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bnull
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Quote: Originally posted by RU_KLO  | | So its not an easy task.... (instead of the second H2SO4 washing flask, sodium ethoxide would be used...) |
The first flask is to absorb unreacted ethanol and hydrogen chloride. The second is to absorb water. Without the second flask, the sodium ethoxide
will decompose.
I bought some 20 years ago (I'm quite old, you see) a small bottle of ether:ethanol 50:50. It was sold to remove surgical tapes (because, if you try
to remove them, depending on the way you pull them and where they are stuck, you take out a nice patch of skin still glued to the tape; not much fun
and hurts like hell meanwhile and afterwards. And yes, that was the time when I set my hand on fire accidentally). It's possible you can find the same
kind of solution in a drugstore, a pharmacy, a chemist's (English is a mess), or a supplier of surgical materials, only remaining the question of
separation of ether and ethanol.
Quod scripsi, scripsi.
B. N. Ull
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Keras
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As far as I know, Williamson’s ether synthesis has mediocre yields in the best cases.
(See anisole by ChemPlayer or NileRed)
Might be better with sodium ethoxide, which must be a stronger base than sodium phenoxide.
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RU_KLO
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To help mitigate this issue microwave-enhanced technology is now being utilized to speed up the reaction times for reactions such as the Williamson
ether synthesis. This technology has transformed reaction times that required reflux of at least 1.5 hours to a quick 10-minute microwave run at 130
°C and this has increased the yield of ether synthesized from a range of 6-29% to 20-55% (data was compiled from several different lab sections
incorporating the technology in their syntheses)
Baar, Marsha R.; Falcone, Danielle; Gordon, Christopher (2010). Microwave-Enhanced Organic Syntheses for the Undergraduate Laboratory: Diels−Alder
Cycloaddition, Wittig Reaction, and Williamson Ether Synthesis. Journal of Chemical Education, 87(1), 84–86. doi:10.1021/ed800001x
as Keras said, 30% is not much for all the trouble...
Also putting flammable liquids into a microwave doesnt seem to safe...
Attachment: ed800001x.pdf (611kB)
This file has been downloaded 145 times
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Keras
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| Quote: Originally posted by RU_KLO | | This technology has transformed reaction times that required reflux of at least 1.5 hours to a quick 10-minute microwave run at 130 °C and this has
increased the yield of ether synthesized from a range of 6-29% to 20-55% (data was compiled from several different lab sections incorporating the
technology in their syntheses) |
Thanks for the pointer. The yield remains moderate at best and, above all, I don’t know about any commercial (kitchen) microwave oven that allows to
precisely control the temperature of the heated compound inside – and I don’t think that the common way to regulate the average power, i.e. duty
cycling, is really adapted vs. a continuous power-regulated microwave source.
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chornedsnorkack
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How much heat does solvation of ethanol achieve by itself, and at which concentration?
Water gives about 160 Celsius around 85 % sulphuric acid. Ethanol has a bigger molar heat capacity than water (if lower heat capacity by mass).
Also sulphuric acid/water solution reaches boiling point of about 165 Celsius, which is 65 degrees above pure water, at 70% by mass... which is about
2,3 moles of water per mole of sulphuric acid. At what concentration can ethanol/sulphuric acid solution be heated to 140 Celsius (62 degrees above
pure ethanol) without boiling?
[Edited on 10-6-2024 by chornedsnorkack]
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RU_KLO
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| Quote: Originally posted by chornedsnorkack | How much heat does solvation of ethanol achieve by itself, and at which concentration?
Water gives about 160 Celsius around 85 % sulphuric acid. Ethanol has a bigger molar heat capacity than water (if lower heat capacity by mass).
Also sulphuric acid/water solution reaches boiling point of about 165 Celsius, which is 65 degrees above pure water, at 70% by mass... which is about
2,3 moles of water per mole of sulphuric acid. At what concentration can ethanol/sulphuric acid solution be heated to 140 Celsius (62 degrees above
pure ethanol) without boiling?
[Edited on 10-6-2024 by chornedsnorkack] |
I think is more complicated than that.
Found this, but under reduced pressure:
"For the sulfuric acid + water + ethanol system, the
boiling points increase with decreasing mole fractions of
ethanol in the solution at fixed ratios of sulfuric acid/water,
and they also increase as the ratio of sulfuric acid/water is
increased."
