alking
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Ether synthesis safety
I'm planning to synthesis some ether from ethanol but I am very cautious and want to make sure I fully understand the dangers.
Many write ups people have done suggest using a sand or oil bath to prevent overheating, is there any danger in just using a hot plate? I wouldn't see
why, but I can't find an explanation for why people take the extra precaution. Regardless how hot the plate itself is the sulfuric acid/liquid in the
flask should regulate the temperature just fine, right? I have no concern about being able to maintain the ~130-145C temperature in the flask as it
has very precise temperature controls.
Along the same lines though ether has an auto-ignition temperature of only 160C, yet above 160C ethylene is the major product produced as opposed to
fiery explosions, why is this? Is it just due to the vapor/oxygen concentration or does it become an actual explosion hazard above 160C?
My last question is I had made some ethylsulfuric acid some time back and it has just been stoppered in a flask since. Would there be any dangers in
using this for the synthesis or is there a risk introduced upon storing it for some time?
My planned setup for this was going to include sealing all of my joints with vacuum grease, it will be magnetically stirred to maintain an equal
temperature within the flask, and I will run a bleed tube outside in front of a fan (to PUSH the fumes away) so there should be no concern of ether
fumes getting anywhere near an ignition source. That seems to be more precautions than many take although I'd like to rest any concerns with using a
bare hot plate and pre-prepared ethylsulfuric acid.
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DavidJR
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Ether is very volatile and it's quite possible that some of the dense vapors will make it onto the surface of your hotplate, which is very likely to
be well above the 160c autoignition temperature even if the contents of your flask isn't.
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alking
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Shouldn't that risk be safely mitigated if the system is sealed except for the bleed tube that leads outside? No vapors should make it back inside the
workspace with the fan/positive pressure.
Wouldn't that same vulnerability also exist with an oil bath anyway? The hotplate heating the oil will still be just as hot as it otherwise would be.
[Edited on 11-4-2018 by alking]
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Bert
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As 16 to 17 year old highschool juniors, we did this synthesis in class. All of us, in pairs at our own benches. Without a hood at these benches,
there was only one of them, up front of the classroom. We used BUNSEN BURNERS for a heat source, no bath, directly heating the glass containing the
ethyl alcohol/sulfuric acid mix.
I have never since breathed so much ether in a lab.
Mind you, this is the same chemistry teacher who let me drop a crystal of elemental Iodine into a test tube with a bit of molten white Phosphorus in
the bottom, he at least had me do THAT in the hood, window mostly lowered and wearing protective equipment. BLAM! I think now, perhaps he actively
encouraged us to do such things in order to make us learn hard lessons in small, safe-ish size doses? Because he wasn't actually crazy, and none of us
was ever actually hurt. Although I remember the window in the hood being replaced at least twice, and that wing of the school evacuated once (massive
Sulfur dioxide, not MY class, I don't know what they did).
EVERYONE lost control of the diethyl ether synthesis reaction at some point, boiling the mix over and into the condenser, contaminating the product.
No one had a fire, which I am amazed at now.
Good luck, be careful, and I highly suggest this be done OUTDOORS.
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happyfooddance
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As long as your joints stay intact you should be fine. You seem to be taking the right precautions. I have done this synthesis several times. One
thing I will mention is that it bumps violently; this alone is why you might want to re-think using a bare hotplate. Also, make sure you use good
strong keck clips.
And let us know how it goes.
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alking
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Wow, that sounds very dangerous! Hearing that SORT OF makes me feel safer, but whether my chances of combustion are 10% or 1% doesn't matter so much,
I want to make sure they're 0% before I proceed.
If I could do it outside or in a fume hood I could accept some risk as it would be safely contained, but I have no fume hood and doing it outside is
impractical because it's difficult to haul and setup my water chiller for an otherwise quick and simple synthesis.
Doing it outside would also add the risk of nosy neighbors asking what I'm doing, or worse calling the cops thinking it's something nefarious, and I
can only imagine in explaining that I'm doing it outside for safety because I can't guarantee it will not explode is not likely to quell their
concerns.
