What is flow chemistry? -...
Transcript of What is flow chemistry? -...
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What is flow chemistry?
Flow chemistry is a process in which a reaction is run Continuously
in a flowing stream rather than in batch production
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Comparison between traditional chemistry and flow chemistry
Reaction Stoichiometry:
In traditional chemistry this is defined by the concentration of chemical
reagents and their volumetric ratio. In flow chemistry this is defined by
The concentration of the chemical reagents and the ratio of their flow rate
Residence time:
In traditional chemistry this is determined by how long a vessel is kept at
given temperature. In flow the volumetric residence time is used given
by the ratio of the volume of the reactor and the overall flow rate
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What is residence time?
Residence time of a reagent is defined as the amount of time
that the reaction is cooled or heated.
Residence time = reactor volume/flow rate
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Continuous flow reactors: a perspective
Advantages:
1. Improved thermal management
2. Mixing control
3. Application of the extreme reaction conditions
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Principles of green chemistry:
1. Prevention of waste
O
OHO
NH2
Solvent -freeN
OH
reaction temp : 65 oC
reaction time : 5.1 min
yield : 91%
Green chem., 2012, 14, 38-54
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2. Atom economy
O
toluene
OH
reaction temp : 240 oC
pressure : 100 bar
yield : 95%
O
O
OMeCN
O
O
O
H
Hreaction temp : 60 oC
Green chem., 2012, 14, 38-54
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N
N
N
O
OO
N
N
N
O
OO
O CCl3
NH
electon-withdrawing group
Smallest unit of benzylimidate
N
N
N
O
OO
N
N
N
Cl
ClCl
NaOH (3.4 eq)BnOH (7.8 eq)
0 to 50 oC, 2.5 h
81%
Org. Lett., 2012, 14, 5026-5029
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3. Less hazardous chemical synthesis
Synthetic methods should be designed to use and generate Substances
that possess no toxicity to humans and to the environment as well
4. Designing for safer chemicals
Chemical products should be designed to effect their desired function
while minimizing their toxicity
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5. Safer solvents and auxiliaries
The use of auxiliary substances should be avoided
6. Design for energy efficiency
Energy requirements of chemical process should be recognized
for their environmental and economic impacts and should be
minimized
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7. Use of renewable feedstocks
A raw material should be renewable whenever technically and
economically practical
8. Reduce derivatives
Unnecessary derivatisation must be avoided because such steps
can generate waste
9. Catalysis
Catalytic processes are superior to stoichiometric reagents
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10. Real-time analysis for pollution prevention
In- process monitoring and control to minimize the formation of
hazardous substances
11. Inherently safer chemistry for accidental prevention
Substances used in a chemical process must be chosen to minimize
The potential for chemical accidents
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Org. process. Res. Dev. 2004, 8, 455
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N
MeO
MeO
O
H
-Oxomaritidine
A flow process for the multi-step synthesis of the alkaloid
natural product: Oxomaritidine
Chem. commun., 2006, 2566-2568
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Chem. commun., 2006, 2566-2568
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1. Product obtained with >90% purity by H NMR
2. 40% isolated yield overall (phenolic oxidation gave 50% yield
3. Natural product can be obtained in less than 1day
4. Only obtained 20 mg of (±)-oxomaritidine
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NMeO
MeO
NH
MeO
MeO
HO HO
10% Pd/C, THF
flow hydrogenation
Efficient reduction of imines to amines
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Continuous flow-through reduction of imines into amines
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Continuous flow-through reduction of imines into amines
H-Cube flow hydrogenator
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H-Cube Flow Hydrogenator front panel
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NMeO
MeO
OH
N
N
OH
N O
O
N N
OH
quant. quant.
quant. quant.
Flow hydrogenation scope
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Bestmann-Ohira reagent for the formation of alkynes
and triazoles
Flow synthesis of terminal alkynes:
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Two-step formation of triazoles from alkynes
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Three step synthesis of triazole 5 from alcohol 3
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Vapourtec R2+/R4
flow system
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Multi-step synthesis strategies
Chem.sci., 2010, 1, 675-680
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Generation and reaction of o-bromophenyllithium
Br
Br
PhCHOin THF
n-BuLiin hexane
TMSClin THF
TMS
Ph
OH
tR= 0.82 s
-78 oC -78 oC
tR= 6.93 s tR= 0.49 s
0 oC
tR= 0.49 s
0 oC
= the introduction of an input stream to the reactor network
tR= residence time in the reactor
n-BuLiin hexane 74%
J. Am. Chem. Soc. 2007, 129, 3046
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Generation of kilogram quantities of 3-methoxybenzaldehyde
BrtR= 0.82 s
0 oC
= the introduction of an input stream to the reactor network
tR = residence time in the reactor
n-BuLiin hexane
tR= 0.15 s
0 oC
H NMe2
O
in THF
MeO
MeO
O
H
88%
59 g/h throughput1.4kg produced in 24h
Difficult to reproduce on kilogram scales using batch methods (24% yield, -40 oC)
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Continuous flow synthesis of ibuprofen
tR= 5 min
150 oC
= the introduction of an input stream to the reactor network
tR = residence time in the reactor
TfOH5 equiv
tR= 2 min
50 oC
20 equiv KOHin MeOH/H2O
1 equiv PhI(OAc)24 equiv HC(OMe)3
in MeOH
65 oC
tR= 3 min
O
OHHO
O
Angew. Chem. Int. Ed. 2009, 48, 8547
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Synthesis of a Mur ligase inhibitor
N
tR= 20 min
100 oC
tR= 15 min
75 oC
N
OH
NH2
HO
O
Br
O
N O
HN
HN
CO2Me
OH
H2N
HN
CO2Me
HOBt, EDC(1.2equiv in DMF)
(2.0 equiv in DMF)
1 equiv in DMF
1.2 equiv in DMF
Org. Lett., 2010, 12, 412
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Curtious rearrangement of Carboxylic acids
Org. Biomol. chem., 2007, 5, 1559-1561
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3+2 cycloaddition of actylenes with azides
N
NN
HO
NO2
N
NNN
NN
S
O
O
91%85%
93%
NNN
HO
85%
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Conclusions
large quantities of synthetically use intermediates can be accessed
through flow chemistry
Multiple reactors in tandem can be used to build molecular complexity
Micro reactors have the potential to increase reaction efficiency
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It is better to prevent waste than cleanup after creation!!!
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