An easy way to test if your 3A sieves are activated is by placing a few in your hand and running a few mL of cool water over them. If the sieves get real hot they're sucking up water and good to go. I don't think I've ever gotten a new batch that needed to be activated. Tested solvents after with KF titrator to check in the past too.
@@That_Chemist could just be certain brands or batches? We only had to buy a few over my PhD since we regenerated most of them so they lasted a really long time.
Molecular sieves are really amazing, I've had some very sensitive chemistry become frustrating when inhibited by the smallest traces of water. It doesn't matter if you use bone dry solvents or practice good technique, if its not working, its probably your reagents. Eventually, I dried EACH reagent specifically, dissolving them in reaction solvent to sit over sieves for a few days...and then combining them via cannula, and that went from 0% conversion to 100% conversion!
This video puts me in mind of my PhD days back in the mid 2000s; when one of us used a mechanical press to divide sodium chunks into wire, the other one would HOLD a 5 litre flask by hand underneath to collect said wire. After that, we simply threw in a load of lovely THF and indicator into the flask. God, how I miss those highly dangerous, potentially fire-inducing times!
Someone writing his habilitation had a funny story last week: The paper stated, that he has to do a reaction with THF and water added separately Didn't work Turns out the problem was, he thought the autors used dry THF, whereas the reaction needed (in addition to the added water) more water, which was already present in their poorly dried THF Didn't see too dry THF before, I think this is funny
Hey I just wanted to say thank you for this channel. I ended up mastering out of my PhD program two years in because I just couldn't do it and never had any success with any project. I'm probably not cut out for research and am still looking for a different avenue in chemistry, but your videos are a nice reminder of the good aspects I remember from being in lab.
Awesome video. Tried to ask my Orgo 2 Prof about this once and got a vague answer. Not his fault, it's not like he could talk for 11 mins on it. But I'm glad to get the full answer here.
What sounds to you like a vague answer can often involve an internal conversation like this: - This person is curious, and I love that, so I want to help - But this is a really complicated subject - And I don't want to steer this person wrong - Oh, and there's that one common thing that would otherwise make this suggestion go really badly wrong, so I can't just say that - That meeting I have to attend is in six minutes, and I'd love not to arrive sweating from running to it, and even that wouldn't be enough time
@@davidfetter That mostly sums up why I put that sentence about 'not his fault' in there (I added that just before posting). You can explain a lot more in detail with a video/presentation than an off the cuff response to a question.
I've effectively used anhydrous potassium carbonate to lower the water content of alcohols. Ethanol in particular was a great success, obtaining 98-98.5% ethanol after treatment. After decanting, I simply heated the residue in an oven to restore the potassium carbonate to an anhydrous state, regenerating the starting drying agent. I then used the magnesium method to lower the water content some more. But the molecular sieves have so much drying power, they're easy to manage, and reactivation after use is just one more little lab chore, no big deal. Speaking of, I also would have made it my own business to ensure everyone was up to speed on the whole "shorting out the heating element" thing. Six errors is no longer a mistake. I have an e-copy of the Purifications text you recommended, for sure useful to have around. Good presentation, thanks for sharing.
Potassium carbonate is an excellent desiccant, it's far better than magnesium sulfate, at least for quick drying solvent after an aqueous workup. It also has the benefit of presenting as dense granules, rather then the magnesium sulfate powder, which means you could even get away with just decanting instead of filtering.. I always use it when I am extracting a freebase amine, as well as other compounds that is not sensitive to alkali.
@@moosehead4497 I agree. The actual physical presentation of the drying agent after its use is very helpful for removing it. It tends to clump together and is very, very easy to decant. I've never had an issue with needing to separate any layers; simply decant the dried alcohol into its own container. Repeat the treatment if necessary (like I said, it usually got to 98% first try).
The way we used to activate mol sieves (sensitive organometallic chem) was as follows: hang them on your schlenk line, pull max vacuum and blast with a heatgun. As you drive off the water you'll see a very small increase in pressure. Our pressure meters went down to 1x10^-3 mbar and would usually rise to 5-8x10^-3 mbar while drying the sieves. Keep blasting until the pressure stays at a constant minimum. Doing it this way you avoid using arbitrary time limits and can judge the progress with a measurement. Negative: it's slow as hell because you're heating something inside a vacuum.
