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Author: Subject: Synthesis of symmetrical polyethers, how is it done?
BromicAcid
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Synthesis of symmetrical polyethers, how is it done?

When it comes to ethers I know two ways to make them. The dehydration way with something like H2SO4:

2EtOH --H2SO4--> EtOEt + H2O

And the Williamson ether synthesis way:

EtBr + EtONa ---> EtOEt + NaBr

But how to go about making ethers with several linkages. Specifically I am wondering about 2-methoxyethyl ether (a.k.a diethylene glycol dimethyl ether) which has a backbone like this:

COCCOCCOCO

Put the hydrogen on there and you're all set, all ether linkages for the oxygen. Anyway, I figured you could react something like sodium ethoxide with methyl chloride to get the first part, the COCC, but from there how to install a hydroxyl group on that last carbon to possibly do a dehydration reaction to connect the ether halfs? Or maybe starting from ethylene glycol, is there a way to put a methyl group on only one of the hydroxyl groups without some crazy methylating agent?

I have googled a bit on this but answers are not forthcomming. So, any hints on producing this, any other ether synthesis procedures? Thoughts would be much appreciated on the production of this great high-temperature solvent.

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guaguanco
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Many of the poly-ethoxy things are made with ethylene oxide.
methanol + CH2CH2(O) -> 2-methoxyethanol
2-methoxyethanol + H2SO4 -> diglyme
You can perform controlled polymerization with ethylene oxide and make long chains:
(OCH2CH2O)n
Proteios
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yeah... i think you will find all the poly ethylene oxide/polyethylene glycol derivates are made by anionic polymerisation of ethylene oxide, with a low degree of polymerisation, followed by distillation. The end hydroxyl can the be capped as desired.
BromicAcid
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Proteios, guaguanco, thank you very much for you imput. But I think I figured out an even easier method, starting with diethylene glycol, which you can buy @100% in canned heat applications (which I didn't know). So, diethylene glycol @ 75C in DMSO with KOH then run MeCl through it for about 3 hours and violla, almost entirely OTC method to diethylene glycol dimethyl ether.

[Edited on 3/11/2004 by BromicAcid]

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Geomancer
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Synchronicity! I was just looking for ways to these goodies yesterday. Alas, what I'd really like is triethylene gylcol, preferably with nice leaving groups for Williamson type synthesis of a crown-like compound.
Nice find, the DEG. If you have some catechol, you can make yourself a nifty little crown ether.
BromicAcid
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Speak of the devil! I was just considering the possibilities of crown ethers from this compound. If you were to react an allocate with HCl to produce, ClCH2CH2OCH2CH2Cl then react that with the OHCH2CH2OCH2CH2OH under exceedingly basic conditions you would get the 12-crown-4 ether which is good for stablizine lithium ions. Although seperating this from the mix of products present might be difficult.

The triethylene glycol would produce the 18-crown-6 good for making potassium ions soluble in organic solutions, considerably better for oxidizing agents whereas the lithium would be better for the reducing agents.

I'd be nice to come up with a good synthesis of trioxane or THF as well though. Maybe this topic will grow.

[Edited on 3/12/2004 by BromicAcid]

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Proteios
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lol..... i think you will find syntheis of crown ethers is more of a black art than that!.....the reaction you have written down... the dichloro PEG under extreme basic conditions will just hydrolyse the Cl.... if you react it with the dianioninc oligo-ethylene glycol you are much more likely to just get PEG (the polymer) than the crown ether....need high dilutions and templates etc!

[Edited on 12-3-2004 by Proteios]
BromicAcid
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 Quote: the dichloro PEG under extreme basic conditions will just hydrolyse the Cl....

By exceedingly basic conditions I ment high concentration of KOH in DMSO, that is one of the traditional rxn. mediums that I have used for williamson ether synthesis in the past, or maybe in xylene.

 Quote: if you react it with the dianioninc oligo-ethylene glycol you are much more likely to just get PEG (the polymer) than the crown ether....need high dilutions and templates etc!

