ISOBUTYLENE Chemical Properties

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

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

CAS DataBase Reference

115-11-7(CAS DataBase Reference)

EPA Substance Registry System

Isobutene (115-11-7)

Safety Information

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

Toxicity

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

MSDS

• Language:EnglishProvider:SigmaAldrich

ISOBUTYLENE Usage And Synthesis

Physical properties

Colorless gas with a coal gas-like odor. The odor threshold concentration is 10 ppm_v Nagata and Takeuchi (1990).

Uses

Primarily used to produce diisobutylene, trimers, butyl rubber, and other polymers; also to produce antioxidants for foods, packaging, food supplements, and for plastics: Hatch, Pet. Refin. 39, No. 6, 207 (1960).

Definition

ChEBI: An alkene that is prop-1-ene substituted by a methyl group at position 2.

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 ISOBUTYLENE may be stenched. ISOBUTYLENE is shipped as a liquefied gas under its own vapor pressure. Contact with the liquid can cause frostbite. ISOBUTYLENE 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. ISOBUTYLENE can asphyxiate by the displacement of air. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. ISOBUTYLENE 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.

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).

Solubility in water

(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.]

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