This critical review examines transition metal-catalyzed decarboxylative couplings that have emerged within recent years as a powerful strategy to form carbon–carbon or carbon–heteroatom bonds starting from carboxylic acids. In these reactions, C–C bonds to carboxylate groups are cleaved, and in their place, new carbon–carbon bonds are formed. Decarboxylative cross-couplings constitute advantageous alternatives to traditional cross-coupling or addition reactions involving preformed organometallic reagents. Decarboxylative reaction variants are also known for Heck reactions, direct arylation processes, and carbon–heteroatom bond forming reactions.

Decarboxylative coupling reactions: a modern strategy for C–C-bond formation

A novel method for production of diesel-like hydrocarbons via catalytic deoxygenation of fatty acid is discussed. The model compound stearic acid is deoxygenated to heptadecane, originating from the stearic acid alkyl chain. The deoxygenation reaction is carried out in a semibatch reactor under constant temperature and pressure, 300 °C and 6 bar, respectively. A thorough catalyst screening was performed to obtain the most promising metal and support combination. The catalysts were characterized by N2-physisorption, CO-chemisorption, and temperature-programmed desorption of hydrogen. A highly active and selective in the deoxygenation reaction of stearic acid carbon supported palladium catalyst converted stearic acid completely with >98% selectivity toward deoxygenated C17 products.

Heterogeneous Catalytic Deoxygenation of Stearic Acid for Production of Biodiesel

Considerable worldwide interest exists in discovering renewable energy sources that can substitute for fossil fuels. Lignocellulosic biomass, the most abundant and inexpensive renewable feedstock on the planet, has a great potential for sustainable production of fuels, chemicals, and carbon-based materials. Fast pyrolysis integrated with hydrotreating, one of the simplest, most cost-effective, and most efficient processes to convert lignocellulosic biomass to liquid hydrocarbon fuels for transportation, has attracted significant attention in recent decades. However, effective hydrotreating of pyrolysis bio-oil presents a daunting challenge to the commercialization of biomass conversion via pyrolysis-hydrotreating. Specifically, the development of active, selective, and stable hydrotreating catalysts is problematic due to the poor quality of current pyrolysis bio-oil feedstock (i.e., high oxygen content, molecular complexity, coking propensity, and corrosiveness). Significant research has been conducted to...

Recent Advances in Hydrotreating of Pyrolysis Bio-Oil and Its Oxygen-Containing Model Compounds

This review deals with the mechanism that is arbitrarily called below the Mars and Van Krevelen (MvK) mechanism. The characteristic feature of this mechanism is that some products of the reaction leave the solid catalysts’ surface with one or more constituents of the catalysts’ lattice. First in this review, the position of this mechanism amongst other ways of catalytic activation will be defined. Then, the experimental evidence for this mechanism will be presented. Some less common reactions running with this mechanism will be discussed in more detail, among them the deoxygenation of nitrocompounds and carboxylic acids. The participation of the lattice components (O, S, Cl, H) in the formation of products leads to a relation of the catalytic activity with the thermodynamic parameters characterizing the catalysts lattice. A proper use of such quantified relation will be also discussed.

The universal character of the Mars and Van Krevelen mechanism

Recent advances in heterogeneous catalysts for bio-oil upgrading via “ex situ catalytic fast pyrolysis”: catalyst development through the study of model compounds

Reactions of Carboxylic Acids on Oxides: 1. Selective Hydrogenation of Acetic Acid to Acetaldehyde

Reactions of Carboxylic Acids on Oxides: 2. Bimolecular Reaction of Aliphatic Acids to Ketones

Four carboxylic acids with a number of α-hydrogen atoms ranging from three to zero were tested in the selective hydrogenation to aldehyde. The acids used were acetic, propanoic, isobutyric, and pivalic acid. The oxides of iron, vanadium, zirconium, and titanium were used as catalysts. It was found that by decreasing the number of α-hydrogen atoms the selectivity to the aldehyde increased, while the formation of the main by-product, ketone, was suppressed. It is suggested that this is due to the fact that the ketonisation proceeds via a ketene-like intermediate, the formation of which needs the presence of α-hydrogen. Furthermore, the reactions to aldehyde and ketone seem to be in competition with each other.

J.A.Z. Pieterse

Papers

Reactions of Carboxylic Acids on Oxides: 1. Selective Hydrogenation of Acetic Acid to Acetaldehyde

Reactions of Carboxylic Acids on Oxides: 2. Bimolecular Reaction of Aliphatic Acids to Ketones

The formation of ketones and aldehydes from carboxylic acids, structure-activity relationship for two competitive reactions