Neal Munyebvu, Technical Support Specialist, Syrris
Building up a compound library in continuous flow
Plug-flow, or segmented flow chemistry
It is often not considered that one of the solutions to this is, in fact, one of the largest benefits of using flow chemistry. The ability to run flow experiments in segments. This is what we call ‘plug-flow’ or ‘segmented flow’ chemistry.
This is where you set up a flow system to run specific volumes of reagents in line which are separated by a volume of carrier solvent.
This can be the case for each input line, segmenting each reagent. This allows you to create segments which can be set to run under different stoichiometries and conditions in an automated fashion.
Designing the experiment
Consider the reaction:
R + Y → O
Where R and Y are the same volume and concentration (this does not have to always be the case).
This can be set up using a Flow Chemistry system to run each reaction one after the other in series to give the following reaction profile:
- Reaction 1: 40 ºC, Residence Time: 16 minutes
- Reaction 2: 80 ºC, 10 bar, Residence Time: 4 minutes
Optimizing the experiment
These can be set and automated using Design of Experiment (DoE) software, which allows the user to try to create a matrix of potential conditions and variables.
An example of this is given in the matrix below which is similar to what would be found in DoE software and allows the user to set the desired conditions and variables for each reaction:
|Run||Name||Flow Rate – Reagent Injector 1||Flow Rate – Reagent Injector 2||Temperature||Pressure||Collection Volume|
|1||Reaction 1||50 μL/min||50 μL/min||40 °C||0 bar||1600 μL|
|2||Reaction 2||200 μL/min||200 μL/min||80 °C||10 bar||1600 μL|
The DoE software programs this and implements the conditions to run one after the other as below:
Using the conditions in Reaction 1, A and B react to produce product O at low yield and purity
In Reaction 2, R and Y react to create O in much more favorable conditions and results in a much more optimized reaction.
At the point of collection, however, this would not always be clear. Segmented flow chemistry means you can set up your experiments to ensure the products of reaction 1 and reaction 2 are collected in separate vials to create a sequence of products which can then be analyzed together.
The fact that the volume of your reagent makes up a small amount of the total volume of your flow system (which is made up primarily of carrier solvent) ultimately saves a significant amount of reagent per experiment.
Screening various different reactions
Not only can you end up creating a library for optimization of a single reaction, but you can also run an array of different reactions, one after the other using an automated reagent injector.
Consider the reactions:
Reaction 3: R + Y → O
Reaction 4: R + B → P
Reaction 5: B + Y → G
All different reagents running different reaction profiles each set to run one after the other in series and collected in 3 separate vials for analysis.
This allows the creation of a library of compounds all at once which can be analysed quickly and easily.
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About Neal Munyebvu (MChem)
As a Flow Chemistry Technical Specialist for the Syrris Support Team, Neal is responsible for installing Asia Flow Chemistry Systems in sites around the world, helping chemists overcome issues, and enabling chemists to get the most out of their flow chemistry equipment.