Lehrstuhl Technische Chemie

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Towards continuous Rh-hydroformylation of long chain alkenes: handling methodology for the long-term stability of Biphephos in a continuous reactor with an attached membrane separation unit
(2024-12-04) Söderholm, Viktor; Stajer, Marc; Savage, Carolin; Splittgerber, Leon; Vogt, Dieter
Diphosphites like Biphephos are known for their combination of high activity and high linear selectivity in the Rh-catalyzed hydroformylation of terminal alkenes. However, like most phosphite-type ligands, Biphephos is prone to hydrolysis under acidic conditions and oxidation in the presence of oxygen, resulting in detrimental catalyst performance loss. In this work, we identified practical aspects that safeguard the long-term stability of Biphephos during the Rh-catalyzed hydroformylation of alkenes. Furthermore, different additives (amines and one epoxide) were explored as stabilizers for Biphephos. The Biphephos/Rh/stabilizer system was first extensively investigated via31P-NMR, followed by batch autoclave experiments (100 ml reactors), and finally applied in an upscaled reactor (300 ml) with an attached nanofiltration membrane unit for catalyst retention. With cyclohexene oxide (CHO) as a stabilizer for the ligand, stable operation with high catalyst retention (95%) was achieved for over 100 h at high product selectivity (l/b = 78).
Synthesis and catalytic testing of the first hydrophilic derivative of Shvo's catalyst
(2024-11-26) Diekamp, Justus; Schmidt, Annika; Holstein, Julian J.; Strohmann, Carsten; Seidensticker, Thomas
Although commonly applied in various reactions, Shvo's catalyst has not been modified towards solubility in highly polar solvents until now. Here, we report the straightforward synthesis of a disulfonate derivative of the complex, which allows to (transfer) (de-)hydrogenate aldehydes and ketones in aqueous solutions. A proof of principle for the recycling of the catalyst is also provided.
The effect of polyunsaturation
(2024-09-12) Roth, Thomas Friedrich Hubertus; Spiekermann, Maximilian Lukas; Lütkenhaus, David; Niefer, Fabian; Vogt, Dieter; Seidensticker, Thomas
Although the hydroformylation of vegetable oil-derived oleochemicals, such as methyl oleate, is a highly demanded reaction and has been intensively studied, little is known about the influence of naturally occurring polyunsaturated (PU) components and their effect on the homogeneous rhodium catalyst. This is now examined in detail in the presented work by conducting systematic perturbation experiments. For the first time, it can be verified that the isomerisation of double bonds in polyunsaturated oleochemicals generates conjugated double bond systems that form stable η3-Rh allyl species and thus temporarily inhibit the catalyst. However, based on these findings, hydroformylation activity can be significantly increased by selective hydrogenation of PU to monounsaturated components. In the case of sunflower methyl ester, the turnover frequency multiplied by a factor of 8 and reached 3201 h−1, the highest rate reported in the context of methyl oleate hydroformylation. These effects were shown for both phosphine and phosphite ligands under both mono- and biphasic conditions and for methyl esters with different PU content, stressing the magnitude of this effect. This work makes it possible to support long-observed phenomena with the underlying mechanism scientifically. This lays the scientific basis for efficiently converting oleochemicals into valuable intermediates through hydroformylation for an increased share of renewable carbon in the chemical value chain.
Catalytic processes for the selective hydrogenation of fats and oils
(2024-06-26) Spiekermann, Maximilian L.; Seidensticker, Thomas
The selective hydrogenation of polyunsaturated fatty acids (PUFAs) and their derivatives to their monounsaturated counterparts is a critical catalytic step in various disciplines, such as biofuels and food chemistry. Furthermore, the necessary transformation of the chemical industry towards sustainability and circularity demands the development of new platform chemicals from renewable resources. The selective hydrogenation of PUFAs offers the flexibility to use a variety of commodity feedstocks in existing processes in the chemical value chain; this is indispensable for staying competitive and in shaping a sustainable future-proof chemical industry. The naturally occurring differences in the composition of vegetable fats and oils, especially the degree of saturation of the carbon chain, necessitate a preparation step to provide a standardized feedstock for existing chemical processes. Since many chemical reactions towards valuable intermediates start from mono-unsaturated substrates, selectivity plays a crucial role in hydrogenation. Furthermore, standardization alleviates the need to grow speciality monocultures or to utilize edible substrates, to further reducing the negative impact on society and the environment. In this critical review, all the relevant and pioneering catalytic transformations throughout history up to this time and place are discussed and evaluated towards their applicability and usefulness for the provision of renewable-based resources for the chemical industry, with particular emphasis on the selectivity towards mono-unsaturated substrates.
