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Industrial methods[ edit ] Alkenes are produced by hydrocarbon cracking. Raw materials are mostly natural gas condensate components principally ethane and propane in the US and Mideast and naphtha in Europe and Asia. Alkanes are broken apart at high temperatures, often in the presence of a zeolite catalyst, to produce a mixture of primarily aliphatic alkenes and lower molecular weight alkanes.
The mixture is feedstock and temperature dependent, and separated by fractional distillation. This is mainly used for the manufacture of small alkenes up to six carbons. This process is also known as reforming. Both processes are endothermic and are driven towards the alkene at high temperatures by entropy.
Elimination reactions[ edit ] One of the principal methods for alkene synthesis in the laboratory is the room elimination of alkyl halides, alcohols, and similar compounds.
Most E2 eliminations start with an alkyl halide or alkyl sulfonate ester such as a tosylate or triflate. When an alkyl halide is used, the reaction is called a dehydrohalogenation. Two common methods of elimination reactions are dehydrohalogenation of alkyl halides and dehydration of alcohols.
A typical example is shown below; note that if possible, the H is anti to the leaving group, even though this leads to the less stable Z-isomer. For example, the dehydration of ethanol produces ethene: Alkenes can be prepared indirectly from alkyl amines.
The amine or ammonia is not a suitable leaving group, so the amine is first either alkylated as in the Hofmann elimination or oxidized to an amine oxide the Cope reaction to render a smooth elimination possible.
Synthesis from carbonyl compounds[ edit ] Another important method for alkene synthesis involves construction of a new carbon—carbon double bond by coupling of a carbonyl compound such as an aldehyde or ketone to a carbanion equivalent.
Such reactions are sometimes called olefinations. The most well-known of these methods is the Wittig reactionbut other related methods are known. The Wittig reagent is itself prepared easily from triphenylphosphine and an alkyl halide. The reaction is quite general and many functional groups are tolerated, even esters, as in this example: This uses a less accessible silicon-based reagent in place of the phosphorane, but it allows for the selection of E- or Z-products.
If an E-product is desired, another alternative is the Julia olefinationwhich uses the carbanion generated from a phenyl sulfone. The Takai olefination based on an organochromium intermediate also delivers E-products. A pair of carbonyl compounds can also be reductively coupled together with reduction to generate an alkene.
Symmetrical alkenes can be prepared from a single aldehyde or ketone coupling with itself, using titanium metal reduction the McMurry reaction.
If two different ketones are to be coupled, a more complex, indirect method such as the Barton—Kellogg reaction may be used. A single ketone can also be converted to the corresponding alkene via its tosylhydrazone, using sodium methoxide the Bamford—Stevens reaction or an alkyllithium the Shapiro reaction.
Olefin metathesis Alkenes can be prepared by exchange with other alkenes, in a reaction known as olefin metathesis. Frequently, loss of ethene gas is used to drive the reaction towards a desired product. In many cases, a mixture of geometric isomers is obtained, but the reaction tolerates many functional groups.
The method is particularly effective for the preparation of cyclic alkenes, as in this synthesis of muscone: Transition metal catalyzed hydrovinylation is another important alkene synthesis process starting from alkene itself.
The hydrovinylation reaction was first reported by Alderson, Jenner, and Lindsey by using rhodium and ruthenium salts, other metal catalysts commonly employed nowadays included iron, cobalt, nickel, and palladium.
The addition can be done highly regio- and stereoselectively, the choices of metal centers, ligands, substrates and counterions often play very important role.
Reduction of the alkyne by sodium metal in liquid ammonia gives the trans-alkene. Rearrangements and related reactions[ edit ] Alkenes can be synthesized from other alkenes via rearrangement reactions. Besides olefin metathesis described abovea large number of pericyclic reactions can be used such as the ene reaction and the Cope rearrangement.
In the Diels—Alder reactiona cyclohexene derivative is prepared from a diene and a reactive or electron-deficient alkene. Nomenclature[ edit ] Although the nomenclature is not followed widely, according to IUPAC, alkenes are acyclic hydrocarbons with one double bond between carbon centers.
Olefins comprise a larger collection of cyclic and acyclic alkenes as well as dienes and polyenes.The two key intermediates in the catalytic cycle are a metal carbene (a compound with a metal-carbon double bond) and a metallacyclobutane.
New Student (ENG, PL) positions are available in Grela's group from the FNP TEAM-TECH srmvision.comne for applications is Please apply! New PostDoc position is open in our labs in the NCN BEETHOVEN 2 grant "Anionic Carbenes and Borylanions: Tuning the properties of ruthenium metal complexes in olefin metathesis".
Hey, A very large deal of the drugs that are produced and used in tons every day to treat diseases are synthesized using chemicals or reactants that would be quite poisonous or dangerous, but the drugs itselves are quite safe in the appropiate dosage. Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds.
  Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by-products and hazardous wastes than alternative organic srmvision.com ontology ID: RXNO