Isobutylene (Isobutene)
The branched C₄ olefin with a terminal double bond. A colourless, flammable gas — feedstock for butyl rubber, MTBE, polyisobutylene, and the t-butyl chemical family.
Molecular Structure
What is Isobutylene (Isobutene)?
Isobutylene (2-methylpropene) is a branched four-carbon alkene with a terminal C=CH₂ group. The methyl substituents make the double bond highly reactive toward cationic and radical processes.
The gem-disubstituted terminal double bond of isobutylene is exceptionally reactive in cationic polymerisation — Lewis acid catalysts (BF₃/AlCl₃) at low temperature give polyisobutylene (PIB) chains ranging from viscous liquids to high-MW elastomers. Co-polymerisation with isoprene gives butyl rubber (IIR), the gas-impermeable elastomer used in inner tubes and pharmaceutical closures.
Chelora sources isobutylene from C₄ refinery and cracker streams, purified by extractive distillation. Available as pressurised gas, with full purity certification and transport documentation.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
Isobutylene (Isobutene)'s reactivity is defined by its C=CH₂ (terminal) — the site of polymerisation and other industrially important reactions.
Lewis structure — sp² at C1, C2
Structural Identity
- IUPAC Name2-Methylpropene
- Molecular FormulaC₄H₈
- Molecular Weight56.11 g/mol
- Hybridisationsp² at C1, C2
- Bond typeC=CH₂ (terminal)
- C=C bond length1.34 Å
- GeometryPlanar at C=C; tetrahedral C3
- CAS Number115-11-7
- InChI KeyVQTUBCCKSQIDNK-UHFFFAOYSA-N
Product Specifications
Chelora supplies Isobutylene (Isobutene) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Chemical name | Isobutylene (Isobutene) |
|---|---|
| CAS Number | 115-11-7 |
| Molecular formula | C₄H₈ |
| Molecular weight | 56.11 g/mol |
| Purity (standard grade) | ≥ 99.0 mol% |
| Purity (commercial grade) | ≥ 98.0 mol% |
| Physical state (ambient) | Gas (ambient) |
| Boiling point | −6.9 °C at 1 atm |
| Melting point | −140.4 °C |
| Flammable limits | 1.8 – 9.6% v/v v/v in air |
| 1-Butene + 2-Butenes (max) | ≤ 1000 ppm vol |
| n-Butane / i-Butane (max) | ≤ 500 ppm vol |
| 1,3-Butadiene (max) | ≤ 20 ppm vol |
| Moisture (max) | ≤ 10 ppm wt |
| Critical temperature | 144.7 °C |
| Critical pressure | 40.0 bar |
| UN Number | UN 1055 |
| IMO / IMDG Class | Class 2.1 (Flammable Gas) |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Isobutylene (Isobutene).
Butyl Rubber (IIR)
Cationic co-polymerisation with isoprene gives isobutylene-isoprene rubber (IIR) — prized for its outstanding air impermeability in tyre inner tubes, curing bladders, and pharmaceutical closures.
MTBE & ETBE
Acid-catalysed addition of methanol to isobutylene gives methyl tert-butyl ether (MTBE) — used as a gasoline octane enhancer and oxygenate. ETBE uses ethanol instead.
Polyisobutylene (PIB)
Cationic polymerisation gives PIB ranging from low-MW viscous fluids (lubricant additives, adhesives) to high-MW (>1M) elastomeric grades for sealants and chewing gum base.
t-Butyl Compounds
Reaction with isobutane (alkylation) or with alcohols/acids gives t-butyl derivatives: TBA (tert-butanol), t-butyl acrylate, di-t-butyl peroxide, and other specialty chemicals.
Antioxidants & Additives
t-Butylation of phenols gives hindered phenol antioxidants (BHT, Irganox series) — critical stabilisers in polymer processing, food packaging, and lubricant formulation.
Specialty & Custom Synthesis
Supplied for Friedel–Crafts alkylation, pharmaceutical synthesis, and custom chemical manufacturing requiring a reactive, branched C₄ alkene building block.
Why source Isobutylene (Isobutene) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
Standard and custom grades available. Impurity specifications can be tailored to your process and catalyst system.
Full Documentation
CoA, SDS, UN transport docs, REACH compliance, and destination-market certificates with every shipment.
Logistics Support
Experienced in specialised chemical logistics for compressed gases and volatile liquids — Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store in a well-ventilated, dedicated area away from ignition sources, heat, and sunlight.
- All electrical equipment in storage and handling areas must be ATEX/IECEx rated for the applicable zone.
- Ensure full bonding and earthing of all transfer equipment during any transfer operation.
- Never store with strong oxidisers, halogens, or materials that generate static.
- Install continuous gas detection with audible and visual alarms set below the LEL.
- Use only approved pressure-rated piping, valves, and fittings with compatible materials.
- Conduct pre-use and post-use leak checks with suitable gas detection equipment.
- Maintain inhibitor levels where applicable; check on receipt and periodically during storage.
Hazard Summary
Classification: Flammable Gas/Liquid · Flammable limits 1.8 – 9.6% v/v v/v · UN 1055.
Flammability: Highly flammable — never rely on odour to detect leaks. Use continuous gas monitoring below LEL.
Health: Asphyxiant in enclosed spaces. Oxygen monitoring mandatory in confined areas. Follow occupational exposure limits (OELs) per SDS.
PPE minimum: Chemical goggles, appropriate gloves, flame-retardant clothing, and supplied-air respirator where oxygen deficiency is possible.
Consult the full SDS for exposure limits, spill containment, emergency response, and disposal before any use.
Frequently Asked Questions
Technical and commercial questions about Isobutylene (Isobutene) sourcing and specifications.
What is isobutylene used for?
Isobutylene is the feedstock for butyl rubber (IIR) and its halogenated forms (BIIR, CIIR), polyisobutylene (PIB), MTBE/ETBE fuel oxygenates, hindered phenol antioxidants, and a range of tert-butyl specialty chemicals.
What makes butyl rubber valuable?
Butyl rubber (IIR) has the lowest gas permeability of any commercial elastomer — approximately 10× lower than natural rubber for air — making it the standard material for tyre inner tubes, curing bladders, and pharmaceutical vial stoppers where airtight performance is critical.
How is isobutylene separated from C₄ streams?
Isobutylene is separated from mixed C₄ fractions by selective reaction (e.g. with methanol to give MTBE, which is then cracked back), extractive distillation, or catalytic skeletal isomerisation routes. High-purity isobutylene typically involves reaction–recovery sequences rather than straight distillation, due to the close boiling points of the C₄ isomers.
What purity is required for butyl rubber synthesis?
Butyl rubber synthesis requires very low levels of impurities — particularly 1,3-butadiene (chain terminator), water, and other dienes — typically specified at the low-ppm level. Chelora can supply to agreed impurity specifications with batch CoA confirmation.
What is the CAS number for isobutylene?
Isobutylene has CAS number 115-11-7, IUPAC name 2-methylpropene, molecular formula C₄H₈, and molecular weight 56.11 g/mol. The terminal C=CH₂ double bond with two methyl groups gives it distinctive cationic reactivity.
What documentation does Chelora provide?
Every shipment is accompanied by a Certificate of Analysis, Safety Data Sheet (GHS/REACH), UN transport documentation (UN 1055, Class 2.1), and any destination-market regulatory certificates.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Isobutylene (Isobutene) grade, volume, logistics, documentation, and lead times. We respond within one business day.
