2-Methylpropene: Properties, Uses & Lab FAQ

2-Methylpropene is a branched-chain gaseous alkene (isobutylene, CAS 115-11-7) widely used in organic synthesis, polymer chemistry, and as a key industrial and research-grade building block.

Chemical Name

2-Methylpropene (Isobutylene)

CAS Number

115-11-7

Molecular Formula

C₄H₈

Molecular Weight

56.11 g/mol

Physical State (at RT)

Colorless gas (bp −6.9 °C at 1 atm)

Aladdin SKU

M1547887

Key Hazard

Extremely flammable gas; asphyxiant at high concentrations

What Is 2-Methylpropene and What Are Its Key Chemical Properties?

2-Methylpropene, commonly known as isobutylene or isobutene (CAS 115-11-7), is a four-carbon branched alkene with the molecular formula C₄H₈ and a molecular weight of 56.11 g/mol. At room temperature and atmospheric pressure it is a colorless, flammable gas with a faint petrochemical odor. Its boiling point is approximately −6.9 °C, meaning it is typically handled and shipped as a liquefied gas under pressure.

The compound features a terminal, trisubstituted double bond, making it one of the more reactive simple alkenes toward electrophilic addition, cationic polymerization, and Friedel–Crafts-type reactions. It readily undergoes acid-catalyzed hydration, halogenation, hydrohalogenation (following Markovnikov's rule), and free-radical or cationic polymerization to form polyisobutylene (PIB). Its high degree of substitution at the double bond also makes it useful as a protecting-group precursor in organic synthesis (e.g., tert-butyl ester formation).

What Are the Common Research and Industrial Applications of 2-Methylpropene?

In academic and industrial research, 2-methylpropene serves multiple roles:

• Polymer synthesis: Cationic polymerization of isobutylene yields polyisobutylene (PIB), a commercially important elastomer and viscosity modifier. Butyl rubber is produced by copolymerization with small amounts of isoprene.
• Organic synthesis building block: The compound is used to introduce tert-butyl groups via alkylation reactions. In protecting-group chemistry, reaction with carboxylic acids under acid catalysis gives tert-butyl esters, which are cleaved under mild acid conditions.
• Fuel and petrochemical industry: Isobutylene is an intermediate in the production of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and isooctane (via dimerization and hydrogenation), all used as fuel oxygenates and octane boosters.
• Antioxidant production: It is a precursor to hindered phenol antioxidants such as BHT (butylated hydroxytoluene), widely used in food, rubber, and plastics.
• Metathesis and cross-coupling studies: As a gaseous alkene, isobutylene serves as a substrate and model compound in catalytic reaction development.

How Should 2-Methylpropene Be Safely Handled and Stored in the Laboratory?

Because 2-methylpropene is a liquefied flammable gas at ambient temperature, specific safety precautions are mandatory:

• Storage: Store cylinders in a cool, well-ventilated area away from heat sources, open flames, and oxidizers. Cylinders must be secured upright and kept below 50 °C. Segregate from oxidizing agents and strong acids.
• Personal protective equipment (PPE): Use cryogenic-rated gloves when handling cold liquefied gas. Safety goggles or a face shield, and a lab coat are required. Work in a well-ventilated fume hood or use an appropriate gas-handling manifold.
• Flammability: The flammable range of isobutylene in air is approximately 1.8–9.6% v/v. Eliminate all ignition sources (sparks, open flames, hot surfaces) in the work area. Use explosion-proof electrical equipment.
• Asphyxiation risk: As a heavier-than-air gas, isobutylene can accumulate in low-lying areas. Ensure adequate ventilation and deploy gas detectors where appropriate.
• Emergency response: In case of a leak, evacuate the area, ventilate, and contact emergency services. Do not attempt to stop a gas leak unless trained and equipped to do so safely.

Always consult the current Safety Data Sheet (SDS) for 2-Methylpropene (M1547887) before use.

How Is 2-Methylpropene Typically Used in Synthetic Protocols?

