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Extraction and Salting-Out

I really enjoyed this paper, because it goes into detail on a technique that organic bench chemists the world over have all used at some point: “salting out”. I’ll go into some background for the nonchemists for a few paragraphs and then return to the paper itself, which all working organic chemists should have a look at (and they can, because it’s open access).

In the lab, we spend a good amount of time dealing with what looks like salad-dressing mixtures – layers of water and some other solvent. It’s not usually olive oil, as with Italian dressing, but it might as well be, chemically. The key point is that you have two liquids that don’t really mix with each other. Given time, they’ll settle out into top and bottom layers. Water, being as dense as it is, usually shows up on the bottom, but if you use dichloromethane, your water layer will be on the top, because that one’s even denser.

The point of having two layers is that different substances will dissolve in each of them. That, in fact, is where the famous-to-medicinal-chemists concept of “logP” comes from. Experimentally, it comes from shaking up a measured amount of a compound with equal volumes of water and octanol (a completely water-immiscible solvent) and seeing how much of it ends up in each layer. A compound with a logP of 3 has a 1000:1 ratio of going into the octanol layer versus the water layer; a logP of 1 is a 10:1 ratio, logP of -2 means it went 1:100 towards the water layer, and so on. To stick with salad dressing, analysis would show that any salt present is virtually 100% in the bottom (aqueous) layer, because table salt just flat doesn’t dissolve in olive oil. Meanwhile, some of the aromatic compounds that are found in the oregano, basil, and black pepper will have extracted almost entirely into the oil layer, because they have a lot of hydrocarbon character to their structures and don’t go into water very well at all.

And that’s why we chemists like the two-solvent trick, because such extractions let us quickly separate mixtures of compounds. The bulk of the compounds that medicinal chemists make, for example, have logP values that indicate that they’re far happier dissolving in octanol rather than water. And if you use a solvent that’s even less greasy than octanol but still won’t quite mix with water (ethyl acetate is a classic for this purpose), then the ratio is even higher. Anything with a logP of 3 is going to go into ethyl acetate over water much more than merely 1000:1 (update: or not! There’s experimental evidence that ethyl acetate is about the same as octanol for this purpose, although the data in this paper would suggest that ethyl acetate is indeed a better solvent for some compounds), and a logP of 3 is considered a perfectly reasonable level of “greasiness” for most drug compounds. So a quick “aqueous workup”, as the phrase goes, will clear out all the water-soluble stuff while leaving behind whatever’s in the organic-solvent layer – that’s where the classic lab item, the separatory funnel, comes in. It’s a convenient way to shake up the two layers, let them settle out again, and drain them off into separate flasks. Two or three rounds of that with fresh ethyl acetate each time and you’re ready to move on.

Now, salting out. That is a trick for those times that you’ve made something whose logP is heading down into the more polar range. If your desired substance shows some tendency to go into water, a quick sep-funnel workup may lose you some material, or it may also form a thick, cloudy emulsion that takes hours (days, years) to settle out again. A truly nasty emulsion is basically a milkshake in your sep funnel and is sometimes nearly that thick. Sometimes you have a compound or crude mixture that’s especially prone to that sort of thing, and that’s especially enjoyable if both layers are pitch-black. You’ll occasionally see organic chemists searching for a flashlight to shine through their sep funnels to see if they can spot two layers forming or not in such situations.

One way to deal with these problems is to add some salt to the aqueous layer. The basic principle behind this is pretty straightforward: hardly anything dissolves better in water than a classic ionic solid (like good ol’ table salt, sodium chloride). The interaction between the ions and the water molecules are so strong, in fact, that if you give the water a chance to form up around the salt components, it may well release its hold on your desired compound, which is probably not quite so desirable in comparison. When this works well, it can be downright dramatic – flooosh, the emulsion unravels in front of your eyes, or you actually see small liquid bubbles of your desired product forming up and rising out of the salty aqueous layer to the organic solvent above. Good times!

But the classic “throw some salt in there” technique is only the beginning. What’s so informative about the paper linked above is that it brings together a lot of lab lore about the different kinds of salting-out effects. There are many details and complications to that simple mechanistic picture in the paragraph above, and the paper is all about making use of just those factors. The authors, from the well-respected Merck process chemistry department, were working on a rather water-soluble nucleoside drug and needed better extraction procedures:

A cursory inspection of the organic and process chemistry primary and reference literature revealed a surprising absence of detailed information regarding the topic of salting-out extraction. However, a more thorough search through older literature and in journals considered out of field to organic chemists actually revealed a wealth of useful information on salting-out that is currently underappreciated.