Primary amines from alkenes and carbonyl compounds
(2024-04-17) Hares, Kevin; Wegener, Hannes W.; Roth, Thomas F. H.; Reichert, René; Vogt, Dieter; Seidensticker, Thomas
The efficient production of aliphatic primary amines is still a major challenge despite their production on a large scale. Particularly when considering the overall production route starting from alkenes, current strategies suffer in at least one reaction step from poor regio- or chemoselectivity. This work presents an efficient and selective synthesis protocol for primary aliphatic amines via their corresponding aldoximes. These are readily produced from the condensation of hydroxylamine and the respective aldehydes. This straightforward condensation can be carried out either with isolated aldehydes or with crude reaction solutions from the hydroformylation of alkenes. It allows a straightforward separation of the aldoximes via their precipitation, which then serve as intermediates for the final reduction. In a newly developed protocol for aldoxime reduction, yields of up to 90% of the desired primary amines from several different aldoximes are achieved. The ruthenium/triphos catalyst system showed activities exceeding 7500 h−1, which is significantly faster than other amination protocols, and complete conversion is achieved within minutes. Our approach allows the synthesis of the polyamide-12 precursor (methyl 12-aminododecanoate) from the unsaturated, renewable oleochemical methyl 10-undecenoate via the hydroformylation, condensation, reduction sequence on up to 6 g scale with up to 68% overall selectivity.
Hydroaminomethylation of methyl 10-undecenoate with integrated catalyst recycling via a thermomorphic multiphase system for the continuous production of renewable amines
(2024-04-29) Kampwerth, Anna; Riemer, Tim B.; Pöttker-Menke, Jonathan; Oppenberg, Nadine; Windisch, Arno M.; Vogt, Dieter; Seidensticker, Thomas
A thermomorphic multiphase system (TMS) consisting of methanol and n-dodecane was successfully applied to the hydroaminomethylation (HAM) of the renewable methyl 10-undecenoate. By using different amine substrates, a variety of α,ω-bifunctional products with potential use as intermediates for the polymer industry were obtained with high yields of up to 96%. The full potential of our TMS was shown in a miniplant, with over 90 h of continuous operation showing a stable selectivity towards the desired amine product of 80%. Combining the TMS with an OSN membrane for continuous separation of the by-product water from the reaction system was a key factor for the excellent results. The water concentration in the recycle could be kept below 4% so that only 3% of the undesired aldol condensate was obtained after 90 hours. The low catalyst leaching via the TMS and the OSN membrane is particularly remarkable. The total loss of rhodium over the 90 hours continuous operation is 2.5% of the initial amount used, and for the ligand SulfoXantphos only 0.4% of the initial amount. The loss of rhodium via the TMS and the OSN is 6 ppm per produced desired amine product.
Homogeneous catalysis at its edge: high-temperature Ru-catalysed amination of alcohols under continuous flow conditions
(2023-01-20) Heider, Christian; Winter, Alina; Voß, Viktoria; Vogt, Dieter; Seidensticker, Thomas
Combining a tubular flow reactor with a robust homogeneous catalyst enabled running the alcohol amination at unique conditions, i. e., very high temperatures at low residence times. Catalytic activities were thus increased to unprecedented values of >900 h−1 in the synthesis of tertiary dimethylalkylamines directly from alcohols with excellent selectivities exceeding 99 %. Furthermore, several alcohols could be converted to the desired tertiary amines.