Handling a gaseous reagent like 2-methylpropene requires adapted laboratory techniques compared to liquid reagents:

• tert-Butyl ester protection: A common protocol involves condensing isobutylene (from a lecture bottle) into a reaction vessel cooled in a dry-ice/acetone bath (−78 °C), followed by addition of the carboxylic acid substrate and an acid catalyst (e.g., H₂SO₄ or BF₃·Et₂O). The vessel is sealed and allowed to warm to room temperature. This provides tert-butyl esters in good yield and with high chemoselectivity.
• Cationic polymerization: Isobutylene is condensed into a polymerization reactor at low temperature (typically −70 to −40 °C) in an inert atmosphere (N₂ or Ar). A Lewis acid initiator (e.g., BF₃·Et₂O, TiCl₄) is added to initiate living cationic polymerization, allowing control over molecular weight and dispersity.
• Gas-phase reactions: For catalytic studies, isobutylene can be metered as a gas using mass-flow controllers into a continuous-flow reactor or a pressure vessel.
• Alkylation reactions: Under Friedel–Crafts conditions with a Lewis acid catalyst, isobutylene can alkylate aromatic rings to give tert-butyl-substituted arenes.

Always purge apparatus with inert gas before introducing isobutylene to prevent formation of flammable mixtures.

Ordering and Product Information for 2-Methylpropene at Aladdin Scientific

Aladdin Scientific supplies 2-Methylpropene under SKU M1547887. When placing an order, researchers and procurement staff should note the following:

• Regulated shipping: As a liquefied flammable gas, 2-methylpropene is classified as a hazardous material (Dangerous Goods). Shipment is subject to IATA, DOT, or ADR regulations depending on the transport mode and destination. Please contact Aladdin Scientific's customer service team to confirm available shipping options for your region.
• Packaging: Typically supplied in lecture bottles or small cylinders. Specify the required quantity and cylinder size at the time of ordering.
• Documentation: An SDS is available upon request and can be downloaded from the product page. Ensure your institution's safety office approves receipt of compressed flammable gases prior to ordering.
• Lead time: Availability and lead times may vary; contact customer service or check the product page for current stock status.
• Returns: Compressed gas cylinders are generally non-returnable once shipped. Review Aladdin Scientific's return and refund policy before purchase.

Frequently asked questions

What is the difference between 2-methylpropene and isobutylene?

There is no difference; they are the same compound. 2-Methylpropene is the IUPAC systematic name, while isobutylene (or isobutene) is the common or trivial name. Both refer to the branched C₄ alkene with CAS number 115-11-7.

Is 2-methylpropene a liquid or a gas at room temperature?

2-Methylpropene is a gas at room temperature and standard atmospheric pressure, with a boiling point of approximately −6.9 °C. It is commercially supplied as a liquefied gas under pressure in cylinders or lecture bottles, where it exists as a liquid in equilibrium with its vapor.

Can 2-methylpropene be used for tert-butyl ester synthesis?

Yes. 2-Methylpropene is a classic reagent for installing tert-butyl ester protecting groups. Under acid catalysis (e.g., concentrated H₂SO₄ or BF₃·Et₂O), it reacts with carboxylic acids to give tert-butyl esters. These esters are selectively cleaved under mild acidic conditions (e.g., TFA in DCM), making them valuable orthogonal protecting groups in multi-step synthesis.

What special equipment is needed to handle 2-methylpropene in the lab?

Handling 2-methylpropene requires a compressed gas regulator compatible with the cylinder valve, gas-tight Schlenk or sealed glassware, and a dry-ice/acetone cooling bath for condensation procedures. A flame-arrestor-equipped fume hood, gas detector, and explosion-proof electrical fittings are strongly recommended. Cryogenic gloves and safety goggles are required PPE.

What are the flammability limits of 2-methylpropene and why do they matter?

The lower and upper flammable limits (LFL/UFL) of 2-methylpropene in air are approximately 1.8% and 9.6% by volume, respectively. Any gas concentration within this range can ignite in the presence of a spark or flame. This wide flammable range means strict elimination of ignition sources and use of continuous gas monitoring are essential whenever the compound is used.

References

1. NIST WebBook: Isobutylene (2-Methylpropene), CAS 115-11-7. National Institute of Standards and Technology.
2. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.; Wiley: Hoboken, NJ, 2007.
3. Kennedy, J. P.; Iván, B. Designed Polymers by Carbocationic Macromolecular Engineering; Hanser: Munich, 1992.
4. Occupational Safety and Health Administration (OSHA). Chemical Sampling: Isobutylene. US Department of Labor.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.