But for the same paper, it seems that Sulfuric acid could be recovered at lower temperature with butyl acetate (Acid + Water + Butyl Acetate + Ethanol
Quaternary System
how difficult is to get/make Butyl acetate? From wikipedia: It is a component of fingernail polish.[8]
(I found ethyl acetate un fingernail polish, not butyk
the paper talks about models, but can someone "translate" this for non engineer people? in the sense, how do you apply it and what are the benefits.
Does the sulfuric acid destilates with the butyl acetate (and how to separate it) or the butyl acetates remains in the boiling flask with water?
Determination and Modeling of Vapor–Liquid Equilibria for the Sulfuric Acid + Water + Butyl Acetate + Ethanol System
Geng Li, Zhibao Li*, and Edouard Asselin
https://pubs.acs.org/doi/10.1021/ie303197a
Attachment: ie303197a.pdf (1MB)
This file has been downloaded 125 times
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jackchem2001
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After experimenting with this procedure a little bit I would like to put something into text that is probably quite obvious - you can't just feed all
of the distillate back into boiling flask and redistill to try enrich it in ether. You just end up fractionating the mixture. The matching of the
addition rate and distillation rate is done because a high concentration of sulfuric acid raises the boiling point of the mixture (a likely
requirement for a different catalyst in a simple distillation setup).
Unrelated, but has anybody else observed white smoke upon addition of ethanol to the boiling flask? Also, even though this contradicts the pdf posted
on page 1 which casts doubt on alkylation agents as intermediates in this reaction, has anybody tried adding sodium sulfate to potential catalyse
formation of sulfuric esters? (https://www.sciencemadness.org/talk/viewthread.php?tid=78772)
[Edited on 13-6-2024 by jackchem2001]
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jackchem2001
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Continuing from my last post suggesting the addition of sodium sulfate to catalyse the formation of sulfuric esters (allowing a lower temperature to
be used to avoid tarring), in ethyl bromide procedures diethyl ether is observed as a major impurity. Evidently, ethanol does react with some
alkylating agents at much lower temperatures to give diethyl ether.
As I hate the smell of ether so I likely won't do this procedure again, but if anybody happens to be doing a run then consider adding a small amount
of sodium sulfate to the boiler and report the results 
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MrDoctor
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I have attempted this reaction and noticed something strange. thermal runaways.
At first i thought some sort of hydrolysis was occuring which could explain things, since i was using 95% ethanol, but i see now that water simply
cannot accumilate in this reaction, which increases the mystery.
What i observed was that at seemingly arbitrary temperatures between each runaway, my PID controller would suddenly find itself unable to heat the
acid solution further. it would get stuck at say, 140C. no reflux or enough distillate was comming over to explain the heat loss, i also re-attempted
without a fractionating column thinking it was trapping the water leading to exothermic splitting/reformation of ethyl sulfate <-> sulfuric acid
+ ethanol. energy is being applied but it is not being reflected in a change of temperature, nor, any notable distillate although the head temp would
begin to increase, but only after the runaway began, not leading up to it.
Suddenly, the column head temperature would skyrocket from the boiling point of ether to the boiling point of a low-ethanol +water steam, and the
distillate would reflect as much. the addition of more ethanol during this runaway would instantly and increase the temperature.
eventually my acid tarred up and became so thick it would foam so i had to stop, but this phenomena occured long before any viscosity changes or
clarity occured.
During a runaway, over the course of a minute, regardless of if the PID was still applying power, the temperature would suddenly rise from wherever it
began, in this case, 140C, and it would rise up to around 156C. this temperature change did not correspond to any thermal-momentum, the lag between
heat being generated by the mantle, and then transferring to where the thermometer could read it. it also occured in a span that almost matched how
quickly the temperature would rise with a manunally set 100% duty cycle. (also yes i did verify the PID wasnt simply defective and suddenly locking on
100%)
ethanol was pumped in consistently by peri pump, shutting off automatically when the temperature had risen above 60C as i was concerned that ethanol
would simply boil on the surface of the acid without reacting.
Eventually the runaways would accompany foaming that caused the ejection of the black thick acid so i had to stop. there was a major viscosity change
after i tried to vacuum concentrate the acid, but this phenomena was present prior to that, i had just assumed the acid had become too diluted with
water or something, since runaways would end with noticeable amounts of water in the condenser.
Does anyone know what was happening?