Optimizing nickel-based hydrocyanation catalysts
(2024) Köhler, Till; Vogt, Dieter; Tiller, Jörg
Nitriles are versatile and highly desired chemical intermediates for a broad range of products. Thus, their economic large-scale production requires highly efficient and selective synthesis. The nickel-catalyzed hydrocyanation of C=C double bonds provides such selective and 100% atom-economical access to nitriles. Nevertheless, the catalysts hitherto lack activity and longevity. The catalytic activity can be increased slightly by using AlCl3 as the Lewis acid, still the overall activity remains unsatisfactory. As there is no literature focused on increasing the cooperativity between the Nickel catalyst and the Lewis acid cocatalyst, first in depth studies are conducted in this thesis. It was found, that adding acetonitrile as a promotor enhances the nickel-Lewis acid cooperation, boosting activity further. Furthermore, it was found that the Lewis acid AlCl3 deactivates the nickel-catalyst reducing catalyst productivity. To increase the catalysts productivity and activity further, the catalyst stability needed investigation. It was found that the extremely oxygen sensitive catalyst requires an optimized experimental procedure to exclude oxygen contamination persisting of septum usage, HCN-addition as a solution and GC-standard addition after the reaction. That way, the full catalytic potential was utilized, resulting in a TOF20 of more than 300,000 h−1. These findings also provide a beneficial insight and help to develop a deeper understanding of current limitations caused by deactivation of the highly sensitive catalyst in nickel-catalyzed hydrocyanations. Conclusively, this catalytic system is applied in hydrocyanation of the renewable C10 1,3-diene β-myrcene under the ptimized procedure, yielding C11-nitriles with excellent selectivity not described in literature to date. It was found that three major products can be formed depending on the choice of ligand, which marks an important step towards the synthetic accessibility of mid-chain nitriles based on renewable resources.
Synthesis strategies towards tagged homogeneous catalysts to improve their separation
(2023-05-11) Diekamp, Justus; Seidensticker, Thomas
The recycling of homogeneous catalysts while keeping them in the homogeneous matrix is an ongoing challenge many reactions face if they are to find industrial applications. While a plethora of different synthetic approaches towards better, recyclable homogeneous catalysts exist, the literature shows a gap when one searches for a concise overview of the different catalyst modifications. This Review is designed to close that gap by summarising the existing synthesis pathways towards polar, non-polar, fluorous, and molecular-weight-enlarged catalysts and by examining their respective synthesis routes with a focus on modular and late-stage approaches. Furthermore, we map out the potential for a generally applicable tag library that allows straightforward catalyst modifications to tune them for each desired recycling strategy.
Selective introduction of nitrogen into bulk chemicals via homogeneously catalyzed reactions
(2024) Hares, Kevin; Vogt, Dieter; Tiller, Jörg
Nitrogen-containing chemical compounds are used everywhere in our day-to-day lives, from high-performance polymers to pharmaceuticals and crop protection. Despite being produced on very large scale, many of their production lines lack efficiency and have a significant impact on the environment. Amides are often synthesized by highly activated coupling agents with an inherently low E-factor. Therefore, developing a catalytic reaction that can produce amides directly from bulk chemicals is highly desired. Primary amines are essential intermediates in the chemical industry, and their selective synthesis is challenging due to their reactive properties. Although they are also produced from bulk feedstock, they require many steps when a renewable substrate is used. This dissertation addresses these challenges by developing and optimizing homogeneous transition metal catalysts. The work is structured into three main parts, each addressing different types of reactions to introduce nitrogen into bulk chemicals: 1. Carbonylative telomerization is a complex chemical reaction that synthesizes amides from simple feedstock molecules, but its high catalyst loading presents a challenge, as well as a limited scope. Both were addressed by optimizing the reaction conditions and adding new dienes and nucleophiles to the reaction portfolio of carbonylative telomerization. 2. Converting fatty esters directly into amines in a one-pot reaction is sought to streamline chemical production, requiring the development of a new catalyst to facilitate the process and improve resource and energy efficiency. Therefore, modified triphos ligands were synthesized and combined with ester amination. 3. The conversion of aldoximes into primary amines, offers a possible alternative to the highly desired hydroamination of alkenes. This is achieved through the combination with hydroformylation, which enables the conversion of alkenes into primary. These contributions offer new efficient ways of introducing nitrogen into bulk feedstock to synthesize more complex amides and primary amines through homogeneous transition metal catalysts.
Synthesis of biobased amines via Pd-catalysed telomerisation of the renewable β-myrcene in a water/ethanol multiphase system: catalyst recycling enabled by a self-separating product phase
(2023-07-25) Kampwerth, Anna; Terhorst, Michael; Kampling, Nils; Vogt, Dieter; Seidensticker, Thomas
We developed an aqueous multiphase system for the synthesis of biobased alkyl amines via palladium-catalysed telomerisation based on the terpene β-myrcene. Ethanol was employed as a harmless co-solvent. With this “green” switchable multiphase solvent system, the recycling of the expensive homogeneous catalyst was successfully enabled by self-separating products at room temperature. The total turnover number (TON) was increased to almost 12 000 over 9 runs, with high selectivities towards the desired amine telomer products between 80 and 93% in each run. Furthermore, various amine nucleophiles were successfully used allowing to produce a wide variety of long-chain unsymmetrical alkyl amines with potential applications as, for instance, surfactant precursors or lubricants. In each case, the products self-separated after reaction from the aqueous multiphase system containing the homogeneous palladium catalyst allowing straightforward isolation by simple decantation. Finally, we proved the successful use of spirits (vodka) as solvents in this sustainable amine synthesis.
