Sciencemadness Discussion Board - DCM vs ether

DCM vs ether

Magpie - 24-3-2015 at 10:16

My 1960's college organic chemistry manual never specified DCM as solvent in any of the procedures although it was mentioned in a list of solvents. Chloroform and carbon tetrachloride were occaisionally used as well as, of course, diethyl ether.

Now, during my recent refresher course the lab manual relies very heavily on the use of DCM, and rarely specifies chloroform, carbon tet, or ether.

Surely this must be due to the lower toxicity of DCM vs chloroform and carbon tet. And compared to ether there is the big advantage DCM's non-flammability.

What I'm wondering is: If lower boiling point and somewhat higher solubility in water aren't an issue, is there any reason that DCM can't be generally substituted for these other chlorinated methanes?

For a specific example take the case of the extraction of phenol from water.

Many, if not most, of the synthesis procedures found in Vogel, OrgSyn, Gattermann, etc, specify ether for the workup. I dislike the use of ether because of its flammability and lingering stench. If at all possible I would much rather use DCM (dichloromethane). Although this question has been discussed tangentially in other threads I wanted to ask this question formally to get your opinions for discussion.

So, barring a good reason to not use DCM (eg, reactivity, azeotrope formation, etc) can it be assumed that where ether is specified DCM can be substituted?

Loptr - 24-3-2015 at 10:23

I can't speak for the generality of DCM, but one issue I have had with DCM is emulsions, which I don't remember with ether. It might just be me, though.

I also imagine that DCM could more easily be deprotonated than Et2O.

[Edited on 24-3-2015 by Loptr]

careysub - 24-3-2015 at 10:31

This interests me as well - DCM is safer and cheaply and easily available where I live (California) in paint stripper.

Similarly, I have resolved to try isopropyl alcohol instead of methanol or ethanol in most procedures (if their only role is as a solvent) since IPA is so cheap and easy to get.

In Williamson's "Microscale and Macroscale Organic Chemistry" (second edition) published in 1994 he used methyl tert-butyl ether (MBTE) as the all purpose replacement for diethyl ether citing its cheapness and ready availability since it was widely used in gasoline/petrol. 20 years on it is not cheap nor readily available, having been effectively banned from gasoline in 2004-2005.

Chemosynthesis - 24-3-2015 at 11:04

I have considered this very question before, and seen the substitution used on a few different reactions without apparent issue so far. Interested in seeing anyone come up with exceptions.

Loptr - 24-3-2015 at 12:30

I just recently purchased a gallon of DCM in hopes of it being my general purpose non-polar solvent, even though it is slightly polar.

According to this http://web.pdx.edu/~wamserc/Research/jo100276m.pdf, pyridine and its derivatives react with dichloromethane under ambient conditions to form methylenebispyridinium dichloride compounds. I know that diethyl ether is used to dissolve the pyridine salt as part of extraction, so it DCM might not be a good candidate in conjunction with pyridine. Of course, there are other methods, but this is one I have run across in a quick search for incompatibilities.

* I am just trying to find a set of general example where DCM might not be a good idea. I am in no way an authority on this, and might be wrong.

EDIT: I think it also goes without saying that being it's a chlorinated solvent, you don't dry with alkali metals as you would with diethyl ether. I have read the usage of sodium with chlorinated solvents has led to explosions. I am not in the industry, but is something that has stuck in my head since college.

[Edited on 24-3-2015 by Loptr]

[Edited on 24-3-2015 by Loptr]

[Edited on 25-3-2015 by Loptr]

Amos - 24-3-2015 at 16:42

Is there any reason that hexane or heptane wouldn't be suitable for many of the procedures using DCM or ether as a solvent? One of the other is often found alongside ether in engine starter fluid. Forgive my ignorance if there's a blatantly obvious reason why it wouldn't work; I haven't really seen many compounds explicitly described as being soluble in alkanes.

[Edited on 3-25-2015 by Amos]

DraconicAcid - 24-3-2015 at 16:47

Long ago, when I worked with funky organometallic compounds, DCM was our standard solvent due to its polarity. Ether was used to precipitate out the compounds from solution.

Chemosynthesis - 24-3-2015 at 18:58

Quote: Originally posted by Loptr

According to this http://web.pdx.edu/~wamserc/Research/jo100276m.pdf, pyridine and its derivatives react with dichloromethane under ambient conditions to form methylenebispyridinium dichloride compounds. I know that diethyl ether is used to dissolve the pyridine salt as part of extraction, so it DCM might not be a good candidate in conjunction with pyridine. Of course, there are other methods, but this is one I have run across in a quick search for incompatibilities.

* I am just trying to find a set of general example where DCM might not be a good idea. I am in no way an authority on this, and might be wrong.