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BAV Chem
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A successful semi-automated ether preparation and an exercise in tar chemistry
So apparently the process described by Diachrynic does not work for everyone so far. I've done the procedure myself with a few minor changes and for
me it worked out pretty much perfectly on the first try.
Setup: The reaction was carried out in basically the same way as described on page 1. To ensure a successful experiment only the
highest quality reagents were used. The sulfuric acid was tar grade and recovered from previous experiments and as such it contained the boiled down
remains of a hydrazine sulfate preparation (azine method) and a failed nitration mix amongst other things (Note 1). It was the nastiest sample of
H2SO4 that could be found in the back of the storage shelf. This reagent's purity was determined to be a seven on the browning index as defined by
Kahverengi et al.[1]
Similarly part of the ethanol was recovered from previous experiments or distilled from some exceptionally bad booze. Most of it however was store
bought denatured alcohol (95%).
Procedure: A 3-neck 500ml RBF was charged with 50ml of sulfuric acid and 50ml of ethanol (Note 2). Heating was accomplished using a
bath of melted candle wax with the hot plate set to nearly 200°C surface temp. The mix was constantly stirred and ethanol was added using an arduino
controlled peristaltic pump system. This was set to run for 500ms at a time, which is equivalent to adding roughly 0.3 - 0.4ml of EtOH. Additions were
automatically made whenever the reaction temperature was above 142°C with a minimum dead time of 15s between additions. A type K thermocouple was
used to monitor the temperature inside the reaction flask. This technique worked out flawlessly and the temperature stayed within 0,5°C of the set
temperature of 142°C for the majority of the experiment, that is assuming there was no drift in the thermocouple measurements. 4000ml or 3200g of 95%
ethanol were added using the pump system before the reaction was stopped. Toward the end of the experiment there was quite a large amount of tar
buildup in the flask and the mixture started to foam a little. It is also important to note that even at this point there was still a considerable
amount of sulfuric acid left in the reaction flask and the experiment could've easily been continued.
Workup: The distillate obtained was fractionally distilled as described on page 1. Diethyl ether was collected up until 40°C and
ethanol between 75°C and 80°C. A small amount of distillate came over while the temperature rose from the boiling point of ether to that of ethanol
and this was simply included in the next batch.
Acid recovery: According to Evans and Foresman[2] about 79% of the sulfuric acid that is lost is still contained in the
distillate as either sulfuric acid or diethyl sulfate. The latter of these two should at least partially hydrolyze to give the former so it was
attempted to recover some of the lost acid by boiling down the residue from the fractional distillation. However this only yielded a small amount of
black sludge that presumably consisted of mostly charred organics and some sulfuric acid. The corresponding browning score would have been an eight to
nine.
The leftover sulfuric acid in the RBF was treated in a similar manner. It was boiled down and heated until most of the impurities were digested and
the material returned to its typical viscosity. This way about 33ml of H2SO4 were recovered which was of similar quality as the starting material.
Results: In total 4050ml or 3240g of ethanol were used which was converted to 2936g or roughly 3500ml of crude distillate. Fractional
distillation of the latter yielded 1175g or 1650ml of diethyl ether, 1500ml or 1200g of ethanol and 430ml of a watery residue (Note 3). With the
distilled ethanol being the same concentration as the starting material this equates to a conversion efficiency of 75% (Note 4). Assuming the other
25% have been converted to ethylene the amount of water that would be expected to form can be calculated to be 473.8ml. The 430ml of H2O obtained thus
equate to 91% of the expected amount so these numbers seem to make sense. 50ml of tar grade sulfuric acid were employed of which 33ml could be
recovered. This puts the amount of acid that was actually lost to just 17ml. Without recovering the acid the volume of ether produced would've been
33x that of the sulfuric acid employed. Accounting for the recovered sulfuric acid this factor goes up to about 97 (Note 5). Also it seems that the
quality of the acid used doesn't make too much of a difference.
Notes:
1) It is obviously not advisable to boil down nitration mixtures unless it can be done safely.
2) Interestingly the addition of ethanol to the acid led to some white fumes appearing in the reaction flask, exactly as described by
jackchem2001[3], which is strange because no vapor phase reactions should occur here. I suspect it's just ethanol being vaporized from the
exotherm of mixing H2SO4 and EtOH.
3) Diethyl sulfate which is apparently a byproduct of this reaction is said to have a peppermint like odor and this residue had a very weird smell
that did in fact share some similarities with that of peppermint.
