Producing Widespread Monomers from Biomass Using Economical

Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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Producing Widespread Monomers from Biomass Using Economical Carbon and Ruthenium−Titanium Dioxide Electrocatalysts Guido Creusen,†,‡,+ F. Joschka Holzhäuser,†,+ Jens Artz,† Stefan Palkovits,† and Regina Palkovits*,† †

Chair of Heterogeneous Catalysis and Chemical Technology Institute for Technical and Macromolecular Chemistry, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany

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S Supporting Information *

ABSTRACT: 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. KEYWORDS: Electrochemical synthesis, Non-Kolbe electrolysis, Transient processing, Succinic acid, Renewable monomers, Decarboxylation

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INTRODUCTION The current global shift from fossil to renewable energy production brings about the challenges of electrical energy overproduction and storage.1 Applying electrocatalytical methods in green chemistry offers the key advantage of nonstationary, decentralized and readily scalable processing, which is of great importance in dealing with an increasing reliance on fluctuating renewable energy production and valorizing biomass feedstock streams locally in order to minimize logistical costs.2,3 A comparatively recent concept in green electrochemistry is the valorization of biomass-based intermediates. Especially the conversion of cellulose-derived platform molecules like furfural, levulinic acid (LA) and 5hydroxymethyl furfural (5-HMF) proves to be extremely versatile and gives access to both liquid fuels and monomers.4−14 Anodic decarboxylation reactions were discovered as early as the 19th century,15−17 and provide access to saturated and unsaturated compounds making them especially relevant to biomass processing (Scheme 1a).18 A wide variety of carboxylic acids available from biomass subjected to the diverse reaction scheme can facilitate the synthesis of saturated © XXXX American Chemical Society

and unsaturated molecules otherwise inaccessible from oxygenrich platform molecules.19,20 Currently, applications of anodic decarboxylation reactions in biomass valorization still strongly focus on the synthesis of liquid fuel molecules.5,6,9,21,22 Pathways to access higher value products from biomass intermediates are sparse, and the alternate monomers 2,7octadione and 2,5-dimethyladipic acid dimethyl ester are not established industrial monomers.5,6,23 Rather than alternative monomers, access to industrially relevant monomers from biomass-derived intermediates via electrochemical methods is a currently unresolved key problem prohibiting biomass valorization using fluctuating electricity streams. Seeking a direct and efficient electrochemical production route toward adipic acid from readily available renewable intermediates, herein, we successfully demonstrate the synthesis of diethyl adipate (DEA) from monoethyl succinic acid (MESA) (Scheme 1b, pathway 1). The dimerization of sodium Received: September 5, 2018 Revised: October 30, 2018

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DOI: 10.1021/acssuschemeng.8b04488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering

workup (Table 1). In methanol, both the selectivities toward adipic acid diethyl ester (69%) and the current efficiency (57%) are high (Table 1, entry 3). In pure water, the selectivity (20%) and current efficiency (12%) both drop significantly (Table 1, entry 1). Notably, the hydrophobic adipic acid

Scheme 1. Reaction Scheme for (a) the Main Reaction Pathways in the Anodic Decarboxylation of Carboxylic Acids Leading to Both Kolbe and Non-Kolbe Products and (b) the Conversion of Mono-Ethyl Succinic Acid to Diethyl Adipate and Ethyl Acrylate by Kolbe Dimerization and NonKolbe Electrolysis, Respectively

Table 1. Electrolysis of MESA Using a Pt Anode (1.0 cm2) in Various Water/Methanol Solvent Mixturesb Entry

Vwater/ Vmethanol

Product phase separation

XMESA [%]a

SDEA [%]a

εDEA [%]

1 2 3

100/0 50/50 0/100

Yes Yes No

58.6 66.0 83.3

20.1 51.8 68.5

11.8 34.2 56.9

a As determined by 1H- and 13C NMR spectroscopy, see experimental section (Supporting Information) for further details. bReaction conditions: 1.0 M MESA, 0.1 M NEt3, 0 °C, current density j = 100 mA cm−2, Qtotal = 0.1 Faradaic equivalent. Deuterated solvents are used in order to facilitate quantitative analysis by 1H- and 13C NMR spectroscopy. XMESA is the conversion of mono-ethyl succinic acid, SDEA is the selectivity towards diethyl adipate, and εDEA is the current efficiency for the production of diethyl adipate.

