Isobutylene (Isobutene) – C4H8, 115-11-7

Isobutylene (C₄H₈) is a colorless gas used in the production of fuels and chemicals. It is highly flammable and has a sweet odor.

IUPAC Name2-methylpropene
Molecular FormulaC₄H₈
CAS Number115-11-7
SynonymsIsobutene, 2-methylpropene, methylpropene
InChIInChI=1S/C4H8/c1-4(2)3/h1H2,2-3H3

Isobutylene Properties

Isobutylene Formula

The formula of isobutene is C₄H₈. It consists of four carbon atoms and eight hydrogen atoms. This molecular formula represents the composition of isobutene, showing the number of each type of atom present in a molecule.

Isobutylene Molar Mass

The molar mass of isobutene is calculated by summing the atomic masses of its constituent atoms. It is approximately 56.11 grams per mole (g/mol). Molar mass is a crucial parameter in chemical calculations and is used to determine the amount of substance present in a given quantity.

Isobutylene Boiling Point

Isobutylene has a boiling point of approximately -6.9 degrees Celsius. Boiling point refers to the temperature at which a substance changes from a liquid to a gas phase under standard atmospheric pressure. Isobutylene vaporizes at this temperature, becoming a gas.

Isobutylene Melting Point

The melting point of isobutene is around -140.3 degrees Celsius. Melting point is the temperature at which a solid substance transitions into a liquid state. Isobutylene undergoes this change when heated to the specified temperature.

Isobutylene Density g/mL

The density of isobutene is about 0.588 grams per milliliter (g/mL). Density represents the mass per unit volume of a substance. It determines how closely packed the molecules are within a given volume of the material.

Isobutylene Molecular Weight

The molecular weight of isobutene is approximately 56.11 grams per mole (g/mol). Molecular weight is the sum of the atomic weights of all the atoms in a molecule. It is essential for various calculations, including stoichiometry and determining the proportion of different elements in a compound.

Isobutylene

Isobutylene Structure

Isobutene has a structure consisting of a branched chain of four carbon atoms. Each carbon atom is bonded to other atoms, including hydrogen atoms. The structure is represented as CH₃C(CH₃)CH₂. This arrangement of atoms determines the chemical and physical properties of isobutene.

Isobutylene Solubility

Isobutene is sparingly soluble in water. It exhibits a low solubility due to its nonpolar nature. Nonpolar compounds like isobutene do not readily dissolve in polar solvents like water. However, isobutene can dissolve in organic solvents such as alcohols, ethers, and hydrocarbons.

AppearanceColorless gas
Specific Gravity0.588
ColorN/A
OdorSweet
Molar Mass56.11 g/mol
Density0.588 g/mL
Melting Point-140.3 °C
Boiling Point-6.9 °C
Flash Point-49 °C
Water SolubilitySparingly soluble
SolubilitySoluble in organic solvents
Vapour Pressure215 kPa (at 25 °C)
Vapour Density2.48 (air = 1)
pKaN/A
pHNeutral

Isobutylene Safety and Hazards

Isobutene poses several safety hazards. It is highly flammable, which means it can ignite easily when exposed to an ignition source. Therefore, proper precautions should be taken to prevent fire and explosions. Isobutene vapors are heavier than air and can accumulate in low-lying areas, increasing the risk of fire hazards. Direct contact with isobutene may cause skin and eye irritation. Inhalation of high concentrations can lead to respiratory issues, dizziness, and even asphyxiation. Adequate ventilation and personal protective equipment should be used when handling isobutene to minimize exposure risks. It is essential to follow proper safety protocols and handle this substance with caution.

Hazard SymbolsFlammable Gas
Safety DescriptionKeep away from ignition sources.
Use in a well-ventilated area.
Wear protective clothing and eyewear.
Un IDsUN 1075
HS Code2901.11.00
Hazard Class2.1 (Flammable Gas)
Packing GroupPG II
ToxicityAcute toxicity by inhalation, harmful if swallowed or in contact, with skin/eyes.

Isobutylene Synthesis Methods

There are various methods for synthesizing isobutene.

One common method involves catalytically dehydrogenating isobutane, where isobutane passes over a catalyst, typically a metal oxide or supported metal catalyst, at elevated temperatures. The catalyst facilitates the removal of hydrogen from isobutane, resulting in the formation of isobutene.