I figured as much, although it seems like it would to some extent thats why I mentioned the pain of seperating by-products. Anyway, for the diethylene glycol dimethyl ether, what sounds like the better idea to everyone here:

HOCH2CH2OCH2CH2OH + CH3Cl ---(KOH/DMSO)---> CH3OCH2CH2OCH2CH2OCH3 + 2KCl + 2H2O

Or

ClCH2CH2OCH2CH2Cl + CH3OH ---(KOH/DMSO)---> CH3OCH2CH2OCH2CH2OCH3 + 2KCl + 2H2O

Basically, does it sound better from a mechanistic standpoint to bubble CH3Cl through diethyleneglycol or chlorinate the diethylene glycol and add it to the CH3OH? Also, for the chlorination of diethylene glycol, to transform it to ClCH2CH2OCH2CH2Cl I would imagine I could use the HCl method but any ideas on how to purify a product or the reaction conditons. There are people here much better at organic chem then me.

[Edited on 3/13/2004 by BromicAcid]

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Geomancer
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Actually, the template effect is so strong in simple crown ethers that high dilutions are not needed. See Orgsyn CV 6, 301 (18-crown-6) for example.
I suggest using the methyl chloride route since SN2 reactions like as little to be in the way as possible.
Proteios
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Of the black magic I remember from synthesis..... its been a while....add some KI to the reaction.... you only need a few mg.....this speeds up the reaction hugely (I subs. Cl, I displaced many time more easily than Cl). Im still uneasy that OH is not a powerful enough nucleophile to displace you halide, but OR will be... but like i say... its been a while since ive done this sort of thing. A simpler alternative.... K2CO3 is a good irreversible proton plucker...(its weak but at reasonable T it can b okay) I remember it worked v. well for making phenolic anions as precursor to the ethers (but then phenols are much more acidic than alcohols).

[Edited on 13-3-2004 by Proteios]
BromicAcid
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Well, I was at the library again today, and you know what that means, I got new information on the topic!

Well, first off, check this out, it's a PDF that's 110 pages all about DMSO, with solubilities and such, very nice, regarding ether synthesis:

"The high activity of alkoxide ions in DMSO shows up in their enhanced basicity... In this case, the acidity of alcohol's in dilute solutions is about 103 times that of DMSO so that only a minor equilibrium quantity of the DMSO anion is present.... The Willamson ether synthesis from alcohol's and alkyl halides (chlorides) with sodium hydroxide as the base can be considerably improved using DMSO as a solvent in place of excess alcohol... The rate of reaction of alkoxide ions with alkyl halides in alcohol-DMSO mixtures to form ethers increases with the increasing amount of DMSO."

But here is what I got from my school, not what I wanted but interesting considering where this thread has went. From Organic Synthesis Collective Volume, VI Noland 1988:

HoCH2CH(OCH2CH2)2OH + Cl(CH2CH2O)2CH2CH2Cl ---(KOH/THF(aq))--> 18-crown-6 K+complex ---(acetonitrile and vacuum distillation)--> 18-crown-6

This reaction actually has decent yields without a template because the potassium ions are the template, the crown ethers form around the potassium ions! So it might stand to reason that the 12-crown-4 might be attemptable with lithium hydroxide in place of the potssium hydroxide and diethylene glycol in place of the triethylene glycol. The whole procedure would be attemptable if it were not for some of the exotic solvents (but you could probably find substitutes) and intensive vacuum distillations. Very interesting though.

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BromicAcid
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More interesting information. I was looking up some of the precursors for crown ethers and found that triethylene glycol and triethylene dimethylether are used as phase transfer catalysts and are known as linear crown ethers, i.e., they will wrap around cations and solvate them in non-polar mediums making insitu crown ethers, very interesting.

In addition I found that of the many cations crown ethers can put into solution they can do Ag+ ions. Would it be possible to solvate AgNO3 in a hexachlorobenzene solution and make hexanitrobenzene. The AgCl would precipitate out, the lattice energy is way too high for even the crowns to solvate. But then you would have to convert your AgCl back to Ag otherwise it would be way too price intensive.

General information about glymes:
http://www.glymes.com/images/Glycol%20Diethers%20Brochure.pd...

