Neue Synthesen mit Ölen und Fetten als nachwachsende Rohstoffe für die chemische Industrie

An updated review of fatty acid residue-tethered heterocyclic compounds: synthetic strategies and biological significance

Heterocyclic compounds have been featured as the key building blocks for the development of biologically active molecules. In addition to being derived from renewable raw materials, fatty acids possess a variety of biological properties. The two bioactive ingredients are being combined by many researchers to produce hybrid molecules that have a number of desirable properties. Biological activities and significance of heterocyclic derivatives of fatty acids have been demonstrated in a new class of heterocyclic compounds called heterocyclic fatty acid hybrid derivatives. The significance of heterocyclic-fatty acid hybrid derivatives has been emphasized in numerous research articles over the past few years. In this review, we emphasize the development of synthetic methods and their biological evaluation for heterocyclic fatty acid derivatives. These reports, combined with the upcoming compilation, are expected to serve as comprehensive foundations and references for synthetic, preparative, and applicable methods in medicinal chemistry.

General, Metal-free Synthesis of Carbon Nanofiber Assemblies from Plant Oils

We designed a metal-free synthesis of carbon nanofiber based on ketene chemistry using phosphorus pentoxide (P2 O5 ) and vegetable oil. Based on the characterization of intermediates, P2 O5 -oil reaction yielded most possibly alkylketenes, which polymerized into poly(ketene) with abundant enol groups. The enol groups further reacted with P2 O5 , forcing the poly(ketene) to assemble into a nano-sized preassembly structure. Moderate heating transforms these structures into carbonaceaus nanofibers. This approach is applicable to other chemicals with similar structure to vegetable oil. The carbon nanofibers with P-O-C functionalization show relatively high graphitization degree and promising textural properties. The C-O-P environment accounts for 66 at % of the total P and creates a superior thermal stability. As a model application, a CDI system built of a carbon-nanofiber-based electrode countered by an activated carbon-based electrode exhibited exceptional performance.

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.

The Oxidative Cleavage of 9,10-Dihydroxystearic Triglyceride with Oxygen and Cu Oxide-based Heterogeneous Catalysts

This paper deals with a new heterogeneous catalyst for the second step in the two-step oxidative cleavage of unsaturated fatty acids triglycerides derived from vegetable oil, a reaction aimed at the synthesis of azelaic and pelargonic acids. The former compound is a bio-monomer for the synthesis of polyesters; the latter, after esterification, is used in cosmetics and agrochemicals. The reaction studied offers an alternative to the currently used ozonization process, which has severe drawbacks in terms of safety and energy consumption. The cleavage was carried out with oxygen, starting from the glycol (dihydroxystearic acid triglyceride), the latter obtained by the dihydroxylation of oleic acid triglyceride. The catalysts used were based on Cu²⁺ , in the form of either an alumina-supported oxide or a mixed, spinel-type oxide. The CuO/Al₂ O₃ catalyst could be recovered, regenerated, and recycled, yielding promising results for further industrial exploitation.

Biobased Aldehydes from Fatty Epoxides through Thermal Cleavage of β-Hydroxy Hydroperoxides*

The ring-opening of epoxidized methyl oleate by aqueous H₂ O₂ has been studied using tungsten and molybdenum catalysts to form the corresponding fatty β-hydroxy hydroperoxides. It was found that tungstic acid and phosphotungstic acid gave the highest selectivities (92-93 %) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty β-hydroxy hydroperoxides with 30-80 % isolated yields (8 examples). These species were fully characterized by ¹ H and ¹³ C NMR spectroscopy and HPLC-HRMS, and their stability was studied by differential scanning calorimetry. The thermal cleavage of the β-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68 % GC yield, and nonanal and methyl 9-oxononanoate were isolated with 57 and 55 % yield, respectively. Advantageously, the overall process does not require large excess of H₂ O₂ and only generates water as a byproduct.

