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Rotating Rings of Solvents

Now here’s a chemistry technique I don’t think I ever would have thought of. This new paper in Nature presents what could be a new way of doing multistep chemistry in a single vessel by the use of solvent layers of different densities in a rapidly rotating container (the examples below are in vessels are spinning at 5400 rpm). You inject these solvents from the central inlet and/or via channels running underneath the container. Folks who have spent a fair amount of money in bars might be reminded, with good reason, of a pousse-café.

The chart illustrates the solvent layers for the “e” example on the left, which are a mixture of aqueous and organic phases along a gradient of densities: W is water with sodium polytungstate (SPT), sodium metatungstate (SMT) or cesium chloride (CsCl), and these are thin clear “separator” layers between the organic phases. Those are dyed and are mixtures of tetrabromomethane (TBM), dibromomethane (DBM), 1,4-dibromobutane (DBB) and n-decane (D), and the whole assembly is stable over time. Meanwhile, the example on the right is all done in various mixtures of polyethylene glycol, methanol, and sodium iodide, and that one does gradually diffuse and blur.

OK, you are probably wondering why anyone would want to do this. Folks who are familiar with an old (and for many chemists, relatively obscure) technique called countercurrent chromatography might be getting some ideas, though: CCC is a separation technique that does a sort of continuous extraction between two immiscible solvent layers. There are several ways to realize this, some of which use this same sort of rotating-cylinder effect. My impression has always been that it needs a good deal of experimentation on the front end of the process, but when it works it can provide clean separations without your desired products ever touching a solid support that might degrade them.

So there are possibilities for (say) having a reaction take place in one solvent layer and allowing a differentially soluble product to be extracted out into another adjacent one (thus providing, in its slickest manifestation, a driving force for the reaction itself as you keep feeding in starting materials). The paper illustrates several multistep sequences that are performed across different solvent layers, where the intermediates alternate (for example) between aqueous-soluble and organic-soluble and work their way out towards the outer immiscible layer as the sequence proceeds. There are several interesting effects to do with the thickness of the various layers, the mixing between them that can be turned on and off by varying the rotation speed, and so on.

And you can do tricks that would otherwise be rather hard to pull off – one example is a simultaneous acid-base extraction, where a chlorinated solvent layer sits in between an acidic layer and a basic one, and the components introduced into the middle split off in both directions at the same time. Quinine nitrobenzoate, for example, disappears from the central organic layer and ends up as quinine hydrochloride in an aqueous HCl layer and sodium nitrobenzoate in an adjacent aqueous NaOH one. Similarly, the paper also demonstrates selective extraction of phenylalanine from a mixture of glucose and lactic acid (as one might find in a fermentation broth). These sorts of things could also be applied to biomolecules, inorganic compounds and clusters, and other species (the paper shows an example with silver nanoparticles which seems to be a real improvement over the known ways of handling them).

So while I don’t expect every bench chemist to jump at the chance to start revving up some rotating reactors, this should get some real interest from process chemists who are looking to optimize particular high-value reaction sequences and separations. It’s going to take a while for people to get the feel of this sort of reactor, but you can imagine situations where it could have some real advantages. . .

26 comments on “Rotating Rings of Solvents”

  1. A Nonny Mouse says:

    There was a CCC company spun out of Brunel University in the UK (Dynamic extractions) which had some pretty impressive kit which they had designed, such that they could effectively extract a couple of steroid isomers to over 95% purity on just a couple of passes. Apparently quite easy to set up and use.

    A (very crude) version used to be used for removing methyl benzene sulphonate in the atracurium besylate production final stage, though it tended to leave considerable amounts of toluene in there (and this went straight into vials….. The Italian monograph, which is the only one that could be found at the time, had <4,000ppm!)

    1. whitequark says:

      Gives “spun out” a whole new meaning.

    2. Tim says:

      Please pardon the tangent: what is the meaning of “atracurium besylate”? The chemical formula in Wikipedia doesn’t look like it has curium in it.

      1. Michael Turner says:

        It’s a skeletal muscle relaxant, nothing to do with curium at all.

