What molecule am I?
Isobutylene, formally 2-methylpropene, is a hydrocarbon gas originally obtained from oil refinery streams. In US patent 2,424,186 (1947), John W. Packie and Walter H. Rupp at Standard Oil of New Jersey (now Exxon) described the extraction of isobutylene from hydrocarbon mixtures with sulfuric acid. The inventors improved the process in US 2,509,885 (1950) to exclude 1-butene from the extracted isobutylene.
Researchers later discovered that isobutylene with sufficient purity for polymer or chemical synthesis could be prepared by dehydrating tert-butyl alcohol (t-BuOH). In one example, Ralph Levine and Jerome R. Olechowski at Cities Service (Tulsa, OK) dehydrated t-BuOH using a p-toluenesulfonic acid catalyst in xylene solution (US 4,165,343, 1979).
Isobutylene is used to make important chemicals such as isooctane and methacrolein; but its largest use is in the production of polyisobutylene, or butyl rubber. Often referred to simply as “butyl”, the polymer’s strength, elasticity, and impermeability make it suitable for use in a wide variety of products, including sporting goods, rubber sealants, audio speakers, gas masks, and even chewing gum.
During the holiday season, many people’s attention naturally turns to . . . football. As you’re watching your favorite bowl game, keep in mind that the bladders in every football you see are constructed from butyl rubber.
Isobutylene hazard information
| Hazard class* | GHS code and hazard statement | |
|---|---|---|
| Flammable gases, category 1 | H220—Extremely flammable gas |  |
| Gases under pressure, liquefied gas | H280—Contains gas under pressure; may explode if heated |  |
| Simple asphyxiant** | May displace oxygen and cause rapid suffocation | |
*Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
**Not a GHS classification.
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In October 2022, Puneet Kumar and colleagues at the Central University of Punjab (Bathinda) and Chitkara University (Rajpura, both in India) published a comprehensive account of monkeypox and the drugs used to combat it.
1. CAS Reg. No. 869572-92-9.
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Isobutylene fast facts
| CAS Reg. No. | 115-11-7 |
| SciFinder nomenclature | 1-Propene, 2-methyl-- |
| Empirical formula | C4H8 |
| Molar mass | 56.11 g/mol |
| Appearance | Colorless gas |
| Boiling point | –6.9 °C |
| Water solubility | 263 mg/L (25 °C, 1 atm) |
MOTW update
Bupropion1, the Molecule of the Week for May 2, 2011, is an antidepressant and antianxiety drug. Dextromethorphan2, the Molecule of the Week for January 6, 2014, is a commonly used cough suppressant. Now the two have been combined by Axsome Therapeutics (New York City) into a pill for treating major depressive disorder. Dextromethorphan is believed to modulate neurotransmission of glutamate, which likely plays a role in depression. In addition to its antidepressant properties, bupropion increases dextromethorphan levels in the blood.
1. CAS Reg. No. 34911-55-2.
2. CAS Reg. No. 125-71-3.
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