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alking
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Quote: Originally posted by happyfooddance  | As long as your joints stay intact you should be fine. You seem to be taking the right precautions. I have done this synthesis several times. One
thing I will mention is that it bumps violently; this alone is why you might want to re-think using a bare hotplate. Also, make sure you use good
strong keck clips.
And let us know how it goes. |
It will bump even with magnetic stirring? I have seen some suggest putting sand/boiling chips in it to prevent that, but I had assumed it was just
because they did not have a magnetic stirrer.
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happyfooddance
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| Quote: Originally posted by alking |
It will bump even with magnetic stirring? I have seen some suggest putting sand/boiling chips in it to prevent that, but I had assumed it was just
because they did not have a magnetic stirrer. |
Sand does next to nothing for bumping, this is a myth. You can use porous chip, but just use your mag stirrer on high. It will still bump to high
hell, there is simply no avoiding it. I mean, you're adding a reactant to a mixture that is almost 100°C above its bp, and the product created boils
at an even lower temp.
I guess to clarify, this is what problem I have: if I attempt to slow the rate of delivery in an attempt to stop bumping, the alcohol in the delivery
tube boils, and ejects from the tube, and the whole thing bangs around for like 15 seconds. I have had reaction mixture suck back up the delivery
tube... So the best way I have found is to go slow and steady... You may find a way to stop bumping, but I haven't. In fact, now I like doing the
addition at a faster rate, it bumps like hell but you can make ether at the rate of 1l/hour 
[Edited on 4-11-2018 by happyfooddance]
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DavidJR
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Best thing in my opinion for situations where you know something will bump pretty badly is to use a tube to bubble air (or N2) under the
surface of the liquid. That's the only technique I've used which resulted in absolutely no bumping when distilling H2SO4 (and I
tried just about every type of boiling chip suggested online).
Edit: to be fair though I did not use magnetic stirring for distilling H2SO4 as the boiling point of azeotropic sulphuric acid
is well above what stir bars can handle. It's not the PTFE that's the problem, it's the magnet itself.
[Edited on 11-4-2018 by DavidJR]
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aga
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Meh.
Boiling sulphuric acid isn't much bumpy.
Somewhat dangerous, especially the bit where you add the cold 3% H2O2 to the boiling acid to remove the bulk of the
contaminants, but not crazy bumpy, with or without any kind of mitigation.
Try phenol.
No stirbar or boiling chips or whatever and it is like a still pond, then it explodes.
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happyfooddance
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| Quote: Originally posted by aga | Meh.
Boiling sulphuric acid isn't much bumpy.
Somewhat dangerous, especially the bit where you add the cold 3% H2O2 to the boiling acid to remove the bulk of the
contaminants, but not crazy bumpy, with or without any kind of mitigation.
|
Boiling sulfuric acid in a beaker and distilling it in an rbf are two completely different things, aga.
When you distill sulfuric acid, any water comes off first, and drips back on to the hot acid. And you know what happens when you drip water on boiling
acid? It bumps.
When after many hours you are finally collecting 98% acid, it does get much better, but it still can be bumpy.
As to the topic, DavidJR's idea about the bubbler sounds like a great idea, I will try it next time I make ether.
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DavidJR
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Actually the bumping was always worst for me towards the end. With the pieces of smashed unglazed porcelain tile that I use as general-purpose boiling
chips, it starts out a little bit bumpy but nothing too concerning, but ended up pretty violent. It would sit still for a good 5 seconds before
erupting.
You can mitigate the water dripping situation by warming the neck of the flask and the stillhead with a heat gun.
Also, there's really no need to add H2O2 to drain cleaner sulphuric acid since boiling it alone is enough to destroy the organic
impurities.
Re the bubbler tube, I actually use a broken glass thermometer, though you could also use a pipette or just a piece of glass tubing drawn to a thin
point. You don't need a lot of airflow. You can either pump air into the tube or if you're applying a vacuum, you can just leave it open to the air.