That it is, and it’s a great service to see it brought together into one place. These problems are especially acute on scale, because classic extraction procedures can take you into solvent volumes that cause difficulties in cost, time, handling, and disposal. (Remember, all that solvent that you used in the extraction is going to have to be evaporated at some point!) Table 2 in the paper is a glorious sight, because that’s where the group took their nucleoside and partitioned it between the same polar organic solvent mixture and aqueous salt solutions with eighty-six different salts. If the prospect of assembling those data doesn’t excite you, then you probably don’t have what it takes to be a good process chemist. Here’s the take-home:

Although relative salting effects were only established for a single compound, our findings are expected to be general based on parallel trends to the extensive solubility studies reported by others and the generality of the Hofmeister series. In view of the frequency that chemists encounter difficult extractions, we wholeheartedly recommend expanded use of salting-out liquid−liquid extraction, particularly with salts that are consistent with green chemistry principles. At least in the context of process development, Na2SO4 has been underutilized in salting-out extractions, but we highly recommend increased use based on cost, efficiency, and chemical inertness considerations. In a broader context, and in view of the extensive literature available, we recommend testing a particular set of salts in addition to NaCl when significant aqueous losses are encountered during a workup: K3PO4, K4P2O7 (potassium pyrophosphate), K2HPO4, NaH2PO4, Na2FPO3, K2CO3, NaOH, (NH4)2SO4, Na2SO4 (at 30−40 °C to increase the amount that can dissolve in water), Na3-citrate, NaK-tartrate, and Na2-malonate. These salts should always be tested at high concentrations, and interpretation should account for acid− base equilibria, solute stability, and any potentially interfering ions in the mixture.

(Link in the above added by me). In the Merck case, good ol’ sodium sulfate, used warm as mentioned, turned out to do the trick, providing product that crystallized cleanly on concentrating at scale. The group was already using 2-methyl-THF/dimethoxyethane as the organic layer, which the organic chemists in the crowd will immediately recognize as pushing it already, but it was clearly a great relief to be able to move to a clean extraction procedure as opposed to multiple passes and compound loss.

The paper is excellent work, and goes into interesting details that I haven’t mentioned here (such as what happens when you start varying the ratios of the two organic solvents, etc.) It’s pure 200-proof process chemistry, but it’s also immediately applicable to bench-scale synthesis around the world, since it recommends cheap, easily available salts that can improve aqueous recoveries immediately. Read and heed, fellow chemists!

62 comments on “Extraction and Salting-Out”

  1. JakeO says:

    Isn’t logP based on octanol/water, not isooctane/water? That’s what I was taught, but I could be wrong.

    1. Derek Lowe says:

      Jayzus, of course it is. I was reading a paper a while back on delta-logP between the octanol/water and isooctane/water partitions, and it apparently stuck in my hippocampus. Fixed.

      1. Dr Zoidberg says:

        Bit of your accent slipping out there.

  2. Rhodium says:

    Walking around orgo lab, trying to be useful, a common question I’d ask when we used sep funnels was “How do you know which layer is water?” Non chemists can ponder that for a minute, the standard answer is add more water (or brine, the jargon term for salty water) and see which layer gets bigger.

    1. Flourine says:

      Unless you have a fluorine / organic separation going on.

      What’s more fun than a three phase separation?

      1. tangent says:

        Let me see… A three-phase emulsion?

        (Hm, whereas for a two-phase you can make “A in B” or “B in A” emulsions, with three you could theoretically have (A in B) in C, (B in A) in C, A in (B in C), and B in (A in C), and so on. Are these preparable? Do they have distinguishable properties? I guess I’d be disappointed but not surprised if the identity of the continuous phase turns out the the only big factor.

        For that matter how about an “enclave emulsion” like oil-in-water-in-oil?)

  3. Torchwood says:

    Good paper. Chemical engineers should have this already in their undergrad separations course. I implore chemical engineers to use this paper and continue to encourage development groups to measure partition coefficients and actually optimize your extraction and solvent volumes/quantity. Too many times have I seen a process using excess water for logP of >2

  4. bhip says:

    As one of the many biologists who read your blog daily, I appreciate your efforts to explain the chemistry to the great unwashed. No one will ever mistake me for a medicinal chemist but every little bit helps.

