Electrosynthesis - sustainable and disruptive

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1 Electrosynthesis - sustainable and disruptive Prof. Dr. Siegfried R. Waldvogel waldvogel@uni-mainz.de Bingen, November 15 th, 2017

Dark side of the green world Current discussion: electrosyntheses as potential component in smart grids Conventional: Coal / gas nuclear power Power-tochemistry "

2 Dark side of the green world Current discussion: electrosyntheses as potential component in smart grids Conventional: Coal / gas nuclear power Power-tochemistry " Power sources Regenerative: wind power photovoltaics solarthermal hydro power bio mass supply electricity grid Energy storage, buffer systems Customers demand time time

3 Pros for electrosynthesis Inherently safe Saving metals and rare elements/resources No reagent waste Reactive power adjustable New synthetic approaches (short cut of many steps and IP space!) Power to chemicals Green aspects Disruptive technology / game changer C&EN 2017, (March 13th)

4 Why higher organic molecules Reduction of CO 2 only to CO cost efficient Electro-conversion to larger molecules (value-added)

5 Electroorganic synthesis classical synthesis electroorganic synthesis reagents: e.g. oxidizer Folie Nr. 7 no reagent waste 0.06 per mole (2F@3V in Germany)

6 Electroorganic synthesis oxidation reduction radical reactions radical sequences generated bases Challenges: accumulation of product control following up reactions reversibility Folie Nr. 8

potential over-potential Electrolyte: supporting electrolyte ionic strength

7 Electroorganic synthesis + substrate product A N O D E intermediate intermediate intermediate Electrode material: inert/electrocatalysis potential over-potential Electrolyte: supporting electrolyte ionic strength solvation temperature convection, flow Current density Org. Process Res. Dev. 2016, 20,

GC/GC-MS or LC/LC-MS Divided/undivided cells Optimization: - current density - applied

8 Screening with product-driven criteria Electrode materials (10 different usually, >50 in stock) Electrolyte combinations (set of 5-8 tested, >200 possible) Product portfolio: GC/GC-MS or LC/LC-MS Divided/undivided cells Optimization: - current density - applied charge - temperature - separator material (> 20 available) - mediators Org. Process Res. Dev. 2016, 20,

9 Electrolysis cells (selection) Screening: 1-4 ml Small scale: ml Up-scaling to 1700 ml

10 Challenge: anodic cross-coupling reaction Electrochemical potential as strong selector Oxidation potential and nucleophilicity correlated Potential solutions: Separation of oxidation and coupling event: Cation-pool method Over stoichiometric amount of reagents: Hypervalent iodine reagents Mostly not compatible with phenols. Novel concept by electrolytes required! T. Morofuji, A. Shimizu, J. Yoshida, Angew. Chem. Int. Ed. 2012, 51, 7259.

HFIP as electrolyte Large electrochemical window Strong H-bonding donor Phase separation on nano-scale H-bonding network in solid state Increases half-life of spin centers dramatically A.

11 HFIP as electrolyte Large electrochemical window Strong H-bonding donor Phase separation on nano-scale H-bonding network in solid state Increases half-life of spin centers dramatically A. Berkessel et al. J. Am. Chem. Soc. 2006, 128, L. Eberson et al. Angew. Chem. Int. Ed. 1995, 34, 2268; J. Chem. Soc., Perkin Trans. II 1995, Electrochim. Acta, 2012, 62, 372. ACS Catal. 2017, 7, 1846.

nucleophilic B less electron rich A + electrophilic

12 Decoupling of nucleophilicity and oxidation potential A electron rich easy to oxidize less nucleophilic B less electron rich A + electrophilic coupling B nucleophilic solvate based explains cross-coupling 14

13 Next level Product Selectivity in HFIP/MeOH Yield HFIP/MeOH >100:1 50% >100:1 36% >100:1 61% >100:1 63% Angew. Chem. Int. Ed. 2014, 53,

14 Merit of electrosynthesis (application) Shortcut of 5-6 steps! Angew. Chem. Int. Ed. 2014, 53,

15 Phenol-phenol cross-coupling Metal-free and reagent-free cross-coupling! Angew. Chem. Int. Ed. 2014, 53, (VIP manuscript) Highlighted in C&EN April 7, 2014, 34. Highlighted in ChemCatChem 2014, 6,

Partially protected biphenols Partially protected non-symmetric biphenols: Selective modification of hydroxy groups Control of reactivity and selectivity of desired

16 Partially protected biphenols Partially protected non-symmetric biphenols: Selective modification of hydroxy groups Control of reactivity and selectivity of desired ligands / catalysts Non-symmetric catalysis products via nonsymmetric ligands Challenge for conventional synthesis: Selective protection of chemically similar hydroxy groups

17 Partially protected biphenols: Conventional synthesis Partial demethylation of protected biphenols with strong Lewis acids: R. Francke, R. Reingruber, D. Schollmeyer, S. R. Waldvogel, J. Agric. Food. Chem. 2013, 61, Partial protection of non-protected biphenols: N. Nishimura, K. Yoza, K. Kobayashi, J. Am. Chem. Soc. 2010, 132,

