Continuous anodic oxidation of TEMPO as a mediator for selective synthesis of aldehydes from primary alcohols

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+ Continuous anodic oxidation of TEMPO as a mediator for selective synthesis of aldehydes from primary alcohols Christoph Deckers 1, Martin Linden 1, Julian Heinrich 1, Holger

1 + Continuous anodic oxidation of TEMPO as a mediator for selective synthesis of aldehydes from primary alcohols Christoph Deckers 1, Martin Linden 1, Julian Heinrich 1, Holger Löwe 1,2* 1 Johannes Gutenberg-University Mainz, Duesbergweg 10-14, D Mainz, Germany 2 Fraunhofer ICT-IMM, Carl-Zeiss-Str , Mainz, Germany * loewe@uni-mainz.de

2 Outline Anelli Oxidation One-Phase Approach Mixing and Residence Time Multi-Phase Approach Mixed Double Emulsions Electrooxidation Voltammetry Experiments Batch Process Continuous Process Outlook 2

3 Anelli Oxidation 1 TEMPO+ 2 TEMPOH V.A. Golubev, E.G. Rozantsev, M.B. Neimann, Izv.Akad.Nauk SSSR, 1965, 11, P.L. Anelli, C. Biffi, F. Montanari, S. Quici, J.Org.Chem., 1987, 52, M. Zhao, J. Li, E. Mano, et al., J.Org.Chem., 1999, 64, TEMPOH TEMPO TEMPOBr TEMPO TEMPO+ TEMPOH 3

4 Anelli Oxidation 2 Preoxidation 2 + TEMPO TEMPO+ + Comproportionation + Pre-oxidation of TEMPO NaOCl in situ causes side products Br 2 in organic solvents (requires separation) electrochemical oxidation in water (several alcohols insoluble, solvent changes, phase separation) multiphase flow with excess of TEMPO+ TEMPO+ TEMPOH 4

5 One-Phase Approach Mixer Segment T-Piece SIMM-V2 Continuous flow Small window for efficient mixing; broad residence time distribution Mixing controlled; broad residence time distribution Segmented flow Residence time controlled Mixing and residence time controlled 5

6 One-Phase Approach Residence time t R = Channel length Volume flow Constant volume flow; different capillary length t R = f(capillary length) Measurable Constant mixing efficiency Constant capillary length; different volume flow t R = f(volume flow) Programmable Variable mixing efficiency 6

One-Phase Approach C 1.00 0.75 0.50 SIMM-V2, heterogeneous SIMM-V2, homogeneous T-Jct., heterogeneous T-Jct.

7 One-Phase Approach C SIMM-V2, heterogeneous SIMM-V2, homogeneous T-Jct., heterogeneous T-Jct., homogeneous Residence time dependency: Fixed flow rates Observation by GC and by eye (bleaching) Full conversion after approx. 3.5 min No significant differences between mixer types and flow patterns Kinetic limit reached t R / min 7

8 One-Phase Approach C Flow rate/mixing dependency: Fixed reactor volume Conversion decreases with increasing residence time Decreasing flow rate/mixing efficiency Increased reaction time unable to compensate loss in mixing efficiency t R / min 8

shell conti Multi-Phase Approach core PTFE-capillary OD = 1/16, ID = 1,0 mm water

Video: Link toluene FC-40 TM Coaxial double emulsion generator 2 T-junctions to insert

droplet is infused into shell droplet while latter is generated V. Misuk, A. Mai, Y.

9 shell conti Multi-Phase Approach core PTFE-capillary OD = 1/16, ID = 1,0 mm water PEEK-Capillary OD = 360 µm, ID = 150 µm PTFE-Capillary OD = 1/32, ID = 0,5 mm outlet Video: Link toluene FC-40 TM Coaxial double emulsion generator 2 T-junctions to insert core and shell capillary into main channel Coplanar outlet of inner capillaries Core droplet is infused into shell droplet while latter is generated V. Misuk, A. Mai, Y. Zhao, J. Heinrich, D. Rauber, K. Giannopoulos, H. Löwe, J. Flow Chem., 2015, 5(2),

Crosses shell droplet twice every winding Video: Link Reversal point V. Misuk, A. Mai, Y.

10 Gravity Multi-Phase Approach Video: Link Reversal point Passive mixing: Gravity induced Capillary coiled on cylinder Double emulsion, core droplet pulled downwards by gravity Crosses shell droplet twice every winding Video: Link Reversal point V. Misuk, A. Mai, Y. Zhao, J. Heinrich, D. Rauber, K. Giannopoulos, H. Löwe, J. Flow Chem., 2015, 5(2),

Multi-Phase Approach FC-40 TM aqueous TEMPO+ C 1.00 0.75 0.50 0.25 0.

11 Multi-Phase Approach FC-40 TM aqueous TEMPO+ C excess 1:1 excess 3:1 excess 6:1 excess 10: t R / min Gravity induced mixing: Oxidant and alcohol in different phases Interface reaction Extended reaction time necessary 9-fold excess of TEMPO+ reduces reaction time to 17 min Easy recycling of remaining TEMPO+ 1 in toluene 11

jiggling of core droplet Stirring of shell phase with adjustable frequency V. Misuk, A.

