Propylene Oxide
Ethylene oxide's methylated cousin, and easier to handle for it — a low-boiling liquid rather than a gas. The starting point for polyurethane polyols and propylene glycol.
Molecular Structure
What is Propylene Oxide?
Propylene oxide is a three-membered epoxide ring carrying a methyl group — ethylene oxide with one hydrogen replaced. That small change makes it a volatile liquid boiling at 34 °C rather than a gas, which is why it is handled and shipped quite differently.
The ring strain is essentially the same, so the reactivity is too. Nucleophiles open the ring to release that strain, adding a three-carbon hydroxypropyl unit. Hydrolysis gives propylene glycol, alcohols and glycols give the polyether polyols, and the methyl group's steric and electronic influence directs where the ring opens.
The methyl group also makes propylene oxide chiral — the substituted carbon is a stereocentre. Commercial material is the racemate, and that is fine for polyol chemistry, but stereochemistry becomes relevant in pharmaceutical and specialty synthesis where a single enantiomer is required.
Chelora supplies propylene oxide at ≥99.9 wt% under nitrogen pad, with water, acidity, aldehydes and chloride certified because each affects polymerisation stability. Supply is arranged only to facilities equipped for PG I flammable liquid receipt and storage.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
A strained three-membered ring with a methyl group on one carbon. The strain drives the ring-opening chemistry; the methyl group makes the two ring carbons different from each other, which controls where nucleophiles attack and creates a stereocentre.
Structure — oxirane ring with methyl substituent at C-2
Structural Identity
- IUPAC Name2-Methyloxirane
- Common namesPropylene oxide, PO, methyloxirane
- Molecular FormulaC₃H₆O
- Molecular Weight58.08 g/mol
- RingThree-membered epoxide
- Ring bond angles≈ 60°, against ≈109° preferred
- StereochemistryChiral — commercial grade is racemic
- Key reactionNucleophilic ring opening
- Versus ethylene oxideLiquid at ambient, not a gas
- CAS Number75-56-9
- InChI KeyGOOHAUXETOMSMM-UHFFFAOYSA-N
Product Specifications
Chelora supplies Propylene Oxide in standard and custom grades. Contact us for specification sheets tailored to your process.
| Chemical name | Propylene oxide |
|---|---|
| CAS Number | 75-56-9 |
| Molecular formula | C₃H₆O |
| Molecular weight | 58.08 g/mol |
| Purity (min) | ≥ 99.90 wt% |
| Water (max) | ≤ 0.05 wt% |
| Acidity as acetic acid (max) | ≤ 10 ppm wt |
| Aldehydes as acetaldehyde (max) | ≤ 50 ppm wt |
| Total chlorides (max) | ≤ 10 ppm wt |
| Non-volatile residue (max) | ≤ 20 ppm wt |
| Iron (max) | ≤ 0.1 ppm wt |
| Colour | ≤ 10 Pt-Co (Hazen) |
| Distillation range | 33.5 – 35.5 °C |
| Density at 20 °C | 0.829 – 0.832 g/cm³ |
| Vapour pressure | ≈ 0.59 bar at 20 °C |
| Flash point | −37 °C (closed cup) |
| Autoignition temperature | 449 °C |
| Flammable limits | 2.3 – 36% v/v in air |
| Storage | Under nitrogen pad, cool, dedicated |
| UN Number | UN 1280 (Propylene oxide) |
| IMDG / ADR Class | Class 3 (Flammable Liquid), PG I |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Propylene Oxide.
Polyether Polyols
Ring opening onto glycerine, sucrose or glycol initiators builds polyether polyols — the largest PO outlet by far, and the backbone of flexible and rigid polyurethane foam.
Propylene Glycol
Hydrolysis gives mono propylene glycol, with di- and tripropylene glycol as co-products, feeding unsaturated polyester resins and the food, pharmaceutical and cosmetic markets.
Glycol Ethers
Reaction with alcohols gives the P-series glycol ethers — propylene glycol methyl ether and its acetate — the low-toxicity coalescing solvents that displaced E-series ethers in coatings.
Polypropylene Glycol
Controlled oligomerisation gives PPG for lubricant base stocks, hydraulic fluids, quenchants, antifoams and surfactant intermediates.
Surfactants & Amines
Propoxylation gives block copolymer surfactants and demulsifiers, and reaction with ammonia gives isopropanolamines for detergents and gas treating.
Specialty Intermediates
Routes to allyl alcohol, propylene carbonate, flame retardant intermediates and hydroxypropyl derivatives of cellulose and starch.
Why source Propylene Oxide through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
High-purity grade supplied under nitrogen pad. Water, acidity, aldehyde and chloride limits certified because each affects polymerisation stability and polyol quality.
Full Documentation
CoA, SDS, UN transport docs, REACH compliance, and destination-market certificates with every shipment.
Logistics Support
Handled only into facilities equipped for PG I flammable liquid receipt — dedicated nitrogen-padded storage, vapour control, and full UN 1280 documentation with pre-shipment facility verification.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Keep the liquid under a nitrogen pad at all times and store cool — propylene oxide boils at 34.2 °C, so a warm day alone will build significant vapour pressure.
- Exclude polymerisation catalysts absolutely: acids, alkalis, amines, metal chlorides, metal oxides and rust all initiate violent exothermic polymerisation. Vessels must be clean, dry and passivated before filling.
