Electrochemical Conversion of Lignin

Berlin, 2009 March 10th

Prof. Dr. Siegfried R. Waldvogel

Kekulé-Institut für Organische Chemie und BiochemieRheinische Friedrich Wilhelms-Universität Bonn

Outline

• Historical aspects

• Why electrochemistry?

• Boron-doped diamond electrodes

• Consortium and concept of ELEKTRA

• Organic electrochemistry on boron-doped diamond electrodes

• Summary

Historical aspects

Previous work:

• EP 00 245 418 B1 (1985): Electrochemical treatment of lignins

Conversion of lignin by heavy metal electrodes and their salts.

• EP 01 036 836 B1 (1999): Verfahren zur elektrochemischen Umsetzung

organischer Verbindungen an Diamantelektroden.

Owner: BASF AG

• WO 2005 066 390 A2: Elektrochemische alkoxylierende Kohlenstoff-Kohlenstoff-Bindungsspaltung am 1,2-Diphenylethan und Derivaten an

der Diamantelektrode.

Owner: BASF AG

Why Electrochemistry?

Advantages Drawbacks

• No reagent waste

• Selectivity by oxidation potential

• Reaction rate by current density

• Mild reaction conditions

• Novel electrode materials

• Heterogeneous reaction

• More specific set up

• Coupled processes

• Oxidation: O2 as competitor

Green Chemistry

Electroorganic synthesis of aldehydes

direct and selective oxidation of substituted toluenes to benzaldehydes:

- technical process

- as paired electrolysis highly energy efficient

CH

anode, MeOHR

CH3

R

CHO

R

H3CO OCH3

MeOH

H2O

Novel electrodes:Boron doped diamond (BDD)

- inexpensive coating by carbon plasma, 100-2000 ppm B

- support Si, Ti or Nb, diamond coating 1-10 µµµµm

- electrochemically inert

- non toxic

- sustainable

- large overpotential in aqueous media:

cathode: ≈ 1.1 V for H2 (like mercury)anode: ≈ 2.3 V for O2 (superior to platinum)

- direct generation of .OH / O3

⇒⇒⇒⇒ total oxidation/mineralization⇒⇒⇒⇒ disinfection

-60

-40

-20

0

20

40

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

E [V vs. ESH]

j [mA cm-2]

Pt

BDD

Novel electrodes:Boron doped diamond (BDD)

BDD production plants at CONDIAS, Itzehoemaximum size: > 1m x 1m

Boron doped diamond (BDD) electrodes

- hydroxyl species stronger oxidants than O3

- free path length of •OH approx. 100 nm

⇒⇒⇒⇒ mediator necessary

- commonly methanol recommended as mediator

U. Griesbach, I. M. Malkowsky, S.R. Waldvogel, Green Eletroorganic Synthesis Using BDD Electrodes,

in Environmental Electrochemistry, Springer, 2009, in press.

Boron doped diamond (BDD) electrodes

- no tarring or colorizing effect

- side effect: mineralization

⇒⇒⇒⇒ control of reactivity crucial

Collaborative project ELEKTRA

ELEKTRA – Elektrochemische Transformation

nachwachsender Rohstoffe an Bor-dotierten

Diamant-Elektroden zu wertvollen Chemikalien.

Collaborators:

BASF SE, Ludwigshafen (GCI/E)

CONDIAS GmbH, Itzhoe

Universität Bonn, AK Prof. Waldvogel

(coordination)

Collaborative project ELEKTRA

Products:

reaction parameters:

electrolytes

mediators

separation technique

type of lignin

…

CHO

OH

OCH3

OH

H3CO OCH3

CHO

OH

CHO OH

OCH3

vanillin syringaaldehyde 4-hydroxybenzaldehyde guaiacol

Advantages of approach:

no organic solvents

no heavy metal contamination

residue highly carboxylated

…

Boron doped diamond electrode

Oxidation of 2,4-DMP on BDD electrodes

BDD anode

OH OH

HO

+

O

O

11% H2O, 6% salt

70 °C, 10 mA/cm2

32

43

30

42

29

CE [%]

5

4

3

2

1

No.

19:147Si, 10 µmTEMAMS

18:149Nb, 10 µmTEMAMS

17:139Si, 1 µmMe4NOH

16:146Si, 1 µmEMIMS

17:156Si, 1 µmTEMAMS

selectivitybiphenol : ketone

biphenol [%]BDD

support, thicknessammonium salt

N+ MeOSO3−

N+N

HOSO3−

N+ HO−

Eur. J. Org. Chem. 2006, 4569-4572.

Boron doped diamond electrode

Reaction progress of the oxidation of 2,4-DMP on BDD electrodes

oxidationBDD anode

OH OH

HO

+ ...

yieldbiphenol

[%]

[F per mol 2,4-DMP]

Eur. J. Org. Chem. 2006, 4569-4572; WO 2006077204 A2 20060727; Nachr. Chem. Tech. 2008, 56, 525-527.

Diamonds are a chemist´s best friend

Eur. J. Org. Chem. 2006,

Issue 20 (October).

Boron doped diamond electrode

Challenge: narrow scope of substrates

⇒ mediators, inert to degradation

e.g. fluorinated alcohols

74 %

OH

OHR

2BDD anode

Et3NMe MeOSO3HFIP

OH

HO

R

R

O

O2

41 %

OH

2

24 %

OH

2

H3C

F

Chem. Eur. J. 2009, 15, 2273-2277.

Summary

• Generation of oxyl radicals at BDD electrodes

• Degradation of lignin to aldehydes and other aromatic compounds

• BDD electrodes as efficient and sustainable tool for chemical synthesis

Acknowledgement

Carsten SieringJörn KulischAxel KirsteUrsula BissaAnke SpurgKathrin WehmingMartin BomkampNina WelschoffPia KönigsKristina HackelöerJoaquin Vallet BarjauDaniel Lubzcyk

AlumniDr. Itamar MalkowskyDr. Daniela MirkDr. Jürgen LörgenDr. Matthias SchopohlDr. Beate KramerDr. Alen IanniDr. Andreas FaustDr. Björn RinkerChristina RommelLisa MausKatharina Gottfried

Funding

Fonds der Chemischen Industrie

SFB 813 Chemistry at Spin Centers (DFG)

BASF SE

Collaborators (BASF)

Dr. Andreas Fischer

Dr. Ulrich Griesbach

Dr. Florian Stecker