Discovery and Engineering of a Novel Baeyer-Villiger Monooxygenase with High Normal Regioselectivity

Baeyer-Villiger monooxygenases (BVMOs) are remarkable biocatalysts for the Baeyer-Villiger oxidation of ketones to generate esters or lactones. The regioselectivity of BVMOs is essential for determining the ratio of the two regioisomeric products ("normal" and "abnormal") when catalyzing asymmetric ketone substrates. Starting from a known normal-preferring BVMO sequence from Pseudomonas putida KT2440 (PpBVMO), a novel BVMO from Gordonia sihwensis (GsBVMO) with higher normal regioselectivity (up to 97/3) was identified. Furthermore, protein engineering increased the specificity constant (k_cat /K_M ) 8.9-fold to 484 s^-1  mM^-1 for 10-ketostearic acid derived from oleic acid. Consequently, by using the variant GsBVMO_C308L as an efficient biocatalyst, 10-ketostearic acid was efficiently transformed into 9-(nonanoyloxy)nonanoic acid, with a space-time yield of 60.5 g L^-1  d^-1 . This study showed that the mutant with higher regioselectivity and catalytic efficiency could be applied to prepare medium-chain ω-hydroxy fatty acids through biotransformation of long-chain aliphatic keto acids derived from renewable plant oils.

Properties and degradation of castor oil-based fluoridated biopolyurethanes with different lengths of fluorinated segments

To develop a durable, biodegradable polymer, this study successfully synthesized a castor-oil-based prepolymer by using methylene diphenyl diisocyanate as a hard segment, polycaprolactone as a soft segment, and castor oil as a functional monomer. We added perfluorinated alkyl segments with varying chain lengths into the castor-oil-based polymer to synthesize castor-oil-based fluoridated biopolyurethanes (FCOPUs) with different fluorinated segment lengths. The castor-oil-based polyurethanes with different fluorinated segment lengths had similar molecular weights, which enabled accurate analysis of the effect of the lengths of fluorinated segments on FCOPUs. Nuclear magnetic resonance (NMR) was used to perform 1H NMR, 19F NMR, 19F-19F COSY, 1H-19F COSY, and HMBC analyses on the FCOPU structures. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy curve fitting verified the interaction between C-F⋯H-N and C-F⋯C[double bond, length as m-dash]O. This interaction increased as the fluorinated segments became longer. Regarding the thermal properties of the FCOPUs, the thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis results revealed that long fluorinated segments were associated with increased thermal stability in the FCOPUs. The atomic force microscopy and tensile strength test suggested that long fluorinated segments contained in the FCOPUs increased the degree of phase separation and tensile strength in FCOPUs. Finally, we dipped the FCOPUs in a 3 wt% NaOH solution, calculated the weight loss of the FCOPUs, and observed their surface structure by using scanning electron microscopy.

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis

The use of triglycerides as an important class of biomass is an effective strategy to realize a more sustainable society. Herein, three heterogeneous catalytic methods are reported for the selective one-pot transformation of triglycerides into value-added chemicals: i) the reductive amination of triglycerides into fatty amines with aqueous NH₃ under H₂ promoted by ZrO₂ -supported Pt clusters; ii) the amidation of triglycerides under gaseous NH₃ catalyzed by high-silica H-beta (Hβ) zeolite at 180 °C; iii) the Hβ-promoted synthesis of nitriles from triglycerides and gaseous NH₃ at 220 °C. These methods are widely applicable to the transformation of various triglycerides (C₄ -C₁₈ skeletons) into the corresponding amines, amides, and nitriles.

Polymers Based on Cyclic Carbonates as Trait d'Union Between Polymer Chemistry and Sustainable CO2 Utilization

Given the large amount of anthropogenic CO₂ emissions, it is advantageous to use CO₂ as feedstock for the fabrication of everyday products, such as fuels and materials. An attractive way to use CO₂ in the synthesis of polymers is by the formation of five-membered cyclic organic carbonate monomers (5CCs). The sustainability of this synthetic approach is increased by using scaffolds prepared from renewable resources. Indeed, recent years have seen the rise of various types of carbonate syntheses and applications. 5CC monomers are often polymerized with diamines to yield polyhydroxyurethanes (PHU). Foams are developed from this type of polymers; moreover, the additional hydroxyl groups in PHU, absent in classical polyurethanes, lead to coatings with excellent adhesive properties. Furthermore, carbonate groups in polymers offer the possibility of post-functionalization, such as curing reactions under mild conditions. Finally, the polarity of carbonate groups is remarkably high, so polymers with carbonates side-chains can be used as polymer electrolytes in batteries or as conductive membranes. The target of this Review is to highlight the multiple opportunities offered by polymers prepared from and/or containing 5CCs. Firstly, the preparation of several classes of 5CCs is discussed with special focus on the sustainability of the synthetic routes. Thereafter, specific classes of polymers are discussed for which the use and/or presence of carbonate moieties is crucial to impart the targeted properties (foams, adhesives, polymers for energy applications, and other functional materials).

