The Chugaev elimination is a chemical reaction that involves the net removal of water from

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

s to produce

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

s. The intermediate is a

xanthate A xanthate is a Salt (chemistry), salt or ester of a xanthic acid. The formula of the salt of xanthic acid is (where R is organyl group and M is usually Sodium, Na or Potassium, K). Xanthate also refers to the anion . The formula of a xanthic a ...

. It is named for its discoverer, the Russian chemist Lev Aleksandrovich Chugaev (1873–1922), who first reported the reaction sequence in 1899. In the first step, a xanthate salt is formed out of the

alkoxide In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...

and

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is an inorganic compound with the chemical formula and structure . It is also considered as the anhydride of thiocarbonic acid. It is a colorless, flammable, neurotoxic liquid that is used as ...

(CS₂). With the addition of iodomethane, the alkoxide is transformed into a methyl xanthate ester. When heated to about 200 °C, this ester decomposed by an intramolecular elimination. In a 6-membered cyclic

transition state In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked w ...

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 Carbonyl sulfide is the chemical compound with the linear formula . It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl double bonded to a sulfur atom. Carbonyl sulfide can be considered to ...

(OCS) and

methanethiol Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. In small amounts, it is pervasive in nature and found in certain foods, such as some n ...

. 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. Thus, the decomposition of xanthates is advantageous because the milder conditions minimize side reactions, such as alkene isomerization. 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 Stilbene may refer to one of the two stereoisomers of 1,2-diphenylethene: * (''E'')-Stilbene (''trans'' isomer) * (''Z'')-Stilbene (''cis'' isomer) See also * Stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C ...

and the erythro isomer to the trans version. :

References

* * {{Organic reactions

External links

Animation of the mechanism of the Chugaev elimination
1899 introductions 1899 in science Elimination reactions Olefination reactions Name reactions