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Roger A. Sheldon
Delft University of Technology
&
CLEA Technologies
Green Catalytic Oxidations
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Green Catalytic Oxidations
Outline
1.Introduction
2.Pd-catalyzed oxidations in water
3.Organocatalysts; stable N-oxy radicals
4.Biocatalysis
5.Conclusions & Prospects
2
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Tonnage E Factor
Oil Refining 106-108 <0.1
Bulk Chemicals 104-106 <1 - 5
Fine chemical Industry 102-104 5 - >50
Pharmaceutical Industry 10-103 25 - >100
R.A.Sheldon, Chem & Ind, 1992, 903 ; 1997, 12
E Factor = kg waste/kg product
[i]
“Another aspect of process development mentioned by all pharmaceutical process chemists who spoke with C&EN is the need for determining an E Factor”. A. N. Thayer, C&EN, August 6, 2007, pp. 11-19
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What about process water? Only counts if it needs to be treated?
Major Sources of Waste • Stoichiometric Reagents
- Acids & Bases (e.g H2SO4 and NaOH)
- Oxidants & reductants (e.g. K2Cr2O7 & Fe/HCl)
• Solvent losses ( 85% of non-aqueous mass)
- Air emissions & aqueous effluent
• Multistep syntheses
The Solution :
Atom & step economic catalytic processes
in alternative reaction media (H2O, scCO2, ILs)
(the best solvent is no solvent)
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5
Oxidation & Reduction
OXIDATIONS
Traditional inorganic oxidants • Generation of large amounts of pollutants (Cr, Co, Mn ….)
• Waste streams costly to treat and dispose of.
Use of benign oxidants • H2O2 and O2
• Cheap & readily available
• H2O as byproduct
REDUCTIONS
Traditional metal (Fe /HCl) and metal hydride (LiAlH4) reagents • Generation of large amounts of metal salts as waste
• Often expensive & hazardous
Catalytic hydrogenation & enzymatic reduction • Cheap & readily available H2
• Atom efficient / low E factor
• No byproduct (or H2O)
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Alcohol Oxidation 6
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Classical Alcohol Oxidations
I O
O
A c O O A c O A c
+
H3C S
CH3
Cl
Dess-Martin Swern
Atom Utilisation = 44% E = > 3
3
OH
2 CrO3 + 3 H2SO4
- Cr2 (SO4)3 3
O
Other reagents favoured by organic chemists
• Poor atom economy • Hazardous reagents
“It’s hexavalent chromium, highly toxic, highly
carcinogenic. Gets into your DNA, so you
pass the trouble along to your kids.”
Julia Roberts in ‘Erin Brokovich’
(Jones reagent)
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PIPO/NaOCl
TEMPO/NaOCl
Cr(VI)
PCC/PDC
SCOPE SCALABILITY
GREENNESS SUSTAINABILITY
IBX
Dess-Martin
DMSO/DCC
Moffat
DMSO/(COCl)2
Swern
Me2S/Cl2
Air/TEMPO/H2O
MnO2
BaMnO4
NiO2
Air/Metal cat./H2O
Air/Metal cat.
Oxidation of Primary Alcohol to Aldehyde
P. Dunn et al, Green Chem. 2008, 10, 31-36
Venn and the Art of Green Chemistry
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Water - Polar, inert and clean solvent - Facile product separation - Cheap and widely available - Non-flammable and non-toxic - Odourless and colourless
Recycling of catalyst
Catalytic Oxidations in Water
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Jöns Jacob Berzelius, Ann.(1828) 13, 435
E= >10
K2PdCl4 + C2H5OH
Pd(0) + C2H4O
+ 2 HCl + 2 KCl
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Pd2+ L water
air
R
OH
R
O
Green, Catalytic Alcohol Oxidations
G.J. ten Brink, I.W.C.E. Arends and R.A. Sheldon,
Science 287 (2000) 1636-9.
