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Author: Subject: Diethyl ether from ethanol and something else than sulphuric acid
Keras
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[*] posted on 9-9-2023 at 05:53
Diethyl ether from ethanol and something else than sulphuric acid


Folks,

I was wondering if anyone had already attempted the synthesis of diethyl ether by the classical dehydration process but using something else than sulphuric acid.

Personally, I tried using 75% phosphoric acid (H₃PO₄ is mentioned as another possible acid for this reaction), but it failed miserably: all I collected was the ethanol at 70 °C. Probably too much water. Concentrating phosphoric acid could work, but I’m a bit weary because hot phosphoric acid attacks glass.

I was thinking about using solid acids, such as citric acid. Boiling ethanol over citric acid leads to the citric acid dissolving. Either citric acid is soluble in ethanol (maybe?) or it dissolves in the water produced by the dehydration.

My main concern is to avoid the tarry products you get as the reaction progressing, and use an easier to get acid (as you know, in the EU concentrated sulphuric acid is restricted for w/e reason). I’m going to try p-toluenesulphonic acid with is solid, and is not banned.
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[*] posted on 9-9-2023 at 06:29


Perhaps thorough study of:

https://en.m.wikipedia.org/wiki/Sulfuric_acid

will provide the answer to your query :cool:
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[*] posted on 9-9-2023 at 06:43


Quote: Originally posted by leau  
Perhaps thorough study of: https://en.m.wikipedia.org/wiki/Sulfuric_acid will provide the answer to your query :cool:


If you mean that I could produce sulphuric acid myself, I actually tried producing sulphur trioxide by pyrolysis of sodium bisulphate and dissolving it in (already made) concentrated sulphuric acid. It works, as the following picture demonstrates (the test tube is actually made of quartz to withstand 800 °C+).

IMG_1686.jpeg - 2.6MB

[Edited on 9-9-2023 by Keras]
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[*] posted on 9-9-2023 at 08:40


There's and old saying that may be applicable:

"If at first you don't suceed, try, try again"

A diagram of a small lead lined reaction tower was posted long ago as this particular situation was foreseen. One could bubble the sulfur trioxide through electrolyte for an automotive battery if one were creative enough :cool:

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[*] posted on 9-9-2023 at 12:47


...this might help,...solo

https://the-hive.archive.erowid.org/forum/dosearch.pl




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[*] posted on 9-9-2023 at 15:01


Ether forms by the following mechanism:

EtOH + HX >> EtOH2+ + X- (HX is any acid)

EtOH2+ + EtOH >> Et2OH+ + H2O (ethyl transfer)

Et2OH+ + H2O >> H3O+ + Et2O (diethyl ether is a much weaker base than water)

The pKa (a poor measure in nonaqueous solvents, but useful nonetheless) of EtOH2+ is about -2.5 (H3O+ is about -1.5). But the pKa of H3PO4 is a much weaker +2.5. Phosphoric acid just isn't strong enough to protonate ethanol.

Another problem is that the second step is energetically unfavorable, so the reaction usually occurs around 130 C, well above the boiling point of ethanol. Sulfuric acid is a strong hydrogen-bond donor which keeps the ethanol in the liquid phase. Usually, you need to keep the concentration of water pretty low, too, since the reaction is reversible.

p-TsOH might do it. It's much stronger than phosphoric acid. I can't guarantee you won't get any tar, though. The monohydrate is a solid mp 104 C, but the anhydrous form has an mp of 38 C. You probably want the anhydrous form. I don't know much about drying p-TsOH.

Give it a shot and tell us how it goes?




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 9-9-2023 at 15:24


Somebody here on the board claimed the reaction works with sodium bisulfite instead of H2SO4 and that this has a much reduced tarring. No details were provided and I could fiond nothing regarding this so I do not know.
H3PO4 stronger then 85% is for sure able to dehydrate the ethanol, it is commonly used when ethylene is the desired product and not ether. Temp for this is 150 °C and surprisingly there is little attack on the glassware.
This shows that H3PO4 has no problems with alcohol just distilling off whatever the pk-something may say or not say.