diester product forms a separate organic phase, a feature that is of significant industrial importance as it allows feeding the reagent into the aqueous phase while continuously collecting the organic product phase. Up to a certain extent, both high selectivity and facile product separation can be achieved at the same time using methanol−water mixtures (Table 1, entry 2). Note that in Table 1 the yield equals the current efficiency toward DEA εDEA, as exactly 1 Faradaic equivalent is passed through the reaction mixture. A Faradaic equivalent describes the amount of electrons required to convert the reagent taking into account the amount of electrons involved in a conversion (in this case 2). Seeking to omit reliance on solid Pt anodes, we investigate RuO2-coated Ti as a cost-effective alternative. RuO2- and (RuxTi1−x)O2-coated Ti electrodes are prepared using a facile thermal decomposition technique on a Ti metal substrate based on a modified literature procedure,28 varying the Ruloading from 1.6 to 0.4 mg cm−2 (Table S1, Figure S4). The Ti base metal provides mechanical stability and conductivity. RuO2 is the active electrocatalyst, and admixing TiO2 provides additional chemical stability in addition to improving adhesion of the coating. Prior to electrochemical experiments, we investigate the crystal structure of the electrocatalytical coatings containing various ratios of RuO2 to TiO2 using Xray diffraction. RuO2 forms a rutile phase during the annealing at 470 °C. In the presence of Ru, the TiO2 part of the coating largely adapts the rutile structure (Figure 1). Without RuO2, the TiO2 forms as the anatase modification under these conditions. The TiO2 can be converted into the rutile modification at higher temperatures (Figure S5), but upon doing so loses its conductivity. Employing the same conditions used with solid Pt electrodes, we demonstrate that the RuO2- and (RuxTi1−x)O2-coated electrodes are excellent electrocatalysts for the dimerization of MESA to DEA (Figure 2a). In methanol, the RuO2-coated electrodes perform similarly to elemental Pt in terms of both product selectivity and current efficiency toward DEA, and do not lose activity even when 75 mol % of the RuO2 is replaced by TiO2. In aqueous systems, the current efficiency of the tested electrodes drops off significantly when TiO2 is present, leaving the RuO2-coated Ti as the most

succinic esters to adipic acid diesters was named as early as 1895,24 and once referred to in 1990 as a means to accessing deuterated adipic acid.25 Taking into account the need for new green pathways toward petro-based monomers from biobased materials employing renewable energy, we shed new light on this reaction taking into account economic and environmental considerations, especially regarding electrode materials and processing parameters. RuO2-coated Ti electrodes have surfaced in literature as a possible replacement for Pt.26,27 We show the production of diethyl adipate is possible in both aqueous and organic systems using RuO2-coated electrocatalysts. We furthermore replace up to 75% of the RuO2 with TiO2 without a drop in selectivity toward the dimer product in organic solvents, accomplishing a 4-fold reduction of the ruthenium content. We further expand the spectrum of accessible industrial monomers from the same intermediate by demonstrating the direct synthesis of ethyl acrylate (EA) with good acrylate selectivity using highly economical carbon anodes (Scheme 1b, pathway 2).

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RESULTS AND DISCUSSION In order to selectively obtain an adipic acid derivate by dimerization, we start from monoethyl succinic acid (Scheme 1b, pathway 1). We first demonstrate the feasibility of the reaction and set a benchmark by conducting the reaction using solid Pt electrodes precisely positioned by an in-house 3Dprinted bracket (Figure S1). Using various water−methanol solvent systems, we evidence the choice of solvent allows for either high selectivity and current efficiency (ε) with respect to the dimerization product DEA, or phase separation facilitating B