4) I was hoping for something more like 90% but oh well...
5) This figure may be subject to various measurement errors and might actually be somewhat lower.
References:
1) K. Kahverengi, M. de la Mierda, R. von Braun and G. Schlonk (2021) '50 Shades of Brown: An Index of Chemical Misery', J. Immat. Sci., 1, https://jabde.com/wp-content/uploads/2021/12/50-Shades-of-Br...
2) P. N. Evans, G. K. Foresman, "Sulphur By-Products of the Preparation of Ether", Proc. Indiana Acad. Sci. 1917, 27, 211-216, https://journals.indianapolis.iu.edu/index.php/ias/article/v...
3) https://www.sciencemadness.org/talk/viewthread.php?tid=78772
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BAV Chem
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We might not even need to search for an alternative catalyst although admittedly that would be a very interesting topic to look at. I recently tried
my hand at the process of making sulfuric acid using ethanol and sodium bisulfate and things worked out quite well (see this thread).
tl;dr I obtained about 50ml of reasonably pure sulfuric acid from 250g of pool grade NaHSO4 which should be more than good enough to make
liters of ether.
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Organikum
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maybe better with a hot tube and H2SO4 on pumice?
lugh from the HIVE once provided a German paper which I sadly do not have anymore but I have a still well working memory and the paper told this:
Ethanol vapors (~90% EtOH was used IIRC) were passed through a glass-tube heated to 135° - 150° C and filled with pumice pebbles soaked with 70%
H2SO4, and the resulting mixture of water, ethanol and ether was condensed, the ether removed and the ethanol distilled from the water and returned to
the feeding vessel.
They claimed up to 50% yield on ether per run whereby the higher the temperature the higher the yield but also more crap deposition on the pumice
leading to shortened standing time of the catalyst. But at lower temperatures with 35% yield they claimed next to infinite (weeks) of activity.
This is the part I am sure about, more shaky is the following:
Tube was made of glass (I am sure of this), 3 to 5 cm diameter, pumice pebbles like 2-3 mm diameter and tube-length like 50 cm heated, catalyst
filled.
To avoid massive temperature fluctuations it would be for sure best to immerse the tube into a liquid heating medium or maybe metal block and to use a
rather thin walled tube. I wager thinner tube beats thicker tube one might consider a bundle of thinner tubes for a production setup.
But generally it works this is sure, I know it as I tried back then it in a quick and dirty test and there is absolutely no reason why it should not
and with clean alcohol a high TOF seems plausible, a small setup running for days can produce copious amounts of ether I suppose. Put a flame-arrestor
between boiling flask and hot tube and this should be quite save. As far as ether can be called save of course.
The integrated ethanol recovery - well I would skip this and I also would use absolute ethanol which I can buy for ethanol ovens cheap and easy (just
condense out the MEK before use, add NaOH or KOH and let sit in a warm place for some weeks and use as is, I mean why distill when it gets distilled
anyways?)
It for sure saves a lot of H2SO4 and the temperature in the hot tube is reasonable.
There is some back-pressure building up in the boiling flask that is understood, the pumice i must fill the tube completely to ensure contact, so
clamp joints properly down and when using an addition funnel to refill, use a pressure equalized one.
Darn! I am tempted to build one myself, ether is still my favorite solvent, well as long the floor is not covered in eeri blue flames all of a
sudden..... 
Hope somebody finds this interesting and there is not already a thread about it, I did not search tbh.
regards
/ORG
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bnull
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I found it. It's a note in French (which at least I can read without Google): Jean-Baptiste Senderens, "Déshydratation catalytique, en phase gazeuse,
des alcools forméniques en presence de la ponce sulfurique et phosphorique",Compt. Rend. 192, 1335-7(1931) (Source gallica.bnf.fr / BnF). It is short (3 pages) and small, so it is also attached (if someone happens
to be too lazy or not curious enough to check out the Comptes Rendus).
I don't know what are the rules of Sciencemadness regarding content from The Hive but, since it is not cookery, here's the (sort of) original post.
Attachment: Senderens - Synthesis of ether using pumice stone soaked in sulfuric acid in a hot tube (more or less) (363kB)
This file has been downloaded 107 times
[Edited on 28-7-2024 by bnull]
Quod scripsi, scripsi.
B. N. Ull
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wg48temp9
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Just in case, nobody has seen the papers on Silica sulfuric acid as Solid Acid Catalyst. It's used for esterification and for producing ethers.