I propose that H3PO4 with a catalytic amount of H2SO4 or p-toluenesulphonic acid, or maybe even sodium bisulfite will provide the wanted product - diethylether - in good yields with much reduced tarring at about 130 °C.




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[*] posted on 10-9-2023 at 08:05


Thanks for your input. Probably my phosphoric acid wasn't concentrated enough.

pK is a good indicator for an equilibrium reaction. But since you distill off one of the products, the reaction is driven forward, even though the equilibrium is unfavourable.

I will give a shot at sodium bisulphate, and I just thought that sulphamic acid, which is pretty strong too (pK = 1), might also do the trick (unfortunately, that will have to wait a couple of weeks).

[EDIT]

I found this patent which describes a convenient way to get crystalline orthophosphoric acid from a 1:1 mixture of 75% orthophosphoric acid and glacial acetic acid. Orthophosphoric acid doesn’t attack glass. Metaphosphoric acid (HPO₃) does.



[Edited on 10-9-2023 by Keras]

[Edited on 11-9-2023 by Keras]
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[*] posted on 10-9-2023 at 10:32


Running ethanol vapor through a heated solid acid reaction tube (=spongy alumina) will produce ethene and ether. I think it was hyperspace pirate on youtube who did that, he was after the ethene for a cascade coolant-system, and got ether as a side-product.
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[*] posted on 10-9-2023 at 11:38


According to:

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

such batteries usually use sulfuric acid as an electrolyte :D One should be able to get fresh electrolyte at an auto parts supplier and concentrate it using vacuum distillation :P An article titled Chamber Process Manufacture of Sulfuric Acid by Edward Jones from Industrial and Engineering Chemistry pp 2208-10 (1950) is attached ;) Methods utilized in the chemical industry are used because they are cost effective :cool:

Attachment: jones1950.pdf (538kB)
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[Edited on 10-9-2023 by leau]
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[*] posted on 10-9-2023 at 21:49


My problem is not getting sulphuric acid. I still have 10 l circa of 98% sulphuric acid, plus several other bottles of less concentrated mixtures such as pure 37% for batteries or drain cleaner. So that’s not the issue. Besides, if I want to get more, I can get sulphur trioxide the way I indicated and use it to get oleum I can dilute afterwards to 100% sulphuric acid.

The problem I want to address is that of a messy reaction due to the oxidising properties of hot sulphuric acid. And also find an alternative acid for those who don’t have access to concentrated sulphuric acid. Car batteries are now often completely sealed for safety reasons, and getting 37% sulphuric acid from them means ripping them apart, messing with strong acid and lead, which you cannot get rid of just by throwing to the bin.



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[*] posted on 11-9-2023 at 00:34


Keras,

the reaction is not dehydration, the reaction is formation of ethyl sulfate which undergoes further transformations (actually, reacts with ethanol) at high temperature.
(Also clearly_not_atara points to generalization of this mechanism).

If you are searching H2SO4 substitute I would recommend studying of this patent:
https://patents.google.com/patent/US3024263A/en

As you can see, ethyl sulfate formation is reversible and to make it go in one direction you need to bind water somehow (yes, here is dehydration). In the case of bisulfate they use decahydrate formation under 32C, so this is how you can get it with bisulfate. Otherwise water will prevent the reaction.



[Edited on 11-9-2023 by teodor]
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[*] posted on 11-9-2023 at 01:50


Quote: Originally posted by teodor  
Keras,

the reaction is not dehydration, the reaction is formation of ethyl sulfate which undergoes further transformations (actually, reacts with ethanol) at high temperature.
(Also clearly_not_atara points to generalization of this mechanism).


Aha? For me, ethanol is protonated, loses H₂O to form C₂H₅O⁺ which subsequently attacks one of the lone pairs on the oxygen of another ethanol molecule. The resulting molecule (C₂H₅)₂OH⁺ then expels its superfluous proton, giving diethyl ether and regenerating H⁺, as not_atara detailed. The first molecule of alcohol loses water, that’s why I call it a dehydration, but this might be a slightly abusive use of the term.

The patent you point to seems to suggest that replacing sulphuric acid by sodium bisulphate is hopeless, since, as you point out, alkyl sulphates are formed instead of diethyl ether.

