Olefin metathesis of fatty acids and vegetable oils

Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis

Ruthenium-based Hoveyda-type olefin metathesis catalysts bearing novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed. They are characterized by exceptional stability toward decomposition through β-elimination and bimolecular pathways, thus enabling unprecedented efficiency in the cross-metathesis of seed oil-derived fatty acid esters with ethylene (ethenolysis). Catalyst loading as low as 100 ppb was applied to the ethenolysis of the model substrate methyl oleate, leading to a remarkable turnover number (TON) of 2.6 million, significantly higher than previously reported (TON 340 000 at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis of methyl esters derived from high oleic sunflower oil and rapeseed oil, readily available on an industrial scale, inexpensive, and renewable feedstocks, was for the first time effectively carried out with 0.5 ppm catalyst loading with TON as high as 964 000.

The Limited Palette for Photonic Block-Copolymer Materials: A Historical Problem or a Practical Limitation?

Block-copolymer self-assembly has proven to be an effective route for the fabrication of photonic films and, more recently, photonic pigments. However, despite extensive research on this topic over the past two decades, the palette of monomers and polymers employed to produce such structurally colored materials has remained surprisingly limited. In this Scientific Perspective, the commonly used block-copolymer systems reported in the literature are summarized (considering both linear and brush architectures) and their use is rationalized from the point of view of both their historical development and physicochemical constraints. Finally, the current challenges facing the field are discussed and promising new areas of research are highlighted to inspire the community to pursue new directions.

The Limited Palette for Photonic Block-Copolymer Materials: A Historical Problem or a Practical Limitation?

Block-copolymer self-assembly has proven to be an effective route for the fabrication of photonic films and, more recently, photonic pigments. However, despite extensive research on this topic over the past two decades, the palette of monomers and polymers employed to produce such structurally colored materials has remained surprisingly limited. In this Scientific Perspective, the commonly used block-copolymer systems reported in the literature are summarized (considering both linear and brush architectures) and their use is rationalized from the point of view of both their historical development and physicochemical constraints. Finally, the current challenges facing the field are discussed and promising new areas of research are highlighted to inspire the community to pursue new directions.

Comparison of the Spectroscopically Measured Catalyst Transformation and Electrochemical Properties of Grubbs' First- and Second-Generation Catalysts

According to UV-vis spectroscopy (0.10 mM, CH₂Cl₂ at 25 °C), the catalyst transformation (which could possibly include ligand dissociation with active catalyst formation, dimer formation, and decomposition) rate constants (k _obs) of Grubbs' first (1) and second (2) generation catalysts are 7.48 × 10^-5 and 1.52 × 10^-4 s^-1, respectively. From ³¹P NMR (0.1 M, CD₂Cl₂, at 25 °C), the catalyst transformation was 5.1% for 1 and 16.5% for 2 after 72 h. However, due to the larger concentrations of the NMR samples compared to the UV-vis samples, the extent of transformation did not correspond. The oxidation potential of the Ru^II/Ru^III couple of 2 (E°' = 27.5 mV at v = 200 mV s^-1) was considerably lower than that of 1 (E°' = 167 mV at v = 200 mV s^-1). In the case of 1, a second reduction peak appeared at slow scan rates. This may probably be ascribed to an electrochemically active compound that was formed from the intermediate cation 1 ^•+ and the subsequent reduction of the latter. The oxidation/reduction of 1 proceeds according to an E_rC_i electrochemical mechanism (E_r = electrochemically reversible step, C_i = chemically irreversible step), whereas 2 proceeds according to an E_rC_r electrochemical mechanism (E_r = electrochemically reversible step, C_i = chemically reversible step).

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

Oils and fats of vegetable and animal origin remain an important renewable feedstock for the chemical industry. Their industrial use has increased during the last 10 years from 31 to 51 million tonnes annually. Remarkable achievements made in the field of oleochemistry in this timeframe are summarized herein, including the reduction of fatty esters to ethers, the selective oxidation and oxidative cleavage of C-C double bonds, the synthesis of alkyl-branched fatty compounds, the isomerizing hydroformylation and alkoxycarbonylation, and olefin metathesis. The use of oleochemicals for the synthesis of a great variety of polymeric materials has increased tremendously, too. In addition to lipases and phospholipases, other enzymes have found their way into biocatalytic oleochemistry. Important achievements have also generated new oil qualities in existing crop plants or by using microorganisms optimized by metabolic engineering.

