This extra methylene group allows Guerbet alcohols to have higher molecular weights and better solubility properties than normal alcohols of the same carbon number.
Discovery and Naming
The first Guerbet Alcohol, 2-hexyldecanol, was accidentally discovered in 1897 by French chemist Charles Moureu while experimenting with mineral oil refining processes. He named these "doubled alcohols" after French chemist Marcellin Berthelot, who was part of the Berthelot–Guerbet reaction that produces primary alcohols from alkenes. Despite their discovery over a century ago, industrial applications of it have only emerged more recently as chemists further explored their unique properties.
Structure and Physical Properties
They have the general formula CnH2n+1(CH2)2OH. Their structure consists of a linear alkyl chain with a primary hydroxyl group attached to the second carbon. This makes them branched at the beta position. Due to the extra methylene group, they have higher molecular weights than traditional n-alcohols.
For example, 1-octanol (C8H17OH) has a molecular weight of 130.23 g/mol, while the corresponding Guerbet alcohol 2-decyl tetrahydroethanol (C10H21(CH2)2OH) has a molecular weight of 158.27 g/mol. The additional carbon also improves the solubility, hydrotropy, and oil solubilizing properties of it compared to straight-chain alcohols. Their higher molecular weights also result in higher melting points and boiling points.
Applications
Due to their improved properties over normal alcohols, they have found several important applications:
Surfactants: With better solubilizing abilities, they act as excellent solubilizers and detergents in various formulations. The C10-C14 are commonly used as feedstock for producing nonionic surfactants used in detergents, cosmetics, and agrochemicals.
Lubricant Additives: Certain long-chain alcohols function as outstanding lubricant additives. As multifunctional extreme pressure and antiwear additives, they aid oil formulation, protect metal surfaces, and lower friction in lubricating oils.
Plasticizers: As high-boiling, low-volatility plasticizers, Guerbet like 2-heptyltriacontanol are gaining favor in PVC applications such as medical tubing and wire insulation where safety is critical. They provide flexibility and softness without the toxicity issues of phthalates.
Emollients: In cosmetic formulations, medium-chain alcohols between C12-18, such as behenyl alcohol, serve as excellent moisturizing emollients and thickeners. They leave a soft, lubricious feel to the skin without greasiness.
Biofuels: Long-chain alcohols like 2-tetradecanol have higher energy density and better low-temperature properties than ethanol, rendering them promising renewable biofuel candidates. Research is exploring their microbial production from biomass.
Production Methods
There are two principal methods for producing them:
1. Guerbet Reaction: As the namesake reaction that created the first Guerbet alcohol in 1897, this catalyzed reaction dimerizes normal alkenes in the presence of an acid or base catalyst to form the Guerbet dimer alcohol.
2. Hydroformylation & Hydroboration-Oxidation: In this microbial or chemical route, normal alkenes undergo initial hydroformylation with syngas to form aldehydes, followed by stereo-selective hydroboration and subsequent oxidation to the products.
Both routes allow production of it from inexpensive alkene feedstock. Continuous development aims to drive down costs and improve atom efficiency of these multi-step syntheses. Biocatalytic methods also emerging as promising greener options.
Since their discovery over a century ago, Guerbet alcohols have emerged as commercially important linear alcohols distinct from traditional n-alcohols. Their inherent physical properties confer advantages in numerous applications as surfactants, lubricants, plasticizers, and renewable fuels. Continued research further optimizing reliable production methods will broaden industrial utilization of these unique alcohols. Looking ahead, their promising features indicate Guerbet alcohols have strong potential as sustainable alternatives in various materials and formulations.
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