Keras
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Dimethoxyethane (glyme) synthesis
Folks,
has anyone attempted the synthesis of dimethoxyethane using the traditional Williamson synthesis with ethylene glycol + methanol and sulphuric acid?
Is there any hope to get more dimethoxyethane than, say, dimethyl ether or some sort of multi-ethoxy compound?
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clearly_not_atara
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I think you may be confused: the Williamson synthesis is the SN2 reaction of alkyl halides with alkoxides. According to this paper, it can be
achieved, but dioxane formation is a significant side reaction:
https://www.researchgate.net/profile/Lu-Rui-4/publication/31...
"SAPO-34 zeolite was found to be an efficient and highly selective catalyst for this etherification via a continuous flow experiment."
Since acidic etherification proceeds through the oxonium, we should consider which alcohol is more easily protonated; this is probably ethylene
glycol. So using methanol in excess could be a good strategy. But do note:
| Quote: | The catalytic etherification of EG with methanol has not been extensively reported in the literature. Scheffel et al. used H 2 SO 4 as the catalyst,
the conversion of EG was 61.2%, and the concentration of dimethoxyethane was only 9.9% in the mixture solution, less than that of 2-methoxyethanol
(23.5%). 18 Due to the environmental impact by liquid acid, solid acid has been reported for its application in the etherification reaction.
Baimbridge et al. used Nafion 15 as a catalyst for etherification of EG with methanol, and selectivity for 2-methoxyethanol and dimethoxyethane was
67% and 28%, respectively, with 75.7% of EG conversion.19 Ikariya et al. used s–Si–P (1 : 5 : 0.8) oxide catalyst to obtain 2-methoxyethanol with
76% selectivity at 23% conversion under 300 C and
12 MPa. However, dimethoxyethane was not detected in the products under these harsh conditions. 20,21 From the abovementioned reports, we found that
2-methoxyethanol was the main product during the etherification of EG with methanol, and it could not be efficiently converted to dimethoxyethane
further, which resulted in low yield. Another finding from the abovementioned reports was that the by-product 1,4-dioxane was detected. EG was easily
activated in the presence of an acid catalyst, and self-etherification would finally form 1,4-dioxane.22,23 In addition, the etherification of EG with
methanol is an equilibrium reaction. |
It seems that a tricky purification could be in your future.
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Texium
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Thread Moved
10-4-2023 at 19:12 |
Keras
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You’re right about Williamson, of course. I realised that soon after posting the message, but I was already in bed. I've got a tendency to mix up
things when I’m tired.
Thanks for the input. So I guess the only chance to do it is to use Williamson synthesis from sodium methanolate and 1,2-dichloro (or dibromo) ethane,
and use methanol as solvent…
I wonder why I can’t find anyone selling it for a reasonable price, since it seems to be in wide general use.
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clearly_not_atara
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Will dioxolane work for your rxn? It seems to be a little easier to produce:
https://pubs.acs.org/doi/abs/10.1021/acs.iecr.9b00331
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Keras
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Good question. This is linked to the thread about using BnBr (this time I got it right) as a Grignard reagent. I was reading Rieke’s articles about
producing highly reactive metals by reduction of halides into finely divided zero-valent metallic particles using lithium and naphthalene, and the
article clearly states that ‘glyme is the best solvent’ to use for this reduction. I have no idea if dioxolane would work satisfactorily (EDIT:
given that tetrahydrofuran is namely cited as being inferior, I doubt it).
Attachment: Rieke.pdf (322kB)
This file has been downloaded 147 times
[Edited on 11-4-2023 by Keras]
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clearly_not_atara
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There was a paper about using base with diethylene glycol and dimethyl carbonate to obtain diglyme. I don't know if that would work for the monomer,
but maybe it's worth a try. At least Me2CO3 can sometimes be obtained at a good price.
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Keras
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Quote: Originally posted by clearly_not_atara  | | There was a paper about using base with diethylene glycol and dimethyl carbonate to obtain diglyme. I don't know if that would work for the monomer,
but maybe it's worth a try. At least Me2CO3 can sometimes be obtained at a good price. |
Incidentally, I have ordered some dimethyl carbonate together with caesium carbonate to experiment with a greener way to methylate phenols.
Apparently, 4 h of refluxing dimethyl carbonate with phenol using caesium carbonate as a base gives 100% anisole. No methyl iodide needed, no need to
use sodium.
So why not give it a go? If you can find the paper, I’m your man 
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clearly_not_atara
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Unfortunately, I mis-remembered. What actually happened was a post by monolithic where he mentioned that "dimethyl carbonate can work under mild conditions" but linked to a methylation of syringaldehyde, not
DEG.
Sorry for the confusion! The thread does also mention a prep of MeOTs from DMC + TsOH, though this adds an extra step and requires a lot of TsOH. Back
to the drawing board, apparently.
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Keras
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| Quote: Originally posted by clearly_not_atara |
Sorry for the confusion! The thread does also mention a prep of MeOTs from DMC + TsOH, though this adds an extra step and requires a lot of TsOH. Back
to the drawing board, apparently. |
Yeah. I think the best way is to use methanolate and dibromoethane (made from hydrobromic acid and ethylene glycol), and recycle the NaBr.
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