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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
P.S.: Did you know that we have a Library?
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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 69 times
Go SAFE, because stupidity and bad Luck exist.
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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 65 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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