- Treat the flash point of −37 °C as the governing fire control — an ignitable vapour is present at any ambient temperature, in any season, anywhere.
- Bond and earth every tank, tanker and hose before transfer, and use ATEX/IECEx-rated equipment throughout the storage and transfer area.
- Monitor storage temperature continuously with alarms; an unexplained rise indicates polymerisation has started and requires immediate emergency response.
- Keep water out of the system except where hydrolysis is intended — the reaction is exothermic and generates glycol that can concentrate catalytic impurities.
- Run fixed vapour detection with alarms below the LEL, plus personal exposure monitoring against the occupational limit, which is 2 ppm under the ACGIH TLV.
- Maintain a written PO-specific emergency plan covering leak response, cooling, vapour suppression and evacuation, and exercise it.
Hazard Summary
Classification: Flam. Liq. 1 (H224) · Carc. 1B (H350) · Muta. 1B (H340) · Acute Tox. 4 oral and inhalation (H302, H332) · STOT SE 3 (H335) · Skin Irrit. 2 (H315) · Eye Irrit. 2 (H319).
Carcinogen and mutagen: Propylene oxide is classified Carc. 1B and Muta. 1B under CLP, and sits in IARC Group 2B as possibly carcinogenic to humans. In most jurisdictions the CMR classification triggers specific duties — closed systems, exposure records and health surveillance.
Extreme flammability: Packing Group I with a flash point of −37 °C and a flammable range up to 36%. There is no ambient condition under which the vapour is not ignitable. Unlike ethylene oxide it does not decompose explosively in the absence of air, so nitrogen inerting is effective — but the flammability itself is more severe than EO's on a liquid-handling basis.
Runaway polymerisation: Acids, bases, amines, metal chlorides, metal oxides and rust all catalyse violent exothermic polymerisation. Contamination of a storage vessel is a credible route to catastrophic failure, so dedicated, clean, passivated storage is not negotiable.
Exposure limits: ACGIH TLV 2 ppm 8-hour TWA. The OSHA PEL of 100 ppm dates from an era before the carcinogenicity data and is far higher than current practice; work to the lower value and to whatever your jurisdiction requires.
PPE minimum: Chemical splash goggles, butyl gloves, flame-retardant antistatic clothing, and supplied-air respiratory protection for any task where the exposure limit could be exceeded. Ordinary organic-vapour cartridges are not adequate.
Consult the full SDS for exposure limits, spill containment, emergency response, and disposal before any use.
Frequently Asked Questions
Technical and commercial questions about Propylene Oxide sourcing and specifications.
What is propylene oxide used for?
Polyether polyols take the great majority — PO is ring-opened onto glycerine, sucrose or glycol initiators to build the polyols that react with isocyanates to make flexible and rigid polyurethane foam. The second largest outlet is hydrolysis to propylene glycol. Beyond that: P-series glycol ethers for coatings, polypropylene glycols for lubricants and antifoams, block copolymer surfactants, and isopropanolamines.
How does propylene oxide differ from ethylene oxide?
Chemically they are close relatives with the same strained epoxide ring and similar ring-opening reactivity. The practical differences are large. PO's methyl group makes it a liquid at ambient temperature, boiling at 34 °C, where EO is a gas — so PO ships as a Class 3 flammable liquid rather than a Class 2.3 toxic gas. PO also does not undergo the explosive decomposition without oxygen that gives EO its 100% upper flammable limit, so nitrogen inerting is an effective control for PO in a way it is not for EO.
How is propylene oxide produced?
Several routes coexist. The legacy chlorohydrin process uses chlorine and produces large volumes of salt-laden effluent. Co-product routes are widely used — PO/SM makes styrene alongside PO, and PO/TBA makes tert-butyl alcohol. Newer plants favour HPPO, direct oxidation with hydrogen peroxide, which produces only water as a by-product and avoids being tied to a co-product market. Sumitomo's cumene-based process recycles its co-product internally.
Why is propylene oxide chiral, and does it matter?
The ring carbon bearing the methyl group has four different substituents, making it a stereocentre, so PO exists as (R) and (S) enantiomers. Commercial material is racemic. For polyol and glycol chemistry this is irrelevant — the resulting polymers are not stereoregular and nobody needs them to be. It matters only in pharmaceutical and fine chemical synthesis where a single enantiomer is required, in which case enantiopure PO is a specialty product rather than a commodity.
What makes propylene oxide storage hazardous?
Two things at once. First, extreme flammability — a flash point of −37 °C means the vapour above the liquid is always ignitable, and Packing Group I reflects that. Second, polymerisation: acids, bases, amines, metal chlorides and even rust catalyse exothermic ring-opening that accelerates itself as it heats. Vessels must be dedicated, clean, dry, passivated and nitrogen-padded, with continuous temperature monitoring, because an unexplained temperature rise is the early warning of runaway.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering purity, water, acidity, aldehydes, total chlorides, non-volatile residue, iron, colour, distillation range and density; a Safety Data Sheet (GHS/REACH); UN 1280 Class 3 PG I transport documentation; receiving-facility verification; an origin certificate; and any destination-market licences required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Propylene Oxide grade, volume, logistics, documentation, and lead times. We respond within one business day.