Continuous production of amines directly from alkenes via cyclodextrin-mediated hydroaminomethylation using only water as the solvent
(2023-03-28) Roth, Thomas; Evertz, Rebecca; Kopplin, Niklas; Tilloy, Sébastien; Monflier, Eric; Vogt, Dieter; Seidensticker, Thomas
Aqueous hydroaminomethylation (HAM) is an atom economical route for the efficient production of amines in one reaction step, starting from basic chemicals like alkenes. Herein we present the first successful establishment of a continuous process for HAM in an aqueous multiphase system. The green mass transfer agents randomly methylated-β-cyclodextrins (CD) enabled the catalytic system consisting of rhodium/sulfoXantphos to achieve high yields of up to 70% with selectivities of up to 80% in several continuous experiments with a total run time of more than 220 h. The key here is that water and products have large polarity differences, but the reaction still proceeds effectively due to the addition of cyclodextrin, which made the application of solvents obsolete. The main achievements in this way were the investigation of the influence of the randomly methylated-β-cyclodextrin concentration on the reaction rate and the selectivity in batch studies and finding promising operating points in the first continuous experiments. In a final experiment, the separation temperature was investigated. It was shown that the catalyst loss in the product phase is enormously small at 0.003% h−1 of the initial mass (0.24% in total), which is the lowest ever reported value for the HAM on this scale. Within a run time of 78 hours, 2.87 kg of tertiary amine were produced using only 0.2 g (>14[thin space (1/6-em)]000[thin space (1/6-em)]:[thin space (1/6-em)]1) of transition metal, while the loss of rhodium per kg of product produced was mostly around 0.15 mg kg−1, suggesting possible economical applicability.
Sodium ethoxide as an environmentally benign and cost-effective catalyst for chemical depolymerization of post-consumer PET waste
(2023-01-19) Javed, Saqib; Ropel, Dennis; Vogt, Dieter
Polyethylene terephthalate (PET) waste is mounting up in the environment due to its poor biodegradability and low recycling rate. Glycolysis is a promising chemical recycling technique to convert PET into its monomer bis(2-hydroxyethyl)terephthalate (BHET). Here, we present our work on the glycolytic depolymerization of post-consumer PET waste using sodium ethoxide (EtONa) as a low-cost catalyst. In order to optimize the reaction in terms of PET conversion and BHET yield, response surface methodology (RSM) based on the Box–Behnken design was applied for the reaction temperature (160–190 °C), the molar ratio of PET : EtONa (50–150), the molar ratio of ethylene glycol to PET (EG : PET) (3–7), the reaction time (2–6 h) and the PET particle size (0.25–1 mm). Based on the experimental results, regression models as a function of significant process parameters were obtained and evaluated by analysis of variance (ANOVA) to predict the depolymerization performance of EtONa. By further optimization and expanding the parameter space beyond the initial upper limits, high PET conversion (98%) and an isolated yield of BHET (76%) were achieved. Under similar conditions, its depolymerization performance was compared to other widely studied catalysts, such as zinc acetate (PET conversion 97%, BHET yield 75%) and cobalt acetate (PET conversion 93%, BHET yield 70%). BHET precipitation without water is also demonstrated and it was found that EG and catalyst recycling is possible at least for 5 recycled runs with persistent conversion. Hence, EtONa is a very promising low-cost catalyst for PET depolymerization which has potential feasibility for a large-scale process.
Nickel(BiPhePhos)-catalyzed hydrocyanation of styrene - highly increased catalytic activity by optimized operational procedures
(2024-03-21) Köhler, Till; Rienhoff, Bernd; Vogt, Dieter
Nitriles are versatile and highly desired chemical intermediates for a range of products. Their economic large-scale production requires highly efficient and selective synthesis. The nickel- catalyzed hydrocyanation of C=C double bonds provides such selective and 100% atom-economical access to nitriles, but the catalysts hitherto lack activity and longevity. Yet, the literature focusing on increased catalytic activity or optimized operational procedures is scarce, at the least. Here, we present a thorough investigation and optimization of operational procedures using a commercially available diphosphite ligand and styrene as a model substrate. This led us to achieve a TOF20 of more than 300,000 h−1.