Glad this topic got picked! I don't ever need "analytically dry", but "pretty dry" solvents can be useful for predictable paint and finish. The residues in wal-mart grade 91% iso also seem to be mostly aqueous and I think getting some of the water out makes it a bit cleaner although I haven't actually studied it other than "oh that looks a little bit cleaner with the dryer stuff".
Our lab usually dries solvent by stirring with CaH for 30 mins over CaCl2 tube, then distill and proceed to add them into activated 3A molecular sieves. But for reactions that need to be very very dry, we have THF dispenser that is dried through a special column which was cool.
Not sure as to whether this is the go-to in the States, but in Blighty, we used to find the Perrin textbook a terrific resource for drying organic and inorganic chemicals.
Generally what we do for sieves is just heat them at 300 C for 12 hours under dynamic vacuum for 12 hours. Sieves get bone dry and then we store our already dried solvents over them in the glovebox. But I guess that is just what we do since we do very air sensitive chemistry
Great topic, I learned some things. On the industrial scale I designed and built a large THF mol sieve column. Regeneration was a beast due to the ceramic nature of mol sieves. - those things heat up and cool down sloooowly. That was not one of my favorite processes - flaring hot THF/N2 gas - yikes. An additional property of hyper dry solvents is the electrical conductivity. On the large scale this becomes an issue. "Wet" solvents quickly dissipate electrical charges acquired by pumping and flowing through pipes. Dry solvent stay charged up and can create discharges. Discharges are not good in large scale solvent systems. Inert atmospheres help managed the hazard but you'd rather not have a solvent tank behaving as a giant capacitor. People have reported looking into large tanks and seeing glowing sort of like the aurora borealis. The known incidents tend to occur when solvent is transferred and hoses are connected/disconnected. One solvent supplier had a recommendation to hang grounding elements inside the tank to collect this type of charge and dissipate it safely. Final story: When a mundane solvent like hexane or heptane is shipped from Houston TX to anywhere north the solvent will cool off, because anywhere north of Yewston is cooler. When the solvent cools water drops out of solution. It's not uncommon to receive a tanker load of solvent and collect a receipt sample and see people (at a Lithium plant) freak TF out because the sample is 99% water. Pro-tip: be prepared to collect, handle and discard some water in these situation.
For THF distilleries, I guess one important thing apart from the drying itself is also the removal of the BHT stabilizer before use, which is present in most commercial THF.
Usually heating mol sieves in the glass oven overnight isn't enough for me. What I do is to just put them in a Schlenk or Straus flask, put that in the microwave until I see the water vapour coming off, and then I let them dry in the vacuum until they're cold. Run this three or four times, and that usually does the deal.
In the literature there is a method for purifying acetone via cristallizing the complex with NaI, filtering the solid complex and distilling the acetone from it. Should produce quite pure and dry acetone. Maybe hard to scale, but for small amounts should work well. Didn't use it myself though.
Trying to tell another students supervisor who grew up using classical drying techniques such as Na/benzophenone that 3A sieves is better was quite an experience, can be hard to teach an old dog new tricks.
In the (inorganic) lab I worked at, we stirred pre-dried (from a solvent purification machine) solvents over NaK Alloy and then distilled them. Also everyone told me that Acetonitrile destroys Molecular Sieves, which speaks for the chemistst beliefs in things that "somebody told them once or something" I guess.
@@davidfetter re "somebody told them once or something" NaOH seems to be a good example of that, at least outside of professional labs. "Errmgrd don't open that bottle of lye without a full hazwopper suit, It's caustic and 'll melt yer arm!". Likely stories passed down from old industry where they would do stupid stuff like dump [not pour] a 55galllon drum of lye into an open top water tank at chest level, (I've seen films documenting processes where they do this very thing.) and it was actually the heat of violently boiling water that was the real burn hazard, not the incidental lye solution. Side note: I've used my bare fingers to handle small amounts of lye and even for stirring it into solution, it is not a big deal. Circumstance matters.