  5. Magrinho says:

    @bhip – if you wear an ugly plaid shirt you get mistaken for a medicinal chemist.

    1. Michael says:

      I’m a chemist, but if I wear ugly cutoff jeans I might be mistaken for a herpetologist

    2. Bender says:

      Plaid flatters my figure!

    3. John Wayne says:

      I was about to get mad, then I looked at my shirt. Well played.

      1. Anonymous says:

        Well, plaid!

  6. Some idiot says:

    Another quick tip
    For the non-process folks here: particularly using toluene:water, if the separation is annoying, warm it to 40 oC and separate it. Makes a surprisingly big difference… with or without salt…! 🙂

    1. DrOcto says:

      Sounds like your compound (or an imputity) had a slightly too low solubility in toluene. This can typically look like small bubbles that are encapsulated in a thin membrane.

      When moving up to a stirred reactor level, which of the two phases is the bulk continuous phase (due to the addition order) and which is the suspended droplet phase also makes a huge difference in separation time. Worthwhile looking up if you’re not sure what I’m refering to.

      1. Some idiot says:

        Many thanks! Excellent point, and I know exactly what you are talking about… We will have a closer look at that… 🙂

  7. Chrispy says:

    I am surprised by the equipment that biochemists use that chemists typically don’t. A centrifuge will make quick work of that emulsion, for example, but I rarely see chemists use centrifuges. I also rarely see chemists use Pipetmen, which biologists use all the time. I rarely even see chemists use common bench vortexers. Yeah, you do have some compatibility issues to be aware of (that centrifuge may not be explosion proof, and THF will probably melt pipette tips), but a lot of the equipment chemists use seems medieval.

    1. Ted says:

      That saw cuts both ways. I’ve used air pipettes for years, when appropriate, much to the consternation of the guy that does calibration (“how did these salts get in here?”). In fact, ‘calibration’ is something many folks on the wet side of the lab view as a form of religious observation (blessed be these instruments for the next six months, and hallowed be thy results if they occur within the next three), rather than someone just weighing distilled water.

      On the other hand, when I show the bio folks how much easier and more reproducible it is to make a 10% w/w Tween 20 or Tergitol stock, they always seem somewhat suspicious…(“That seems like cheating…”).

      For what it is worth, liq/liq centrifugation doesn’t scale very well. However, modified versions of tangential-type filtration can dramatically improve industrial scale emulsion settling times from months down to hours…

      -t

      1. Chris Phoenix says:

        Platelet donors will be familiar with apheresis machines, which centrifuge a near-continuous flow of fluid, without reconfiguring any plumbing. A machine the size of a domestic clothes washer can, I’m told, process a person’s entire blood volume (5 liters) in 1-2 hours.

        I know that’s not practical for thousand-gallon batches, but it’s certainly a lot more than 50 ml.

    2. flblbl says:

      “A centrifuge will make quick work of that emulsion” Ha ! If there is 50mL of said emulsion, sure. It’s not our fault if your field is under the spell of some totemic technology craze because you need it to make visible results out of your miniature cooking. We don’t, and that certainly doesn’t make our equipment “medieval”.

  8. David Borhani says:

    Derek, could you please point us to a reference for “Anything with a logP of 3 is going to go into ethyl acetate over water much more than merely 1000:1”?

    The classic paper by Leo, Hansch, and Elkins—“Partition coefficients and their uses” Chemical Reviews 1971 71(6):525—suggests that there is little difference between logP (octanol) and logP(ethyl acetate), namely:

    logP(ethyl acetate) ~= 0.9 * logP(octanol) + 0.05 (albeit for a limited number of solutes)

    (The situation is different for some other solvents, e.g. toluene, where the additive (second) parameter is -1.8 (H-bond donor solutes) or -0.9 (acceptors) instead of +0.05. Most of the slopes are near 1.)

    See Table VIII (p. 540) for the regression parameters, and Table XVII (p. 555 ff) for the extensive listing of logP values for solutes in octanol vs. other solvents.

    1. Derek Lowe says:

      Interesting! This was just my own lab lore, and I’ve heard it expressed by others as well. But if the classic data refutes it, I’m going to have to adjust my thinking. I’ll make a note in the post.