Sorry, i could not find the paper. I will try again later
I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
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Organikum
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| Quote: Originally posted by bnull |
I found it. It's a note in French (which at least I can read without Google): Jean-Baptiste Senderens, "Déshydratation catalytique, en phase gazeuse,
des alcools forméniques en presence de la ponce sulfurique et phosphorique",Compt. Rend. 192, 1335-7(1931) (Source gallica.bnf.fr / BnF). It is short (3 pages) and small, so it is also attached (if someone happens
to be too lazy or not curious enough to check out the Comptes Rendus).
I don't know what are the rules of Sciencemadness regarding content from The Hive but, since it is not cookery, here's the (sort of) original post.
[Edited on 28-7-2024 by bnull] |
Thanks for the paper, nice you can read it, most can not so I tell the essence of it. And lo and behold! It is - so true - looking like the holy grail
of ether production!
Pumice granules soaked in H2SO4 of 62% to 64% strength catalyze the dehydration of ethanol to ether at 135° C to 140 °C whereby the the dehydration
is complete (if the stream of ethanol is adjusted accordingly and no side-reactions occur at 135°C, at 140° C small amounts of ethylene are formed.
They ran the reaction 8 days, 8 hours a day t 135° C with no degradation or tarring of the catalyst.
The pumice was in "nacelles" what I interpret as a bag of wire and heating was done electrically.
Now thats pretty neat, isn't it?
Oh, they also mention that sodium bisulfite does NOT work, what hopefully ends this myth once and for all.
Whats your problem with The HIVE? SCM has no limitations as long the posts are trying to follow scientific rules in wording and this refers to all
posts be it energetic (physically) energetic (mentally) or washing your dishes.
regards
/ORG
PS: And for "cookery" let's quote Alexander Shulgin:
"Orbitals are for mathematicians, Organic Chemistry is for people who like to cook!"
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bnull
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Being a Romance speaker has its advantages. Thanks for mentioning the paper anyway.
| Quote: Originally posted by Organikum | Pumice granules soaked in H2SO4 of 62% to 64% strength catalyze the dehydration of ethanol to ether at 135° C to 140 °C whereby the the
dehydration is complete (if the stream of ethanol is adjusted accordingly and no side-reactions occur at 135°C, at 140° C small amounts of ethylene
are formed.
They ran the reaction 8 days, 8 hours a day t 135° C with no degradation or tarring of the catalyst.
The pumice was in "nacelles" what I interpret as a bag of wire and heating was done electrically.
Now thats pretty neat, isn't it?
Oh, they also mention that sodium bisulfite does NOT work, what hopefully ends this myth once and for all. |
Sodium bisulfate, but here Senderens was talking about passing alcohol vapor over heated sodium bisulfate, which doesn't mean that other processes involving it are doomed to failure. The main issue
with bisulfate is that the catalytic dehydration of vapors ocurrs from 175 °C upwards, where ethylene, not ether, is the main product. In liquid
phase, ethanol boils off unchanged in a common distillation setup at ambient pressure (Senderens again) but it is quite possible that it converts to ether in a sealed tube (a thought that occurred after reading van Alphen). The latter is not amateur-friendly, so while not exactly a myth until someone tries out the sealed tube method, the necessary
conditions make it more interesting from a theoretical/academical point of view than a proper preparative method of large quantities of ether for the
home chemist. It seems feasible with the right equipment but not at home with lab glassware or threaded pipes. And the "nacelles en porcelaine" are
simply combustion boats made of porcelain, by the way.
Anyway. The process is quite neat and can be easily automated, with Arduino and stuff. An apparatus the size of a tabletop water cooler where you
insert ethanol and receive ether. With a replaceable "sulfuric pumice" cartridge perhaps. Not bad. Not a holy grail but not bad either.
With the chemical aspects, none at all; I love Chemistry, and science in general. As for the recreational and commercial aspects and their legal
developments, I don't effing care. I don't do or cook drugs or have problems with the Law itself or its supposed representatives. I don't really
effing care. The problem is, there are delusional elements within the forum that become so paranoid at the briefest mention of drugs or drug-related
content and sources (most of The Hive has been archived by Erowid, you see; no problem with that too) that they begin fearing for their lives and
freedom as if the "drug police" were monitoring them 24/7 and ready to fall upon them in a sec just because they had read that content. In such state,
they would start spewing their unreasonable fears (check out Detritus) in this thread while being annoying and unhelpful, and cheesing me and everyone
else off in the process. Hence my excessive caution, like the monkey.
