CO2 as a chemical feedstock
Professor Michael North
School of Chemistry
Synthesis of heterocycles
from epoxides
All are known reactions but often with harsh reaction conditions (e.g.
20 bar CO2 pressure and >100 oC for cyclic carbonate synthesis)
Could a bimetallic catalyst activate both substrates?
Can we use only sustainable elements in the catalyst?
Sustainable catalysis
Red/orange = rising threat from increased use;
Red = serious threat in next 100 years;
Orange = limited availability;
Many elements are endangered.
http://www.chemistryinnovation.co.uk/
A bimetallic aluminium(salen)
catalyst
N
t
OH
Bu
t
Bu
N
t
HO
t
Bu
Bu
Al / EtOH, I2 (cat)
then H2O
(salen)Al O Al(salen)
1 bimetallic catalyst
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326;
Chem. Eur. J. 2010, 16, 6828–6843; Patent WO/2008/132474.
Cyclic carbonate synthesis
from terminal epoxides
O
O
CO2 (1 atmosphere) /
1 (2.5 mol%) / Bu4N+Br- (2.5 mol%)
room temperature, 3h, no solvent
O
R
O
R
R
Yield
R
Yield
R
Yield
Ph
PhCH2
Bu
C8H17
62%
44%
87%
64%
Me
H
CH2OH
CH2Cl
77%
76%
36%
60%
CH2OCOMe
CH2OCOPh
CH2OPh
CH2OtBu
50%
58%
55%
50%
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326; Chem. Eur. J. 2010, 16, 6828–6843.
Supported catalysts
Br
Et2(Bn)N
Br
t
N
N
Et2(Bn)N
Br
N
N
O
O
O
O
Br
Al
Al
O
t
N
N
t
n
N(Bn)Et
O
O
O
N
Al
O
N
t
Bu Bu
Br
Br
Et2N
Br
Bu
O
Al
support
t
Bu
N(Bn)Et2
Et2N
N(Bn)Et2
Bu-catalyst
support = polystyrene (PS), n = 1
all other supports, n = 3
Br
silica
N(Bn)Et2
3
H-catalyst
Results with supported
catalysts
Support
Yield
tBu-silica
69%
tBu-MCM-41 (silica)
57%
tBu-Solgel (silica)
52%
tBu-Aluminium pillared clay 21%
O
O
O
O
Ph
Ph
M. North et al. Patent WO/2009/109765;
Chem. Commun. 2009, 2577–2579; Dalton Trans. 2011, 40, 3885–3902
Gas phase flow reactor
Column dimensions:
3-15 cm x 1 cm.
M. North, et al. Chem. Eur. J. 2009, 11454–11457;
Dalton Trans. 2011, 40, 3885–3902
Continuous flow results
o
at 60 C
Catalyst /
support
Catalyst mL / min
amount CO N
2
2
evaporation % CO2
TOF
rate EO
consumed (h-1)
tBu-silica
2.17 g
1.0
2.5 0.15 mL/h
97
2.6
tBu-MCM41
1.57 g
1.1
2.5 0.15 mL/h
95
8.3
tBu-solgel
1.94 g
1.0
2.5 0.15 mL/h
97
5.2
tBu-PS
1.94 g
1.0
2.5 0.15 mL/h
63
2.6
H-silica
2.17 g
1.0
2.5 0.15 mL/h
98
1.1
In each case, CO2 is 21% of the gases passing into the reactor.
Ethylene oxide (EO) flow rate ca 1.2 mL / min. Column length 15 cm
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902.
Continuous flow results with
tBu-silica catalyst at 100 oC
3cm reactor containing 0.65g catalyst.
Catalyst
reactivated
with BnBr
%CO2 absorbed
16
14
12
10
8
6
4
2
0
1
2
3
4
5
time (days)
6
7
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902
8
Doosan Power systems test
facility
Flue gas composition
Flow rate 20 mL/min
Gas
T
53 oC
CO2 5%
Coal
52 oC
15%
O2 9%
3%
SO2 26ppm 291ppm
CO 189ppm 40ppm
NOx 33ppm
M. North et al. Energy Environ. Sci.,
2011, 4, 4163–4170.
443ppm
Used El Cerrejon coal (typical hard coal):
74%C; 0.5%S; 1.5%N; 5%H; 7% H2O
Real flue gas flow reactor
results with ethylene oxide
TOF (h-1)
1.2
control
combined 8 and 16 h coal
0.8
Catalyst
reactivated
0.4
0
0
3
6
Time (days)
M. North, et al. Energy Environ. Sci., 2011, 4, 4163–4170.
9
12
Synthesis of di- and
trithiocarbonates
R1
R2
50 oC
yield A:B
90 oC
yield A:B
CH3
CH2Me
(CH2)3Me
(CH2)5Me
H
H
H
H
97
54
56
61
89:11
85:15
66:34
70:30
94
90
87
81
5:95
47:53
43:57
39:61
CH2Cl
H
CH2OPh H
(CH2)4
76
97
35
85:15 84
97:3 87
58:42 76
36:64
71:29
19:81
Ph
62
0:100 91
0:100
H
M. North, et al. Synlett 2010, 623–627; J. Org. Chem. 2010, 75, 6201–6207.
Stereochemistry
• Internal epoxides are substrates.
• Reaction involves inversion of epoxide stereochemistry.
M. North, et al. J. Org. Chem. 2010, 75, 6201–6207.
Oxazolidinone synthesis
1
Cocatalyst
Conv.
A:B
5 mol%
2.5 mol%
2.5 mol%
Bu4NBr
Bu4NBr
86%
63%
37%
18%
1.8:1
2:1
1:1.8
1:0
2.5 mol%
2.5 mol%
2.5 mol%
Et3N
DMAP
Ph3PO
38%
24%
29%
1:8.5
1:5
3.1:1
2.5 mol%
PyNO
64%
1:1.1
Best conditions eventually found to be 5 mol% 1 at 80 oC in toluene
for 24 h with no cocatalyst. Gave 100% yield with A:B = 2.2:1
Other epoxides and
isocyanates
Acknowledgements
Dr. Riccardo Pasquale
Dr. Jaisiel Melendez
Dr. Pedro Villuendas
Dr. Carl Young
Professor Bill Clegg
Dr. Ross Harrington
EPSRC, TSB, SSE
DoosanBabcock
CarbonConnections
Newcastle University