chemistry

Methylcyclopentadienyl manganese tricarbonyl

Methylcyclopentadienyl manganese tricarbonyl is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Methylcyclopentadienyl manganese tricarbonyl rather than just read about it. In short: Methylcyclopentadienyl manganese tricarbonyl (MMT or MCMT) is an organomanganese compound with the formula (C5H4CH3)Mn(CO)3. Initially marketed as a supplement for use in leaded gasoline, MMT was later used in unleaded gasoline to increase the octane rating.

Key takeaways

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Reference excerpt

Methylcyclopentadienyl manganese tricarbonyl (MMT or MCMT) is an organomanganese compound with the formula (C5H4CH3)Mn(CO)3. Initially marketed as a supplement for use in leaded gasoline, MMT was later used in unleaded gasoline to increase the octane rating. Following the implementation of the Clean Air Act (United States) (CAA) in 1970, MMT continued to be used alongside tetraethyl lead (TEL) in the US as leaded gasoline was phased out (prior to TEL finally being banned from US gasoline in 1995), and was also used in unleaded gasoline until 1977. Ethyl Corporation obtained a waiver from the U.S. EPA (Environmental Protection Agency) in 1995, 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 (manganese per liter). MMT has been used in Canadian gasoline since 1976 (and in numerous other countries for many years) at a concentration up to 8.3 mg Mn/L (though the importation and interprovincial trade of gasoline containing MMT was restricted briefly during the period 1997–1998) and was introduced into Australia in 2000. It has been sold under the tradenames HiTEC 3000, Cestoburn and Ecotane. MMT is also used in China.

History of usage in the United States Although initially marketed in 1958 as a smoke suppressant for gas turbines, MMT was further developed as an octane enhancer in 1974. When the United States Environmental Protection Agency (EPA) ordered the phase out of TEL in gasoline in 1973, new fuel additives were sought. TEL has been used in certain countries as an additive to increase the octane rating of automotive gasoline but has been phased out in all countries since July 2021. In 1977, the US Congress amended the CAA to require advance approval by the EPA for the continued use of fuel additives such as MMT, ethanol, ethyl tert-butyl ether (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 was required to demonstrate that the fuel additive would not lead to a failure of vehicle emission control systems. Ethyl Corporation applied to the US EPA for a waiver for MMT in both 1978 and 1981; in both cases the applications were denied because of stated concerns that MMT might damage catalytic converters and increase hydrocarbon emissions. In 1988, Ethyl began a new series of discussions with the 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, the U.S. EPA determined that use of MMT at 8.3 mg Mn/L would not cause, or contribute to, vehicle emission control system failures. Despite that finding, the EPA ultimately denied the waiver request in 1994 due to uncertainty related to health concerns regarding manganese emissions from the use of MMT. As a result of this ruling, Ethyl initiated a legal action claiming that the 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 alternative to TEL has been controversial. Manganese compounds have, in general, very low toxicity, but their combustion products still irreversibly foul catalytic converters. Opposition from automobile manufacturers and some areas of the scientific community has reportedly prompted oil companies to stop voluntarily the usage of MMT in some of their countries of operation. MMT is currently manufactured in the U.S. by the Afton Chemical Corporation, a subsidiary of New Market Corporation. It is also produced and marketed as Cestoburn by Cestoil Chemical Inc. in Canada.

Structure and synthesis MMT is manufactured by reduction of bis(methylcyclopentadienyl) manganese using triethylaluminium. The reduction is conducted under an atmosphere of carbon monoxide. MMT is a so-called half-sandwich complex, or more specifically a "piano-stool" complex (since the three CO ligands are like the legs of a stool). The manganese atom in MMT is coordinated with three carbonyl groups as well as to all five main carbon atoms of the methylcyclopentadienyl ring. These hydrophobic organic ligands make MMT highly lipophilic. A variety of related complexes are known, including ferrocene, which has also been used as an additive to gasoline. Many derivatives of MMT are known.

Safety MMT can impact human and environmental through direct exposure to the compound or exposure to its combustion products. MMT itself photodegrades rapidly, and the Australian National Industrial Chemicals Notification and Assessment Scheme (NICNAS) concluded that there is "low occupational risk associated with MMT" both "for workers involved in formulating and distributing LRP or aftermarket fuel additives and those involved in automotive maintenance". Further, they also concluded that there is a "low risk" to the public from the use of MMT. Regulatory agencies, including NICNAS and Health Canada, have generally concluded that manganese-containing combustion products (manganese phosphate, manganese sulfate and manganese dioxide) from MMT are unlikely to generate significant health impacts. In 2013, ARCADIS Consulting prepared a report on MMT during the implementation of a European Fuel Quality Directive (2009/30/EC). The conclusions of a risk assessment are that "for MMT and its transformation products, when MMT is used as a fuel additive in petrol, no significant human health or environmental concerns related to exposure to either MMT or its transformation [combustion] products (manganese phosphate, manganese sulfate and manganese tetroxide [sic]) were identified at use at levels up to 18 mg Mn/L. Depending on the regional needs and the vehicle emission control technology available, an MMT treat rate in the range of 8.3 mg Mn/L to 18 mg Mn/L is scientifically justified and may deliver both environmental and economic benefits without significant adverse effects."

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Illustrations

Worked examples

Example 1 — a first encounter with Methylcyclopentadienyl manganese tricarbonyl

Start with the simplest possible case. Write down what Methylcyclopentadienyl manganese tricarbonyl claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Methylcyclopentadienyl manganese tricarbonyl before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Methylcyclopentadienyl manganese tricarbonyl ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Methylcyclopentadienyl manganese tricarbonyl

In research: Methylcyclopentadienyl manganese tricarbonyl appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Methylcyclopentadienyl manganese tricarbonyl in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Methylcyclopentadienyl manganese tricarbonyl is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antiknock agents, Carbonyl complexes, Cyclopentadienyl complexes, so understanding it makes those chapters shorter.
In everyday life: Look for Methylcyclopentadienyl manganese tricarbonyl outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

What is Methylcyclopentadienyl manganese tricarbonyl in simple terms?

Why does Methylcyclopentadienyl manganese tricarbonyl matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Methylcyclopentadienyl manganese tricarbonyl?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Methylcyclopentadienyl manganese tricarbonyl.