Isobutylene (2-methylpropene) CAS 115-11-7

Isobutylene (2-methylpropene, CAS 115-11-7) is a colorless gas with a slight petroleum odor, a key raw material for the production of polyisobutylene and various copolymers. Boiling point -6.9 °C. Highly flammable, forms explosive mixtures with air. Insoluble in water. Storage under pressure.

1. Introduction
Isobutylene, often referred to as 2-methylpropene, is an important representative of olefins. It is one of the key monomers in the petrochemical industry. Due to the double bond and branched structure, isobutylene is actively used to produce a number of polymers and fuel components.

2. Nomenclature and synonyms
In Russian: isobutylene, 2-methylpropene
International name (English): isobutylene, isobutene, 2-methylpropene
German versions: Isobutylen, 2-Methylpropen
CAS number, under which the substance is registered in all international databases, is 115-11-7.

3. Molecular formula and main parameters
Molecular formula: C₄H₈
Chemical structure: CH₂=C(CH₃)₂
Molecular weight: ~56.1 g/mol
The presence of a methyl group on the central atom makes the molecule more branched compared to linear alkenes, which determines some of its physical and chemical characteristics.

4. Physicochemical properties
Appearance: colorless gas (under normal conditions). In a liquefied state, it is a transparent liquid.
Odor: light oil-like or "hydrocarbon", sometimes slightly noticeable.
Density:
The gaseous phase is approximately twice as heavy as air.
Under normal conditions (0 °C, 1 atm), the gas density is ~2.0 kg/m³.
Boiling point: -6.9 °C - the main indicator important for distillation and storage of isobutylene in liquid form.
Melting point (freezing point): about -140 °C.
Flash point: due to its low boiling point and high volatility, isobutylene is highly flammable. At atmospheric pressure, the liquid/vapor phase has a high fire hazard.

Solubility:
In water: practically insoluble, but can form unstable emulsions with turbulent mixing.
In organic solvents (benzene, ethers, alcohols): more soluble, like many non-polar and weakly polar hydrocarbons.
Decomposition: in air at high temperatures, it can oxidize to form peroxides and other products. Under extreme heating, it decomposes to release carbon and carbon monoxide.
Storage conditions:
Store in steel cylinders or tanks under pressure at a temperature not exceeding +45…+50 °C.
Avoid sources of heat, sparks, open flames and electrostatic discharges.
Stability: under normal conditions, it is physically and chemically stable, but in the presence of light and trace amounts of oxygen, peroxide compounds may form, which is why polymerization inhibitors are often used.

5. Potential impact on humans and the environment
Toxicity and hazards: at high concentrations in the air, isobutylene causes suffocation, can lead to dizziness and loss of consciousness. It is highly flammable and forms explosive mixtures.
Environmental impact: hydrocarbon emissions into the atmosphere contribute to the formation of ground-level ozone when interacting with NOₓ and sunlight. In the aquatic environment, it is volatile and evaporates quickly; long-term bioaccumulation is not observed.

6. Main areas of application
Production of polyisobutylene: polymerized by catalytic means, the resulting materials are used as oil-soluble thickeners, sealants and adhesives.
Rubber feedstock: so-called butyl rubber (and copolymers) are used to make tires and rubber products.
MTBE (methyl tert-butyl ether): the most important additive to gasoline, increasing the octane number. Isobutylene is a key component in the synthesis of MTBE.
Other alkylated products: interacts with isobutane, benzene and other substrates, forming components of high-octane fuels.
Chemical intermediates: tert-Butanol can be obtained by hydration of isobutylene, which is used as a solvent and raw material for pharmaceuticals.

7. Conclusion
Isobutylene (2-methylpropene, CAS 115-11-7) is one of the key hydrocarbon gases in the petrochemical industry. Its branched structure and reactivity open up a wide range of applications from the production of high-quality polymers to advanced fuel components. When handling this substance, increased safety precautions are required due to its explosiveness and volatility.