Chugaev elimination
Chugaev elimination | |
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Named after | Lev Chugaev |
Reaction type | Elimination reaction |
Identifiers | |
RSC ontology ID | RXNO:0000538 |
The Chugaev elimination is a chemical reaction that involves the elimination of water from alcohols to produce alkenes. The intermediate is a xanthate. It is named for its discoverer, the Russian chemist Lev Aleksandrovich Chugaev (1873–1922), who first reported the reaction sequence in 1899.
![](http://up.wiki.x.io/wikipedia/commons/thumb/e/e8/Cugaevalg.png/700px-Cugaevalg.png)
In the first step, a xanthate salt is formed out of the alkoxide and carbon disulfide (CS2). With the addition of iodomethane, the alkoxide is transformed into a methyl xanthate.
![](http://up.wiki.x.io/wikipedia/commons/8/85/Chugaev2.gif)
At about 200 °C, the alkene is formed by an intramolecular elimination. In a 6-membered cyclic transition state the hydrogen atom is removed from the carbon atom β to the xanthate oxygen in a syn-elimination. The side product decomposes to carbonyl sulfide (OCS) and methanethiol.
![](http://up.wiki.x.io/wikipedia/commons/8/8f/Chugaev3.gif)
The Chugaev elimination is similar in mechanism to other thermal elimination reactions such as the Cope elimination and ester pyrolysis. Xanthates typically undergo elimination from 120 to 200 °C, while esters typically require 400 to 500 °C and amine oxides routinely react between 80 and 160 °C.
In the development of Cram's rule, structural assignment of the reaction products were made by applying Chugaev elimination, wherein the threo isomer reacts to the cis isomer of -α-methyl-stilbene and the erythro isomer to the trans version.[1]
See also
[edit]References
[edit]- ^ Cram, Donald J.; Elhafez, Fathy Ahmed Abd (1952). "Studies in Stereochemistry. X. The Rule of "Steric Control of Asymmetric Induction" in the Syntheses of Acyclic Systems". Journal of the American Chemical Society. 74 (23): 5828–5835. doi:10.1021/ja01143a007.
- Latscha, Hans P. (2002). Chemie-Basiswissen. Berlin: Springer.
- L. Tschugaeff (1900). "Ueber das Thujen, ein neues bicyclisches Terpen". Berichte der deutschen chemischen Gesellschaft. 33 (3): 3118–3126. doi:10.1002/cber.19000330363.