      1. David Borhani says:

        But very limited data for solutes with logP > 3…

        1. Derek Lowe says:

          Just found a fairly recent table of EtOAc partition values, and it looks like it can in some cases be a better solvent (https://digital.library.unt.edu/ark:/67531/metadc155629/m2/1/high_res_d/Man-Pub-466.pdf). Not sure if there’s been a recent comparison head-to-head with octanol, though – I just took some of the values (ethylcyclohexane, t-butylbromide, etc.) and compared them to various reported experimental and calculated values.

      2. Edge says:

        But on a practical level it doesn’t make much difference if you have 1000:1 or 10,000: 1 or 1,000,000:1 in your separatory funnel. Especially if you do 2-3 extractions!! That is what I believe Derek meant.

        1. David Borhani says:

          I think the real reason is that EtOAc is (relatively) cheap, immiscible, easily evaporated. Et2O is great as well, but has issues (flammability, peroxides). Chlorinated solvents: great as well, but … well, they’re chlorinated.

          Why not hexanes? Too non-polar?

          1. Some idiot says:

            Go for isopropyl acetate instead… Good solvent, and holds much less water. Also, accidental hydrolysis is almost non-existent…

            🙂

        2. Chemystery says:

          That’s a good point, actually – 1000:1 is going to give you 99.9% of whatever you have in there in the first extraction. When I did a placement in a process lab, the first thing I learnt was the golden rule of extract 3 times with [whatever your favourite extraction solvent] should be checked for each extraction – if you cant see product in the aqueous by TLC or LCMS, then dont make more work/waste by doing a second/third/fourth extraction!

  9. Doug Steinman says:

    Teaching undergrads how to use a separators funnel was always one of the most enjoyable experiences of teaching orgo lab. I found out fairly quickly that you could not trust the students to use the funnel correctly and constantly had to check that the stopcock was closed when they filled the funnel and that the stopper was inserted correctly. Good times.

    1. Chrispy says:

      My favorite is the shake and POOF as the pressure was not relieved and the stopper blew out.

      In fairness, all of us had to start somewhere, and I have seen the telltale peaks of floor wax in the NMRs of even experienced chemists…

    2. Nick K says:

      Pouring a solution into a sep funnel with the tap open is a blunder which happens even to experienced chemists.

  10. AQR says:

    Back when I was in the lab, I found that if an ethyl acetate extraction didn’t pull my organic compound out of the aqueous layer, a 3:1 mixture of chloroform:isopropanol usually did the trick. I later switched to 3:1 dichloromethane: isopropanol and found it worked as well.

  11. a. nonymaus says:

    Of course, with some salts it is all fun and games until you get nice big crystals of e.g. Na2SO4 decahydrate clogging up the works. Extra hilarity ensues when the heat of crystallization starts boiling the ether/pentane mixture being used as the nonpolar phase.
    On the other hand, when using concentrated salt solutions, is the polar phase still water or is it better thought of as a molten salt hydrate?

  12. Ted says:

    In my last stop as a process chemist, I spent quite a bit of time stretching the bounds of p-chem and sensibility with extraction systems.

    A final mixture contained a witches brew of copper, boronic acids, pyridine, NMP, etc… (this was after the process had been stripped to an apparent minima!). Remarkably enough, toluene to dissolve and 9M sulfuric acid to wash was the magic cocktail… at >70°C. As a byproduct, I corrupted an entire cohort of organic chemists who regularly watched me stirring a sep funnel with a thermocouple while blasting a heat gun, all the while admonishing them to avoid doing anything that would set their hair on fire…

    That one scaled wonderfully, although long hours in a small pilot facility with hot reactors wearing full Tyveks isn’t (legally) for the faint of heart. The real payoff came after draining the last layer of smoking ‘wash’ away and finally cooling things down: crystallization was always spontaneous and fast.

  13. Anonymous says:

    I have quite a few Separation Science stories. Every organic chemist here will disagree with the “exact” percentage, but roughly ** 50% of organic chemistry IS Separation Science **. Students: Tell THAT to your PIs who haven’t done it since grad school! Anybody can throw stuff into a flask or beaker, stir it around, and get the reaction to work. Organic chemists know how to get the right stuff isolated and purified.

    Two sep funnel stories:

    RB Woodward story: RBW came into the lab to see what was going on. One student was having trouble with a prep. (I can’t remember the detail! It was either a separation problem or an in vitro (literally, in the glass sep funnel) reaction.) RBW took a lump of iron chloride, which most of you know is as hard as a rock, plopped it into the funnel, gave it a shake, and the “rock” broke the funnel spilling the contents all over RBW. RBW calmly left the lab and, it was said, did not return until years later to throw the switch on Mark Wuonola’s B12 synthesis reaction (1976).