18 Protection of phenols as silyl ethers First direct synthesis of AB PG not viable by conventional chemical methods No deblocking while coupling reaction, high yields, and selectivity! Broad scope (synthetic scale ~ 2 g product) Selection out of >40 screened substrate combinations

Improved ratio of A:B TIPS : 1:3 1:2 Selective

19 Up-scaling of anodic cross-coupling Scale-up: 25 ml 200 ml beaker-type cell 8-fold reaction size No drop in yield: 84% Improved ratio of A:B TIPS : 1:3 1:2 Selective coupling-reaction: Improved work-up via short-path distillation 1,5 g AB TIPS 12,5 g AB TIPS

Rationale Protecting group leads to torsion angle

selectivity for partially protected biphenols

groups Very good yields up to 92% High selectivity:

20 Rationale Protecting group leads to torsion angle >60, aryl moiety turns in EWG Improved yields and selectivity for partially protected biphenols Broadened substrate scope when using protection groups Very good yields up to 92% High selectivity: 100:1 22 Angew. Chem. Int. Ed. 2016, 55, (VIP and front cover)

21 Motivation Using waste streams of pulping Kraft process wood waste cellulose lignin hemicellusose tall oil turpentine fraction

22 Lignin Wood as superior renewable (no competition with nutrition purposes) Waste mostly serve for energy production Lignin is a side product of the Kraft process and the most abundant, renewable source for aromatic compounds (1 mio t/a // mio t/a)

23 Lignin Anodic treatment Partial use of waste stream as a feedstock Work-up concept should be cost efficient Most scientist ignore down stream processing!

Electrochemical degradation of lignin Vanillin Anodic

formation of aromatic compounds - Mild reaction

derivatives Challenges: - Selective conversion low

24 Electrochemical degradation of lignin Vanillin Anodic cleavage Acetovanillone Guaiacol Goals: - Selective formation of aromatic compounds - Mild reaction conditions - Highly selective formation of phenol derivatives Challenges: - Selective conversion low yield but value-added - Non-selective degradation very complex mixture 26

) Strongly basic media Our approach: T <100 C Ambient pressure Weakly alkaline media Challenge: anode

25 Electrochemical degradation of lignin Known conversions: [1] Classic oxidants Toxic by-products Direct electrochemical oxidation Yields up to 6 wt% * Problem: Very drastic conditions T >150 C p ~ 5 bar (autoclave!) Strongly basic media Our approach: T <100 C Ambient pressure Weakly alkaline media Challenge: anode corrosion! * Based on used Kraft lignin 27 [1] C. Z. Smith, J. H. P. Utley, J. Hammond, J. Appl. Electrochem. 2011, 41,

26 Chemical background Lignin conversion: - inexpensive media - electrocatalysis - simple anodes Initial conditions (2010): 3M NaOH, 80 C current density: j = 0.68 ma/cm 2

27 Nickel anodes Lignin upon dissolving in NaOH Aromatic compounds already in lignin After electrolysis at Ni/Ni Strong enrichment of vanillin

28 Silver versus Nickel Electrolysis at Ag Ni Ag and Ni as anodic materials represent the key selective formation of vanillin minor components only in traces Electrolysis at Ni Ni

29 The anode will be the key Yield Nr. Anode Cathode Electrolyte Q [C g -1 ] V [%] * AV [%] * VS [%] * 1 Ag Ni 3 M NaOH Ni Ni 1 M NaOH Ni Ni 2 M KOH NiOOH NiOOH 3 M NaOH Ag/Ni Ni 1 M NaOH Monel Monel 3 M NaOH up to 2.84% vanillin for electrolysis run highly selective formation of vanillin silver prone to corrosion

30 Electrochemical degradation of lignin Yield of vanillin / wt% * Important influence of the anode material Materials with high stability against corrosion Influence of the base concentration on the yield of vanillin 3,5 Nickel basis Cobalt basis 3 2,5 2 1,5 1 0,5 0 Vanillinausbeuten Yield (1 M NaOH) (1 M NaOH) Vanillinausbeuten Yield (2 M NaOH) (2 M NaOH) Vanillinausbeuten Yield (3 M NaOH) (3 M NaOH) * Based on used Kraft lignin Yield >3 wt% * for electrolysis run Beil. J. Org. Chem. 2015, 11,

31 Electrochemical degradation of lignin Nickel foam electrodes: - Current density strongly enhanced (only 5% of electrolysis time) - 3D electrode / cell design - Inexpensive electrode (Ni/P alloy) - Stable in black liquor Beil. J. Org. Chem. 2015, 11,

32 Intensity Intensity Electrochemical degradation of lignin/black liquor Highly selective reaction Vanillin and acetovanillone are the predominant products which can be observed by gaschromatic methods Gaschromatogram of the lignin/bl components prior electrolysis time / min Highly selective enrichment of vanillin due to electrochemical treatment 34 time / min