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happyfooddance
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| Quote: Originally posted by DavidJR | Actually the bumping was always worst for me towards the end. With the pieces of smashed unglazed porcelain tile that I use as general-purpose boiling
chips, it starts out a little bit bumpy but nothing too concerning, but ended up pretty violent. It would sit still for a good 5 seconds before
erupting.
You can mitigate the water dripping situation by warming the neck of the flask and the stillhead with a heat gun.
Also, there's really no need to add H2O2 to drain cleaner sulphuric acid since boiling it alone is enough to destroy the organic
impurities.
Re the bubbler tube, I actually use a broken glass thermometer, though you could also use a pipette or just a piece of glass tubing drawn to a thin
point. You don't need a lot of airflow. You can either pump air into the tube or if you're applying a vacuum, you can just leave it open to the air.
|
Yes, boiling chips only have a certain amount of air adsorbed onto them, once it's gone, it's gone. Storing them in the freezer increases their
stamina, as does using bigger chips for longer distillations. Sometimes the distillation needs to be stopped and new chips added. This is very
dangerous by the way. Stopping a distillation and resuming without adding new chips is also bad, as it cools the chips suck up liquid and then they
really don't work.
The heat gun trick is also a trick I have used, but I use a claisen packed with glass when distilling sulfuric, so it would be tedious in this case. I
just let it do its thing outside, rattling away. I have faith in my clamps and stands, and I connect joints with steel wire (steel keck clips anneal
at those temps).
I bought a pack of a dozen long kimax capillary tubes for this purpose, I will use one of those. I will have to keep the airflow as low as possible
because I don't want it running off with my ether. In fact, it might just not work well for that reason. We will see, I am out of ether, and the
ethanol is a-brewing...
Edit: a note to the OP: my vacuum grease, which is dimethylsiloxane, turns black in the joints, and can seize ground glass joints with sulfuric acid.
Also, a tube from the vacuum take-off out a window is great; you won't need a fan blowing the vapor away; that is super overkill!
[Edited on 4-12-2018 by happyfooddance]
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Deathunter88
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Personally I wouldn't worry too much about having fire issues as long as you don't make some crazy mistake. The system is sealed (mostly) and so even
if there a fire it won't be very big and can easily be put out. Ether is volatile, not explosive, so it won't detonate like an explosive.
If it makes you feel better, I did some experiments with the autoignition of ether a while back (by pouring 50ml of it on my hotplate set to 380
degrees celsius) and there was not a single time I could get it to ignite. I even dipped a red hot iron rod into a beaker and the stuff would not
catch. (Keep in mind that theses tests were not very controlled, and there is good reason that the literature AI temperature is 160, but practically
the AI temperature is likely to be higher)
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ninhydric1
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By the way, are you synthesizing diethyl ether to gain the experience or to obtain the ether for other purposes?
If you're making diethyl ether because you need it for something else, it's easier to distill it from car starting fluid. If it's for the experience
it's probably a good idea to synthesize it for fun.
The philosophy of one century is the common sense of the next.
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JJay
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It is more economical to make ether yourself than it is to distill it from starting fluid.
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happyfooddance
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Only if obtaining ethanol is relatively cheap for you (which it should be).
I have found some cheap starter fluid, from time to time.
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DavidJR
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Is ether-containing starter fluid readily available in the UK/EU?
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alking
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Well I feel much safer now, I might give this a shot tonight even if I have the time. I was thinking about this last night and I realized that there's
probably so many cautions mentioned when people talk about ether not because it's especially dangerous so much but because it's so often done as a
learning experience early on so the extra warnings are more so for that audience than specific to the synthesis itself. You can find much more
hazardous write ups/discussions yet because it's already assumed you have a certain level of experience to be doing them it's also assumed you're
already reasonably aware of the hazards involved. I didn't really view it in that context before so all the extra warnings probably lead me to
overestimate the dangers (which is not a bad thing).