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against prolonged high anodic potentials remains a concern in such systems. At the time of writing, the price of Pt is more than 3-fold that of Ru, further reducing the cost of noble metal content. Aiming to demonstrate the robustness of this reaction toward nonstationary conditions in terms of current flow, we conduct the reaction using an irregular current density profile simulating that of wind energy output (Figure 2b). The reactions with both a constant and variable current density are carried out using a RuO2-coated Ti anode. The conversion of the reagent into the adipate product shows a similarly high efficiency using these nonstationary conditions (Figure 2c). In order to investigate the characteristic electrocatalytical activity of Pt electrodes in the Kolbe dimerization reaction, and compare the Ru−Ti-dioxide-coated electrodes, cyclic voltammetry (CV) is performed. Although this reaction is not well suited for CV measurement, a recent and detailed study outlines a methodology making well-contemplated compromises allowing a meaningful analysis.31 Figure 3a shows CVs comparing the electrolyte solution with and without the addition of MESA using a Pt anode. Addition of the carboxylic acid shifts the onset potential from 1.6 to 2.2 V vs standard hydrogen electrode (SHE), which is characteristic for Kolbe electrolysis and indicates suppression of water oxidation on the anode. Figure 3b shows the oxidation and reduction phenomena typical for RuO2, and a comparison of a solid Pt electrode with a RuO2-coated electrode (Figure 3c) shows a high onset potential (2.17 V vs SHE for Pt and 2.10 for RuO2) for both electrodes. This is perfectly in line with the previous experimental results, and indicates that the RuO2 coating is indeed covered with carboxylate suppressing the oxidation of water,18 which results in the high current efficiency similar to Pt. Compared to Pt, the RuO2-coated electrode shows a higher dj/dEWE. Although Figure 2a does indicate a slightly higher

Figure 1. (a) XRD of the metal oxide coatings prepared by thermal decomposition at 470 °C using various ratios of RuO2 to TiO2, with (b,c) excerpts showing reflexes characteristic for each phase. The powder sample for XRD analysis was scratched off the electrodes, being careful not to scratch the metal surface.

versatile electrocatalyst. Product phase separation occurs in the same aqueous mixtures as with solid Pt, meaning Ru−Ti dioxide-coated Ti electrodes are an excellent substitute for the solid Pt electrocatalysts commonly used. Considering a 50 μm thick Pt foil glued to a conductive base substrate as benchmark bulk electrode,29 the noble metal content (107 mg Pt cm−2) greatly exceeds that of the electrodes employed in this work (1.6−0.4 mg Ru cm−2). Although alternative technical implementations, such as Pt electroplated onto nafion membrane,30 yield electrodes with a lower Pt content, stability

Figure 2. (a) Comparison of solid Pt and (RuxTi1−x)O2-coated Ti electrodes in various water−methanol solvent systems, (b) chronopotentiograms showing a constant and a simulated wind-energy current density profile and (c) a comparison of the efficiency and selectivity for the respective electrolysis using a RuO2-coated Ti electrode. Reaction conditions: 1.0 M MESA, 0.10 M NEt3, current density j = 100 mA cm−2, Qtotal = 1 Faradaic equivalent unless specified. Deuterated solvents are used in order to facilitate quantitative analysis by 1H- and 13C NMR spectroscopy. C


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Figure 3. Cyclic voltammetry for the Kolbe dimerization of MESA in water showing (a) a reference experiment with and without the carboxylic acid using a Pt electrode, (b) the Ti\RuO2 electrode in the electrolyte, (c) a comparison between Pt and Ti\RuO2 electrodes and (d) the effect of the Ru concentration in Ti\(RuxTi1−x)O2 electrodes on activity and onset potential. Conditions: 0.1 M MESA in water, 0.01 M KOH, 20 mg mL−1 Na2SO4, scan rate 10 mV s−1 unless specified. The onset potential is determined as the intersection of the E-axis with a linear fit of the last 0.5 V of each measurement.

(Figure 4). Although strength of the base employed does not influence the reaction rate, the emergence of an acrylic acid signal in the 1H NMR spectra at high conversion for KOH points at an important consideration. During the course of the reaction, carboxylic acid is consumed and the pH rises rapidly toward the end of the reaction. The observation that no second acrylate peak appears when triethylamine is employed further strengthens the hypothesis that regeneration of a strong base catalyst at high conversion causes hydrolysis, and thus, using the weaker triethylamine provides an elegant solution without losing conductivity.