[Edited on 11-9-2023 by Keras]
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[*] posted on 11-9-2023 at 06:57


Old documents concerning this reaction:

The Catalytic Preparation of Ether from alcohol by means of aluminum oxide
Clark, Graham & Winter
JACS 47 pp 2748-54

The catalytic dehydration of ethyl alcohol and ether by alumina
Pease & Yung
JACS 46 pp 394-403

The position of equilibrium in the alcohol-ether reaction at 130 and 275 Pease & Yung
JACS 46 pp 2397-2405

The influence of temperature in acid catalysis
Hugh Stott Taylor
JACS 37 pp 551-7


are in the attached archive :) Organic chemistry is messy and no matter how many times various alternatives are posted that's very unlikely to change :o The end results from the effort applied :cool:

Attachment: EtherSynthesis.zip (1.2MB)
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[*] posted on 11-9-2023 at 09:04


Quote: Originally posted by leau  
Old documents concerning this reaction […]


Thanks for that.
I wonder what I would get passing gaseous ethanol in a U tube filled with alumina and placed into a heating mantle set to 250 °C… This might be worth to try.
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[*] posted on 12-9-2023 at 04:55


I think the formation of ethyl sulfate would actually slow down the reaction. EtSO4H should be a weaker ethyl-transfer agent than EtOH2+. But if EtSO4H2+ forms this is a very strong ethyl transfer agent.

Going off this hypothesis, one possible alternative catalyst would be the noncoordinating HB(C2O4)2, bisoxalatoboric acid, derived by the Dean-Stark toluene technique from oxalic acid and B2O3:

https://patents.google.com/patent/EP0784042A1/en




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 12-9-2023 at 06:04


Ethanol dehydration on silica-aluminas: Active sites and ethylene/diethyl ether selectivities

Thanh Khoa Phung & Guido Busca

Commercial silica-alumina catalysts prepared by different procedures have been characterized. Both present strong Lewis acidity together with Brønsted sites able to protonate pyridine. No evidence of “zeolitic” bridging OH's but significant heterogeneity of terminal silanol groups, part of which are likely “pseudobridging”, was found. Similar high activity in ethanol conversion but markedly different selectivities to ethylene and diethyl ether were found. They are less active than both zeolites and γ-Al2O3. Lewis sites with alumina-like acidobasic neighbor are more selective for ethylene production while Lewis sites with silica-like covalent neighbor are more selective for diethyl ether.


is attached :cool:

Attachment: phung2015.pdf (690kB)
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[Edited on 12-9-2023 by leau]
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[*] posted on 13-9-2023 at 02:55


Quote: Originally posted by clearly_not_atara  

Going off this hypothesis, one possible alternative catalyst would be the noncoordinating HB(C2O4)2, bisoxalatoboric acid, derived by the Dean-Stark toluene technique from oxalic acid and B2O3


Well, I have oxalic acid but no boron oxide (I have boric acid, though), so I’ll pass on this one.

Would P₂O₅ work? [EDIT: idiotic question. It has no proton to lend.]

[Edited on 13-9-2023 by Keras]
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[*] posted on 13-9-2023 at 05:50


I suspect that would rapidly become ethyl oxalate and ethyl borate.

Even if ethanol vapour and a U tube of alumina at 250C gave only a 10% yield of ether, the whole set-up is so cheap, it's worth a try.
The product's probably going to want a good wash with bisulphite to strip out acetaldehyde.
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[*] posted on 13-9-2023 at 05:56


Continuous dehydration of ethanol to diethyl ether over aluminum phosphate–hydroxyapatite catalyst under sub and supercritical condition

