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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 methathesismetathesis operates on a carbon-carbon single bond.
==Examples and catalysts==
Alkane metathesis is [[catalysis|catalyzed]] by metal-containing compounds or complexes. One such class of catalyst systems, discovered and developed by the group of [[Jean-Marie Basset]], comprises [[tantalum]] [[hydride]] supported on [[silica]] (SiO<sub>2</sub>)TaH at temperatures of 25°C to 200°C. These systems catalyze the conversion of [[ethane]] to give [[methane]], [[propane]] and traces of [[butane]].<ref>"{{cite journal|doi=10.1126/science.276.5309.99|pmid=9082995|title=Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides." Véronique Vidal, Albert Théolier, Jean Thivolle-Cazat, Jean-Marie Basset, [[|journal=Science (journal)|Science]], Vol volume=276, Issue |issue=5309, 99-102 4 April '''|pages=99–102|year=1997''' [http://www|last1=Vidal|first1=V.sciencemag|last2=Theolier|first2=A.org/cgi/content/abstract/276/5309/99?rbfvrToken|last3=3b4c3f0f99df3104d7aea932f81bee3c683a0e75Thivolle-Cazat|first3=J.|last4=Basset|first4=J. Abstract]M.}}</ref> [[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]].<ref>"{{cite journal|doi=10.1021/ja051679f|pmid=15954760|title=Primary Products and Mechanistic Considerations in Alkane Metathesis."|journal=Journal Jeanof Mariethe American Chemical Society|volume=127|issue=24|pages=8604–8605|year=2005|last1=Basset, Christophe|first1=Jean Marie|last2=Copéret, Laurent |first2=Christophe|last3=Lefort, |first3=Laurent|last4=Maunders|first4=Barry M. Maunders, Olivier |last5=Maury, Erwan |first5=Olivier|last6=Le Roux, |first6=Erwan|last7=Saggio|first7=Guillaume Saggio, |last8=Soignier|first8=Sophie Soignier, |last9=Soulivong|first9=Daravong Soulivong, |last10=Sunley|first10=Glenn J. Sunley, |last11=Taoufik|first11=Mostafa Taoufik, and Jean |last12=Thivolle-Cazat [[J. Am. Chem. Soc.]]., 127 (24), 8604 -8605, '''2005'''. [http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2005/127/i24/abs/ja051679f.html Abstract]|first12=Jean}}</ref>
'''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.<ref>"{{cite journal|doi=10.1016/0021-9517(73)90270-4|title=Mechanism and poisoning of the molecular redistribution reaction of alkanes with a dual-functional catalyst system." Burnett, R. L.; Hughes, T. R. ''|journal=Journal of Catalysis'' '''|volume=31|pages=55–64|year=1973''',|last1=Burnett|first1=Robert 31, 55-64L.|last2=Hughes|first2=Thomas [http://dxR.|doi.org/10.1016/0021-9517(73)90270-4 Abstract]access=free}}</ref> Systems based on [[pincer ligand| pincer]]-iridium dehydrogenation catalysts and either "[[Richard_RRichard R._Schrock Schrock|Schrock]]-type" Mo-based olefin metathesis catalysts have been reported by [[Maurice Brookhart| Brookhart]] and [[Alan S. Goldman| Goldman]].<ref>"{{cite journal|doi=10.1126/science.1123787|pmid=16614220|title=Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis." |journal=Science|volume=312|issue=5771|pages=257–261|year=2006|last1=Goldman, |first1=A. S.; |last2=Roy, |first2=A. H.; |last3=Huang, |first3=Z.; |last4=Ahuja, |first4=R.; |last5=Schinski, |first5=W.; |last6=Brookhart, |first6=M. [[Science (journal)|''Science'']] '''2006''', 312, 257-261bibcode=2006Sci. [http://www.sciencemag.org/cgi/content/abstract/312/5771/257 Abstract]..257G}}</ref> 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 [[Diesel fuel|diesel]] grade n-alkane (C<sub>9</sub>H<sub>20</sub> to C<sub>19</sub>H<sub>40</sub>) from [[Fischer-TropschFischer–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-C<sub>8</sub>H<sub>16</sub>), for example is converted to a mixture of cyclohexadecane (cyclo-C<sub>16</sub>H<sub>32</sub>) and higher rings as well as polymers.<ref>"{{cite journal|doi=10.1039/B712197K|pmid=18092104|title=Catalytic ring expansion, contraction, and metathesis-polymerization of cycloalkanes."|journal=Chemical Communications|issue=2|pages=253–255|year=2008|last1=Ahuja, R.; |first1=Ritu|last2=Kundu, S.; |first2=Sabuj|last3=Goldman, A.|first3=Alan S.; |last4=Brookhart, M.; |first4=Maurice|last5=Vicente, B.|first5=Brian C.; |last6=Scott, S.|first6=Susannah L. ''Chem. Commun.'' '''2008''', 253-255. [http://www.rsc.org/publishing/journals/CC/article.asp?doi=b712197k Abstract]}}</ref>
* [[ OlefinAlkene metathesis]] ▼* [[Alkyne metathesis]]
==References==
{{reflist}}
* [[Metathesis reaction]]
[[Category:Carbon-carbon bond forming reactions]]
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