Ethenolysis

Ethenolysis is a chemical process in which internal olefins are degraded using ethylene as the reagent. The reaction is an example of cross metathesis. The utility of the reaction is driven by the low cost of ethylene as a reagent and the selectivity with which it forms compounds containing a terminal alkene functional group (α-olefins). The general reaction equation is:

A=B + CH2=CH2 → A=CH2 + B=CH2

Applications

Using ethenolysis, higher molecular weight internal alkenes can be converted to more valuable terminal alkenes. The Shell higher olefin process (SHOP process) uses ethenolysis on an industrial scale. The SHOP α-olefin mixtures are separated by distillation, the higher molecular weight fractions are isomerized by alkaline alumina catalysts in the liquid phase. The resulting internal olefins are reacted with ethylene to regenerate α-olefins. The large excess of ethylene moves the reaction equilibrium to the terminal α-olefins. Catalysts are often prepared from Rhenium(VII) oxide (Re2O7) supported on alumina.[1]

In one application, neohexene, a precursor to perfumes, is prepared by ethenolysis of diisobutene:[2]

(CH3)3C-CH=C(CH3)2 + CH2=CH2 → (CH3)3C-CH=CH2 + (CH3)2C=CH2

α,ω-Dienes, i.e., diolefins of the formula (CH2)n(CH=CH2)2, are prepared industrially by ethenolysis of cyclic alkenes. For example, 1,5-hexadiene, a useful crosslinking agent and synthetic intermediate, is produced from 1,5-cyclooctadiene:

(CH2CH=CHCH2)2 + 2 CH2=CH2 → 2 (CH2)2(CH=CH2)2

The catalyst is derived from rhenium(VII) oxide on alumina.[2] 1,9-Decadiene, a related species, is produced similarly from and cyclooctene.

In an application directed at using renewable feedstocks,[3] methyl oleate, derived from natural seed oils, can be converted to 1-decene and methyl 9-decenoate:[4][5]

CH3(CH2)7CH=CH(CH2)7CO2Me + CH2=CH2 → CH3(CH2)7CH=CH2 + MeO2C(CH2)7CH=CH2

References
  1. K. Weissermel, H. J. Arpe: Industrial Organic Chemistry: Important Raw Materials and Intermediates. Wiley-VCH Verlag 2003, ISBN 3-527-30578-5
  2. Lionel Delaude, Alfred F. Noels (2005). "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Weinheim: Wiley-VCH. doi:10.1002/0471238961.metanoel.a01.CS1 maint: uses authors parameter (link)
  3. Metzger, J. O.; Bornscheuer, U. (2006). "Lipids as renewable resources: current state of chemical and biotechnological conversion and diversification". Applied Microbiology and Biotechnology. 71: 13-22. doi:10.1007/s00253-006-0335-4.
  4. Marinescu, Smaranda C.; Schrock, Richard R.; Müller, Peter; Hoveyda, Amir H. (2009). "Ethenolysis Reactions Catalyzed by Imido Alkylidene Monoaryloxide Monopyrrolide (MAP) Complexes of Molybdenum". J. Am. Chem. Soc. 131 (31): 10840–10841. doi:10.1021/ja904786y. PMID 19618951.
  5. Schrodi, Yann; Ung, Thay; Vargas, Angel; Mkrtumyan, Garik; Lee, Choon Woo; Champagne, Timothy M.; Pederson, Richard L.; Hong, Soon Hyeok (2008). "Ruthenium Olefin Metathesis Catalysts for the Ethenolysis of Renewable Feedstocks". CLEAN - Soil, Air, Water. 36 (8): 669–673. doi:10.1002/clen.200800088.
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