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Author: Subject: Crown ethers via sulfur mustard?
clearly_not_atara
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[*] posted on 26-4-2017 at 11:23
Crown ethers via sulfur mustard?


NB: I do not recommend that this reaction sequence be attempted by anyone.

It is noteworthy that crown ethers are difficult to produce, even industrially. Thus it is difficult to buy 12-crown-4 for less than $10/mL, even in large quantities. This is unfortunate because such crown ethers may serve as useful electrolyte additives for lithium-ion batteries, and batteries using crown ethers are not commercially viable because of the cost of the ethers. Simply adding 12-crown-4 to the battery electrolyte increases cycling performance:

http://jes.ecsdl.org/content/134/9/2107.abstract

However there is a method of production which the corporations may not have tried because a crucial intermediate is banned by international convention for having "no civilian uses", which was true until today?

Diethylene glycol is very cheap. Sulfur mustard is also very easy to produce and the method is fully atom-economical:

SCl2 + 2 C2H4 >> (ClEt)2S

The reaction then simply comprises the reaction of disodium diethylene glycolate with sulfur mustard, with preferably both reagents in as low concentration as possible:

(ClEt)2S + (NaOEt)2O >> 1-thia-12-crown-4 + 2 NaCl

The reaction is first-order in both reactants whereas polymerization side-reactions are all second-order in one of the reactants so it stands to reason that the side reactions can be suppressed by performing the reaction at low concentration. It is crucial to generate the dianion. Possibly solid sodium diethylene glycolate can be treated with sulfur mustard gas. Yields may thus be much better than methods utilizing the oligomerization of ethylene oxide, and no byproducts of similar molecular weight are formed. The conversion is simply:

1-thia-12-crown-4 + HgO >> 12-crown-4 + HgS

This apparently works even for divinyl sulfide so it should be fine here. The method can be made cyclic so the only byproduct is NaCl:

HgS + 2Cl2 >> HgCl2 + SCl2
HgCl2 + 2NaOH >> HgO + 2NaCl

EDIT: I realized that you can apply the same reaction to synthesize 15-crown-5 and 18-crown-6 by replacing diethylene glycol with tri- and tetra-ethylene glycol. The particular advantage over the use of e.g. chlorinated glycol ethers is the much higher alkylating power of sulfur mustard, and the milder reaction conditions made possible thereby.


[Edited on 26-4-2017 by clearly_not_atara]
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Boffis
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[*] posted on 29-4-2017 at 08:32


Why do you have to go through the dichloro-thioether? Can you not convert di-ethyleneglycol into a dichloroether analogue and thus avoid the de-sulphurization step. I have also seen discussions about the use of ditosylated polyethylene glycols in the preparation of macrocyclic ethers. I am pretty sure I have seen a thread on SM about the preparation of these compounds

Interestingly the macrocyclic thio-ethers have greater affinities for the chalcophile elements like Cu and Ag than for alkali metals; whole new field of chemistry here.
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Lambda-Eyde
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[*] posted on 6-5-2017 at 15:11


Quote: Originally posted by Boffis  
I am pretty sure I have seen a thread on SM about the preparation of these compounds

Right you are! https://www.sciencemadness.org/whisper/viewthread.php?tid=17...




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clearly_not_atara
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[*] posted on 6-5-2017 at 20:39


Quote:
Why do you have to go through the dichloro-thioether? Can you not convert di-ethyleneglycol into a dichloroether analogue and thus avoid the de-sulphurization step.


In fact this is a standard synthesis of crowns:

http://www.orgsyn.org/demo.aspx?prep=cv6p0301
(nb: orgsyn likes to change their links so this may rot; Google "orgsyn 18-crown-6" if you're reading this years from now and the link doesn't work)

A 3-l., three-necked flask equipped with a mechanical stirrer, a reflux condenser, and an addition funnel is charged with 112.5 g. (100.0 ml., 0.7492 mole) of triethylene glycol and 600 ml. of tetrahydrofuran (Note 1). Stirring is begun and a 60% potassium hydroxide solution, prepared by dissolving 109 g. (1.65 moles) of 85% potassium hydroxide in 70 ml. water, is added (Note 2). The solution warms slightly. After about 15 minutes of vigorous stirring (the solution begins to develop color and gradually becomes rust brown; (Note 3)), a solution of 140.3 g. (0.7503 molione) of 1,2-bis(2-chloroethoxy)ethane (Note 4) in 100 ml. of tetrahydrofuran is added in a stream. After the addition is complete, the solution is heated at reflux and stirred vigorously for 18–24 hours.

As you may have noticed it takes 24 hours of refluxing to get a poor yield of crown due to side reactions such as polymerization. The reason that oligomerization, which is second-order in the glycolate anion, is a favorable competing reaction, is that the glycolate is present at a high concentration -- all of the glycolate is added before the reaction initiates.

Sulfur mustard, by contrast, is billions of times more reactive than a mere beta-chloroether. It is reasonable to expect the reaction between sulfur mustard and the glycolate anion to be nearly instantaneous, which allows you to perform the whole reaction at low concentrations by using e.g. a flow process. This should reduce polymerization to negligible levels and markedly simplify the purification process.

In other words, the extreme alkylating activity of sulfur mustard is the whole point. As to why I was interested in industrial production -- well, batteries are cool I guess.

[Edited on 7-5-2017 by clearly_not_atara]
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Boffis
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[*] posted on 9-5-2017 at 09:23


@clearly_not_atara; that's interesting I had not thought about it like that. It didn't occur to me that it might improve yields by out-competing side reactions.

I did toy with the idea of producing thio macrocyclic ether using sulphur mustard because I am interested in their cmplexing abilities with thiophile elements but in the end I though it just too hazardous. I actually managed to acquire some in small amounts (0.5 g) of several such sulphur bearing ether from a guy researching it that field.
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