MTBE (Methyl tert-Butyl Ether; C5H120) is is the second largest end use of methanol and has been used since 1979 primarily as a source of oxygen and octane in gasoline and became even more widespread following the passage of the Clean Air Act of 1990 which required oxgenated gas in cities with unhealthy levels of air pollution. As much as 10% to 15% of today's gasoline can be MTBE.

MTBE is produced by mixing ethanol and isobuylene in the presence of heat and a catalyst, and is a flammable liquid with a distinctive, disagreeable, turp odor. Like all ethers, it is highly water-soluable and it may bind to the water molecules. In open containers and surface water it evaporates rapidly, where the sunlight may break it up.

Most prominently, MTBE has been in the environmental spotlight because it is possibly carcinogenic (Rats exposed to high levels developed kidney cancer). Of most concern is that that MTBE may leak from old or unsafe underground tanks or even pipelines and contaminate the groundwater, as it is extremely water-soluable, and will remain for prolonged periods of time. Substantial build-up of it will lead to MTBE's notoriously foul taste/odor in tap water from the affected areas.

MTBE has been suggested to cause headaches, nausea, dizziness, and mental confusion, after people reported these symptoms while driving their car, pumping gas, or working in gas stations. Though these could be the result of other additives in the gasoline.

The possible dangers of MTBE led to the March 25, 1999 California governor Gray Davis passing Executive Order D-5-99 removing MTBE from the state's gasoline by no later then December 25, 2002. In March 2003, it was extended until December 2003. Most are converting to the slightly more expensive, ethanol (i.e. alcohol).

Despite its possible toxicity, there is a medicinal use for MTBE, dissolving gallstones. Patients treated in this way have MTBE delivered directly to their gall bladders through special tubes that are surgically inserted.

Safety Levels

  • Water: The EPA has issued guidelines recommending that, to protect children, drinking water levels of MTBE not exceed 4 milligrams per liter of water (4 mg/L) for an exposure of 1-10 days, and 3 mg/L for longer-term exposures.
  • Exposure:The American Conference of Governmental Industrial Hygienists (ACGIH) has recommended an exposure limit of 40 parts of MTBE per million parts of air (40 ppm) for an 8-hour workday, 40-hour workweek.

NFPA Chemical Hazard Levels

  • Flammability: 3
  • Health: 2
  • Reactivity: 0
  • Special: N/A

Chemical Structure

CH3 ------ C ------ O ------ CH3