current efficiency for RuO2 over Pt, other factors like the real surface area or conductivity of the electrode surfaces could play a significant role. Electrochemical impedance spectroscopy shows features of a porous or rough electrode (Figure S9), indicating the presence of a larger electrocatalytically active area. Surprisingly, admixing TiO2 in the coating initially leads to an increased current−potential slope for 25 mol % TiO2, which decreases again as the concentration of Ru drops further (Figure 3d). When TiO2 is present, the onset potential drops significantly in all cases (1.7−1.8 V vs SHE as opposed to 2.1 for RuO2 only). The decreased onset potential, combined with the initially increased current density, indicates that water oxidation (which has a significantly lower onset potential than the decarboxylation reaction) is a competitive reaction on these electrode surfaces. This also manifests in the lower current efficiency of TiO2-containing coatings in aqueous solvent mixtures. By simply changing the electrode material to carbon under similar conditions, electrolysis of MESA yields the industrially important unsaturated monomer ethyl acrylate (Figure 1b, pathway 2). Carbon is especially unsuitable as a dimerization catalyst, and instead facilitates the formation of non-Kolbe products via a cationic intermediate. Subsequent deprotonation of the carbocation leads to the desired monomer. In order to investigate the effect of base strength on the selectivity toward the desired acrylate product, KOH and NEt3 bases are compared under otherwise identical reaction conditions. The highest selectivity toward EA reached during the reaction is 58% for both NEt3 as well as KOH after 0.5 charge equivalents

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CONCLUSION In this work, we demonstrated that electrochemical methods can fill a key gap in producing valuable industrial monomers from biomass intermediates, with the added benefits of effective nonstationary processing. We introduced efficient pathways to adipic acid and acrylate esters via electrochemical decarboxylation, and additionally demonstrated that Ru−Tidioxide-coated Ti electrocatalysts provide an excellent alternative to the cost-prohibitive Pt electrodes otherwise required for dimerization reactions. The Kolbe dimerization of ethyl succinate to adipic acid diethyl ester can be conducted in both methanol and aqueous mixtures. Whereas the highest selectivity toward diethyl adipate is achieved in methanol (74%), admixing 50 vol % water leads to phase separation of the hydrophobic product, an important feature facilitating energy-effective continuous processing while maintaining reasonable product selectivity (52%). In order to provide an D


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Figure 4. Monitoring the conversion of MESA to EA employing (a) KOH and (b) NEt3 as the base. (c) Excerpts of 1H NMR spectra (400 MHz, CDCl3) showing the unsaturated acrylate protons and the emergence of acrylic acid at high conversion in the presence of KOH. Reaction conditions: 0.25 M MESA in methanol-d4, 0.025 M base, 80 mA cm−2, carbon electrode.

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economical alternative to solid Pt, we demonstrate that Ti \(RuxTi1−x)O2 electrodes serve as a comparable alternative yielding similar current efficiency toward the dimer in methanol even up to 75 mol % TiO2 in the coating. Ti \RuO2 anodes furthermore replace Pt with similar efficiency in aqueous systems. Using a carbon electrode instead, we converted the same succinic acid monoethyl ester reagent into ethyl acrylate, opening up novel pathways toward the electrochemical synthesis of unsaturated monomers under ambient conditions. Although the acrylate product selectivity (58%) is not affected by the base strength, we demonstrated that triethylamine protects against ester hydrolysis at high conversion seen when using KOH as a base. Overcoming the lack of valuable monomer products from an abundant biomassderived intermediate as well as the need for costly Pt electrodes, these reactions pave the way for the economically viable integration of electrochemical oxidative decarboxylation methods in sustainable chemical processing of biomass feedstocks.

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AUTHOR INFORMATION

Corresponding Author

*R. Palkovits. E-mail: [email protected]. ORCID

Regina Palkovits: 0000-0002-4970-2957 Present Address ‡

Institute for Macromolecular Chemistry, University of Freiburg, Stefan-Meier-Strasse 31, 79104 Freiburg im Breisgau, Germany

Author Contributions +

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge financial support by the Cluster of Excellence “Tailor-Made Fuels from Biomass” (TMFB) funded by the Excellence Initiative of the German federal and state governments to promote science and research at German universities (EXC 236).

ASSOCIATED CONTENT

* Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b04488.