I didn't realize that. Room temperature with pyridines is a new one for me. The link didn't work for me, but I might have the citation here: J. Org. Chem., 2010, 75 (12), pp 4292–4295

Loptr - 24-3-2015 at 20:26

Quote: Originally posted by Chemosynthesis

Quote: Originally posted by Loptr

I didn't realize that. Room temperature with pyridines is a new one for me. The link didn't work for me, but I might have the citation here: J. Org. Chem., 2010, 75 (12), pp 4292–4295

http://web.pdx.edu/~wamserc/Research/jo100276m.pdf

There was an issue with a comma included in the url. The link had pictures showing the formed products comparing side by side solutions.

Loptr - 24-3-2015 at 20:32

Quote: Originally posted by DraconicAcid

Long ago, when I worked with funky organometallic compounds, DCM was our standard solvent due to its polarity. Ether was used to precipitate out the compounds from solution.

I have read of DCM being used as a cosolvent in organometallic additions to help with chelation control. Any chance this being one of the reasons? In the particular instance I refer to, they were using temperatures around -78C to keep the DCM from becoming deprotonated. LDA to form dichloromethyllithium is one such example of it being deprotonated.

[Edited on 25-3-2015 by Loptr]

[Edited on 25-3-2015 by Loptr]

subsecret - 25-3-2015 at 06:33

Quote: Originally posted by Amos

Is there any reason that hexane or heptane wouldn't be suitable for many of the procedures using DCM or ether as a solvent? One of the other is often found alongside ether in engine starter fluid. Forgive my ignorance if there's a blatantly obvious reason why it wouldn't work; I haven't really seen many compounds explicitly described as being soluble in alkanes.

[Edited on 3-25-2015 by Amos]

Petroleum ether, toluene, or xylene could be used if hydrocarbons work well for extractions. According to wikipedia, carboxylic acids can easily be extracted with benzene. Bromine and iodine can easily be extracted with these hydrocarbons (which might be a good way to extract iodine from tincture of iodine, after it is acidified and H2O2 added).

But I think we are missing something here, because these solvents are never mentioned for the most common extractions.

Loptr - 25-3-2015 at 07:08

I am considering purchasing P2O5 for use in drying the dichloromethane. Would this be an optimal choice?

I haven't attempted to dry dichloromethane before, however, I have ran across the use of calcium hydride several times so far, which is not easily acquired, for me at least.

http://chemwiki.ucdavis.edu/Reference/Lab_Techniques/Distill...

EDIT: Also, drying it with a more general desiccant, such as calcium chloride might do the trick, and then distill it. I am planning on storing the DCM with 3A molecular sieves. 4A molecular sieves won't exclude any methanol that has been added as a stabilizer, and might cause issues with pressure build up.

[Edited on 25-3-2015 by Loptr]

[Edited on 25-3-2015 by Loptr]

Loptr - 25-3-2015 at 07:45

Here is an old post from back in 2008 that is a translated page showing azeotropes of DCM--might be useful. (way before I got here)
http://www.sciencemadness.org/talk/viewthread.php?tid=10306&...

Here is the thread link: http://www.sciencemadness.org/talk/viewthread.php?tid=10306

* I attached the image to this thread because it wouldn't let me link the image into this post for some reason... redundancy... :-/

[Edited on 25-3-2015 by Loptr]

Magpie - 25-3-2015 at 07:57

Quote: Originally posted by subsecret

I wonder if what we are missing is the somewhat polar nature of both DCM and ether.

DraconicAcid - 25-3-2015 at 08:00

Quote: Originally posted by Loptr

I am considering purchasing P2O5 for use in drying the dichloromethane. Would this be an optimal choice?

That's what we always used back in the day. Reflux over P2O5, then distil.

DraconicAcid - 25-3-2015 at 08:21

Quote: Originally posted by Loptr

Quote: Originally posted by DraconicAcid

Long ago, when I worked with funky organometallic compounds, DCM was our standard solvent due to its polarity. Ether was used to precipitate out the compounds from solution.

No, we just used it because the compounds we were using were very soluble in it, and it didn't react with the stuff we were using.

deltaH - 25-3-2015 at 08:39

I second that, I've found DCM highly useful in dissolving stubborn organic compounds. It is an exceptional solvent IMHO.

careysub - 25-3-2015 at 08:47

Quote: Originally posted by Amos

BTW heptane is available OTC in the US as the rubber cement solvent Bestine, about $16 a quart. Amazon has it, and your better art supply houses have it also (Dick Blick, ArtSupplyWarehouse, etc.).

careysub - 25-3-2015 at 08:50

Quote: Originally posted by Loptr

EDIT: Also, drying it with a more general desiccant, such as calcium chloride might do the trick, and then distill it. I am planning on storing the DCM with 3A molecular sieves. 4A molecular sieves won't exclude any methanol that has been added as a stabilizer, and might cause issues with pressure build up.