Adsorption of oleic acid dissolved in isopropanol–water mixtures on hydrotalcite

Fatty acids are an interesting class of educts for chemical processes as they are available from renewable resources. For obtaining high-purity fatty acids, efficient separation techniques are needed. An interesting option is adsorption. In the present work, therefore, the adsorption of oleic acid on hydrotalcite, a readily available adsorbent, is studied. The focus is on studying the influence of the composition of the solvent on the adsorption. Adsorption isotherms are reported for oleic acid in pure isopropanol and mixtures of isopropanol and water at temperatures between 278 and 308 K. Even though the solubility of oleic acid in isopropanol is higher than in mixtures of isopropanol and water, the highest capacity of the adsorber is found for pure isopropanol. The reasons are discussed. No significant influence of the temperature was observed.

Remarkably Efficient Microwave-Assisted Cross-Metathesis of Lipids under Solvent-Free Conditions

Catalytic transformation of renewable feedstocks into fine chemicals is in high demands and olefin metathesis is a sophisticated tool for biomass conversion. Nevertheless, the large-scale viability of such processes depends on the conversion efficiency, energy efficiency, catalytic activity, selective conversion into desired products, and environmental footprint of the process. Therefore, conversions of renewables by using simple, swift, and efficient methods are desirable. A microwave-assisted ethenolysis and alkenolysis (using 1,5-hexadiene) of canola oil and methyl esters derived from canola oil (COME) and waste/recycled cooking oil (WOME) was carried out by using ruthenium-based catalytic systems. A systematic study using 1st and 2nd generation Grubbs and Hoveyda-Grubbs catalysts was carried out. Among all ruthenium catalysts, 2nd generation Hoveyda-Grubbs catalyst was found to be highly active in the range of 0.002-0.1 mol % loading. The conversions proved to be rapid providing unprecedented turnover frequencies (TOFs). High TOFs were achieved for ethenolysis of COME (21 450 min^-1 ), direct ethenolysis of canola oil (19 110 min^-1 ), for WOME (15 840 min^-1 ) and for cross-metathesis of 1,5-hexadiene with COME (10 920 min^-1 ). The ethenolysis of commercial methyl oleate was also performed with a TOF of 8000 min^-1 under microwave conditions.

Organocatalyzed Synthesis of Oleochemical Carbonates from CO2 and Renewables

Bifunctional phosphorus-based organocatalysts proved to be highly efficient for the atom-economic reaction of CO₂ and epoxidized oleochemicals. Notably, those products are obtained from CO₂ and renewable feedstocks only. Structure-activity relationships have been deduced from a screening of 22 organocatalysts in a test reaction. Bifunctional catalysts based on a phosphonium salt bearing a simple phenolic moiety proved to be extraordinarily active under comparatively mild and solvent-free reaction conditions. In the presence of the most active organocatalyst 12 oleochemical carbonates were isolated in excellent yields up to 99 %. This organocatalyzed reaction represents an excellent example for the realization of the 12 Principles of Green Chemistry as well as the 12 Principles of CO₂ Chemistry.

Shuttle Catalysis-New Strategies in Organic Synthesis

Shuttle catalysis has recently emerged as a powerful new concept that provides a platform for performing both functionalization and defunctionalization reactions. In this concept article, applications of shuttle catalysis as a novel strategy in organic synthesis are discussed. This includes using forward shuttle catalysis reactions for challenging bond-forming processes that avoid the use of hazardous chemicals. Shuttle catalysis also facilitates the transfer of reactive functionality as a route to procure a broad range of compounds using one simple procedure. Reverse shuttle catalysis reactions are also discussed as a method for the valorization of biomass and waste materials. Another area of interest, shuttle-catalysis-assisted reactions, wherein the transfer of a small molecule is utilized in a catalytic cycle, is also described. Possible future directions in this exciting new field are also suggested.

Cross-Metathesis of Brønsted Acid Masked Alkenylamines with Acrylates for the Synthesis of Polyamide Monomers

Ruthenium-alkylidene-catalyzed cross-metathesis of a range of homologous alkenylamine salts provides expedient and high-yielding routes to commercially valuable polyamide monomers using a single catalyst, telescopic workup, and mild experimental conditions.

Xylochemistry--Making Natural Products Entirely from Wood

The first total synthesis of the dimeric berberine alkaloid ilicifoline (ilicifoline B) is reported. Its carbon skeleton is constructed from ferulic acid, veratrole, and methanol. The synthesis reported herein employs starting materials solely derived from wood. The natural product is thus constructed entirely from renewable resources. The same strategy is applied to a formal total synthesis of morphinan alkaloids. The use of wood-derived building blocks (xylochemicals) instead of the conventional petrochemicals represents a sustainable alternative to classical synthetic approaches.