    John Sheehan story: Before joining MIT, Sheehan (more well known for subsequent work on beta-lactams [penicillin]) worked at Merck. He was presented with a separation problem (~1944) that had gone unsolved by many others at Merck: the purification of streptomycin. Long story short: crude strepto, an amino sugar, was dissolved in water to form a brownish solution. HE EXTRACTED THE AQUEOUS WITH PHENOL (an old trick from sugar chemistry). The brown impurities (caramels) went into the phenol, the aqueous was clear and, upon evaporation, provided the purest strepto that Merck had ever seen. I wonder if the recent Merck group working on the nucleoside tried that trick? Obviously, it depends on the properties of the impurities vs the desired product.

    I’ve got a bunch more but will have to see if I have time to post them later.

    1. Jim says:

      I love hero worshipers, they are so funny. Why dont you come up with your own ideas instead of memorizing silly stories lionizing a bunch of unimaginative dead guys.

      1. Barry says:

        If you’re characterizing Robert Burns Woodward as “unimaginative”, you know not of what you speak.

      2. Anonymous says:

        I worked for a PI who thought that all separations were trivial. I read extensively in the Sep Sci and Chem literature to solve some very tough separation problems, sometimes with what I think are clever tricks. NONE of it has been published.

        It was another PI who gave me a sep funnel story of my own. I needed to do a large scale prep. Our largest sep funnel was 6 L and it had a major star crack (and several smaller ones). I said we need to get new glassware or have the glassblower fix the cracks. I was told, roughly, to just make the f’in compound. (“f’in” does not refer to “fluorine”.) … During work-up, I carefully placed the full sep funnel into the ring. That’s when it finally cracked apart and spilled everything onto the floor. At least it was just an early stage starting material.

        If you read the RBW and JCS stories closely, you will see that there is actually some very useful CHEMISTRY in there! (Thanks to Barry for adding info about the RBW story. I sort of remembered that it was an in vitro iron reduction which fits with the iron sulfate lump.)

        I can guarantee you that readers will remember the RBW and JCS chemistry stories much better than they will remember my cracked 6 L.

    2. Barry says:

      As the story reached me, RBW walked into his lab, saw a grad student setting up a 3-necked flask w/ overhead stirrer to do a reduction of a quinone to the hydroquinone. RBW proposed to show him how it was done, loading the quinone and water into a separatory funnel, adding Ferrous Sulfate, and shaking. Alas, the Ferrous Sulfate was lumpy, and a lump smashed the funnel, spilling the contents all over our hero.

    3. David Borhani says:

      Your John Sheehan story reminds me of good ol’ days in grad school. My wife was doing her PhD in molecular biology, and she needed super-pure phenol for DNA/RNA extractions. This was in the days when buying such was exorbitantly expensive. So, I set up a 5- or 10-liter distillation. Beautiful. Only catch was to use a hair drying to keep the phenol from crystallizing in the condenser before dripping into the receiving flask.

      Maybe another time I’ll tell you of my triple-distillation of a liter or two of mercury for my diffusion pump (and why I needed such a pump)…

    4. DanielT says:

      Does anyone know of a good substitute for phenol in extractions that is not so nasty. As a Molecular Biologist we use phenol to remove contaminants from lots of our solutions, but really it is not nice to work with.

      1. wildfy says:

        Depends what you are extracting, but chloroform is a good one. Smells kinda minty

        1. Anonymous says:

          Has a nice peppery taste as well.

        2. DanielT says:

          Chloroform is kind of jumping out of the frying-pan and into the fire – trading burns and a quick death for cancer.

      2. skeptic says:

        I’ve always had good luck with using DNA binding to silica particles as a cleanup method, ala Qiagen.

  14. Analysis has given me an interest in separating acetonitrile/water/salt mixtures to get polar stuff you’re interested in away from all the inorganics which would ruin your LC/MS/NMR. They separate best at low temperature, which I’m guessing means that salt concentration is less important and that the separation is driven by enthalpy overcoming entropy tho’ I’ve never really thought about it. There’s a lot in the literature so I’ve linked to one from 1990 on explosives to fit in with a popular topic on the blog.

  15. Arnob Endry says:

    I found out fairly quickly that you could not trust the students to use the funnel correctly and constantly had to check that the stopcock was closed when they filled

    1. Scott says:

      You’re *still* a spammer, copy/pasting someone else’s words in an attempt to not get caught by the filters.