I find CaCl2 listed as a dessicant for DCM in multiple places. That would be the one to start with, for cheapness.

I intend to use it to dry distilled paint stripper DCM to remove any methanol and ethanol as well.

gdflp - 25-3-2015 at 11:19

Quote: Originally posted by Magpie

Quote: Originally posted by subsecret

I wonder if what we are missing is the somewhat polar nature of both DCM and ether.

Perhaps one of the issues arises in removing the solvent. Both DCM and ether are very volatile compounds with low boiling points. This allows for easily removing the solvent after an extraction with a hot water bath. If the product is a liquid, it may have a boiling point similar to that of the solvent, thus requiring a fractional distillation. If the product is a solid, it may melt lower than the boiling point of the solid thus leaving a mess after solvent removal, or decompose below the solvent's boiling point, undesirable for obvious reasons(liquids could suffer this problem as well). The volatility of ether and DCM will also just allow for the product to dry faster, requiring less time taking up oven space or taking up space sitting in a dish.

Loptr - 25-3-2015 at 11:42

Quote: Originally posted by gdflp

Quote: Originally posted by Magpie

Quote: Originally posted by subsecret

I wonder if what we are missing is the somewhat polar nature of both DCM and ether.

Aren't higher boiling solvents more difficult to remove given Raoult's law, meaning you want the solvent be as volatile as is practical?

Magpie - 25-3-2015 at 12:26

Yes, the low boiling point of DCM (40°) and ether (35°) is important for the reasons you have stated. But pet ether can also have a very low boiling point depending on the petroleum cut selected (30°-40°, 40°-60°, etc). But it would be a non-polar solvent.

gdflp - 25-3-2015 at 12:42

Yes, I think that multiple factors come into play. For example, one of my recent orgo labs(synthesis of methyl 3-nitrobenzoate) called for the product to be extracted with and dissolved in methanol, then ligroin(similar to pet ether, higher boiling fraction in this case) added and the methanol evaporated at which point the methyl 3-nitrobenzoate precipitated due to the insolubility in the non polar solvent and was filtered. So a desirable solvent has to be moderately polar to have desirable solvent characteristics, but also needs to have a low boiling point to be a viable extraction solvent.

Quote: Originally posted by Loptr

Aren't higher boiling solvents more difficult to remove given Raoult's law, meaning you want the solvent be as volatile as is practical?

Yes, that was the point that I was trying to make. Sorry if I wasn't clear.

[Edited on 3-25-2015 by gdflp]

Dr.Bob - 25-3-2015 at 13:46

DCM is often the best solvent for extractions of both non-polar and somewhat polar compounds. Ether works well with similar compounds, but is not as good at either end of the spectrum, in general (it will not dissolve grease or really polar compounds as quickly as DCM). So DCM can be used in place of ether, except that it can actually extract out some unwanted compounds that ether will not extract, like amines, acids, etc, which you often want to stay in the water layer, for instance in an amide formation. Chloroform is as good or better then DCM for most cases, but is considered less safe. CCl4 is too non-polar for most work, other then very non-polar compounds, and becoming hard to find.

Hexane, heptane and pet ether are all all great for extracting oily compounds, but are very poor solvents for most even slightly polar compounds, which is why ethyl acetate is more often used for moderately polar compounds. Heptane is often used in process chemistry, due to higher flash point, BP, and lower toxicity (in theory at least). And many process chemists use isopropyl acetate instead of EtOAc for safety as well.

MTBE is also used by process chemists in place of ethyl ether, higher BP and flash point, but similar in peroxide formation, so still have to watch that. It was cheap until most fo the plants to make it closed suddenly due to being banned in gasoline.

So chemists often want the lowest BP for ease of removal, engineers want the highest BP for safety and avoidance of evaporation loses. There are tables of the "polarity" of most solvents, but if you stick with "like dissolves like", that will tell you if a solvent will work.

So for the least polar compounds, aromatics, hexane, heptane and pet ether all work well.

For intermediate polarity, I like ethyl acetate, DCM, ether, and sometimes THF (although it is somewhat miscible with water, unless mixed with DCM or hexane).

And for very polar extractions from water, you might need n-butanol, THF, DCM/MeOH (9:1 is common). If the extraction is from a solid, then methanol, ethanol, or isopropanol can work well, also acetonitrile can work, not as well as most alcohols. If you need DMSO or DMF, then you are not going to extract anything from water, but they are great polar solvents.

adk - 26-3-2015 at 03:09

I generally prefer DCM as it allows faster workup & extraction from a sep funnel. As a general rule, the organic layer is going to be on the bottom meaning that you do not have to drain the aqueous layer every time you shake & extract.