Quod scripsi, scripsi.
B. N. Ull
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chornedsnorkack
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Is it feasible to set up reactive distillation so that "no reaction" results in nothing distilling over - unreacted ethanol just flows back to the
still?
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Organikum
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| Quote: Originally posted by chornedsnorkack | | Is it feasible to set up reactive distillation so that "no reaction" results in nothing distilling over - unreacted ethanol just flows back to the
still? |
This makes not more sense on closer inspection then it made on first glance, maybe you try sorting your thoughts and understanding the process before
posting?
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Organikum
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Well we are talking about doable processes so bisulfite is obviously out - if you want to chase dead cows, well do it, but do not send others to do do
it.
The HIVE as mentioned here shows that one does not have to be a druggie to be a paranoid fuck, this is long known, same the the bad effects drugs
like LSD and Crystal Meth have on people who do not consume them but only came in contact via TV shows and YouTube.
regards
/ORG
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bnull
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| Quote: Originally posted by chornedsnorkack | | Is it feasible to set up reactive distillation so that "no reaction" results in nothing distilling over - unreacted ethanol just flows back to the
still? |
No. As explained in the second paper by Senderens (Catalytic dehydration of alliphatic alcohols by alkaline bisulfates, in French), while a proper proportion of ethanol:sulfuric acid can be used so
the solution can reach the reaction temperature (~140 °C), the same can't be done with sodium bisulfate because the increase in boiling temperature
is negligible given the amounts of bisulfate used. This was verified by @Keras several posts ago. Even a paste made of bisulfate and ethanol would
just dry up and the alcohol boil off unchanged.
So we're still dealing with sulfuric acid (with or without additives) and other possible substitutes at about 1 atm.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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chornedsnorkack
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| Quote: Originally posted by Organikum | | Quote: Originally posted by chornedsnorkack | | Is it feasible to set up reactive distillation so that "no reaction" results in nothing distilling over - unreacted ethanol just flows back to the
still? |
This makes not more sense on closer inspection then it made on first glance, maybe you try sorting your thoughts and understanding the process before
posting? |
You have offered two options:
Entirely open apparatus - vapour is free to get out and liquid flow out at constant pressure regardless of any reaction with volume
change - with free return inflow of air
Rigidly closed apparatus - glass welded closed against pressure, no change of volume till the glass violently breaks
How about apparatus which allows only a small difference of pressure between inside and outside, which the glass and joints are designed to fit? Like
a liquid lock?
Since the likely vapours to reach the gas lock (ethanol, ether, water) may dissolve in water and/or oil, a liquid lock proof of these might be a metal
one (Hg or Ga based).
If there were no catalyst, or if the catalyst were completely insoluble in the liquid (like a solid superacid), bringing the reaction
2C2H5OH=(C2H5)2O+H2O to completion (but equilibrium would not be completion), the
liquid would separate, and its boiling point would drop from 78,3 degrees to 34,2 degrees of ether/water azeotrope - meaning that at constant
thermostat temperature, the ether would boil off and bubble through the liquid lock.
What we want is ethanol/sulphuric acid solution of such concentration that its boiling point is 140 degrees. What concentration is that? And if the
reaction goes on, how much does its vapour pressure increase, at constant temperature?
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bnull
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I guess it was I who offered those options, @chornedsnorkack. And yes, it was either a distillation setup open to the atmosphere, which is the
original idea of the thread and the only safe (as hot sulfuric acid goes) option so far, or a sealed tube, which seems feasible with the right
equipment (i.e., professional lab or industry) but not at home with lab glassware or threaded pipes, as I pointed a page ago. Since the
quantities produced by the latter are inevitably too small (< 20 mL), it remains of theoretical interest.
