The Experts below are selected from a list of 156 Experts worldwide ranked by ideXlab platform
Hans J Schafer - One of the best experts on this subject based on the ideXlab platform.
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electroorganic synthesis 62 anodic heterocoupling mixed Kolbe Electrolysis of carbohydrate carboxylic acids with alkanoic acids to c glycosides
Liebigs Annalen, 2006Co-Authors: Michael Harenbrock, Agnes Matzeit, Hans J SchaferAbstract:2-Deoxy carbohydrate carboxylic acids 1–3 were prepared from glucal 4, acetobromoglucose 5, and D-galactose (7), respectively. The acids 1–3 were electrolyzed with different coacids at controlled current in methanol at platinum electrodes in an undivided cell to afford C-glycosides as heterocoupling products in 46–70% yield. Compound 28, obtained by deacylation of 17, has a critical micelle concentration (cmc) of 2.4 mM, which is about 2.5 times lower than that of the corresponding O-glycoside 29. Compound 28 forms liquid crystals with a smectic A phase in the range between 96 and 190°C, which is twice as large as that of 29. Compounds 31 and 32, obtained by deprotection of 23 and 24, respectively, also exhibit liquid crystalline behavior.
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electroorganic synthesis 57 synthesis of advanced prostaglandin precursors by Kolbe Electrolysis ii preparation of coacids and anodic initiated tandem radical addition radical coupling reaction with 1 r 4 s 3r s 3 cis 4 acetoxycyclopent 2 enyloxy 3 ethoxypropionic acid
European Journal of Organic Chemistry, 1994Co-Authors: Jens Weiguny, Hans J SchaferAbstract:The α-silyl-substituted carboxylic acids 4 and 10 were prepared and with other coacids subjected to a mixed Kolbe Electrolysis with β-cyclopentenyloxypropanoate 1. The stereochemical course of this cyclization reaction was determined on the basis of the 4-methyl-substituted product 23 by 1H-NMR-NOE spectroscopy. Conversion of the bicyclic reaction products 21b–d to advanced prostaglandin precursors such as lactone 30 was achieved in few steps.
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electroorganic synthesis 56 synthesis of advanced prostaglandin precursors by Kolbe Electrolysis i preparation of 1 r 4 s 3rs 3 cis 4 acetoxycyclopent 2 enyloxy 3 ethoxypropionic acid
European Journal of Organic Chemistry, 1994Co-Authors: Jens Weiguny, Hans J SchaferAbstract:The key intermediate of a novel synthesis of prostaglandin precursors, (1′R,4′S,3R/S)-3-(cis-4-acetoxycyclopent-2-enyl oxy)-3-ethoxypropionic acid (3), is prepared by two different synthetic sequences: In a first strategy transacetalization of ethyl 3,3-diethoxypropionate (6) with (1R, 4S)-4-acetoxy-1-hydroxy-2-cyclopentene (7) leads to the formation of the mixed acetal 8. By subsequent hydrolysis and acylation 8 could be converted into acid 3 in six steps in 6% overall yield. However, the generation of acid 3 by bromoalkoxidation of 3-ethoxyacrylates 13d, e and subsequent electrochemical reduction proved to be more efficient. In this reduction it is possible to debrominate the α-bromo esters 14d, e and to remove the 2-haloethyl ester group in one step. Using this reaction sequence, we could synthesize acid 3 in five steps in 38% overall yield.
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electroorganie synthesis 55 1 influences on the selectivity of the Kolbe versus the non Kolbe Electrolysis in the anodic decarboxylation of carboxylic acids
Chemische Berichte, 1993Co-Authors: Elisabeth Klocke, Agnes Matzeit, Marianne Gockeln, Hans J SchaferAbstract:The anodic decarboxylation of 3-oxanonanoic acid (2a) and 3-oxapentadecanoic acid (2b) in methanol leads exclusively to products of the non-Kolbe Electrolysis. The influence of co-Electrolysis, solvent, current density, degree of neutralization and chain length of the alkoxy group on the anodic decarboxylation of 2a, b have been investigated. An extended alkyl chain in the alkoxy group, coElectrolysis with long-chain fatty acids, ethanol or dimethylformamide as solvent, and a high current density favor the Kolbe coupling against the non-Kolbe Electrolysis.
