Reppe vinylation

What is Reppe vinylation?

The Reppe vinylation or Reppe synthesis is a strong-base catalyzed addition of acetylene that was first reported by Reppe in 1931.

Reppe vinylation has been used to prepare various vinylic compounds, including vinyl ethers, vinyl sulfides, vinyl phenyl ethers, vinyl esters, and vinyl amines, by adding acetylene to alcohols, thiols or disulfides, phenols, carboxylic acids, and amines, respectively, at temperatures ranging from 160 to 200 ºC and acetylene pressure from 100 to 300 psi.

Reppe vinylation - general reaction scheme - Reppe synthesis
Reppe vinylation

Acetylene is an explosive substance, but it can be safely handled under these reaction conditions by diluting it with inert materials like N2 or CO2, using special apparatus to minimize free space, or employing bunches of small reaction tubes. The best catalysts for preparing vinyl ethers from alcohols are KOH and potassium alkoxide, and the reactivity order is:

primary alcohols > secondary alcohols > tertiary alcohols

Polyhydroxyl alcohols such as ethylene glycol, glycerol, sorbitol, pentaerythritol, and sugar derivatives can also be vinylated under these conditions.

Reppe vinylation - general reaction scheme - Reppe synthesis
Reppe vinylation

R = alkyl

Zinc or cadmium acetates are used as catalysts for the reaction between amines and acetylene, but alkylidenimines are formed instead of vinyl amines from primary aliphatic amines.

Fatty acids such as lauric acid, stearic acid, and oleic acid have been converted into corresponding vinyl esters, and many phenols, particularly monoalkylated phenols, can be vinylated using zinc naphthenate as a catalyst at 160 ºC. Carbazoles, cyclic amides, pyrrolidones, and N-monoalkyl sulfonamides have also been successfully vinylated under similar conditions with acetylene, whereas N-monoaryl sulfonamide, p-toluenesulfonanilide, butanesulfonamide, and unsubstituted sulfonamides failed in the Reppe vinylation.

References

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