The Guerbet reaction
, named after Marcel Guerbet
(1861-1938), is an organic reaction
converting a primary aliphatic alcohol
into its β-alkylated dimer alcohol
with loss of one equivalent of water. This reaction requires a catalyst
and elevated temperatures.
The original 1899 publication concerned the conversion of n-butanol to 2-ethyl-1-hexanol. The alcohols dervied from this reaction are called Guerbet alcohols. Application of long-chained aliphatic alcohols gives access to surfactants.
The reaction requires alkali metal hydroxides or alkoxides and hydrogenation catalysts such as Raney Nickel at higher temperature (220 °C) and pressure.
The reaction mechanism
for this reaction is a four-step sequence. In the first step the alcohol
to the aldehyde
. These intermediates then react in an Aldol condensation
to the vinyl aldehyde which the hydrogenation catalyst then reduces to the alcohol.
The Cannizzaro reaction is a competing reaction when two aldehyde molecules react by disproportionation to form the corresponding alcohol and carboxylic acid. Another side reaction is the Tishchenko reaction.
New catalyst systems are actively researched which can bring down the processing temperature. In one study 1-pentanol
is reacted with an iridium
dehydrogenation catalyst (Cp* stands for the pentamethylcyclopentadiene
ligand) and potassium tert-butoxide
as a base in p-xylene
. A small amount of the diene 1,7-octadiene
is required as a proton acceptor.
- A Review of Guerbet Chemistry Anthony J. O’Lenick, Jr. http://www.zenitech.com Link