        1. Rhenium says:

          If it doesn’t curium then barium…

      2. gippgig says:

        I think the “cur”, & the compound, is derived from (in terms of having a related structure, not being made from) the dart poison curare rather then the element curium.

        1. theasdgamer says:

          Curious…

          In other news, did you see a paper published today about cross-reactive T-cells in people not previously exposed to covid?

          “Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans”

          https://science.sciencemag.org/content/370/6512/89

  2. Ezra Abrams says:

    I haven’t been there in 20 years, but the Rockefeller University in NYC use to have a museum, under the main lecture hall iicr

    And in that museum were some incredible countercurrent devices – these things are the size of a chest freezer, with hundreds of feet of pyrex tubing

    Definitely a sight

  3. lfert says:

    This reminds me of the old Chromatatron chromatography system.

    1. John Wayne says:

      Likewise!

    2. Kaleberg says:

      It reminds me of Spin Art.

  4. Daniel Jones says:

    The centrifuge has often played a part in various steps of chemical work but this may be the best example of “centrifugal chemistry” yet.

  5. a says:

    It took more than one year for this paper to be accepted from submission…. My guess is that reviewers wanted lots of controls that weren’t present….

  6. This one was worth sharing with fellow members of a forum I participate in … properly attributed, of course. Click on my name for the link to the post.

  7. Chris Phoenix says:

    I’ve seen microfluidic systems that had extremely laminar flow – three feed channels leading into an end of one common channel, and the liquids stayed very cleanly separated as they traversed the common channel, even (perhaps especially) at sub-mm scales. With care, probably the liquids could be separated again at the other end of the channel by withdrawing (from three exit channels) the same volumes that were fed in.

    I wonder whether that kind of setup could be used for a similar separated-layer-liquid-interface system?

    Separately, I wonder whether this could be used for liquid-electrode batteries?

    1. James Millar says:

      Possibly the most intense laminar flow system I’m aware of is the South African Helikon system for uranium enrichment.

      It compressed 20 or so parallel streams of gas through an axial compressor, while not allowing them to mix.

      1. Semichemist says:

        Thank you for bringing this absolute witchcraft to my attention, this is insane. Vortex tubes always seemed like they were just flipping physics the bird, but this is next level

  8. Tomas says:

    One would think that if the phases separate under many g’s, they might also separate in a regular column, though maybe not as cleanly under various turbulences.

  9. Hadriel says:

    Really nice work. Reminds me of tube-in-tube and in-line liquid extraction for flow chemistry, all very nice innovative methods. Also, a classic example of a two-phase reaction would be extractive esterification of water soluble carboxylic acid and alcohol. A quick water wash then just vac off the heptane layer and you have virtually pure ester.

  10. Daniel Barkalow says:

    I’m amused that it spins at 5400 rpm. It looks like one of them is about 6.35 cm in diameter, too. I guess it makes sense that they’d go for the easy-to-acquire mechanical device, and put all their effort into making the chemistry work. Anyone interested in an electromagnet that can turn on at the right times to affect particular portions of a ring as it goes past?

    1. James Millar says:

      Thinking hard drive?

      1. Ken says:

        I saw that too, fellow nerds. I guess there is still enough life in their lab’s 7200 RPM drives to avoid sacrificing one for this. I also seem to remember a colleague in my grad school group from way back when trying to use an old hard drive to shape an electrospray needle tip for MS so they are good multitaskers.

        Alas, such innovations will be harder to come by when there are nothing but solid state drives in dead lab computers.

  11. Darby says:

    Is something like this happening in cells? Not the spinning bit, but maybe microtubules pulling reactants through areas of different…sorry, not sure of the terminology, solubility-compatible areas where different add-ons could be waiting?

  12. Ken says:

    Reminds me of Polaroid film chemistry

  13. navarro says:

    isn’t this a modified form of what the nakanishi group were using to study the tunichromes 10 or 15 years ago? it’s too bad the venerable professor didn’t live long enough to see something like this.

  14. FoodScientist says:

    There are simple plug and play drivers for the stepper motors in hard drives, They’re used in model aircraft. It seems like the adaptor for the part where the 0rpm inlet and 5400rpm inlet meet could get complicated. I wonder how many times it went out of balance and sprayed the reaction mixture everywhere.

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