When I was talking about Steve Ley of Cambridge the other week, one of his research areas that I mentioned liking was his work on flow chemistry. This is the benchtop application of a type of reaction that’s been done more often on large industrial scales.
Most of the work that medicinal chemists like me do is batch by batch. We weigh and syringe things into flasks, cool, heat, and stir them, and then pour the resulting stuff out of the flask and clean it up. There are all sorts of techniques that have come along to speed these steps up or to allow you to do more of them simultaneously, but all of them are still in “batch mode”.
Flow chemistry is a bit different. The starting materials flow through an apparatus that (one way or another) causes them to react, and then out the other side. The business section of the machine can be a part that heats up the solutions as they go by, or puts them under high pressure, or forces them over a solid support that contains some catalyst. That last category is especially useful, since the number of metal-catalyzed reactions is increasing with no end in sight.
If the reaction isn’t done, you can send the mixture back through for another pass. If the reaction’s complete, you can (ideally) take the resulting solution on to the next step without necessarily having to clean it up – after all, the catalyst is staying behind on the solid support. If you treat it right, the catalyst should be reusable for quite a while as well.
One of the more widely adopted flow reactors so far has been the “H-cube”. Its makers chose a reaction (hydrogenation) which is very useful, but one that a lot of chemists don’t like to run. The opportunity to easily try out catalysts and conditions that aren’t normally run has been another selling point. Now the company has come out with their X-cube, which is a more general flow reactor.
My question is: has anyone out there used this beast or its competition? I’ve had a little (generally positive) experience with the H-Cube, but none with any other flow reactor. There are a lot of homebrew setups out there, but the commercial space has been filling up recently, too.
Of course, as everyone knows, neat-looking equipment can end up gathering dust. For these flow gizmos to be useful, they’ll have to do things that aren’t easy to do in a flask, and do the flask reactions in a more convenient manner. The flow reactor people aren’t competing with each other as much as they’re competing with a drawer full of round-bottom flasks. I’d be interested to hear from anyone who’s put that comparison to a real-world test. . .