Alkane metathesis

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Alkane metathesis is a class of chemical reaction in which an alkane is rearranged to give a longer or shorter alkane product. It is similar to olefin metathesis, except that olefin metathesis cleaves and recreates a carbon-carbon double bond, but alkane metathesis operates on a carbon-carbon single bond.

Examples and catalysts

Alkane metathesis is

Cross metathesis can also take place, for example methane and propane can react to give two molecules of ethane. Ethane reacts with toluene to give ethylbenzene and xylene. The reaction involves metallocyclobutane intermediates just as in olefin metathesis.[2]

Dual-catalyst systems have also been developed which are effective for the metathesis of higher alkanes. These systems are based on the tandem operation of two catalysts, one for transfer-dehydrogenation and one for olefin metathesis.

A heterogeneous system consisting of Pt on alumina mixed with W oxide on silica was reported by Burnett and Hughes.

pincer-iridium dehydrogenation catalysts and either "Schrock-type" Mo-based olefin metathesis catalysts have been reported by Brookhart and Goldman.[4]
Because the iridium-based catalysts show selectivity for the termini of n-alkanes, these systems have the unique ability to effect alkane metathesis with some selectivity for product molecular weight. Thus for example n-hexane can be converted to ethane and n-decane as the major products.

Numerous applications for alkane metathesis involving petrochemicals and fuels can be envisaged. For example, the conversion of n-hexane to n-decane and ethane has been proposed for the purpose of improving the overall yield of

Fischer–Tropsch reactors, which convert syngas
to a broad range of n-alkanes.

Scott, Goldman and Brookhart have reported the metathesis of

cycloalkanes with the pincer-Ir/Mo system. Cyclooctane (cyclo-C8H16), for example is converted to a mixture of cyclohexadecane (cyclo-C16H32) and higher rings as well as polymers.[5]

See also

References

  1. PMID 9082995
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  2. PMID 15954760
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  3. doi:10.1016/0021-9517(73)90270-4
    .
  4. PMID 16614220
    .
  5. PMID 18092104
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