December 19, 2022
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Image of Isobutylene

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 1H220—Extremely flammable gasChemical Safety Warning
Gases under pressure, liquefied gasH280—Contains gas under pressure; may explode if heatedChemical Safety Warning
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.

Molecule of the Future

Tecovirimat1 is an antiviral drug that was first synthesized in 2004 at SIGA Technologies (New York City). The US Food and Drug Administration approved it in 2018 for treating smallpox.


To combat the growing monkeypox breakout, the European Medicines Agency approved the use of tecovirimat against the virus in January 2022. The FDA has not yet approved it for monkeypox, but states that it “may be used for people with severe disease or who are more likely to get severely ill, like patients with weakened immune systems.

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.

Molecule of the Future

Once a month we bring you a newly discovered or developed molecule that has important implications for the future of chemistry or society in general. Look for it the third week of each month. Learn more about this month's Molecule of the Future below.

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Isobutylene fast facts

CAS Reg. No.115-11-7
SciFinder nomenclature1-Propene, 2-methyl--
Empirical formulaC4H8
Molar mass56.11 g/mol
AppearanceColorless gas
Boiling point–6.9 °C
Water solubility263 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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