I am making it because I actually could use some ether more than for learning purposes, but as mentioned it is more economical depending on your
access to ethanol and I happened to already have 2 liters of ~170 proof so it was relatively trivial to dry them for this. I also want a decent amount
so I wouldn't have to make it again for awhile, I plan to make ~400ml, so that would probably be quite a few cans of starter fluid to get there.
[Edited on 12-4-2018 by alking]
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BaFuxa
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I am planning this synthesis as well. I think I am just going to put the apparatus under vacuum and let the ether boil itself off without any heating.
No risk of autoignition.
Potential counts for nothing until realized.
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happyfooddance
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| Quote: Originally posted by BaFuxa | I am planning this synthesis as well. I think I am just going to put the apparatus under vacuum and let the ether boil itself off without any heating.
No risk of autoignition.
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You need heat to form the ether. Optimal temp is 140-160°C. I have found that closer to 160 works best (bath temp).
If you use a vacuum you will need something like dry ice/acetone for both your condenser and reciever. And a vacuum trap for your pump.
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alking
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I successfully carried out the task yesterday, but I still need to do the workup to wash/dry it. I collected about 350-400ml of crude diethyl ether
from 500ml of homemade ethanol. It took a LOT longer than I was expecting, about 10 hours, and I did not even collect it all as there was still more
coming over, but I was too tired to keep it running at that point.
Does it normally take that long or was I just using too long of a fractionating column? I've made alkyl bromides and I recall it being much quicker,
but my memory is vague. Due to a lack of lab jacks my choice was to either use no column or a rather long column so I chose the later, if I did it
again I probably would do it differently.
My pot temperature held right around 140 the whole time, though the distillate seemed to come over at roughly the same rate between ~135 and 150, I
did not go higher than 150. The head temperature was between 29.0-36.0C, averaging at about 31-32C, with a small spike up to 45C when I added the
ethanol too quickly later on hoping to speed it up. No ether fumes were detected throughout except for outside around the bleed tube which smelled
quite noticeably, my condenser temperature peaked at 6C so I'm sure it could be more efficient (started at about -5C I'd guess).
I had no real bumping to speak of except some very minor splattering near the end, which was resolved by turning the magnetic stirrer up, and I do
believe this was only because the solution was getting rather thick with polymerized impurities from the ethanol. The pot was a thick black with
polymerized sludge separating out upon cooling, I guess that speaks to the purity of my ethanol.
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happyfooddance
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@ alking
The column won't affect the speed of the operation, becomes filled with saturated vapor quickly and easily. I myself use a long, 400mm vigreux.
My impression is that your addition rate is too slow. Also, what size boiling flask did you use? I use a 1l rbf.
Good job on a successful synthesis!
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alking
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I used a 1L flask, probably could have used a 500ml though. I played with increasing the drip rate but it didn't seem to affect things too much. I did
notice the first ~20% of the distillation was noticeably faster, perhaps 2-3x so, I wonder how much the purity of my h2so4 (~93% plumbing grade) and
ethanol (homebrewed, not especially pure, albeit dry) had to do with it.
The total yield of crude ether was 299.9g, roughly 400ml worth. After washing I lost 20ml, dried it over CaCl2, and distilled to collect ~340ml in
total. There was maybe 30ml left in the pot, but I wasn't sure if it would be safe to distill it to dryness. The still head peaked at 35.1C so it's
still not totally pure, I assume there's some ethanol in there maybe, but it's good enough for my purposes.
edit: Btw the reason I suspected the column was because my reflux ratio was 3:1 or so. Fractionating aside wouldn't it be most efficient if the reflux
rate was equal to or less than the drip and collection rate? I realize if the reflux was mostly ethanol or water that's a moot point however, and
maybe it was, idk.
[Edited on 16-4-2018 by alking]
[Edited on 16-4-2018 by alking]
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zed
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Ditto Bert!
Do it outside. Protect yourself at all times.
---------------------------------------------
So things went well. As evidenced by your still being alive.
Keep in mind, this status can change.
Especially, if you like.... flip a light-switch, in a room permeated by ether vapor.
Kudos
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