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DraconicAcid
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Ether is slightly soluble in water and vice versa, but they are not miscible, which means they would mix in all proportions.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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The Volatile Chemist
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Can't inflammation of ether be avoided easily if not using an open flame? (e.i. instead using a mantle/hotplate)? It seems ether is generally less
reactive. (All stated in my lack of knowledge on the subject).
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gdflp
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Somewhat, but not really. Ether has a very low auto-ignition temp of 160°C, which means that any surface at or over that temperature can cause the
vapors to ignite(this can also be the heating element of the hot plate). In addition, ether vapors are rather dense and can travel low to the ground
long distances at which point they can meet an ignition source, such as the spark from a light switch, and ignite.
[Edited on 3-27-2015 by gdflp]
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The Volatile Chemist
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Oh. Still, though, can't that be avoided with well sealed apparatus?
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gdflp
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Depends on the application. If you're using it as a solvent, i.e. for a Grignard, you could constantly need to add more and due to the volatility of
ether and the massive amount of heat generated, the reflux condensers aren't 100% efficient. If you're doing an extraction, you may be able to get
away with leaving the ether in the sep funnel the entire time, but you still need a way to evaporate the ether, typically by boiling it off on a hot
plate although in a fume hood for sure.
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The Volatile Chemist
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I see. But, if in a fume hood the whole time, it would greatly reduce the amount of vapors touching surfaces able to ignite the ether.
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gdflp
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Yes, but the vapor is flammable in the 1.9%-36% range and the vapor is dense. Static discharges if the air is dry are also an issue. And once one
small bit ignites...
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Loptr
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Quote: Originally posted by gdflp  | | Depends on the application. If you're using it as a solvent, i.e. for a Grignard, you could constantly need to add more and due to the volatility of
ether and the massive amount of heat generated, the reflux condensers aren't 100% efficient. If you're doing an extraction, you may be able to get
away with leaving the ether in the sep funnel the entire time, but you still need a way to evaporate the ether, typically by boiling it off on a hot
plate although in a fume hood for sure. |
This is why when I get back to the level of knowledge I was in college, I am going to attempt a Grignard, except with toluene or benzene and
triethylamine, as I have read about in several papers. I am sure there will be issues, but it is one of those on my list to attempt at home.
I successfully performed grignard reactions during labs in college using diethyl ether, and would like to see if it can easily be done at home with an
aromatic solvent.
[Edited on 27-3-2015 by Loptr]
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gdflp
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I would be very interested in this. We recently did a Grignard in my Orgo II lab, but they didn't give us large enough condensers. The ether was
refluxing so rapidly that the downward stream plugged the condenser and when the pressure built up, a geyser of ether shot up out of the top of the
condenser. I had such a headache after three hours of that(not enough fume hoods for the students to use them).
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Chemosynthesis
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I have seen some syntheses claim improved yields upon switching the solvent of a performed Grignard from THF or ether to something like toluene
before. I can look for a citation to back that up. Apparently the formation in such solvents has been investigated. It is probably Grignard specific,
as I imagine it shifts the Schlenk equilibrium.
examples Tet Lett 21 (1980) pp155-158 and citations in US 3426087 A, among others.
[Edited on 27-3-2015 by Chemosynthesis]
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Loptr
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I know without any doubt I would have issues with Grignard given my glassware. I have a lot 19/22 joint glassware, which tends to have shorter
columns, smaller parts here and there, etc., so I know diethyl ether vapor would likely escape pretty easily. Hence, the interest in another method.
Also, I have read where the Grignard reagent is prepared in diethyl ether, and then moved to a different solvent for the actual addition. I have read
several examples, even DCM being one of them, except in this case the DCM was kept at very low temperatures in a dry ice/acetone baths.
I think I have a few of these papers I am recalling from in Google Drive, so I will see if I can pull them up some time today and attach them to this
thread.
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The Volatile Chemist
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I'd have trouble too. Our water heater'd probably set it off if I used it.
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Loptr
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I have been building a lab in my attached garage with plans to move it to the shed, but I would hate to do that because of the moisture and
temperature fluctuations.
My plan is to kill the pilot light before I attempt it.
EDIT: Also, at this time I will have a functioning fume hood to move the fumes outside.
[Edited on 27-3-2015 by Loptr]
One of my ultimate goals is to stay away from diethyl ether, or anything similar, that has such a high risk of fire and/or explosion! Methyl
tert-butyl ether is on my shopping list to acquire eventually, and while it still does present peroxide risks, the risk (from what I have read) isn't
as great as with diethyl ether. I might also add some sort of peroxide formation inhibitor, such as BHT, just to make sure.
[Edited on 27-3-2015 by Loptr]
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Magpie
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| Quote: Originally posted by Loptr | I know without any doubt I would have issues with Grignard given my glassware. I have a lot 19/22 joint glassware, which tends to have shorter
columns, smaller parts here and there, etc., so I know diethyl ether vapor would likely escape pretty easily. Hence, the interest in another method.
|
I have run 2 Grignards in 19/22 glassware with no problems. I really don't understand your concerns.
| Quote: Originally posted by Loptr |
Also, I have read where the Grignard reagent is prepared in diethyl ether, and then moved to a different solvent for the actual addition. I have read
several examples, even DCM being one of them, except in this case the DCM was kept at very low temperatures in a dry ice/acetone baths.
