Isobutylene Property

Melting point:

−140 °C

Boiling point:

−6.9 °C(lit.)

Density 

0.5879

vapor density 

2 (vs air)

vapor pressure 

3278 mm Hg ( 37.7 °C)

refractive index 

1.3811

Flash point:

-80 °C

form 

clear liquid

color 

Colorless to Almost colorless

Odor Threshold

10ppm

Water Solubility 

263mg/L(25 ºC)

FreezingPoint 

-140.34℃

Merck 

14,5141

BRN 

773645

Henry's Law Constant

0.20, 0.26, 0.33, and 0.41 at 30, 40, 50, and 60 °C, respectively (Leung et al., 1987:Zhang et al., 2002)

Stability:

Stable. Highly flammable - readily forms an explosive mixture with air. Incompatible with strong oxidizing agents.

InChIKey

VQTUBCCKSQIDNK-UHFFFAOYSA-N

LogP

2.35 at 20℃

CAS DataBase Reference

115-11-7(CAS DataBase Reference)

EPA Substance Registry System

Isobutene (115-11-7)

Safety

Hazard Codes 

F+

Risk Statements 

12

Safety Statements 

9-16-33

RIDADR 

UN 1055 2.1

WGK Germany 

-

RTECS 

UD0890000

F 

4.5-31

Autoignition Temperature

869 °F

DOT Classification

2.1 (Flammable gas)

HazardClass 

2.1

PackingGroup 

III

HS Code 

29012330

Hazardous Substances Data

115-11-7(Hazardous Substances Data)

Toxicity

LC₅₀ (inhalation) for mice 415 g/m³/2-h, rats 620 g/m³/4-h (quoted, RTECS, 1985).

Hazard and Precautionary Statements (GHS)

Symbol(GHS)

Signal word

Danger

Hazard statements

H220Extremely flammable gas

H280Contains gas under pressure; may explode if heated

Precautionary statements

P210Keep away from heat/sparks/open flames/hot surfaces. — No smoking.

P410+P403Protect from sunlight. Store in a well-ventilated place.

Isobutylene Chemical Properties,Usage,Production

Physical properties

Colorless gas with a coal gas-like odor. The odor threshold concentration is 10 ppmv Nagata and Takeuchi (1990). This gas can be liquefied under pressure. The substance has low solubility in water, soluble in organic solvent, easy to polymerize. It is nonexplosive; however, it forms explosive mixtures with air. Containers holding isobutylene under pressure may explode if heated. The boiling point and freezing point of isobutylene are -6.9°C (19.6°F) and -141°C (-221°F), respectively. Isobutylene is extremely flammable. It is stable under recommended storage conditions and no decomposition may occur if stored and applied as directed.

Uses

Isobutylene is used as a monomer for the production of various polymers such as butyl rubber, polybutene and polyisobutylene. The most important application of butyl rubber is the manufacture of tyres for cars and other vehicles. Other applications of butyl rubber, polybutene and poyisobutylene are lubricants (motor oils), adhesives, sealants and coatings. Another major use of isobutylene is the production of methyl-tert-butyl ether (MTBE) and ethy-tert-butyl ether (ETBE) which are gasoline blending components for cleaner burning fuels. Isobutylene is also used for the production of anti-oxidants, fragrances and gas odorization products.

Uses

Isobutylene is an easily liquefied gas that primarily used to produce diisobutylene, trimers, butyl rubber, and other polymers. It is also used to produce antioxidants for foods, packaging, food supplements, and for plastics: Hatch, Pet. Refin. 39, No. 6, 207 (1960).

Definition

ChEBI: isobutylene is an alkene that is prop-1-ene substituted by a methyl group at position 2. It is an alkene and a gas molecular entity.

Application

Isobutylene is an important petrochemical raw material. In the pesticide industry, it is mainly used for the preparation of the organophosphorus insecticide terbufos, the pyrethroid insecticide permethrin and the acaricide pyridaben. Industrially, high-concentration isobutylene is mainly used for the production of polyisobutylene and copolymerization with isoprene to produce butyl rubber. The alkylation reaction of isobutene and isobutane can produce high-octane alkylated gasoline, and methyl tert-butyl ether obtained by reacting with methanol is an excellent gasoline additive.

Production Methods

Isobutene is produced in refinery streams by absorption on 65% H2SO4 at about 15C, or by reacting with an aliphatic primary alcohol and then hydrolyzing the resulting ether.