Jens Weiguny - One of the best experts on this subject based on the ideXlab platform.
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electroorganic synthesis 57 synthesis of advanced prostaglandin precursors by Kolbe Electrolysis ii preparation of coacids and anodic initiated tandem radical addition radical coupling reaction with 1 r 4 s 3r s 3 cis 4 acetoxycyclopent 2 enyloxy 3 ethoxypropionic acid
European Journal of Organic Chemistry, 1994Co-Authors: Jens Weiguny, Hans J SchaferAbstract:The α-silyl-substituted carboxylic acids 4 and 10 were prepared and with other coacids subjected to a mixed Kolbe Electrolysis with β-cyclopentenyloxypropanoate 1. The stereochemical course of this cyclization reaction was determined on the basis of the 4-methyl-substituted product 23 by 1H-NMR-NOE spectroscopy. Conversion of the bicyclic reaction products 21b–d to advanced prostaglandin precursors such as lactone 30 was achieved in few steps.
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electroorganic synthesis 56 synthesis of advanced prostaglandin precursors by Kolbe Electrolysis i preparation of 1 r 4 s 3rs 3 cis 4 acetoxycyclopent 2 enyloxy 3 ethoxypropionic acid
European Journal of Organic Chemistry, 1994Co-Authors: Jens Weiguny, Hans J SchaferAbstract:The key intermediate of a novel synthesis of prostaglandin precursors, (1′R,4′S,3R/S)-3-(cis-4-acetoxycyclopent-2-enyl oxy)-3-ethoxypropionic acid (3), is prepared by two different synthetic sequences: In a first strategy transacetalization of ethyl 3,3-diethoxypropionate (6) with (1R, 4S)-4-acetoxy-1-hydroxy-2-cyclopentene (7) leads to the formation of the mixed acetal 8. By subsequent hydrolysis and acylation 8 could be converted into acid 3 in six steps in 6% overall yield. However, the generation of acid 3 by bromoalkoxidation of 3-ethoxyacrylates 13d, e and subsequent electrochemical reduction proved to be more efficient. In this reduction it is possible to debrominate the α-bromo esters 14d, e and to remove the 2-haloethyl ester group in one step. Using this reaction sequence, we could synthesize acid 3 in five steps in 38% overall yield.
Thomas Wirth - One of the best experts on this subject based on the ideXlab platform.
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difluoro and trifluoromethylation of electron deficient alkenes in an electrochemical microreactor
ChemistryOpen, 2014Co-Authors: Kenta Arai, Kevin Watts, Thomas WirthAbstract:Electrochemical microreactors, which have electrodes integrated into the flow path, can afford rapid and efficient electrochemical reactions without redox reagents due to the intrinsic properties of short diffusion distances. Taking advantage of electrochemical microreactors, Kolbe Electrolysis of di- and trifluoroacetic acid in the presence of various electron-deficient alkenes was performed under constant current at continuous flow at room temperature. As a result, di- and trifluoromethylated compounds were effectively produced in either equal or higher yields than identical reactions under batch conditions previously reported by Uneyamas group. The strategy of using electrochemical microreactor technology is useful for an effective fluoromethylation of alkenes based on Kolbe Electrolysis in significantly shortened reaction times.
Falk Harnisch - One of the best experts on this subject based on the ideXlab platform.
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platinized titanium as alternative cost effective anode for efficient Kolbe Electrolysis in aqueous electrolyte solutions
Chemsuschem, 2021Co-Authors: Katharina Neubert, Matthias Schmidt, Falk HarnischAbstract:Five commercial materials were assessed for electrochemical conversion of n-hexanoic acid by Kolbe Electrolysis. Platinized titanium performed best, achieving a coulombic efficiency (CE) of 93.1±6.7 % (n=6) for the degradation of n-hexanoic acid and 48.3±3.2 % (n=6) for the production of n-decane, which is close to the performance of pure platinum (89.7±14.4 and 55.5±3.5 %; n=6). 56.7 mL liquid fuel was produced per mole n-hexanoic acid, converting to an energy demand of 6.66 kWh and 1.22 € per L. Using optical profilometry and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, it was shown that the degree of coverage of the titanium surface with platinum played the most important role. An uncovered surface of as little as 1-3 % already led to a deterioration of the CE of approximately 50 %. Using platinized titanium requires >36 times less capital expenditure at only <10 % increased operational expenditure; an electrode lifetime of 10000 h can be expected.