I hate solvent stills, but that's probably because during my undergrad I was doing some reactions using tBuLi in the same hood as a big ether still. It really truly frightens me to think about how bad that could've gone. The benzophenone ketyl colors are really cool though
When I finally found the paper you get your data from a couple years ago, I was really excited. So how hot do you keep your glassware oven? Mine is usually around 110-120 C
@@Orchids.and.Endlers How do you filter? I usually use a medium glass frit with vacuum. Buchner funnel or gravity filtration is awful for removing MgSO4 (from experience)
Rigorously dry THF is best obtained by distilling the THF from molten potassium. The norm is to pre-dry over sieves, and then rigorously dry from K or Na/Bz. When using diethyl ether it is dried from NaK. With Na/benzophenone, the benzophenone ketyl stays blue (i.e. rate of production of the ketyl at the surface of Na = rate of destruction of the ketyl) at several hundred ppm residual water once all oxygen is consumed (depending on the surface area of the Na). Blue only indicates O2 free, and not dry. The colour will deepen to purple as the rate of destruction of the ketyl goes down. In the Williams and Lawton paper, then tell us the THF was blue, and so it had not reached ultimate dryness. A problem for all the "active hydrogen" desiccants (alkali metals, metal hydrides etc.) is that they release H2 gas, which K-F registers as lots of water. K-F readings of superdry solvents dried by these desiccants is much, much lower after degassing.
I live in south I'm Bama an humidity is oppressive an it's really hard to keep chems an drying agents dry I found maxi pads an puppy pee pads work well to keep things dry
Yeah, acetone is a tricky one. It forms an addition compound with CaCl2 and MgSO4 doesn't work. Also due to aldol condensation the water content can increase so molecular sieves are no good either. I used freshly oven dried CaSO4, which seems to be the best option and distilled it directly from the desiccant. The literature claims 300 ppm or 0.002 M water with that procedure and that was good enough for my application.
When I tested my analytically dry Dimethoxyethane it still decoloured the sodium benzophenone mixture even though it was stored over 3Å molsive and is supposed to have 2 ppm residual water so now I have been refluxing it over sodium for a further week in hope of drying it further
Love your videos but your nomenclature is so different than what I am taught. I would call CH2CL2 dichloro methane for example. Is this because I'm from the uk?
What is the explanation for the sodium vs sieves results? Is it just because the amount of sodium (or its surface area) was lower? I don't see why sodium would stop reacting with water when concentration goes below certain limit..?
I know that there is information on esters when their characterized on the infrared spectrometer, but is it even useful? The peaks are within the fingerprint region, so is it even worth bothering to verfiy the esters using the IR data in a lab setting?
if it is for library recognition then yes, but typically the only time I would use IR for organic stuff is when my stuff is insoluble, I have literally no idea what it is, or if a reviewer asked for it lol
I dry my acetone with molecular sieves, after usage I will microwave them so I get to reuse them. P2O5 or Anhydrous MgCl is just too expensive for us amateur and NaCl results aren't great
For industrial use set a water spec for your reaction based on lab experiments. Do a K-F, if it does not fairy Chuck the solvent away. But I have set water specs for a manufacturer and then everything was ok.
Interesting that with dioxane that sodium got the solvent drier than sodium-potassium alloy, which I thought was a whole lot more reactive to water. Also, I think when talking about ppm it's useful to think about percentages to get a bigger picture view. Eg 50 ppm on this list isn't that dry but that is still 0.05% water, making your solvent 99.95%. In 100 g of solvent, you only have 0.005 ml of water.
hey THAT Chemist. not him. YOU. question for you. Say, hypothetically, after neutralizing freebase with conc. hcl solution , you have an amine hcl salt dissolved in Toluene azeotrope. you want to crystalize product and would resort to drying solvent using dean stark trap. Can one evoke crystallization in your NPS with sieves? just aas one might do using azeotropic distillation? assuming the chemical in question is larger than 3 angstrom in width. would it not get left behind i have never heard of them being used for crystallization . there has to be a reason as to why it does, or it doesn’t work. enlightenment?? thanks for your time.
hello. I proceeded with solvent drying using molecular sieves. However, after a few minutes the solvent color changed to brown. In this case, isn't it possible to use molecular sieves? The solvents I used are propylene carbonate and NMP.
Thank you, very informative! How often do you re-activate the molecular sieves? And would they be a viable strategy for water removal in moisture-sensitive condensations (like if formation of imine as as an intermediate is expected)?
By warned; you can't stir solutions with sieves in them. They turn into mud with no drying power. You can put them in a Soxhlet thimble, and that works.
That confuses me: why should sodium be so bad for drying THF and so good for dioxane? I have dryed THF over Na/benzophenone to use it in anionic polymerizations (started with tert. BuLi) and did not encounter issues. Perhaps my initial THF was already quite dry.