General Description

Isobutylene is a colorless gas with a faint petroleum-like odor. For transportation it may be stenched. It is shipped as a liquefied gas under its own vapor pressure. Contact with the liquid can cause frostbite. It is easily ignited. Its vapors are heavier than air and a flame can flash back to the source of leak very easily. The leak can either be a liquid or vapor leak. It can asphyxiate by the displacement of air. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. It is used in the production of isooctane, a high octane aviation gasoline.

Air & Water Reactions

Highly flammable.

Reactivity Profile

ISOBUTYLENE is incompatible with oxidizers. ISOBUTYLENE polymerizes easily. ISOBUTYLENE reacts easily with numerous materials, such as alkyl halides, halogens, concentrated sulfuric acid, hypochlorous acid, aluminum chloride, carbon monoxide and hydrogen with a cobalt catalyst. Polymerization is catalyzed by aluminum chloride and boron trifluoride.

Hazard

Highly flammable, dangerous fire and explosion risk, explosive limits in air 1.8–8.8%.

Health Hazard

Inhalation of moderate concentrations causes dizziness, drowsiness, and unconsciousness. Contact with eyes or skin may cause irritation; the liquid may cause frostbite.

Fire Hazard

Behavior in Fire: Containers may explode in fire. Vapor is heavier than air and may travel a long distance to a source of ignition and flash back.

Flammability and Explosibility

Extremely flammable

Carcinogenicity

Groups of 50 male and 50 female F344/N rats were exposed to isobutene at concentrations of 0, 500, 2000, or 8000 ppm6 h/day 5 days/week for 105 weeks. Groups of 50 male and 50 female B6C3F1 mice were exposed to isobutene at concentrations of 0, 500, 2000, or 8000 ppm 6 h/day, 5 days/week for 105 weeks. Under the conditions of these 2 year inhalation studies, there was some evidence of the carcinogenic activity of isobutene in male F344/N rats based on an increased incidence of follicular cell carcinoma of the thyroid gland. There was no evidence of the carcinogenic activity of isobutene in female F344/N rats or male or female B6C3F1 mice exposed to 500, 2000, or 8000 ppm.

Source

Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle-phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rate of 2-methylpropene was 40.1 mg/kg of pine burned. Emission rates of 2-methylbutene were not measured during the combustion of oak and eucalyptus.
California Phase II reformulated gasoline contained 2-methylpropene at a concentration of 170 mg/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without catalytic converters were 15.6 and 427 mg/km, respectively (Schauer et al., 2002).

Environmental Fate

Photolytic. Products identified from the photoirradiation of 2-methylpropene with nitrogen dioxide in air are 2-butanone, 2-methylpropanal, acetone, carbon monoxide, carbon dioxide, methanol, methyl nitrate, and nitric acid (Takeuchi et al., 1983). Similarly, products identified from the reaction of 2-methylpropene with ozone included acetone, formaldehyde, methanol, carbon monoxide, carbon dioxide, and methane (Tuazon et al., 1997).
The following rate constants were reported for the reaction of 2-methylpropene and OH radicals in the atmosphere: 3.0 x 10^-13 cm³/molecule?sec at 300 K (Hendry and Kenley, 1979); 5.40 x 10^-11 cm³/molecule?sec (Atkinson et al., 1979); 5.14 x 10^-11 at 298 K (Atkinson, 1990). Reported reaction rate constants for 2-methylpropene and ozone in the atmosphere include 2.3 x 10^-19 cm³/molecule?sec (Bufalini and Altshuller, 1965); 1.17 x 10^-19 cm³/molecule?sec at 300 K (Adeniji et al., 1965); 1.21 x 10^-17 cm³/molecule?sec at 298 K (Atkinson, 1990).
Chemical/Physical. Complete combustion in air yields carbon dioxide and water. Incomplete combustion yields carbon monoxide.

Solubility in organics

(mole fraction):
In 1-butanol: 0.131, 0.0695, and 0.0458 at 25, 30, and 70 °C, respectively; chlorobenzene: 0.234, 0.132, and 0.0796 at 25, 30, and 70 °C, respectively; octane: 0.333, 0.184, and 0.119 at 25, 30, and 70 °C, respectively (Hayduk et al., 1988).

Purification Methods

Dry isobutene by passage through anhydrous CaSO4 at 0o. Purify it further by freeze-pump-thaw cycles and trap-to-trap distillation. [Beilstein 1 IV 796.]