Guerbet reaction

Higher molecular weight branched alcohols are produced by condensation of lower alcohols ia the Guerbet reaction. 

The Guerbet reaction can be used to obtain higher alcohols 2-propyl-1-heptanol [10042-59-8] from 1-pentanol condensation and 6-methyl-4-nonanol from 2-pentanol (80—83). Condensations with alkah phenolates as the base, instead of copper catalyst, produce lower amounts of carboxyhc acids and requke lower reaction temperatures (82,83). The crossed Guerbet reaction of 1-pentanol with methanol in the presence of sodium methoxide catalyst afforded 2-heptanol in selectivities of about 75% (84). 

The Guerbet reaction (386—389) involving condensation of ethanol in the presence of sodium ethoxide, catalyzed by potassium hydroxide and boric anhydride (390,391) or alkaline phosphates (392), gives / -butanol [71-36-3]. ... 

Guerbet alcohols cosmetic applications, 2 21 in cosmetic molded sticks, 7 840t major producers, 2 27t Guerbet process, 2 27t, 43 Guerbet reaction, 10 558 Guest-host LCDs, 15 115 Guest-host mode LCD systems, 9 339 Guggenheim process, for sodium nitrate, 22 846-848... 

The Guerbet reaction is an important industrial process for increasing the carbon numbers of alcohols. Thus, a primary or secondary alcohol reacts with itself or another alcohol to produce a higher alcohol (Scheme 23). Alkaline earth metal oxides have been used as catalysts for the condensation of alcohols. Ueda et al. (158,159) reported the condensation of methanol with other primary or secondary alcohols having a methyl or methylene group at the )S-position they used MgO, CaO, and ZnO as catalysts. The reactions were performed with gas-phase reactants at 635 K only MgO was found to be both active and selective (>80%). 

Index Entries Biorefinery, alcohols Guerbet reaction methanol-ethanol mixtures catalyst. 

The formation of higher alcohols directly in one step from smaller alcohols via the Guerbet reaction was investigated by passing the alcohol... 

Glycols, see Dihydroxy compounds Glyoxals, see a-(Ceto aldehydes Grignard reagents, see Organomag-nesium compounds Guareschi reaction, 434 Guerbet reaction, 181... 

The conversion of aldehydes into carboxylic acids as a result of disproportionation occurs in the Cannizzaro and Guerbet reactions. The Cannizzaro reaction takes place when aromatic aldehydes are treated with alkali hydroxides and results in the formation of carboxylic acids and the corresponding alcohols. Yields of the acids can therefore be 50% at a maximum. The reaction is catalyzed by silver [363] and silver oxide [362], which is sometimes generated in situ from silver nitrate [364] see equation 357). 

The Guerbet reaction is a complex combination of oxidation of a primary alcohol to an aldehyde, aldol condensation followed by dehydration, hydrogenation of the a,p-unsaturated aldehyde to a saturated alcohol, and oxidation of the aldehyde to an acid. The reaction is catalyzed by sodium and copper bronze and is carried out by heating the mixture in an autoclave at 270-300 °C and 50-60 atm for 6-10 h (equation 352). 

Because the purpose of the reaction is to prepare a branched saturated alcohol, the Guerbet reaction cannot be considered a method of oxidation [346]. 

Guerbet reaction. Condensation of alcohols at high temperature and pressure in the presence of sodium alkoxide or copper by a dehydrogenation, aldol condensation, and hydrogenation sequence. 

Keywords Hydrogen transfer Alkylation Alcohol Metal halide Methanol Guerbet reaction... 

Some of the most commonly reported C-alkylation methods involving the transition-metal-catalyzed transfer hydrogenation of alcohols can be described as follows (1) the a-alkylation of ketones and carbonyl compounds (2) alcohol-alcohol coupling reactions to afford ketones and (3) P-alkylation by alcohol dimerization, which is also referred to as a Guerbet reaction. 

The third of the reactions described above (i.e., the Guerbet reaction of primary alcohols) allows for the self-condensation/dimerization of alcohols to give the... 

Scheme 5 Metal-catalyzed ( -alkylation by alcohol dimerization (Guerbet reaction)...

Alcohol-alcohol coupling reactions leading to the formation of P-alkylated products are known as the Guerbet reaction, and numerous examples of this reaction have been reported in the hterature [179-182]. The Guerbet reaction has been used extensively to afford long-chain higher alcohols from readily accessible short-chain alcohols. 

In an extension of the Guerbet reaction, Obora and co-workers reported the development of an Ir-catalyzed reaction for the conversion of arylalkanols to a,(a-diarylalkanes [187], which have been widely used as chromophores and functional fluorescent materials [188-191]. 

In a typical example of this transformation, 2-phenylethanol (2.0 mmol) was treated with (-BuOK (40 mol%) in p-xylene in the presence of [Cp IrCl2]2 (1 mol%) at 120 °C to give 1,3-diphenylpropane in 81 % yield with a small amoimt of toluene (5 %) as a by-product (Scheme 35). This reaction proceeded via the formation of the dimerized p-alkylation alcohol (Guerbet reaction product) as an intermediate. The resulting alcohol was subsequently dehydrogenated by the iridium complex to afford an aldehyde, followed by sequential decarbonylation and... 

Scheme 33 Ir-catalyzed Guerbet reaction involving the cross-aUsylation of two alcohols...

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