Thiazolylidene-catalyzed cleavage of methyl oleate-derived α-hydroxy ketone to the corresponding free aldehydes

The thiazolylidene-catalyzed cleavage of the α-hydroxy ketone derived from methyl oleate gave the corresponding aldehydes under nonoxidative conditions through a retro-benzoin process. The aldehydes produced are in equilibrium with their corresponding acyloins. To illustrate the synthetic utility of this protocol, the aldehydes were recovered by distillation.

Electrochemistry for biofuel generation: transformation of fatty acids and triglycerides to diesel-like olefin/ether mixtures and olefins

Electroorganic synthesis can be exploited for the production of biofuels from fatty acids and triglycerides. With Coulomb efficiencies (CE) of up to 50 %, the electrochemical decarboxylation of fatty acids in methanolic and ethanolic solutions leads to the formation of diesel-like olefin/ether mixtures. Triglycerides can be directly converted in aqueous solutions by using sonoelectrochemistry, with olefins as the main products (with a CE of more than 20 %). The latter reaction, however, is terminated at around 50 % substrate conversion by the produced side-product glycerol. An energy analysis shows that the electrochemical olefin synthesis can be an energetically competitive, sustainable, and--in comparison with established processes--economically feasible alternative for the exploitation of fats and oils for biofuel production.

Synthesis of ethers by GaBr3 -catalyzed reduction of carboxylic acid esters and lactones by siloxanes

Ethers were synthesized by reduction of the respective esters catalyzed by gallium bromide (GaBr3 ) and using siloxanes, preferentially 1,1,3,3-tetramethyldisiloxane, as reductant. Methyl oleate, triglycerides, that is, tributyrine and glyceryl triundec-10-enoate as well as γ- and δ-lactones were converted into the respective ethers in high to moderate yields. γ-Lactones were reduced with high selectivity in the presence of a methyl ester functionality. The reduction has been carried out at room temperature or moderately elevated temperature of up to 60 °C using stoichiometric amounts of the reductant and 0.005-0.01 equiv of GaBr3 as catalyst per ester functionality without any solvent added. After a reaction time of 1-4 h the conversion of the substrate was 100 %. The product was separated from polymeric siloxanes formed as coupled product by simple distillation.

Recent advances in vegetable oil-based polyurethanes

Polyurethanes are among the most versatile polymers because of the wide range of monomers, particularly diols or polyols, that can be utilized in their synthesis. This Review focuses on the most recent advances made in the production of polyurethane materials from vegetable oils. Over the past several years, increasing attention has been given to the use of vegetable oils as feedstocks for polymeric materials, because they tend to be very inexpensive and available in large quantities. Using various procedures, a very broad range of polyols or diols and in some cases, poly- or diisocyanates, can be obtained from vegetable oils. The wide range of vegetable oil-based monomers leads to a wide variety of polyurethane materials, from flexible foams to ductile and rigid plastics. The thermal and mechanical properties of these vegetable oil-based polyurethanes are often comparable to or even better than those prepared from petroleum and are suitable for applications in various industries.

Improving sustainability in ene-yne cross-metathesis for transformation of unsaturated fatty esters

Ruthenium-catalyzed ene-yne cross-metathesis is performed with stoichiometric proportions of terminal olefins and alkynes. This is made possible by the continuous addition of the alkyne to the reaction mixture. The protocol allows the ene-yne cross-metathesis reaction to be carried out with long-chain terminal olefins and in a one-pot fashion with internal olefins after shortening by ethenolysis. The efficient conversion of renewable unsaturated fatty esters from bioresources into valuable conjugated 1,3-dienes of interest for further transformations is performed using this technique under mild conditions in dimethyl carbonate; an ecofriendly solvent.

A design-of-experiments approach for the optimization and understanding of the cross-metathesis reaction of methyl ricinoleate with methyl acrylate

A design-of-experiments approach for the investigation of the cross-metathesis of methyl ricinoleate with methyl acrylate is described. Two second-generation metathesis initiators were studied using different reaction conditions, revealing optimal reaction conditions for each catalyst. Interestingly, the two catalysts showed completely different temperature response profiles. As a result of these investigations, suitable reaction conditions for the sustainable production of two value-added chemical intermediates were derived. Moreover, the design-of-experiments approach provided valuable information for a thorough understanding of catalytic reactions that would be more difficult to obtain by classic approaches.