Methyl-T-Butyl Ether

OVERVIEW

Methyl-t-butyl ether (METH-el TER-she-air-ee BYOO-till EE-thur) is a volatile (evaporates easily), colorless, flammable liquid that forms an azeotropic mixture with water. Azeotropic mixtures are combinations of two or more liquids that boil at the same temperature and, therefore, cannot be easily separated from each other.

KEY FACTS

OTHER NAMES:

MTBE; see Overview for additional names

FORMULA:

(CH₃)₃COCH₃

ELEMENTS:

Carbon, hydrogen, oxygen

COMPOUND TYPE:

Ether

STATE:

Liquid

MOLECULAR WEIGHT:

88.15 g/mol

MELTING POINT:

−108.6°C (−163.5°F)

BOILING POINT:

55.0°C (131°F)

SOLUBILITY:

Soluble in water; very soluble in ethyl alcohol and ether

MTBE was first synthesized in the 1960s by researchers at the Atlantic Richfield Corporation (now ARCO) as an additive designed to increase the octane number (fuel efficiency) of gasoline. The compound was created as a replacement for tetraethyl lead (Pb(C₂H₅)₄), which had long been added to gasolines to improve their octane number. Tetraethyl lead was commonly called simply "lead." From 1973 until 1996, lead was gradually removed from most gasoline because of its dangerous environmental and health effects. In 1990, a new use for MTBE was found. In that year, legislation passed by the U.S. Congress required that changes be made in the composition of gasoline so that it would burn more cleanly and release fewer pollutants into the atmosphere. One way for companies to meet this regulation was to add oxygenates to their gasoline. Oxygenates are chemical compounds that contain oxygen. They react with fuels, giving off their oxygen and increasing the efficiency with which the fuels burn.

MTBE rapidly became a very popular chemical in the automotive fuel industry. Production rose at a rate of about7 percent per year in the 1980s. It increased from about 500 million kilograms (1 billion pounds) in 1983 to about 3 billion kilograms (6 billion pounds) in 1990. In that year, it ranked twenty-fourth among all chemicals produced in the United States.

In the early 1990s, however, MTBE began showing up in groundwater in a number of states. Upon investigation, researchers discovered that MTBE had leaked out of underground tankers, had been spilled during transportation, and had escaped into the environment in other ways. It sank into the ground, where it mixed with groundwater forming azeotropic mixtures that could not be easily separated. The compound was found in wells, lakes, streams, and public water supplies.

These findings raised concerns because some experts believe that MTBE is a health hazard to humans and other animals. Although strong evidence is not yet available, many authorities believe that MTBE is a carcinogen and that it may be responsible for other health problems and damage to the environment. These concerns have led to legislative and administrative action banning or limiting the use of MTBE in gasoline. The first such action occurred in 1999 when Governor Gray Davis of California announced a program to cut back and eventually eliminate the use of MTBE in the state. A year later, the U.S. Environmental Protection Agency announced similar plans for the nation as a whole.

MTBE is also known by the following names: Methyl-tert-butyl ether; t-butyl-methyl ether; and tert-buty-methyl ether.

Interesting Facts

• Virtually all of the MTBE produced is used as a fuel additive. If proposed bans and limitations go into effect, there will no longer be any demand for the chemical. As such, production is likely to drop nearly to zero. One company that surveys chemical production predicts that the production of MTBE is likely to decrease at the rate of about 8 percent per year over the foreseeable future.

HOW IT IS MADE

MTBE is made by reacting methanol (methyl alcohol; CH3OH) with isobutylene (isobutene; CH₃C(CH₃)=CH₃). The formula for this reaction is CH₃OH + CH₃C(CH₃)=CH₂ → (CH₃)₃COCH₃.

COMMON USES AND POTENTIAL HAZARDS

More than 99 percent of the MTBE produced is used as a gasoline additive. The remaining quantity is used as a solvent and in the production of other chemical compounds.

MTBE is a mild irritant to the skin, eyes, and respiratory system. In larger doses, it may cause more serious problems, including nausea, vomiting, diarrhea, gastrointestinal problems, headache, dizziness, and loss of balance and coordination. In extreme cases, MTBE may produce severe lung damage, respiratory failure, convulsions, respiratory arrest (breathing stops), unconsciousness, coma, and death. The compound has been found to cause cancer in laboratory animals. No similar studies are available for humans, but experts tend to agree that MTBE is likely carcinogenic in humans also.

Words to Know

AZEOTROPIC MIXTURE

A combination of two or more liquids that boil at the same temperature and, therefore, cannot be easily separated from each other.

CARCINOGEN

A chemical that causes cancer in humans or other animals.

OXYGENATES

Chemical compounds that contain oxygen.

SOLVENT

A substance that is able to dissolve one or more other substances.

VOLATILE

Able to turn to vapor easily at a relatively low temperature.

FOR FURTHER INFORMATION

"Groundwater Protection." American Petroleum Institute. http://api-ep.api.org/environment/index.cfm?objectid=9EC44CD5-E167-49C4-8EBE7B354E4B3CD9&method=display_body&er=1&bitmask=002008008000000000 (accessed on December 29, 2005).

"Methyl tert-Butyl Ether (MTBE) and Other Gasoline Oxygenates." U.S. Geological Survey. http://sd.water.usgs.gov/nawqa/vocns/mtbe.html (accessed on December 29, 2005).

"Methyl Tertiary Butyl Ether (MTBE)." U.S. Environmental Protection Agency. http://www.epa.gov/mtbe/ (accessed on December 29, 2005).

"MTBE (methyl tert-butyl ether)." The Innovation Group. http://www.the-innovation-group.com/welcome.htm (accessed on December 29, 2005).