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I've read that diethyl ether has certain properties good for Grignards: (1) the lone pairs of electrons on the oxygen complex with the Mg to keep it
in solution, and (2) its volatility keeps an inert atmosphere cover over the reaction mix isolating it from the ambient air. But as you say, this is
mostly important during the Grignard reagent formation.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Loptr
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| Quote: Originally posted by Magpie | | Quote: Originally posted by Loptr | I know without any doubt I would have issues with Grignard given my glassware. I have a lot 19/22 joint glassware, which tends to have shorter
columns, smaller parts here and there, etc., so I know diethyl ether vapor would likely escape pretty easily. Hence, the interest in another method.
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I have run 2 Grignards in 19/22 glassware with no problems. I really don't understand your concerns.
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How cold was your coolant running through the condenser? It shouldn't be a problem as long as it is very cold, but at the same time, it's not like I
actually have experience doing this yet with 19/22 glassware, and is just something that is in the back of my mind. My thought is the diethyl vapor
might overwhelm the condensing effect of the column and escape, which is something I would like very much to avoid.
I also don't have as mean of a fume hood as you do sitting in your lab! 
(actually, I don't have one yet at all... but that will change at some point!)
EDIT: I tend to be a VERY cautious person, so some of my concerns might be a little out there. It's my job to keep me and mine safe. 
[Edited on 27-3-2015 by Loptr]
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Magpie
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I normally use ice-water for my condenser coolant.
I would feel uncomfortable working with ether without a good fume hood. Caution is good - you are ultimately responsible for your
safety. Home chemists are more sensitized to this fact. It does tend to engage your brain more than if you were working in an institution where you
might think someone else is looking out for your safety (sometimes this is an illusion).
The single most important condition for a successful synthesis is good mixing - Nicodem
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karlos³
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Ive run several grignards in 29/32 glassware, put a 50cm condenser on it, and see if any Et2O escapes? Dont see your concern there as well?
Also, it have to be a symetrical ether, see schlenk-equilibrium why that is so. MTBE wont work for example. Cant see how DCM would work in a grignard
reaction, it sounds to me like a potential disastrous runaway reaction?
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Chemosynthesis
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Nonsense. See JACS (1914) 36, 1022.
Edit: And JACS (1947) 69, 2007.
Asymmetrical ethers can function as Grignard solvents in high yields. It is important to note that Schlenk equilibrium, as with any chemical
equilibrium, is substrate dependent! Kinetics also plays a role: JACS (1937) 59, 1354 and compte rend (1950) 231, 866.
[Edited on 27-3-2015 by Chemosynthesis]
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Loptr
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| Quote: Originally posted by karlos³ | Ive run several grignards in 29/32 glassware, put a 50cm condenser on it, and see if any Et2O escapes? Dont see your concern there as well?
Also, it have to be a symetrical ether, see schlenk-equilibrium why that is so. MTBE wont work for example. Cant see how DCM would work in a grignard
reaction, it sounds to me like a potential disastrous runaway reaction? |
I don't know if my post was clear, I will review it, but the MTBE was not for grignards, but as a diethyl ether replacement with a reduced peroxide
formation potential. As far as I know, MTBE cannot be used in Grignards.
As for the DCM, I will have to dig up the reference I have found where they used it with extreme temperature control. Read what I said about the very
low temperature, and I think I mentioned it earlier in the thread as around -78C.
[Edited on 27-3-2015 by Loptr]
EDIT: I also said that I have smaller glassware, and my longest condensor is approx. 20 cm, as compared to your 50 cm. Does that sound like it
would make a difference? I think it means I have to worry about the temperature of my coolant more than I would usually have to with a longer
condenser.
In fact, just checked the specs, and the effective/jacket length of my reflux condenser is 125mm.
[Edited on 27-3-2015 by Loptr]
EDIT: Also, if my concerns are a bit far fetched, then let me know, but don't attempt to generalize the issue across to a different set of equipment.
I don't have diethyl ether, so can anyone tell me whether a Synthware 19/22 Reflux Condensor (http://www.sigmaaldrich.com/catalog/product/aldrich/sync2691...) would be effective against allowing diethyl ether to escape during a potentially
very exothermic Grignard addition? If so, I am all ears, as I previously mentioned, I don't have much experience with my set up as I am just getting
started in the amateur chemistry business. Any experience that I do have was back in college, so I am just trying to be cautious about what I do and
know my limitations.
[Edited on 27-3-2015 by Loptr]
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DraconicAcid
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If your condenser it too short, you can put two of them together, and just run water through the top one (or have water go in through the top one
first, then the lower one second).
