CO 2 as a chemical feedstock School of Chemistry Professor Michael North
Dec 31, 2015
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?
O
R
OO
O
R SO
S
R
and SS
S
RNR'O
O
R
R'N=C=O
CO2
CS2
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
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326; Chem. Eur. J. 2010, 16, 6828–6843; Patent WO/2008/132474.
N N
OH HO
tBu
tBu
tBu
tBu
Al / EtOH, I2 (cat) then H2O
(salen)Al O Al(salen)
1 bimetallic catalyst
Cyclic carbonate synthesis from terminal epoxides
R Yield R Yield R Yield
Ph 62% Me 77% CH2OCOMe 50%
PhCH2 44% H 76% CH2OCOPh 58%
Bu 87% CH2OH 36% CH2OPh 55%
C8H17 64% CH2Cl 60% CH2OtBu 50%
O
R
OO
O
R
CO2 (1 atmosphere) /
1 (2.5 mol%) / Bu4N+Br- (2.5 mol%)room temperature, 3h, no solvent
M. North et al., Eur. J. Inorg. Chem. 2007, 3323–3326; Chem. Eur. J. 2010, 16, 6828–6843.
Supported catalysts
tBu-catalystsupport = polystyrene (PS), n = 1all other supports, n = 3
N
N
O
O
tBu
tBu
Et2N
Al O
N
N
O
O
tBu
tBu
N(Bn)Et2
Al
N(Bn)Et2
Et2(Bn)N Br Br
Br Br
nsupport H-catalyst3
N
N
O
O
Et2N
Al O
N
N
O
O
N(Bn)Et
Al
N(Bn)Et2
Et2(Bn)N Br Br
Br Br
silica
Results with supported catalysts
Support YieldtBu-silica 69%tBu-MCM-41 (silica) 57%tBu-Solgel (silica) 52%tBu-Aluminium pillared clay 21%
M. North et al. Patent WO/2009/109765; Chem. Commun. 2009, 2577–2579; Dalton Trans. 2011, 40, 3885–3902
O
PhOO
O
Ph
Gas phase flow reactor
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902
Column dimensions:3-15 cm x 1 cm.
Continuous flow results at 60 oC
Catalyst / support
Catalyst amount
mL / min evaporation rate EO
% CO2
consumedTOF (h-1)CO2 N2
tBu-silica 2.17 g 1.0 2.5 0.15 mL/h 97 2.6tBu-MCM41 1.57 g 1.1 2.5 0.15 mL/h 95 8.3tBu-solgel 1.94 g 1.0 2.5 0.15 mL/h 97 5.2tBu-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 1.1In 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.
1 2 3 4 5 6 7 80
2
4
6
8
10
12
14
16
time (days)
%C
O2
ab
so
rbe
dContinuous flow results with
tBu-silica catalyst at 100 oC3cm reactor containing 0.65g catalyst.
Catalyst reactivatedwith BnBr
M. North, et al. Chem. Eur. J. 2009, 11454–11457; Dalton Trans. 2011, 40, 3885–3902
Doosan Power systems test facility
Flue gas compositionFlow rate 20 mL/min
Gas Coal
T 53 oC 52 oC
CO2 5% 15%
O2 9% 3%
SO2 26ppm 291ppm
CO 189ppm 40ppm
NOx 33ppm 443ppmM. North et al. Energy Environ. Sci., 2011, 4, 4163–4170.
Used El Cerrejon coal (typical hard coal): 74%C; 0.5%S; 1.5%N; 5%H; 7% H2O
0
0.4
0.8
1.2
0 3 6 9 12
TO
F (
h-1
)
Time (days)
control
combined 8 and 16 h coal
Real flue gas flow reactor results with ethylene oxide
M. North, et al. Energy Environ. Sci., 2011, 4, 4163–4170.
Catalyst reactivated
Synthesis of di- and trithiocarbonates
M. North, et al. Synlett 2010, 623–627; J. Org. Chem. 2010, 75, 6201–6207.
R1 R2 50 oC 90 oC
yield A:B yield A:B
CH3 H 97 89:11 94 5:95
CH2Me H 54 85:15 90 47:53
(CH2)3Me H 56 66:34 87 43:57
(CH2)5Me H 61 70:30 81 39:61
CH2Cl H 76 85:15 84 36:64
CH2OPh H 97 97:3 87 71:29
(CH2)4 35 58:42 76 19:81
Ph H 62 0:100 91 0:100
O
SO
S
SS
S
1 (5 mol%) / Bu4NBr (5 mol%)CS2 (1.8 equiv.) 50-90 oC
+
R1 R2 R1 R2
R1 R2
A B
Stereochemistry
• Internal epoxides are substrates.• Reaction involves inversion of epoxide stereochemistry.
OS
OS
CS2
CS2 (-COS)
S
SS
M. North, et al. J. Org. Chem. 2010, 75, 6201–6207.
Oxazolidinone synthesis1 Cocatalyst Conv. A:B
5 mol% - 86% 1.8:1
2.5 mol% - 63% 2:1
- Bu4NBr 37% 1:1.8
2.5 mol% Bu4NBr 18% 1:0
2.5 mol% Et3N 38% 1:8.5
2.5 mol% DMAP 24% 1:5
2.5 mol% Ph3PO 29% 3.1:1
2.5 mol% PyNO 64% 1:1.1
1 (2.5-5 mol%) / cocatalyst (2.5 mol%), 80 oC, 24 h
+ Ph-N=C=OO
Ph
OPhN
O
Ph
+ OPhN
O
PhA B
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
ONPh
OO
1 (10 mol%),80 oC, toluene
63%
+
only cis-isomer formed
PhNCO
1, toluene, 80 oC, 24 h
+ Ar-N=C=OO
ROArN
O
R
+ OArN
O
RA B
7 epoxides7 isocyanates
31-100%
All except R= Ph and R = CH2OH give B as major product A:B = 1:5 to 0:1. R = CH2OH gives only A