Catalytic synthesis of methyl 9,10‐dihydroxystearate from technical feedstocks in continuous flow via epoxidation and hydrolysis
(2022-04-30) Vondran, Johanna; Benninghoff, Tobias; Emminghaus, Anahita Irene; Seidensticker, Thomas
The sequence of the homogeneously Ru-catalyzed epoxidation of methyl oleate and acid-catalyzed hydrolysis of the corresponding epoxide methyl 9,10-epoxy stearate is successfully transferred from batch into flow mode, allowing for the continuous production of methyl 9,10-dihydroxystearate. Thereby, methyl oleate is first converted up to 97% within 14 min at excellent selectivity in the epoxidation using aqueous hydrogen peroxide as the sole oxidant. In the subsequent hydrolysis, a residence time of 10 min is sufficient for quantitative conversion of the epoxide. The desired, pure vicinal diol is isolated upon crystallization from the crude reaction mixture in an integrated process starting from technical grade (91.5%) substrate. The isolated yield is increased upon the addition of water as a green antisolvent from 75% up to 97%. Finally, the concept is transferred to methyl oleate of even lower purity (76%), still obtaining an isolated yield of 66% of the vicinal diol. Thus, the integration of sequential epoxidation and hydrolysis into continuous flow and subsequent crystallization allows for high conversion and selectivities within a total residence time of 27 min, corresponding to a space–time yield of 190 g h−1 L−1 in the epoxidation and 164 g h−1 L−1 in the hydrolysis, respectively. Practical applications: The modular flow setup enables the targeted functionalization toward the epoxide intermediate or the vicinal diol. Both offer versatile applications for the production of polymers, surfactants, or toward further conversion as in oxidative cleavage starting from methyl oleate. The application of flow chemistry offers advantages for the safe handling of hydrogen peroxide even at high temperatures. With fats and oils being natural substances, oleochemicals such as fatty acid methyl esters are typically available in technical purity so that efficient strategies for the isolation of pure products are of need. Crystallization of the product is promising, as additional organic solvents are not required. Thus, using the difference in melting point and solubility behavior of the desired product compared to other compounds is a promising method for the applicability of renewable resource-based substrate mixtures.
Selective synthesis of primary amines by kinetic-based optimization of the ruthenium-Xantphos catalysed amination of alcohols with ammonia
(2022-08-03) Heider, Christian; Pietschmann, Dominik; Vogt, Dieter; Seidensticker, Thomas
The selective synthesis of primary amines directly from several alcohols and ammonia using a homogeneous catalyst based on HRuCl(CO)(PPh3)3 and Xantphos is presented. The key to success was the detailed understanding of all mutually influencing parameters such as temperature, ammonia excess, and substrate concentration. These studies were supported by the determination of the kinetics, which allowed the reaction order to be calculated as 0.7. Furthermore, the kinetic model derived from the mechanism was confirmed. After measuring reaction profiles for all influencing parameters, optimized conditions were obtained, which finally allowed the amination of aliphatic, cyclic, as well as primary and secondary alcohols with selectivities to the desired primary amine exceeding 90 % at quantitative alcohol conversion with only minimal formation of the undesired secondary amines. Furthermore, the catalytic activity of the commercially available and robust Xantphos system was drastically improved, corresponding to a turnover frequency (TOF)>60 h−1 after 30 minutes and a turnover number (TON) of 120.
