Kriewitz condensation

What is Kriewitz condensation?

In 1899, Kriewitz was the first to report a reaction that involves the condensation of formaldehyde and olefins to form unsaturated primary alcohols.

Kriewitz condensation - general reaction scheme
Kriewitz condensation

R, R’ = H, alkyl, aryl (see list of acronyms)

Kriewitz condensation takes place at high temperatures, typically around 170 degrees Celsius, and uses water or acetic acid as a solvent. An acid catalyst, such as sulfuric acid H2SO4, is added to facilitate the reaction. Formaldehyde and some ketones can act as an enophile in this reaction.

The unsaturated alcohol produced has a double bond adjacent to its original position in the starting olefin, except in the case of camphene, which results in an allylic alcohol. Among the acyclic olefins used in this condensation, the isobutylene-type olefins are more reactive than monosubstituted or 1,2-disubstituted olefins.

The Prins-Kriewitz cyclization is an extension of this reaction that involves the intramolecular condensation of an α-alkoxycarbenium ion with a double bond to form a hydropyran derivative.

The utility of Kriewitz condensation in organic synthesis is restricted. While it was previously employed in the manufacturing of butadiene or isoprene for the rubber industry, it has since been deemed less desirable than dehydrogenation and cracking processes.