• Air as oxidant
• No organic solvent
• Catalyst recycling via phase separation
(recycled 4 times without activity loss)
N
N
P d ( O A c )2
N a O3 S
N a O3 S
P d 2 + - b a t h o p h e n a n t h r o l i n e ( L )
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Aerobic Oxidation of Alcohols with Pd(II) – Diamine Catalysts
(1) G.J. ten Brink, I.W.C.E. Arends and R.A. Sheldon, Science 287 (2000) 1636 (2) B. P. Buffin, N. L. Belitz, S. L. Verbeke, J. Mol. Catal. A: Chemical, 2008, 284, 149 (3) D. S. Bailie, G. M. A. Clendenning, L.McNamee and M. J. Muldoon, Chem. Commun., 2010, 46, 7238
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Steric Effects
N
N
O H
H O N
N
Pd Pd
R R
R R
2 +
N
N O H
Pd
R
R
+
2
R=Me
Cup*Pd(OAc)2
Structure in aq. solution Active catalyst
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TOF (h-1) 50 150 1800
OH
+ 0 . 5 O2
P d ( O A c )2 / L (0.1-0.5mol%)
O
+ H2O
a i r ( 3 0 b a r ) / 8 0oC / 4 h
NaOAc (25mol%)
L PhenS BathocuproinS Cuproin
N N
SO3Na
N N
N N
SO3Na NaO3S
NaO3S
Solvent H2O H2O H2O / DMSO (1:1)
Steric Effects
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L =PhenS Cuproin
C=C C=O acetylene
OR SR SiR3
(O)S=O SO3R NR2
CN CONH2 CO2R
Alcohol (0.3M),0.5m% LPd(OAc)2
25m % NaOAc in DMSO/H2O
800C/30 bar air,4h
75 %
~ 2 % > 99%
O
OH
O
8 %
O
O
O2 OH
Cuproin/Pd(OAc)2 : Functional Group Tolerance
N N L =
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Pd-nanoparticles
Pd(O2CCF3)2/neocuproin =1/1 ethylene carbonate in H2O
Pd(O2CCF3)2/neocuproin =1/1 PEG3400 in H2O
Particle size: 5 nm Particle size: 3 nm
See also I. I. Moiseev et al, Chem. Commun. 1985, 937-8 16
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Apo-Ferritin
K2PdCl4 Purification H2
Pd-Ferritin as an Oxidation Catalyst
OH
CH3O
O Pd-Frt
O2
H2O, 80oC CH3O
Seda Aksu-Kanbak
Chemomimetic biocatalysis
Thermostable Fer from Pyrococcus furiosus
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Catalytic Oxidation of Alcohols in Water with Pd-Ferritin
O H
1 9 7
O H
36
O H
1 0 1
OH
3
O H
3 7
O H
48
O H
1 38
M e O
O H
1 9
N
O H
3
O O H
12
R1
R2
H
OH
+ 0 . 5 O2 P d - F e r ( 0 . 4 m o l % )
H2O / 8 0 o C
3 0 b a r 8 % O2 / N2
R1
R2
O + H2O
TOF (h-1)
TOF (h-1)
N.B. Pd-Fer catalyzes the Suzuki coupling in aqua
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Organocatalysis
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O H
H
R1
R2 R2
R1
O
TEMPO (1 m%) NaBr (10 m%)
CH2Cl2, H2O, 0°C
+ NaOCl + NaCl + H2O
P.L.Anelli, C.Biffi, F.Montanari, S.Quici,JOC,52,2559 (1987)
OCl .
N
OH
N
O OH
O H
H
R1
R2
R2
R1
O + H2O Cl
-
-
-
+
Stable Nitroxyl Radicals: Versatile Catalysts for Alcohol Oxidations
There are many shades of green!
20
N
O.
TEMPO
PIPO
N N
N N
NH(tert-octyl)
(CH2)6
N
O.
N
N
O.
5
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PIPO Catalyzed Oxidations:Bromide & DCM-Free
A.Dijksman,I.W.C.E.Arends,R.A.Sheldon,Chem.Comm.2000,271
PIPO
N N
N N
NH(tert-octyl)
(CH2)6
N
O.
N
N
O.
