Methylcyclopentadienyl Manganese Tricarbonyl
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Methyl Cyclopentadienyl Manganese Tricarbonyl (MMT) is an organic manganese compound manufactured by the Ethyl Corporation and sold under the names HiTec 3000 and AK-33X.[#endnote_Frumkin] Marketed initially in 1958 as a supplement to the gasoline additive tetraethyl lead, MMT was later used to increase octane in unleaded gasoline. Though banned as a gasoline additive in the United States from 1977 to 1995, MMT has been used in Canadian gasoline since 1976 and was recently introduced in Australia.
History
The Ethyl Corporation was initially founded as a joint venture between General Motors and Dupont with the sole purpose of manufacturing and marketing tetraethyl lead as a fuel additive. However, when the EPA began to phase out the use of leaded gasoline in 1972, new fuel additives were needed to boost the octane of gasoline. Initially marketed in 1958 as a smoke suppressant for gas turbines, it was not until 1974 that the compound was used commercially as a fuel additive in unleaded gasoline. The Clean Air Act of 1977 banned the use of MMT until the Ethyl Corporation could prove that the additive would not lead to failure of new car emissions-control systems. As a result of this ruling, the Ethyl Corporation began a legal battle with the EPA, claiming that MMT was harmless to automobiles. In 1995, the U.S. Court of Appeals ruled that the EPA had exceeded its authority and, as a result, MMT became a legal fuel additive in the United States.[#endnote_Kitazawa]The health hazards associated with MMT use have been hotly debated for decades. Most recently, a 2003 study by the NICNAS in Australia suggested that MMT was highly toxic to humans, but ruled that the airborne concentrations of manganese as a result of car emissions from vehicles using fuel containing MMT were not high enough to cause a major health problem.[#endnote_NICNAS] However, a 2002 study by Masashi Kitazawa argued that dermal absorption from accidental spills, use of gasoline as a solvent cleaner, and deliberate gasoline fume inhalation were the main sources of potential MMT exposure.
Due in part to fears remaining from the environmental disaster that was leaded gasoline and questionable effects of MMT on automobile engines, MMT use in the United States as a gasoline additive has been virtually non-existent.
Structure and Bonding
The manganese atom in MMT is bonded to three carbonyl groups as well as to a methylcyclopentadiene ring. These organic ligands make MMT highly lipophilic. As a result, it has been speculated that the lipophilic nature of the compound causes greater bioacculumation of manganese relative to inorganic forms of the metal. Toxicokinetic studies have shown that manganese derived from MMT absorbs into rat blood plama at a rate 37 times that of inorganic manganese.[#endnote_Zheng]Preparation
[#endnote_MMTPatent]Properties
MMT is a viscous yellow liquid with an herbaceous odor.Precautions
Chronic exposure to manganese has been known to cause manganism. The symptoms of manganism are similar to those of Parkinson's Disease. MMT has been shown to be cytotoxic and especially damaging to dopaminergic PC-12 cells.[#endnote_Kitazawa]Immediate symptoms of MMT exposure are mild skin and eye irritation. Short-term symptoms resulting from MMT poisoning include giddiness, headache, neausea, and difficulties in breathing. Animal studies have shown that long-term exposure to MMT can result in damage to the liver and kidneys.[#endnote_WorldHealth]
References
- ↑ Frumkin, Howard and Solomon, Gena; "Manganese in the US Gas Supply" American Journal of Industrial Medicine, 31: 107-115 (1997)
- ↑ United Nations Environment Programme with World Health Organization; Manganese; Geneva, 1981.
- ↑ National Industrial Chemicals Notification and Assessment Scheme; Methylcyclopentadienyl Manganese Tricarbonyl June 2003. [link]
- ↑ Masashi Kitazawa, Jarrad R. Wagner, Michael L. Kirby, Vellareddy Anantharam, and Anumantha G. Kanthasamy; Oxidative Stress and Mitochondrial-Mediated Apoptosis in Dopaminergic Cells Exposed to Methylcyclopentadienyl Manganese Tricarbonyl J. Pharmacol. Exp. Ther., Jul 2002; 302: 26 - 35.
- ↑ Zheng W, Kim H and Zhao Q (2000) Comparative toxicokinetics of manganese chloride and methylcyclopentadienyl manganese tricarbonyl (MMT) in Sprague-Dawley rats. Toxicol Sci 54: 295-301.
- ↑ US patent #4,946,975
External links
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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