 H302—Harmful if swallowed Chemical Safety Warning
Acute toxicity, dermal, category 3 H311—Toxic in contact with skin Chemical Safety Warning
Skin corrosion/irritation, category 2 H315—Causes skin irritation Chemical Safety Warning
Sensitization, skin, category 1 H317—May cause an allergic skin reaction Chemical Safety Warning
Serious eye damage/eye irritation, category 2A H319—Causes serious eye irritation Chemical Safety Warning
Acute toxicity, inhalation, category 3 H331—Toxic if inhaled Chemical Safety Warning
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3 H335—May cause respiratory irritation Chemical Safety Warning
Specific target organ toxicity, single exposure, narcotic effects, category 3 H336—May cause drowsiness or dizziness Chemical Safety Warning
Germ cell mutagenicity, category 1B H340—May cause genetic defects Chemical Safety Warning
Carcinogenicity, category 1B H350—May cause cancer Chemical Safety Warning
Germ cell mutagenicity, category 1B H361—Suspected of damaging fertility or the unborn child Chemical Safety Warning
Short-term (acute) aquatic hazard, category 3 H402—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 nomenclature Oxirane, 2-methyl-
Molar mass 58.08 g/mol
Appearance Colorless liquid
Melting point 34 °C
Water solubility 425 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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