REFERENCES

(1) Weitemeyer, S.; Kleinhans, D.; Vogt, T.; Agert, C. Integration of Renewable Energy Sources in future power systems: The role of storage. Renewable Energy 2015, 75, 14−20. (2) Eranki, P. L.; Bals, B. D.; Dale, B. E. Advanced Regional Biomass Processing Depots: a key to the logistical challenges of the cellulosic biofuel industry. Biofuels, Bioprod. Biorefin. 2011, 5 (6), 621−630.

Experimental details, supporting figures and details on quantitative analysis by 1H- and 13C NMR spectroscopy (PDF) E


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ACS Sustainable Chemistry & Engineering (3) Lam, C. H.; Das, S.; Erickson, N. C.; Hyzer, C. D.; Garedew, M.; Anderson, J. E.; Wallington, T. J.; Tamor, M. A.; Jackson, J. E.; Saffron, C. M. Towards sustainable hydrocarbon fuels with biomass fast pyrolysis oil and electrocatalytic upgrading. Sustainable Energy Fuels 2017, 1, 258−266. (4) Chadderdon, D. J.; Xin, L.; Qi, J.; Qiu, Y.; Krishna, P.; More, K. L.; Li, W. Electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5furandicarboxylic acid on supported Au and Pd bimetallic nanoparticles. Green Chem. 2014, 16 (8), 3778−3786. (5) dos Santos, T. R.; Harnisch, F.; Nilges, P.; Schroder, U. Electrochemistry for biofuel generation: transformation of fatty acids and triglycerides to diesel-like olefin/ether mixtures and olefins. ChemSusChem 2015, 8 (5), 886−893. (6) dos Santos, T. R.; Nilges, P.; Sauter, W.; Harnisch, F.; Schröder, U. Electrochemistry for the generation of renewable chemicals: electrochemical conversion of levulinic acid. RSC Adv. 2015, 5 (34), 26634−26643. (7) Green, S. K.; Lee, J.; Kim, H. J.; Tompsett, G. A.; Kim, W. B.; Huber, G. W. The electrocatalytic hydrogenation of furanic compounds in a continuous electrocatalytic membrane reactor. Green Chem. 2013, 15 (7), 1869−1879. (8) Kwon, Y.; Schouten, K. J. P.; van der Waal, J. C.; de Jong, E.; Koper, M. T. M. Electrocatalytic Conversion of Furanic Compounds. ACS Catal. 2016, 6 (10), 6704−6717. (9) Nilges, P.; dos Santos, T. R.; Harnisch, F.; Schröder, U. Electrochemistry for biofuel generation: Electrochemical conversion of levulinic acid to octane. Energy Environ. Sci. 2012, 5 (1), 5231− 5235. (10) Nilges, P.; Schroder, U. Electrochemistry for biofuel generation: production of furans by electrocatalytic hydrogenation of furfurals. Energy Environ. Sci. 2013, 6 (10), 2925−2931. (11) Qiu, Y.; Xin, L.; Chadderdon, D. J.; Qi, J.; Liang, C.; Li, W. Integrated electrocatalytic processing of levulinic acid and formic acid to produce biofuel intermediate valeric acid. Green Chem. 2014, 16 (3), 1305−1315. (12) Roylance, J. J.; Choi, K.-S. Electrochemical reductive biomass conversion: direct conversion of 5-hydroxymethylfurfural (HMF) to 2,5-hexanedione (HD) via reductive ring-opening. Green Chem. 2016, 18 (10), 2956−2960. (13) Roylance, J. J.; Kim, T. W.; Choi, K.-S. Efficient and Selective Electrochemical and Photoelectrochemical Reduction of 5-Hydroxymethylfurfural to 2,5-Bis(hydroxymethyl)furan using Water as the Hydrogen Source. ACS Catal. 2016, 6 (3), 1840−1847. (14) Xin, L.; Zhang, Z.; Qi, J.; Chadderdon, D. J.; Qiu, Y.; Warsko, K. M.; Li, W. Electricity storage in biofuels: selective electrocatalytic reduction of levulinic acid to valeric acid or gamma-valerolactone. ChemSusChem 2013, 6 (4), 674−86. (15) Faraday, M. Experimental researches in electricity - seventh series. Philos. T. R. Soc. 1834, 124, 77−122. (16) Kolbe, H. Untersuchungen über die Elektrolyse organischer Verbindungen. Liebigs Ann. Chem. 1849, 69 (3), 257−294. (17) Hofer, H.; Moest, M. Ü ber die Bildung von Alkoholen bei der Elektrolyse fettsaurer Salze. Liebigs Ann. Chem. 1902, 323 (3), 284− 323. (18) Schäfer, H. J. Recent Contributions of Kolbe Electrolysis to Organic Synthesis. Top. Curr. Chem. 1990, 152, 91−151. (19) Alonso, S.; Rendueles, M.; Diaz, M. Microbial production of specialty organic acids from renewable and waste materials. Crit. Rev. Biotechnol. 2015, 35 (4), 497−513. (20) Becker, J.; Lange, A.; Fabarius, J.; Wittmann, C. Top value platform chemicals: bio-based production of organic acids. Curr. Opin. Biotechnol. 2015, 36, 168−175. (21) Levy, P. F.; Sanderson, J. E.; Ashare, E.; Wise, D. L.; Molyneaux, M. S. Liquid fuels production from biomass; Final Report DOE/ET/20050-T1; U.S. Department of Energy, 1980. (22) Andreev, V. N.; Grinberg, V. A.; Dedov, A. G.; Loktev, A. S.; Moiseev, I. I.; Tsivadze, A. Y. Electrocatalytic biomass conversion into petrochemicals. Review. Prot. Met. Phys. Chem. Surf. 2013, 49 (1), 32−39.