33 Electrochemical degradation of lignin Optimization of the anode material allows: Yields up to 3 wt% under mild conditions High stability against corrosion Highly selective formation of vanillin Large amount of unreacted lignin remains! Challenges: Enhanced degradation of lignin Recovery of the reaction products without complete neutralization of the solution

34 Work-up concept Solution: Solid phase extraction of endangered products! adsorption electrolysis next cycle allows multiple cycles of electrolysis and extraction new application for strongly basic anion exchange resins The aim is a partial degradation of the applied lignin

35 Work-up concept Adsorption via ion exchange resin direct adsorption from electrolyte/alkaline solution no loss easy regeneration of ion exchange resin lignin particles remain unaffected (size exclusion) Beil. J. Org. Chem. 2015, 11,

36 Ion exchange resins Ion exchange resins work on a broad range of alkaline media: interactions: Coulomb van der Waals p,p interactions

37 Ion exchange resins Dowex Monosphere 550a OH quatenary ammonium functionalities stable polystyrene backbone up to 90% vanillin adsorption from alkaline solution but: low adsorbate-adsorbent ratio < 0.05 (ratio for technical purposes ~ 0.20) Folie Nr. 39

Raw material black liquor Black liquor lignin-containing liquor from Kraft process black liquor contains aromatic compounds: vanillin, guaiacol, acetovanillone 3 mg/ml aromatic compounds in black

38 Raw material black liquor Black liquor lignin-containing liquor from Kraft process black liquor contains aromatic compounds: vanillin, guaiacol, acetovanillone 3 mg/ml aromatic compounds in black liquor possible loss due to over-oxidation during electrolysis project: adsorption of aromatic compounds before and after electrolytic lignin degradation application of Dowex Monosphere 550a OH to black liquor: adsorption of up to 74% aromatic phenols D. Schmitt, N. Beiser, C. Regenbrecht, M. Zirbes, S. R. Waldvogel, Sep. Purif. Technol. 2017, 181, 8 17.

39 Adsorption from black liquor Adsorption enables easy access to four phenol derivatives Controlled release of adsorbed phenols by acidic treatment Complete depletion of black liquor regarding its content of low molecular phenols Anion exchange resin can be regenerated and reused Int. Guaiacol Vanillin Acetovanillone 4,4 -Dihydroxy-3,3 -dimethoxy stilbene Time / min Total Yield of phenols up to 1.6 mg ml 1 black liquor D. Schmitt, N. Beiser, C. Regenbrecht, M. Zirbes, S. R. Waldvogel, Sep. Purif. Technol. 2017, 181, 8 17.

Combined process of adsorption and anodic oxidation Electrochemical

Composition of completely depleted black liquor Int.

after anodic oxidation time [min] Successful anodic degradation of lignin in

40 Combined process of adsorption and anodic oxidation Electrochemical degradation of lignin in completely depleted black liquor? ISTD Int. Composition of completely depleted black liquor Int. ISTD vanillin acetovanillone Composition of completely depleted black liquor after anodic oxidation time [min] Successful anodic degradation of lignin in depleted black liquor! D. Schmitt, C. Regenbrecht, M. Schubert, D. Schollmeyer, S. R. Waldvogel, Holzforschung 2017, 71,

Combined process of adsorption and anodic oxidation Combined process enables a drastic increase of the vanillin yield Yield [mg ml 1 ] guaiacol

of phenols from 1.6 mg ml 1 up to 1.9 mg ml 1 by combination of adsorption and anodic degradation! D. Schmitt, N. Beiser, C. Regenbrecht, M. Zirbes, S.

41 Combined process of adsorption and anodic oxidation Combined process enables a drastic increase of the vanillin yield Yield [mg ml 1 ] guaiacol vanillin acetovanillone 4,4 -dihydroxy-3,3 -dimethoxy stilbene adsorption anodic oxidation process step combined yield Maximization of the total yield of phenols from 1.6 mg ml 1 up to 1.9 mg ml 1 by combination of adsorption and anodic degradation! D. Schmitt, N. Beiser, C. Regenbrecht, M. Zirbes, S. R. Waldvogel, Sep. Purif. Technol. 2017, 181, D. Schmitt, C. Regenbrecht, M. Schubert, D. Schollmeyer, S. R. Waldvogel, Holzforschung 2017, 71,

42 Summary Electroorganic synthesis is a useful and versatile tool Reagent and metal-free coupling Lignin degradation at Ni based alloys Compatible with lack liquor Utility - workup is crucial Folie Nr. 44

43 Acknowledgement Prof. Dr. Robert Francke (Evonik) Waldvogel group, August 2017

Electrochemical Conversion of Lignin

Electrochemical Conversion of Lignin Berlin, 2009 March 10 th Prof. Dr. Siegfried R. Waldvogel Kekulé-Institut für Organische Chemie und Biochemie Rheinische Friedrich Wilhelms-Universität Bonn Outline