@@sebastiand152 I also find that inconsistent. I believe it is due to the different references. The third reference also shows that indicators (such as benzophenone) give a false sense of dryness to the user, but prolonged exposure to sodium does significantly increase the dryness. So the results from the first reference are somewhat biased, as they rely on this indicator method. I guess the bottom line is that molecular sieves are a great way to passively dry solvents. Distillation, however, has operational parameters, which differ across users/labs, but remains, in my opinion, one of the best methods to obtain dry and pure compounds.
from aldrich's page "The product (Molecular sieves, 13X) have been used for the abstraction of water from the 100% ethanol. Also, they are widely employed as an adsorbent in adsorption studies"
Would you ever recommend also passing the solvent through some sort of drying agent before dispensing/storing away that solvent in a flask filled with molecular sieves?
@@That_Chemist This is my experience too. The Sureseal bottles of supplier dry solvents are fine for organometallics such as Grignards and alkyllithiums. Most of the lab fires I've heard of are related to solvents stills which is why they were removed from our labs.
Dmso and Dmf have high boiling points and When u heat the sieves for activating DMSO doesnt evaporate from the surface of the sieves and if u heat more, DMSO (or Dmf) make a film which covers the pores of the sieves and disables to catch the water.
I did not try this one, but how about drying methanol by dissolving sodium methanolate in it? Water should quickly be converted to NaOH and the by-product would be methanol. Distillation would be needed, but I would expect fast and good results. And yes, I considered writing about Na metal in this context, but I would not recommend it.
@@That_Chemist It being an equilibrium is not a relevant argument. It always depends on the ratio of equilibrium. And: Mol sieves also works in an equilibrium between adsorption and desorption of water.
Some of those charts hardly make sense. How can NaK be 4 times worse than just Na? I would really take that information with a grain of salt. Some facts here definitely contradict the rest of the literature (and my experience too). But in the end 3A MS is a really great thing to dry stuff and generally quite an underestimated one.
I have a question. I used the molecular sieve 3A and the solvent looks unclear maybe because of the dust. Is it possible to use that solvent for my reaction without further purification?
I'm surprised to hear you say you can microwave sieves. I suppose you can but you've got to be very careful. A guy in one lab I worked in tried drying them in a microwave and they melted straight through the glass dish he was using and most of the way though the glass table in the microwave. We never tried again but I assumed some water remained trapped in the sieve and just got hotter and hotter.
Couldn't someone use a soxhlet extractor filled with mol sieves, where e.g. THF can pass through after previous drying? Probably over complicated but may lead to satisfying results.
I am wondering why alcohol such as methanol had to be dry? Methanol contains an acidic proton like water. So, reactions carried out in methanol will not be water sensitive? If it is the case, why do we have to dry methanol in the first place? ( Sorry for the poor English)
Best way to dry hydrocarbon solvent is reflux and partial distillation with sodium metal and place in inert air bottle with some suitable molecule sieve. But this way is very tedious and boring works to do. And it doesn't work on protic solvent, above hydrocarbon substituted some halide (e.g. chloroform) because sodium reacts with the hydrogen of solvent and ruins them all. So better way I feel is buy the solvent with air-seal, which can be bought from sigma-aldrich, or place the solvent in glove-box as soon as you get. And use it all ASAP whenever you get. Don't buy big drum of solvent even if it's cheaper than small one, and you use it within 3 months at least.
@@That_Chemist I'm in lab so I don't know the whole treatment the aldrich does. But in the experiment scale, most of moisture problem was came from old stored solvent, or the someone who doesn't know his reaction and believe the undesired situation in the reaction originated from moisture of solvents.
Unclear - maybe it catalyses some obscure reaction - it’s harder for me to say in the case of benzene, where as for something like acetone it is more conceivable
it would have been nice if you had warned the audience, that HMPA is to be avoided at all costs because its highly cancerous. like with the hepafluoroisopropanol for females. it would help young chemists and other scientist to be aware of the dangers of certain substances. thank you for your work in highly infomativ videos !
@@That_Chemist but its good to think about sieves just think stills that are long term will most likely become better as longer exposure to drying agent bur great video
Purification of lab chemicals is an awesome book. Pretty old-school but that just ads to the charm. Edit: Please don't reuse mol sieves 🤢🤮 Oh and 9:19 here is a pretty neat publication on B2O3: A heterogeneous metal-free lewis acid for CO2 fixation into cyclic carbonates.