      Go do something anatomically improbable.

  16. Joannes says:

    In Dutch, Chemistry is “Scheikunde”, literally the Knowledge (“kunde”) of Separation (“Schei-ding)

  17. Me says:

    My fave piece of equipment to help separate out emulsions:

    bubbles from the N2 line

    OR

    Hand-held massage machine

    1. doc says:

      Do you apply the latter method externally or internally, and if the latter, kindly recommend a brand of massager….

      (great idea, by the way)

    2. Anonymous says:

      Emulsions are a pain. I have also successfully used:
      1. MILD vacuum, applied directly and CAREFULLY to the sep funnel with an appropriate adapter.
      2. Vacuum filtration through a glass frit (Buchner) – fast and effective in several cases
      3. A small amount of additional fresh solvent trickled into the emulsion can
      sometimes help.
      More, as I think of them.

      1. Conker says:

        It also works filtering through celite….

  18. MTK says:

    There’s few more sinking feelings (in the lab at least) than shaking your sep funnel, putting it in the ring clamp, and seeing nothing happening, as in no separation.

  19. RBW says:

    RBW’s lack of practical chemistry knowledge is legendary. An early student von Doering (worked on the quinine synthesis, later faculty in his own right) said he wouldn’t trust Woodward to cook an egg.

    1. Anonymous says:

      But RBW did seem to be well aware of the Separation and Purification problem, even if he didn’t have to do it himself. RBW’s undergrad thesis mentions the mathematical demon of sub-100% yields that plagues multistep syntheses (even 0.99^n hurts you after small n). RBW did a lot of work on peptide coupling to improve yields and simplify separations. RBW was eager to adopt and promote HPLC as a method to separate and purify product mixtures. And, of course, he was keen on crystallization as a method of separation and purification. He would tell his students to “Keep scratching!” He even named his daughter Crystal.

      Unless your product crashes out, you’ll still need a sep funnel to get to the point where you can try some of those other methods.

  20. Li Zhi says:

    I vaguely recall from my days working in processing colloids that their stability is theoretically inversely proportional to the salt ions concentration to the nth power where n is their respective charge. So, it makes sense that the sulfate ion will be more effective than the chloride ion. That’s old stuff. I will pedantically call Derek on the claim that octanol is “completely” immiscible in water. Of course, we can argue over what defines immiscible, but for the non-chemists that comment is directed at is it better to exaggerate the “purity” of the separation or better to say “practically immiscible” and retain more latitude. I’ve been roundly criticized (with some merit) for proclaiming that everything is soluble in everything else to some degree. Its maybe not always measurably true, but is a good attitude when it comes to sourcing trace impurities. The other thing I’m dubious about is the paper’s (I’ve not read it yet) claim to generality. Derek references work with wide variation in logP values between solvent pairs, it is reasonable to expect that different solutes will also show wide variation to the identity of the salt employed. Chemistry still is, imho, based on evidence and generalizing from a sample of one is just a bit too aggressive for me.

    1. Anonymous says:

      “I’ve been roundly criticized (with some merit) for proclaiming that everything is soluble in everything else to some degree.” That reminds me of a riddle (which I might have across from Uncle Al in the days of sci.chem). A chemist has invented a new universal solvent that dissolves everything with which it comes into contact. How will he or she store it?

      1. JHMoot says:

        In vacuum, of course 🙂

      2. Chris Phoenix says:

        Freeze it.

  21. Scott says:

    “Table 2 in the paper is a glorious sight, because that’s where the group took their nucleoside and partitioned it between the same polar organic solvent mixture and aqueous salt solutions with eighty-six different salts. If the prospect of assembling those data doesn’t excite you, then you probably don’t have what it takes to be a good process chemist.”

    Table 2 sounds like a whole lot of tedious work that I’d much rather turn a platoon of undergrads loose doing and supervise than do myself. OK, maybe grad students, since I doubt most undergrads have the lab skills to get everything correct.

    But on the other hand, it looks like the writers of the paper saved everyone else much of the trouble!

  22. GladToMoveToProcess says:

    Regarding breaking lab-scale emulsions, a trick I’ve seen a few times involved putting the business end of a Tesla coil vacuum leak detector into the mixture. Sometimes breaks the emulsion in seconds. Not a good idea with flammable solvents, though! Someone in grad school did this with an aqueous/pentane mixture – ugly.

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