Pushing boundaries—selective cooling crystallization as tool for selectivity compensation and product purification using a recyclable Pd/Xantphos catalyst in the methoxycarbonylation of methyl 10-undecenoate
(2022-09-30) Vondran, Johanna; Moeschke, Rebecca; Deysenroth, Tabea; Seidensticker, Thomas
The homogeneously catalyzed methoxycarbonylation of methyl 10-undecenoate allows for the synthesis of dimethyl 1,12-dodecandioate as an interesting bio-based drop-in alternative for 1,12-dodecandioic acid as polymer building block. Although the benchmark catalyst system of Pd/1,2-bis((di-tert-butylphosphino)methyl)benzene and methane sulfonic acid is very active and selective, long-term stability over a potential catalyst recycling is limited. In this work, modifications of this catalyst system in terms of protonation of the ligand and its replenishment during recycling are first investigated, proving that the reaction system is tolerant against minor changes. Finally, the commercially available ligand Xantphos, featuring higher stability but comes with a rather low l:b selectivity of 70:30, is applied. However, through the application of cooling crystallization, 58 g product (52% isolated yield) with an overall purity of 94% is obtained from the crude reaction solution without further treatment and a ∑TON of 4000 after ten reaction runs, while catalyst loss into the product is low. Practical Applications: Selective syntheses on the basis of renewable resources are a powerful tool for the production of value products in terms of green chemistry. Thereby, homogeneous transition metal catalysts are beneficial regarding selectivity. However, their separation and recycling are challenging due to their limited stability. The combination of a stable, commercially available catalyst with a selective purification method allows for isolation and purification from a crude reaction mixture without the need for any auxiliary or further purification steps. In this work, cooling crystallization is applied for subsequent purification of the linear diester dimethyl 1,12-dodecandioate. Thereby, a lower selectivity from the methoxycarbonylation reaction using the stable Xantphos ligand is compensated and combined with recycling of the homogeneous catalyst. Thus, the development of an integrated process covering a stable catalyst system in the reaction, and high selectivity in the purification is the key toward an efficient homogeneous catalyst recycling.
Polymer-grade bio-monomers from oleochemicals by combining homogeneous catalysis and selective product crystallization in an integrated process
(2023-09-28) Seifert, Astrid Ina; Wegener, Hannes; Brühl, Katharina; Seidensticker, Thomas; Wohlgemuth, Kerstin
The homogeneously catalyzed methoxycarbonylation of bio-based methyl 10-undecenoate (C11-DME) produces linear 1,12-dimethyl dodecanedioate (l-C12-DME). Subsequent selective product crystallization from the reaction mixture with downstream filtration and washing allows for the generation of the bio-monomer in polymer grade quality (>99.9%). This effective purification enables its direct use, e.g., for bio-based polyamides, without further purification. It separates the expensive homogeneous catalyst dissolved in the liquid phase in its active state for efficient catalyst recycling. We present the complex interactions of process parameters regarding reaction and crystallization-based purification in an integrated catalyst recycling process. Furthermore, we demonstrate that purification of l-C12-DME with >99.9% purity over multiple consecutive recycling runs is possible. However, as the crystallization is highly sensitive towards changing concentrations of by-products and particularly unreacted substrates, this high purity is only achieved by maintaining a stable composition in the reaction mixture using a newly developed system for precise conversion control in the reaction step.
Palladium-catalyzed synthesis of mixed anhydrides via carbonylative telomerization
(2022-05-02) Hares, Kevin; Vogelsang, Dennis; Wernsdörfer, Charlotte S.; Panke, Dennis; Vogt, Dieter; Seidensticker, Thomas
For the first time, mixed carboxylic anhydrides were accessed directly via homogeneous palladium catalysis from 1,3-butadiene and carboxylic acids. Under carbonylative telomerization conditions, the respective mixed 3,8-nonadienoic anhydrides are formed in a single reaction step with yields of up to 82%. These very reactive mixed anhydrides can then be used for consecutive reactions in a one-pot manner and selectively transfer the newly formed unsaturated C9 unit. Possible changes in the proposed mechanism were discussed and in a first example, the mixed anhydrides were utilized to form amides.
From tandem to catalysis – organic solvent nanofiltration for catalyst separation in the homogeneously W-catalyzed oxidative cleavage of renewable methyl 9,10-dihydroxystearate
(2022-04-25) Vondran, Johanna; Peters, Marc; Schnettger, Alexander; Sichelschmidt, Christian; Seidensticker, Thomas
Feasibility of oxidative cleavage of methyl oleate in a homogeneous reaction, facilitating the subsequent recovery of the catalyst from a single phase, is a challenge. Using the high molecular catalyst phosphotungstic acid (2880 Da) as an affordable catalyst offers potential for membrane separation. To gain insight into side-reactions, the intermediate methyl 9,10-dihydroxystearate was first applied as a model substrate. Thus, the stability of the intermediate methyl 9,10-epoxystearate and the vicinal diol was significantly improved under reaction conditions. Oxidative cleavage of the vicinal diol as a stable intermediate is very promising reaching an overall selectivity of 90% and a selectivity towards the cleavage carboxylic acids of 80%, considering dilution and acidity as the most important parameters. Retention of the catalyst via organic solvent nanofiltration was investigated and we retained 94% of the catalyst in the monophasic system as the first step towards a process concept for a product purification or catalyst recycling strategy.

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