PDF of the article origionally published on crown ethers:
http://pubs.acs.org/cen/pdf/ja01002a035.pdf

Some crown ethers are expensive:
http://www.sciencelab.com/page/S/PVAR/10410/SC-C1359

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chloric1
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Has anyone delt with Sciencelab.com? I have delt with other suppliers and had decent luck. My interests usually revolve around non-cyanide silver plating, organic oxidations, alkyl halides, and of coarse nitrations. I realize Sciencelab has expanded there product line dramatically since last summer. I remember trying to have them find succinimide for one of my formulas and they said they could only get it for institutions. I asked them if it was controlled or restricted and they said no, but I could buy it from somewhere else. Now they list this on there website. Buy the way I never gave my name becuase they are from Texas.

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BromicAcid
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I wanted to buy some chlorotrimethylsilane from there and it was $18 for 100ml, but they have a$25 minimum order and everything is so expensive there, urea is like $25 for 500g eventually I settled on some glass tubing for$12 or something like that, I got to the total page, $25 for hazmat,$17 for shipping in general, so I just killed the window.

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chloric1
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Yeh I know

That damn hazardous shipping such scam! You iknow when I had my first chemical order in 1991, I ordered 4 500ml bottles of Nitric acid and a bunch of metal salts and the hazardous charge wasonly $5 additional! By 1993 it inched up to$7 and finally $10 by 1995 and it continued the trend upward ever since! I have ordered chemicals that cost$25 and paid $37 shipping! It was a pain but I could not pass it up, the chemical was normally$40 per quart and this was 4 litres! Before you ask I cannot remember which chemical it was.

I just wanted to see if anyone was able to order safely from Sciencelab without getting a shit load of questions. There are some items that are not priced so badly. Just ahve to pick and choose wisely. There selection is very simular to Aldrich. HMmmmm! I wonder?!?!?!

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BromicAcid
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DMSO, a true wonder....

Above this in one of my previous posts I gave a link to a site that has a 110 page report on DMSO. I printed the whole thing out the other day and bound it into a book and took the time to read it. WOW Is there anything DMSO can't do? Well, of course there are lots of things but I cannot stress enough how many useful reactions are listed along with solubilities.

To get to the meat of my post. I somehow diverted myself from my symmetrical polyethers to more ethers in general.
 Quote: When certain diols are heated in DMSO, cyclic ethers result instead of the expected dienes. When 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol are heated, using 2 mols of alcohol per mol of DMSO, the corresponding heterocycles, tetrahydrofuran (70%), tetrahydropyran (47%), and oxepane (24%) are formed.)

Interesting, is it not? In addition there are so many things to be made, 1,4-dioxane could be made from diethylene glycol. 1,4-butanediol is available in heath stores for muscles although not cheaply. Then once you get into triethylene glycol you would be getting into the territory of small crown ethers capeable of holding Li+ ions and higher glycols other crowns, expecially if you added a bit of the potassium salt to help form the template.

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BromicAcid
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I did some reactions on producing 18-crown-6 using the method provided in organic synthesis at 1/6 scale. My yield after purification overall from 1,2-bis(2-chloroethoxy)ethane was approximately 14% compared to their overall yield of 22%. Additionally I tried this reaction with 2-chloroethyl ether and ethylene glycol and got a yield of 0.26% which is terrible in my opinion, reaction between diethylene glycol and 1,2-dichloroethane gave a similar yield. Obviously the template effect isn't that strong Definately not an OTC procedure either, lots of THF used and some methylene chloride (though that is OTC in some areas still). Plus of course the 1,2-bis(2-chloroethoxy)ethane, but that could be made from triethylene glycol which is OTC, providing you had a good halogenating agent. Still the whole experience was fun and crown ethers work great to make ionic compounds soluble in non-polar solution, you would have all marveled at my purple benzene. Still though I wanted to dissolve sodium/potassium alloy in THF with the aid of the crown, I've never personally seen the beautiful blue solution that supposedly results but I can only imagine that it would be fantastic

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bfesser
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[Sorry to resurrect an old thread, but I'd rather not start a new one for such a simple question.]

How prone are crown ethers to peroxide formation? I'm interested in 12-crown-4 and 18-crown-6, in particular. Are they safe to store under normal conditions (dry, ventilated)? Any special considerations?
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