I'm not an organic chemist, but I always thought it was "common knowledge" that you had to have an ether present to make a Grignard reagent. Whether
that's correct or not, I'm not sure, but I have used THF for such reactions, and you could probably use a mixture of an ether and something less
volatile (such as benzene or toluene). Obviously, you can't use acetone or ethyl acetate.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Molecular Manipulations
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| Quote: Originally posted by gdflp | | Somewhat, but not really. Ether has a very low flash point of 160°C, which means that any surface at or over that temperature can cause the vapors
to ignite(this can also be the heating element of the hot plate). |
You're confused as to the meaning of "flash point".
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air.
This is very different than autoignition temperature, which is the temperature that a bond breaks causes it to ignite spontaneously. You are however
correct in that ether's autoignition temperature is 160 °C, you just used the wrong phrase.
Dichloromethane's flash point is at −14 °C but it's autoignition temperature is 556 °C.
Diethyl ether's flash point is −45 °C and it's autoignition temperature is 160 °C.
This is probably because of the instability of the ether bond (-O-), which breaks at a lower temp than a carbon-carbon, carbon-chlorine or
carbon-hydrogen bond.
[Edited on 27-3-2015 by Molecular Manipulations]
-The manipulator
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gdflp
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| Quote: Originally posted by Molecular Manipulations | | Quote: Originally posted by gdflp | | Somewhat, but not really. Ether has a very low flash point of 160°C, which means that any surface at or over that temperature can cause the vapors
to ignite(this can also be the heating element of the hot plate). |
You're confused as to the meaning of "flash point".
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air.
This is very different than autoignition temperature, which is the temperature that a bond breaks causes it to ignite spontaneously. You are however
correct in that ether's autoignition temperature is 160 °C, you just used the wrong phrase.
Dichloromethane's flash point is at −14 °C but it's autoignition temperature is 556 °C.
Diethyl ether's flash point is −45 °C and it's autoignition temperature is 160 °C.
This is probably because of the instability of the ether bond (-O-), which breaks at a lower temp than a carbon-carbon, carbon-chlorine or
carbon-hydrogen bond.
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Yes, sorry. That was a typo.
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Loptr
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| Quote: Originally posted by DraconicAcid | If your condenser it too short, you can put two of them together, and just run water through the top one (or have water go in through the top one
first, then the lower one second).
I'm not an organic chemist, but I always thought it was "common knowledge" that you had to have an ether present to make a Grignard reagent. Whether
that's correct or not, I'm not sure, but I have used THF for such reactions, and you could probably use a mixture of an ether and something less
volatile (such as benzene or toluene). Obviously, you can't use acetone or ethyl acetate. |
I am not a chemist at all, only classes in college, but I have read that aromatics can be used. Ethers are traditional Grignard solvent, not
the only.
I did a quick search on my Google Drive, and here are two that came up. I know I have others, but these were at the top of the list.
Granted: Formation of PhMgBr mentions diethyl ether in toluene
Attachment: Method for the Preparation of Grignard Compounds in Hydrocarbon Solution.pdf (239kB)
This file has been downloaded 287 times
Attachment: Formation of PhMgBr.pdf (164kB)
This file has been downloaded 652 times
[Edited on 27-3-2015 by Loptr]
I will see if I can find the others, one in particular mentions exhaustively drying and deoxygenating toluene for use as a solvent in a Grignard.
[Edited on 27-3-2015 by Loptr]
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Chemosynthesis
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I second the condenser stacking. It's a very good idea. It looks funny, but is perfectly fine, particularly with ground glass joints. Usually, from
what I have seen, ethers are used as solvents during initiation, even with ultrasound activation. There is a patent I found above where people at
least looked into using other initial solvents, but at am not familiar with this. Maybe someone else can shed some light on it.
I have seen and tried to cite a couple examples of forming a Grignard in an ether, then replacing the solvent with a standard hydrocarbon
solvent. Sometimes it is even purported to increase yields, which I would speculate is due to enhanced relative solvation of a transition state. I
imagine this could be useful if ones reaction is amenable and their ether supply subject to some limitation, self imposed or otherwise. At the very
least, the reaction could be slightly topped off with such a solvent (alkanes, perhaps toluene, etc.) if necessary. It is definitely something to
consider.
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Dr.Bob
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If you use a bucket of ice water and a fish tank pump, you can cool any condenser cool enough to condense ether fine. The key is to have at least
some ventilation, either doing it outside, in a hood, or at least in front of an open window with a fan blowing air into the building somewhere away
from the reaction. (Don't want fan blow air out the window by the ether, that sucks fumes through a sparky motor...) Ethers are best for
Grignard, some aromatics might work, but DCM I have never seen used; I suspect it is very bad, but don't have proof.
BTW, ether's flash point is -40C (or F), which is the temp. at which there are fumes enough to ignite from a spark. It has an autoignition point of
160C, which is the point at which it will catch fire without a spark present. So it is very easy to ignite ether with a spark from a motor, static,
whatever, or even without a spark, if it's fumes gets near a hot light bulb, warm hotplate or oven, it can ignite even without a spark at those
temperatures. That is why it is put into engine starting fluid, as it will burn with almost any excuse.
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