12 Multi-Phase Approach camera droplet generation sample collection retention unit orbital shaker Video: Link Active mixing: Retention unit mounted on orbital shaker Double emulsion, jiggling of core droplet Stirring of shell phase with adjustable frequency V. Misuk, A. Mai, Y. Zhao, J. Heinrich, D. Rauber, K. Giannopoulos, H. Löwe, J. Flow Chem., 2015, 5(2),

13 Multi-Phase Approach Stirred double emulsion: 1.7 eq of TEMPO+ used Conversion 12% in 3 min without mixing Increase to approx. 22% conversion between 0.2 Hz and 0.5 Hz Maximum expected around 0.35 Hz Further Investigation necessary f orbital shaker / Hz 13

14 Electrooxidation Disproportionation of TEMPO: Full conversion to TEMPO+ and TEMPOH at ph = 0 At ph = 2 TEMPO+ yield is 68% Proportion of 33% of TEMPO+, TEMPO and TEMPOH each ph 3 suppresses disproportionation ph 14

15 Electrooxidation Comproportionation of TEMPO+ and TEMPOH: TEMPOH formed in situ by adding 1 to TEMPO+ Almost total comproportionation at ph = 9 80% TEMPO+ left in neutral media No comproportionation at ph = Alcohol oxidation with stochiometric amounts of TEMPO+ requires ph < ph 15

I [µa] I [µa] Electrooxidation 2,0 1,5 1,0 0,5 0-0,5-1 -400 ph=2 ph=7 ph=9-200 0 200 400 600 E GC/Pt [mv] CV and RDE measurements of TEMPOH: No conversion to TEMPO+ observed in acidic medium (ph =

16 I [µa] I [µa] Electrooxidation 2,0 1,5 1,0 0,5 0-0, ph=2 ph=7 ph= E GC/Pt [mv] CV and RDE measurements of TEMPOH: No conversion to TEMPO+ observed in acidic medium (ph = 2) Neutral or alkaline medium required Intermediary TEMPO not observed Proved by additional CV/RDE measurements of TEMPO ph=2 ph=7 ph= E GC/Pt [mv] 16

17 Electrooxidation Oxidation path: Easy oxidation TEMPO TEMPO+ No direct oxidation TEMPOH TEMPO+ Only in alkaline media Preceding deprotonation to TEMPO- TEMPO- TEMPO TEMPO+ TEMPO- TEMPO much slower than TEMPO TEMPO+ A. M. Janiszewska, M. Grzeszczuk, Electroanalysis, 2004, 16 (20),

18 Electrooxidation Batch electrolysis: 0.0 (a) TEMPO solution, 5h (b) TEMPO solution, 16h (c) recycled solution from (b), 16h Maximum yield 33% Decomposition of water acidifies anolyte Disproportionation of TEMPO 18

19 Electrooxidation 0.5 A. M. Janiszewska, M. Grzeszczuk, Electroanalysis, 2004, 16 (20), Batch electrolysis: Maximum yield 33% Decomposition of water acidifies anolyte Disproportionation of TEMPO TEMPOH associates with TEMPO Oxidation is prevented 0.0 (a) TEMPO solution, 5h (b) TEMPO solution, 16h (c) recycled solution from (b), 16h 19

20 Electrooxidation Catholyte in 0.1M Na 2 SO 4 Anolyte out Anolyte out + Catholyte in Catholyte out Catholyte out Anolyte in 0.1M Na 2 SO 4 0.1M TEMPOH ph 8 Anolyte in 20

21 Electrooxidation TEMPO+ TEMPO Continuous electrolysis: 0.05 Decomposition of water acidification 0.00 (a) U = 1.5 V; ph = 8 (b) U = 2.0 V; ph = 8 (c) U = 2.0 V; ph = 7, buffered Maximum yield 33% Buffering at ph = 7 prevents dimerization, lowers oxidation yield due to protonation of TEMPO- 21

Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab" Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab"

22 Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab" Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab" Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab" Outlook circulating FC-40 continuous phase Electrochemical microstructured reactor: substrate feed TEMPO+ ph 2 phase separator Divided cell (Nafion TM membrane) Ti meshed metal baffle, platinized Galvanostatic mode Challanges: ph change required anolyte cycle + Flow rate adjustment Continuous phase separation TEMPO initial feed ph 9 TEMPOH oxidans recycling phase separator product Recirculation of mediator Objective: Fully automated process J. Heinrich, Automated reaction monitoring and control with microcontrollers on the way to the "Internet of Lab", Ph.D. Thesis, University Mainz,

Outlook Selective Oxidation CrO 3 Betulin

synthesis from natural/renewable resources

23 Outlook Selective Oxidation CrO 3 Betulin (3β)-Lup-20(29)-en-3,28-diol Betulin aldehyde Betulinic acid and derivates Betula pendule Fraxinus americana Sorbus americana API synthesis from natural/renewable resources Antitumor and inflammatory properties Treatment of leukemia, malaria etc. 23

24 Conclusions One-phase process requires much shorter reaction time than multi-phase reaction Multi-phase approach simplifies oxidans recycling significantly Allows usage of huge excess of oxidans Allows mixing in segmented flow Disproportionation equilibrium of TEMPO requires ph < 2 for optimal oxidation conditions Alkaline medium required for reoxidation of TEMPOH Water decomposition and association of TEMPOH and TEMPO major problems in batch and continuous oxidation, maximum yield of TEMPO+ 33% Fully integrated continuous process requires ph changes and continuous phase separation Applications in API synthesis, focus on betulin and derivates 24

25 Thank You! Prof. Dr. Holger Löwe Christoph Deckers Dr. Julian Heinrich

Prepared for presentation at the 2004 Annual Meeting, Austin, TX, Nov. 7-12

Prepared for presentation at the 2004 Annual Meeting, Austin, TX, Nov. 7-12 New products from partial oxidation of glycerol Martin Ernst, Rolf Marr Department of Chemical Engineering and Environmental Technology Graz University of Technology Inffeldgasse 25, A-81 Graz, Austria