A. Rahmanian & H.S. Ghaziaskar

The Journal of Supercritical Fluids 78 (2013) 34–41

The activity of non-stoichiometric aluminum phosphate–hydroxyapatite for continuous dehydration of ethanol to diethyl ether (DEE) under sub and supercritical condition was investigated. The catalysts were characterized, using different methods viz., XRD, FT-IR, BET, TGA, EDX, Hammett indicators and amine titration. A face-centered composite design was used to investigate the effect of temperature, pressure, and ethanol flow rate on the catalyzed ethanol dehydration. Response surface methodology was used for optimization. Under the optimum conditions of ethanol flow rate of 0.17 mL min−1 (WHSV = 1.01 h−1 ), 340 ◦ C, and 200 bar, the DEE yield, selectivity, ethanol conversion, and liquid selectivity reached above 75%, 96%, 78%, and 97%, respectively. The time-on-stream of the catalyst for DEE synthesis showed that the catalyst remained stable and active without any appreciable loss in activity and selectivity for the time duration[/maroon]

is attached :cool:

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[*] posted on 14-9-2023 at 06:12


Kinetic Studies for Dimethyl Ether and Diethyl Ether Production

Dilek Varsili

Middle East Technical University

Ankara Thesis 2007


The dehydration of ethanol by sulfuric acid to form diethyl ether is a SN2 reaction that's temperature dependent and requires an excess of alcohol to form an ether :) The attached thesis goes into greater detail about the mechanism among other details :cool:

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[*] posted on 15-9-2023 at 08:17


Synthesis of SO4/ZrO2 Catalyst and its Application in the Conversion of Ethanol to Diethyl Ether

Rena Septiyaningrum, Amalia Kurnia Amin, Wega Trisunaryanti & Karna Wijaya

DOI 10.30495/ijc.2022.1963196.1948

SO4/ZrO2 heterogeneous acid catalyst was prepared by wet impregnation method from ZrO2 precursor involved variations in H2SO4 concentration (0.5; 1.0; 1.5 M) and calcination temperature (400, 500, 600 ℃) to yield catalyst with the highest acidity value. The catalysts produced were characterized using Fourier Transform Infrared (FTIR) spectrometer, X-Ray Diffractometer (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX), Thermogravimetry and Differential Scanning Calorimeter (TGA-DSC), Gas Sorption Analyzer (GSA), and acidity test using the gravimetric method with ammonia vapor. The catalyst used to observe activity and selectivity in the dehydration reaction of ethanol to diethyl ether (DEE) was SO4/ZrO2 catalyst with the highest total acidity. The liquid product from the dehydration of ethanol was analyzed using Gas Chromatography (GC). The ZS‐1.5‐500 catalyst showed the best activity and selectivity in the dehydration reaction of ethanol to DEE at a temperature of 225 ℃, yielding 49.85% (w/w) ethanol conversion and a 1.62% DEE selectivity.


is attached :cool:

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[*] posted on 15-9-2023 at 09:36


Quote: Originally posted by leau  

yielding 49.85% (w/w) ethanol conversion and a 1.62% DEE selectivity.[/color]


If I'm reading that correctly it is much more of an ethylene synthesis than an ether synthesis.
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[*] posted on 16-9-2023 at 06:27


Quote: Originally posted by Keras  

Well, I have oxalic acid but no boron oxide (I have boric acid, though), so I’ll pass on this one.

Quote:
I suspect that would rapidly become ethyl oxalate and ethyl borate.

Unfortunately the only paper I found about this acid is in French, although the lithium salt is well-described. Apparently LiBOB forms a monohydrate?

Attachment: lamande1986.pdf (2MB)
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[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 17-9-2023 at 10:49


Dehydration of ethanol over heteropoly acid catalysts in the gas phase

ALHARBI, Walaa; BROWN, Esther; KOZHEVNIKOVA, Elena F; KOZHEVNIKOV, Ivan V

Journal of Catalysis Volume 319, November 2014, Pages 174-181 Dehydration of ethanol was studied at a gas–solid interface over a wide range of solid Brønsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220 °C focussing on the formation of diethyl ether (DEE). The catalysts included H3PW12O40 (HPW) and H4SiW12O40 (HSiW) supported on SiO2, TiO2, Nb2O5 and ZrO2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs2.5H0.5PW12O40 and Cs2.25H0.75PW12O40) and the corresponding core–shell materials with the same total composition (15%HPW/Cs3PW12O40 and 25%HPW/Cs3PW12O40, respectively) comprising HPW supported on the neutral salt Cs3PW12O40. The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10 kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Brønsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs3PW12O40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts


is attached :cool:

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