So, we're stuck with (1) round-bottom flasks and condensers, (2) the sulfuric pumice boat method of Senderens, or (3) the solid acid catalyst
mentioned by @wg48temp9. I have a vague impression of having read about (3) in the forum; memory fails me now.
| Quote: Originally posted by chornedsnorkack | | What we want is ethanol/sulphuric acid solution of such concentration that its boiling point is 140 degrees. What concentration is that? And if the
reaction goes on, how much does its vapour pressure increase, at constant temperature? |
Don't forget the water. There are so many compositions EtOH:H2SO4:H2O with the same minimum boiling point (it is a
minimum because we need the solution to reach at least the reaction temperature). I remember seeing something in the forum, possibly by you, about
those mixtures. Again, memory fails me.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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BAV Chem
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| Quote: Originally posted by bnull |
No. As explained in the second paper by Senderens (Catalytic dehydration of alliphatic alcohols by alkaline bisulfates, in French), while a proper proportion of ethanol:sulfuric acid can be used so
the solution can reach the reaction temperature (~140 °C), the same can't be done with sodium bisulfate because the increase in boiling temperature
is negligible given the amounts of bisulfate used. This was verified by @Keras several posts ago. Even a paste made of bisulfate and ethanol would
just dry up and the alcohol boil off unchanged.
So we're still dealing with sulfuric acid (with or without additives) and other possible substitutes at about 1 atm. |
Just an alkaline bisulfate mixed with ethanol doesn't catalyze the dehydration of the alcohol to ether but I would argue this is only
because the bisulfate itself does not raise the boiling point enough, and is not acidic enough to catalyze the reaction at an appropriate temperature.
Also there's never gonna be enough free sulfuric acid in solution to do this because the eqilibrium of NaHSO4 <--->
Na2SO4 usually lies too far on the left.
However if you were to filter off the sodium sulfate before doing the reaction it would likely work. I have done a similar thing but isolated the
sulfuric acid instead of using it straigt away recently (see somewhere above) and it certainly seems practical. By adding something like 250g of
sodium bisulfate to 500ml of ethanol, stirring, filtering and distilling it should be possible to obtain an impure but usable sulfuric acid
concentrate that would be perfectly suitable for making ether. Yes, it's just the method from the first post with extra steps but it would allow us to
start from bisulfate and not sulfuric acid. You could simply distill off the ethanol until the temp reaches 140°C and then add more ethanol as usual.
| Quote: Originally posted by chornedsnorkack | | Is it feasible to set up reactive distillation so that "no reaction" results in nothing distilling over - unreacted ethanol just flows back to the
still? |
Wouldn't that be the same as a fractional distillation where the ethanol recondenses but ether distills over? Some people actually do it that way and
get terrible conversion efficiencies out of their sulfuric acid because of water build up. However this brings me to a theoretically possible but
frankly impractial idea. If you were to set up a distillation of sorts such that the ethanol would be returned without returning the water it should
be doable. Tbh I have no good idea of how to do this. All I can think of would be a series of condensers, one running at 80-90°C to take out all the
water, another one at like 60°C to take out the ethanol and one to finally condense the ether. That would basically be like building a miniature
chemical plant that you would feed with ethanol and get out ether and water at the other end.
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bnull
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| Quote: Originally posted by BAV Chem | | Just an alkaline bisulfate mixed with ethanol doesn't catalyze the dehydration of the alcohol to ether but I would argue this is only
because the bisulfate itself does not raise the boiling point enough, and is not acidic enough to catalyze the reaction at an appropriate
temperature. |
There's also that.
| Quote: Originally posted by BAV Chem | | However if you were to filter off the sodium sulfate before doing the reaction it would likely work. I have done a similar thing but isolated the
sulfuric acid instead of using it straigt away recently (see somewhere above) and it certainly seems practical. (...) Yes, it's just the method from
the first post with extra steps but it would allow us to start from bisulfate and not sulfuric acid. You could simply distill off the ethanol until
the temp reaches 140°C and then add more ethanol as usual. |
The "somewhere above" is this other thread, The simplest preparation of sulfuric acid?! Another instance of my memory failing.
| Quote: Originally posted by BAV Chem | | Tbh I have no good idea of how to do this. All I can think of would be a series of condensers, one running at 80-90°C to take out all the water,
another one at like 60°C to take out the ethanol and one to finally condense the ether. That would basically be like building a miniature chemical
plant that you would feed with ethanol and get out ether and water at the other end. |
Something like the drawing below? The collectors look familiar...
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Pumukli
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There"s a synth description in Org. Synth somewhere (phorone? diacetone-alcohol?) in which before they let wet acetone dripping back from the reflux
condenser to the flask they let it percolate through dry, anhydrous BaO in a perforated "cup" or something like that.
Something similar, maybe filled with anhydrous Na2SO4 might work with wet ethanol.
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