Flammability is also a concern, plus ether is slightly soluble (edit!) in water so a certain degree.

I also use ethyl acetate quite a lot as it comes off relatively quickly and is probably much less harmful to health than DCM -and much easier to dispose of the waste (not halogenated!).

YMMV though

[Edited on 26-3-2015 by adk]

DraconicAcid - 26-3-2015 at 07:11

Quote: Originally posted by adk

Flammability is also a concern, plus ether is miscible with water so a certain degree.

Ether is slightly soluble in water and vice versa, but they are not miscible, which means they would mix in all proportions.

The Volatile Chemist - 26-3-2015 at 13:59

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).

gdflp - 26-3-2015 at 14:03

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]

The Volatile Chemist - 26-3-2015 at 14:24

Oh. Still, though, can't that be avoided with well sealed apparatus?

gdflp - 26-3-2015 at 14:29

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.

The Volatile Chemist - 26-3-2015 at 14:38

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.

gdflp - 26-3-2015 at 14:53

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...

Loptr - 26-3-2015 at 16:39

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]

gdflp - 26-3-2015 at 16:50

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).

Chemosynthesis - 26-3-2015 at 18:06

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]

Loptr - 27-3-2015 at 08:20

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.

The Volatile Chemist - 27-3-2015 at 08:27

I'd have trouble too. Our water heater'd probably set it off if I used it.

Loptr - 27-3-2015 at 08:33

Quote: Originally posted by The Volatile Chemist

I'd have trouble too. Our water heater'd probably set it off if I used it.

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]

Magpie - 27-3-2015 at 08:40

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.

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.

Loptr - 27-3-2015 at 08:46

Quote: Originally posted by Magpie

Quote: Originally posted by Loptr

I have run 2 Grignards in 19/22 glassware with no problems. I really don't understand your concerns.

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]

Magpie - 27-3-2015 at 09:02

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).

karlos³ - 27-3-2015 at 10:17

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?

Chemosynthesis - 27-3-2015 at 10:51

Quote: Originally posted by karlos³

Also, it have to be a symetrical ether, see schlenk-equilibrium why that is so

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]

Loptr - 27-3-2015 at 11:04

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]

DraconicAcid - 27-3-2015 at 11:20

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.

Molecular Manipulations - 27-3-2015 at 11:27

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]

gdflp - 27-3-2015 at 11:29

Quote: Originally posted by Molecular Manipulations

Quote: Originally posted by gdflp

Yes, sorry. That was a typo.

Loptr - 27-3-2015 at 11:32

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 296 times

Attachment: Formation of PhMgBr.pdf (164kB)
This file has been downloaded 661 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]

Chemosynthesis - 27-3-2015 at 11:35

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.

Dr.Bob - 27-3-2015 at 11:39

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.

Crowfjord - 27-3-2015 at 11:51

Here is another good read on Grignard reagents, their formation and use. It contains info on alternative solvents/solvent mixtures.

Loptr - 27-3-2015 at 11:52

Quote: Originally posted by Dr.Bob

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.

I think what needs to be differentiated here is the solvent used to form the Grignard reagent, or other organometalic, and the solvent used to perform the reaction with a substrate.

I know I keep saying "I have read", but here goes another; I have read about usage of diethyl ether/dichloromethane to help solvate particularly insoluble Grignard reagents (Acetylides ring a bell for some reason)

Quote: Originally posted by Crowfjord

Here is another good read on Grignard reagents, their formation and use. It contains info on alternative solvents/solvent mixtures.

I actually have that document open in one of my browser tabs when you posted. lol.

[Edited on 27-3-2015 by Loptr]

EDIT: Now that I have been thinking about it, the usage of DCM was a solvent switch after formation of the Grignard reagent, so for misleading about the formation of a Grignard reagent in DCM, I apologize.

[Edited on 27-3-2015 by Loptr]

karlos³ - 27-3-2015 at 14:04

Well, yeah, that what Loptr said, Grignard reagents need to be formed in some ether, but then can be transferred in an another, often aromatic solvent.
But for their formation an ethereal solvent is needed as far as I know. Ive also never used another method than the standard methods.

I guess DCM can be used as a starter for a grignard reaction similiarly to ethyl-halides, but that gives probably of flammable methane as gas, similarly to the bubbles of ethane that forms in the preparation of an indole grignard reagent, and THAT i would consider as flammable, Et2O being harmless instead...
That was what ive meant when I said, a disastrous runaway reaction would occur.

The Volatile Chemist - 2-4-2015 at 11:20

Vogel has a few drawings for stacking, doesn't look weird to me. Seems like a natural tendency if something volatile is going to be boiling at all.