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Author: Subject: Deep Eutectic Solvents, safe organolithium and fast alkylation
j_sum1
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[*] posted on 17-12-2016 at 18:26
Deep Eutectic Solvents, safe organolithium and fast alkylation


https://www.chemistryworld.com/news/chicken-feed-and-food-in...

I came across this -- outside my filed of expertise but I (now) know enough to appreciate how stunning this result is. The ability to do alkylation in a matter of seconds, the taming of extremely pyrophoric reagents and the use of ionic liquids that have been discussed here at length -- all of these struck me as rather interesting and beneficial.

I'd love some thoughts and comments from those more knowledgeable than I am.




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DDTea
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[*] posted on 17-12-2016 at 19:21


This is pretty remarkable. I remember the first time I used n-Butyl lithium, which is a pretty mellow among lithium alkyls. The guy who was coaching me ran through the procedure. "Have you used n-BuLi before?" "No.." "You'll be fine. Let me know if you have any questions." and he walked away. The septum was torn to shreds: crappy Alfa-Aesar septum. I upended the bottle, dipped my needle in to pull out an aliquot...and the solution dripped onto my hand. It gets hot FAST! I ripped off the glove and squirted it with IPA. But yeah: these days, I kind of take for granted the whole "flush with inert gas, cool to -78 C, mix, then warm to the reaction temperature." With that in mind, temperature can be important with these reactions--so I wouldn't just go ahead and pitch these nBuLi tablets in without thinking about it. They note some "different" reactivity, though, and that will have to be explored before people feel comfortable using this technique.

Anyhow, this same technique is being used in other contexts. Richard Schrock, who won the Nobel Prize for developing the first homogeneous olefin metathesis catalyst, is applying paraffin encapsulation to his notoriously finicky catalysts. The goal is to make them more usable to the synthetic chemistry community. The paraffin, in turn, dissolves in the reaction solvent. As an aside, I recall Prof. Schrock complaining at a recent ACS meeting that, "You all have to learn how to do air sensitive chemistry!" But really, it seems that if someone wants to do Olefin Metathesis, they usually reach for some flavor of Grubbs 2nd gen. catalyst first--and only branch out further if those don't work.

In industrial fine chemistry, pyrophoric reagents are sometimes added to reactors in dissolving plastic bags--similar to the laundry tablets. Of course, this also means a finite amount of plastic gunk fouls the reactor with each use.

All of these kind of speak to my one concern: introducing more gunk to a reaction always adds more consideration to the separation.




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Dr.Bob
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[*] posted on 18-12-2016 at 18:01


Given how much I hate using some pyrophoric reagents, I do like the idea of anything to make them safer to handle. I had the other day that made the cannula smolder at both ends when I was done. Nothing to make your day more fun than that. But I do think that many profs and PIs are not doing a good job of training people to use them safely and correctly. Doing it wrong can ruin a reaction, if it is does not start a fire. And they can make some pretty big fires if done badly.
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[*] posted on 18-12-2016 at 18:32


I wonder how the workup for one of these reactions would be done. I assume you could just quench the reaction, and extract the mixture with organic solvent and water. Choline chloride and glycerol would go to the aqueous phase, and your product would (hopefully) go to the organic phase.



As below, so above.
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[*] posted on 19-12-2016 at 09:34


Quote: Originally posted by Dr.Bob  
...But I do think that many profs and PIs are not doing a good job of training people to use them safely and correctly....


Cue the number one example of such:

https://en.wikipedia.org/wiki/Sheri_Sangji_case




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[*] posted on 19-12-2016 at 10:29


I only had a chance to skim the paper, but how does the butyllithium not just deprotonate the glycerol?



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clearly_not_atara
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[*] posted on 19-12-2016 at 10:57


Perhaps the behavior can be explained by considering the sterics of the solvent-solvate complex. If an organolithium is dissolved in water, it coordinates water molecules RLi*nOH2 which are small, so an intervening acid can displace the lithium. But in glycerol/choline, it coordinates glycerol and choline molecules, which might protect the organolithium. The paper:

http://onlinelibrary.wiley.com/doi/10.1002/ange.201609929/ab...

mentions using pure glycerol as a solvent for organolithiums as well.
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[*] posted on 19-12-2016 at 11:03


It may also form a alkoxide of the gylcerol, but that would be a poorer base then. I suspect that this great discovery may only have niche uses, which is why no one discovered it yet. Many great discoveries I have heard of proved to be of little lasting value. But some do change the world, like Pd couplings, boronic acids/esters, and olefin metathesis. But even those are mostly known about my experts.
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