Ruthenium Olefin Metathesis Catalysts Featuring N-Heterocyclic Carbene Ligands Tagged with Isonicotinic and 4-(Dimethylamino)benzoic Acid Rests: Evaluation of a Modular Synthetic Strategy

A modular and flexible strategy towards the synthesis of N-heterocyclic carbene (NHC) ligands bearing Brønsted base tags has been proposed and then adopted in the preparation of two tagged NHC ligands bearing rests of isonicotinic and 4-(dimethylamino)benzoic acids. Such tagged NHC ligands represent an attractive starting point for the synthesis of olefin metathesis ruthenium catalysts tagged in non-dissociating ligands. The influence of the Brønsted basic tags on the activity of such obtained olefin metathesis catalysts has been studied.

Selective Production of Bio-Based Linear Alpha-Olefin from Wasted Fatty Alcohol on Al2O3 for Bio-Based Chemicals

The catalytic dehydration of a bio-based fatty alcohol was performed using Al2O3 prepared by solvothermal synthesis for selective production of long-chain linear-alpha-olefins (LAO). The effect of the synthesis temperature of alumina precursors on the dehydration of 1-octadecanol (C18H38O) was examined based on the textural properties and Lewis acid-base properties of the catalysts. Amorphous alumina synthesized at 325 °C showed the highest surface area (233.07 m2/g) and total pore volume (1.237 cm3/g) among the catalysts and the best dehydration results: 93% conversion, 62% selectivity of 1-octadecene (C18H36), and 89% LAO purity. This was attributed to the increased Al/O ratio and atomic concentration of surface O in alumina, which were important factors in the catalytic dehydration of 1-octadecanol through the synergistic catalysis of acid-base pairs. The produced bio-based LAO can be key intermediates for synthesis of oxo alcohols and poly-alpha-olefins, as alternatives to petroleum-based LAO to achieve carbon neutrality in chemical industry.

Ruthenium Complexes Featuring Unsymmetrical N-Heterocyclic Carbene Ligands-Useful Olefin Metathesis Catalysts for Special Tasks

This review describes a distinct class of ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbene (uNHC) ligands, from its historical beginning to the present state of the art. Thanks to advantageous traits, such as pronounced thermodynamic stability, chemical latency, outstanding selectivity, and compatibility with green solvents, these catalysts led to good results in a number of specialized metathesis transformations. Therefore, while being a niche, the uNHC complexes can potentially be implemented in a number of industrial processes, such as valorization of Fischer-Tropsch olefin fractions, ethenolysis of renewable products, and modern pharmaceutical production.

High molar mass poly(ricinoleic acid) via entropy-driven ring-opening metathesis polymerization

High molar mass poly(ricinoleic acid) was synthesized via entropy-driven ring-opening metathesis polymerization of mono-, di- and mixed macrolactones of ricinoleic acid using a Grubbs second-generation catalyst and fully characterized.

Synthesis and Characterization of Partially Renewable Oleic Acid-Based Ionomers for Proton Exchange Membranes

The future availability of synthetic polymers is compromised due to the continuous depletion of fossil reserves; thus, the quest for sustainable and eco-friendly specialty polymers is of the utmost importance to ensure our lifestyle. In this regard, this study reports on the use of oleic acid as a renewable source to develop new ionomers intended for proton exchange membranes. Firstly, the cross-metathesis of oleic acid was conducted to yield a renewable and unsaturated long-chain aliphatic dicarboxylic acid, which was further subjected to polycondensation reactions with two aromatic diamines, 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline and 4,4′-diamino-2,2′-stilbenedisulfonic acid, as comonomers for the synthesis of a series of partially renewable aromatic-aliphatic polyamides with an increasing degree of sulfonation (DS). The polymer chemical structures were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (¹H, ¹³C, and ¹⁹F NMR) spectroscopy, which revealed that the DS was effectively tailored by adjusting the feed molar ratio of the diamines. Next, we performed a study involving the ion exchange capacity, the water uptake, and the proton conductivity in membranes prepared from these partially renewable long-chain polyamides, along with a thorough characterization of the thermomechanical and physical properties. The highest value of the proton conductivity determined by electrochemical impedance spectroscopy (EIS) was found to be 1.55 mS cm⁻¹ at 30 °C after activation of the polymer membrane.