What is Isobutylene? It Keeps Popping Up in the News.

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Reprinted with permission of McGill University's Office for Science and Society. The original article by Ada McVean B.Sc. can be found here


An explosion and fire at a Texas chemical plant fueled by the extremely flammable gas isobutylene has killed one employee and left the public wondering why such a dangerously flammable gas is produced in such large quantities.

Isobutylene (also called 2-methylpropene, isobutene, and γ-butylene because chemists aren’t wonderful at sticking to a one naming system) is a colourless, gaseous hydrocarbon at room temperature.

Its flash point is -80 ˚C meaning that above this temperature, if an ignition source is present, isobutylene will ignite. Since the coldest temperature ever recorded on Earth was -89 ˚C, isobutylene is only a spark away from flames nearly everywhere on earth at all times.

Isobutylene is widely used in the synthesis of many things, largely because it contains a double bond which can be easily reacted to form other products. It can, for example, react with ethanol to form ethyl tert-butyl ether (ETBE), a gasoline additive that raises the octane number, making the fuel more resistant to knocking, or spontaneous combustion. Or it can be combined with itself in a long chain to form a polymer, butyl rubber.

Butyl rubber is hugely useful. It’s airtight, so it can be used to make seals like O-rings, window seals or cling film, as well as bottle stoppers, kickballs and tires. It’s tasteless and odourless, so it can be added to chewing gum, which, once chewed, can be collected and recycled to recover the isobutylene.

Like other forms of rubber, butyl rubber will break down when exposed to solvents like ammonia but will do so much slower than other rubbers. This has led to its widespread use in protective articles of clothing and gas masks.

Where do we get all this isobutylene from? Natural gas. Butane (the fuel that’s in your Zippo lighter) can be derived from mined natural gas and turned into tert-Butyl alcohol, which can then be turned into isobutylene.

So, while it’s not the most sustainable chemical around, isobutylene’s many varied uses can explain its mass production. Unfortunately, due to its extremely flammable nature, precautions do need to be taken to avoid fires like the one that occurred in Texas.