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The Dilemma of Supporting Electrolytes for Electroorganic Synthesis: A Case Study on Kolbe Electrolysis
ChemSusChem, 2015Co-Authors: Carolin Stang, Falk HarnischAbstract:Remarkably, coulombic efficiency (CE, about 50 % at 1 Farad equivalent), and product composition resulting from aqueous Kolbe Electrolysis are independent of reactor temperature and initial pH value. Although numerous studies on Kolbe Electrolysis are available, the interrelations of different reaction parameters (e.g., acid concentration, pH, and especially electrolytic conductivity) are not addressed. A systematic analysis based on cyclic voltammetry reveals that solely the electrolytic conductivity impacts the current–voltage behavior. When using supporting electrolytes, not only their concentration, but also the type is decisive. We show that higher concentrations of KNO3 result in reduced CE and thus in significant increase in electric energy demand per converted molecule, whereas Na2SO4 allows improved space–time yields. Pros and cons of adding supporting electrolytes are discussed in a final cost assessment.
Regina Palkovits - One of the best experts on this subject based on the ideXlab platform.
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non Kolbe Electrolysis in biomass valorization a discussion of potential applications
Green Chemistry, 2020Co-Authors: Joschka F Holzhauser, Joel B Mensah, Regina PalkovitsAbstract:Driven by the goal of a circular economy, the importance of renewable energies and sustainable sources of raw materials is steadily increasing. The electrochemical conversion of biomass-based compounds into liquid energy sources and basic chemicals enables the direct combination of renewable energies with sustainable carbon sources. A variety of carboxylic acids are efficiently accessible from biomass and represent important platform chemicals in a future bioeconomy. With the help of Kolbe and Non-Kolbe Electrolysis, these raw materials offer great potential for electrified value chains as part of bio-refinery concepts. This contribution highlights current developments in these areas as well as the open challenges in order to gain deeper scientific insights and to develop technically viable processes. Moreover, aspects of green chemistry with regard to (Non-)Kolbe Electrolysis are discussed. Last but not least, electrochemical conversions are an attractive approach to implementing modular and dynamic production plants.
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sustainable electrocoupling of the biogenic valeric acid under in situ low field nuclear magnetic resonance conditions
ACS Sustainable Chemistry & Engineering, 2019Co-Authors: Bruna Ferreira Gomes, Fabian Joschka Holzhauser, Carlos Lobo, Pollyana Ferreira Da Silva, Ernesto Danieli, Marcelo Carmo, Luiz Alberto Colnago, Stefan Palkovits, Regina PalkovitsAbstract:In situ nuclear magnetic resonance (NMR) investigations of a Kolbe Electrolysis reaction using a 43 MHz 1H NMR spectrometer were performed in this work. The electrochemical oxidative decarboxylatio...
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Producing Widespread Monomers from Biomass Using Economical Carbon and Ruthenium–Titanium Dioxide Electrocatalysts
2018Co-Authors: Guido Creusen, Stefan Palkovits, Joschka F. Holzhäuser, Jens Artz, Regina PalkovitsAbstract:In a future world economy relying on geographically decentralized renewable feedstocks and fluctuating energy generation, an electrochemical access to industrially relevant chemicals presents a key concept. Herein, we demonstrate the synthesis of industrially relevant adipate and acrylate monomers from the biogenic platform chemical succinic acid. Adipic acid diethyl ester and ethyl acrylate are available with up to 74% and 58% selectivity by Kolbe and non-Kolbe Electrolysis. We show RuO2-coated titanium electrodes are an excellent replacement for bulk platinum electrodes significantly reducing noble metal costs, and reduce the noble metal content further by replacing up to 75% of the ruthenium with titanium in organic systems. Economical carbon electrodes target the acrylate monomer by suppressing dimerization. Applying transient conditions derived from a real windmill energy profile, we confirmed an efficient dynamic operation paving the way for a sustainable chemical industry driven by efficient transient electrocatalytic processes