5
substrate
1-octanol
1-hexanol
2-octanol
cyclooctanol
benzyl alcohol
1-phenylethanol
time (min)
45
45
45
45
45
30
30
conv. (%)
90
80
89
99
100
100
100
sel. (%)
50
94a
95a
>99
>99
>99
>99
• PhCH2OH / PhCH(OH)CH3 95 / 4
• 1-octanol / 2-octanol 86 / 1
• Readily accessible from Chimassorb 944 and recyclable
• But still using NaOCl as stoichiometric oxidant
a. MTBE as solvent
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Biocatalysis is Green & Sustainable • Enzymes are derived from renewable resources and are biodegradable • Avoids use of (and product contamination by)
scarce precious metals • Mild conditions: ambient T & P in water
• High rates & highly specific : substrate, chemo-, regio-, and enantiospecific • Higher quality product • No special equipment needed
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OH H
O
+ 0 . 5 O 2
(5m%)
Cu(II) / bipy (5m%)
Base / MeCN / H2O
Dioxygen (Air) as Oxidant
RCH2OH
RCHO
N
O
+
N
OH
Highly selective for 1e alcohols
Laccase : a blue enzyme for green chemistry
+ H2O
23
N
. O
O2
H2O
l a c c a s e
l a c c a s e o x
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Oxidation of Benzylic Alcohols
Substrate
Product
Conversion %
after 4 hour
3-Methoxybenzyl alcohol 3-Methoxybenzaldehyde 100
Veratryl alcohol 3,4-Dimethoxybenzaldehyde 100
4-Methoxybenzyl alcohol 4-Methoxybenzaldehyde 98
3-Phenyl-2-propene-1-ol Cinnamaldehyde 72
3-(Hydroxymethyl) pyridine
Nicotinaldehyde 98
Benzyl alcohol Benzaldehyde 90
1.6 mmol substrate, Lacc/Subs: 62.5 U/mmol, TEMPO (9.4 mol%), 0.1 M phosphate buffer (pH 4)
RCH2OH RCHO laccase/TEMPO
O2 , 30° C
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Greener Products
• Non- toxic
• Biodegradable
• Produced by green catalytic process • From green raw materials
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O
OH
OH
HO HO
HO
HO HO
OH
O OH
HO H O n
O
O
O
O
OH
OH
HO HO
HO
HO HO
OH
O
HO H O n
O
O
O
COOH
Selective 6-oxidation of starch
• Super absorbent for water (SNAP vs SAP)
• TEMPO/NaOCl environmentally unfriendly (N.B. volume)
• Laccase/TEMPO/O2 : enzyme costs too high (stability problem )
• Immobilize enzyme for higher stability
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Laccase/TEMPO/O2 : Suicide Inactivation
R-CH2OH
N
N
O
Laccase, O2 ?
Trametes versicolor
R-CHO OH + H+
Inga Matijosyte
N
O
+
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Cross-Linked Enzyme Aggregates (CLEAs®)
Dissolved enzyme
precipitant cross-linker
cross-linked enzyme
aggregate (CLEA)
aggregate
- (NH4)2SO4 or water-miscible solvent as precipitant
- glutaraldehyde or dextran polyaldehyde as X-linker
- laccase_CLEA shows increased stability
Org.Lett. 2 , 1361, 2000
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Conclusions and Prospects
• Many green catalytic methods for alcohol oxidation
• Chemo- and biocatalytic
• Oxidation of renewable raw materials - carbohydrates - polysaccharides
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“In an ideal chemical factory there is, strictly speaking, no waste but only products. The better a real factory makes use of its waste, the closer it gets to its ideal, the bigger is the profit.“ A. W. von Hofmann (1884)
Conclusions & Take Home Message
1. There is not one winner. 2. There are many chemo- and bio-catalytic methods 3. There are many shades of green.
Acknowledgements Gerd-Jan ten Brink Arne Dijksman Yuxin Li Patrick Gamez Linqiu Cao Inga Matijosyte Seda Aksu-Kanbak
Fred van Rantwijk Isabel Arends
Funding
ICI
IOP Catalysis
NRSC-C