(23) Wu, L.; Mascal, M.; Farmer, T.; Perocheau Arnaud, S.; Wong Chang, M. A. 2,7-Octanedione and 2,5-Dimethyladipic Acid From the Electrochemical Coupling of Biomass-derived Carboxylic Acids: C8 Platforms for Renewable Polymers and Fuels. ChemSusChem 2017, 10 (1), 166−170. (24) Miller, W. v.; Hofer, H. Synthese von Monocarbonsäuren der Fettreihe auf elektrochemischem Wege. Ber. Dtsch. Chem. Ges. 1895, 28 (3), 2427−2439. (25) Tashiro, M.; Tsuzuki, H.; Goto, H.; Ogasahara, S.; Mataka, S. Preparation of deuteriated adipic [2H2]-, [2H4]-, [2H6]-, and [2H8]-acids by use of kolbe electrolysis as a key reaction. J. Labelled Compd. Radiopharm. 1990, 28 (7), 855−866. (26) Iwakura, C.; Goto, F.; Tamura, H. Anodic Stability and Electrocatalytic Activity of DSA-Type Oxide Electrodes in CH3COOK/CH3COOH Solutions. Denki Kagaku oyobi Kogyo Butsuri Kagaku 1980, 48 (1), 21−25. (27) Markind, L. A.; Al’bertinskii, G. L. Some characteristics of the behavior of ruthenium-titanium oxide anodes in organic solvents. Elektrokhimiya 1980, 16 (6), 911. (28) Näslund, L.-Å.; Sánchez-Sánchez, C. M.; Ingason, Á .S.; Bäckström, J.; Herrero, E.; Rosen, J.; Holmin, S. The Role of TiO2 Doping on RuO2-Coated Electrodes for the Water Oxidation Reaction. J. Phys. Chem. C 2013, 117 (12), 6126−6135. (29) Knolle, J.; Schäfer, H. J. Kolbe-Electrolysis of Unsaturated Carboxylic Acids. Electrochim. Acta 1978, 23 (1), 5−8. (30) Ogumi, Z.; Yamashita, H.; Nishio, K.; Takehara, Z.-I.; Yoshizawa, S. Application of the solid polymer electrolyte (SPE) method to organic electrochemistryIII. Kolbe type reactions on PtSPE. Electrochim. Acta 1983, 28 (11), 1687−1693. (31) Stang, C.; Harnisch, F. The Dilemma of Supporting Electrolytes for Electroorganic Synthesis: A Case Study on Kolbe Electrolysis. ChemSusChem 2016, 9 (1), 50−60.

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Producing Widespread Monomers from Biomass Using Economical

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