Another method entails thermally cracking petroleum fractions rich in branched hydrocarbons, such as butenes, by applying high temperatures. The cracking reaction breaks down larger hydrocarbon molecules into smaller ones, yielding isobutene.

During the steam cracking of hydrocarbons, the process yields isobutene as a byproduct. Steam cracking involves subjecting hydrocarbons, such as ethane or naphtha, to high temperatures in the presence of steam, resulting in the production of a mixture of olefins, including isobutene.

Furthermore, the synthesis of isobutene involves conducting a metathesis reaction between ethylene and 2-butene. Metathesis reactions involve interchanging functional groups or substituents between reactant molecules. By subjecting ethylene and 2-butene to metathesis conditions, one can produce isobutene.

These synthesis methods offer different approaches to obtaining isobutene, catering to various industrial requirements and the availability of feedstocks. Each method presents its own advantages and considerations in terms of reaction conditions, catalyst selection, and yield optimization.

Isobutylene Uses

Isobutene plays a crucial role in a wide range of applications due to its unique properties. Some common uses of isobutene include:

  • Isobutene serves as a key raw material in the production of butyl rubber, which manufacturers use to create tire inner tubes, automotive hoses, seals, and gaskets, thanks to its excellent resistance to heat, chemicals, and impermeability to gases.
  • Industries utilize isobutene as a fuel additive to enhance the octane rating of gasoline, improving combustion efficiency and reducing knocking for better fuel performance.
  • Isobutene undergoes polymerization to produce polyisobutene (PIB), a versatile polymer extensively used in various industrial applications such as lubricants, adhesives, sealants, and as a thickening agent.
  • Manufacturers employ isobutene as a precursor in the production of isobutyl alcohol, a solvent widely used in coatings, resins, and personal care products.
  • Isobutene acts as a building block for the synthesis of various chemicals, including antioxidants, plasticizers, flavors, fragrances, and pharmaceuticals, showcasing its role as a valuable chemical intermediate.
  • Industries add isobutene to liquefied petroleum gas (LPG) as a blending component to enhance its quality and stability, ensuring safe and efficient usage.
  • It finds application as a component in refrigerant blends used in refrigeration and air conditioning systems.
  • Industries rely on isobutene-based adhesives for their strong bonding properties, utilizing them in construction, automotive, and packaging sectors.
  • Isobutene serves as an extraction agent in the production of various chemicals, including pharmaceuticals and flavors.
  • It acts as a propellant in aerosol products such as sprays, foams, and deodorants.

These applications demonstrate the significance of isobutene in various industries and its contributions to numerous everyday products.

Questions:

Q: How much does a gallon of isobutylene weigh?

A: A gallon of Isobutene weighs approximately 4.88 pounds (lb).

Q: What is isobutylene?

A: Isobutene is a colorless gas used in the production of fuels, chemicals, and synthetic rubber.

Q: Does isobutylene have cis or trans isomers?

A: Isobutene does not have cis or trans isomers as it is a branched hydrocarbon.

Q: Does isobutylene have a vinyl group?

A: Yes, isobutylene contains a vinyl group, specifically a double bond between two carbon atoms.

Q: Is isobutylene in RP1?

A: No, Isobutene is not a component of RP-1 (Rocket Propellant-1), which is a highly refined form of kerosene.

Q: Why does isobutylene (-7°C) have a lower boiling point than acetone (56°C)?

A: Isobutene has a lower boiling point than acetone due to its lower molecular weight and weaker intermolecular forces.

Q: Which of the following compounds is appropriate to promote the cationic polymerization of isobutylene?

A: Lewis acids such as boron trifluoride (BF3) or aluminum chloride (AlCl3) can be used to promote the cationic polymerization of isobutylene.

Q: How is isobutylene stored?

A: Isobutene is typically stored in pressurized containers or cylinders to maintain it in its gaseous state.

Q: Which organic bromide(s) would undergo E2 dehydrohalogenation to give isobutylene as a pure alkene?

A: 2-bromobutane (sec-butyl bromide) or tert-butyl bromide can undergo E2 dehydrohalogenation to yield isobutylene as a pure alkene.