The Guerbet reaction, named after Marcel Guerbet (1861–1938), is an organic reaction

Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis,...

 converting a primary aliphatic alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 into its β-alkylated dimer alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 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

N-Butanol

n-Butanol or n-butyl alcohol or normal butanol is a primary alcohol with a 4-carbon structure and the molecular formula C4H9OH. Its isomers include isobutanol, 2-butanol, and tert-butanol...

 to 2-ethyl-1-hexanol. The alcohols derived from this reaction are called Guerbet alcohols. Application of long-chained aliphatic alcohols gives access to surfactant

Surfactant

Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s.

The reaction requires alkali metal hydroxides or alkoxide

Alkoxide

An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...

s and hydrogenation

Hydrogenation

Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

 catalysts such as Raney Nickel

Raney nickel

Raney nickel is a solid catalyst composed of fine grains of a nickel-aluminium alloy, used in many industrial processes. It was developed in 1926 by American]] engineer Murray Raney as an alternative catalyst for the hydrogenation of vegetable oils in industrial processes...

 at higher temperature (220 °C) and pressure.

Reaction mechanism

The reaction mechanism

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...

 for this reaction is a four-step sequence. In the first step the alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 is oxidized to the aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

. These intermediates then react in an Aldol condensation

Aldol condensation

An aldol condensation is an organic reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone....

 to the vinyl aldehyde which the hydrogenation catalyst then reduces to the alcohol.
The Cannizzaro reaction

Cannizzaro reaction

The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical reaction that involves the base-induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position...

 is a competing reaction when two aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

 molecules react by disproportionation

Disproportionation

Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....

 to form the corresponding alcohol and carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

. Another side reaction is the Tishchenko reaction

Tishchenko reaction

The Tishchenko reaction is a chemical reaction that involves disproportionation of an aldehyde lacking a hydrogen atom in the alpha position in the presence of an alkoxide. The reaction product is an ester. Catalysts are aluminium alkoxides or sodium alkoxides...

.

Scope

New catalyst systems are actively researched which can bring down the processing temperature. In one study 1-pentanol

1-Pentanol

1-Pentanol, , is an alcohol with five carbon atoms and the molecular formula C5H12O. 1-Pentanol is a colorless liquid with an unpleasant aroma. There are 8 alcohols with this molecular formula . The ester formed from butanoic acid and 1-pentanol, pentyl butyrate, smells like apricot...

 is reacted with an iridium

Iridium

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...

 dehydrogenation catalyst (Cp* stands for the pentamethylcyclopentadiene

Pentamethylcyclopentadiene

1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diolefin with the formula C5Me5H . 1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand 1,2,3,4,5-pentamethylcyclopentadienyl, which is often denoted as Cp*...

 ligand) and potassium tert-butoxide

Potassium tert-butoxide

Potassium tert-butoxide is the chemical compound with the formula 3COK. This colourless solid is a strong base useful in organic synthesis. It exists as a tetrameric cubane-like cluster...

 as a base in p-xylene

P-Xylene

p-Xylene is an aromatic hydrocarbon, based on benzene with two methyl substituents. The “p” stands for para, identifying the location of the methyl groups as across from one another....

. A small amount of the diene

Diene

In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...

 1,7-octadiene is required as a proton acceptor.

See also

• Two related reactions in the production of butadiene are the Lebedev process and the Ostromisslenskii reaction.

External links

• A Review of Guerbet Chemistry Anthony J. O’Lenick, Jr. http://www.zenitech.com Link