Methylcyclopentadienyl Manganese Tricarbonyl - History

History

Tetraethyl lead (TEL) has been, and still is on a limited scale, used as an additive to increase the octane rating of gasoline. TEL was manufactured and marketed by the Ethyl Corporation, a joint venture between General Motors and DuPont. When the United States Environmental Protection Agency (EPA) ordered the phasing out of leaded gasoline in 1973, new fuel additives were sought. Developed as an octane improver, though initially marketed in 1958 as a smoke suppressant for gas turbines, MMT was used in 1974 as an additive in unleaded gasoline.

In 1977, the U.S. Congress amended the CAA to require advanced approval by the EPA for the continued use of fuel additives such as MMT, ethanol, ETBE, etc. The new CAA amendment required a “waiver” to allow use of fuel additives made of any elements other than carbon, hydrogen, oxygen (within certain limits) and nitrogen. To obtain a waiver, the applicant has to demonstrate that the fuel additive will not lead to a failure of vehicle emission control systems.

Ethyl Corporation applied for a waiver in both 1978 and 1981 and in both cases the applications were denied because of stated concerns that MMT might damage catalytic convertors and increase hydrocarbon emissions. In 1988 Ethyl began a new series of discussions with EPA to determine a program for developing the necessary data to support a waiver application. In 1990 Ethyl filed its third waiver application prompting an extensive four-year review process. In 1993, EPA determined that use of MMT at 8.3 mg Mn/l would not cause, or contribute to, vehicle emission control system failures.

EPA ultimately denied the waiver request in 1994, however, due to uncertainty whether manganese emissions from use of MMT might present a potential public health concern.

As a result of this ruling, Ethyl Corporation began a legal battle with the EPA claiming that EPA had exceeded its authority by denying the waiver on these grounds. This was upheld by the US Court of Appeals and EPA subsequently granted a waiver which allows the use of MMT in US unleaded gasoline (not including reformulated gasoline) at a treat rate equivalent to 8.3 mg Mn/l.

Implementation of this less toxic alternative to TEL has been controversial. Opposition from automobile manufacturers and some areas of the scientific community has reportedly prompted oil companies to voluntarily stop the use of MMT in some of their countries of operation.

MMT is currently manufactured by the Afton Chemical Corporation, a subsidiary of Newmarket Corporation. It is also produced and marketed as "Cestoburn" by Cestoil Chemical Inc. in Canada.