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Klute
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[*] posted on 30-8-2008 at 18:51
DCM or Et2O?


In the past, dichloromethane was my favourite solvent for extractions. It was very efficent, very easily distilled and recyled, and is uninflammable.

But I hear more and more of how toxic it is, and that long-term exposure can be pretty bad. Living in a place where temp goes often over 30°C in summer, I'm often exposed to it's vapors.

I've been trying to limit it's use to the cases where it really is needed, when the product extarcted needs to be devoid of any solvent traces, etc
I have been pretty satisfied by using toluene and AcOEt, which can be removed easily under vacuum, and pretty much complet each other. Both are less toxic than DCM, especially AcOEt, which smells nice and is very effective, except for very basic or acidic conditions.

But as there are timew here a low boiling solvent, or a more powerfull one is needed, and my DCM supply is getting low.
I've been thinking of using diethyl ether instead. I've always been reluctant to use Et2O, being very volatil, and especially flammable.

One major problem is that I do my home-experiments in a garage, right next to a gas-powered boiler, so ther eis consatntly a little flamme near the floor. Now, I use adequate ventilation, and have a large door, so the place is pretty well vented. But Et2o vapors are notorious of easily acumulating, and exploding in fairly low concentrations...

So I'm still unsure of my choice:

- either I stick to DCM, none-flammable, slightly less volatil than ether, but expose myself to it's vapors, and risk cancer in several years,

-or I switch to Et2O, basicly none-toxic, but extremely inflammable. It would also require stabilization when distilled and recyled, although this isn't a major problem.

Choose the lesser of two evils...

I would like to hear anyone's opinion, and experience on this. I DCM really a cancerigenic hazard, or is it exagerated?

I ether really an fire/explosion hazard in presence of a boiler, or is it exagerated (I fear it is..)?

What is your favourite low boiling non-polar solvent?


EDIT: forgot to add: cost-wise both are very similar, ether being slightly more expensive than DCM at same purity grade.

[Edited on 31-8-2008 by Klute]




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[*] posted on 30-8-2008 at 19:41


Klute,

For home use, I would go with DCM everytime (if it will get the job done). I have accidentally endured DCM vapor exposure sufficient to cause temporary impairment of vison (black spots, almost unconscious). That was a lot (25 x 500 mL L/L extractors in a confined space). I switched to Dr. Martens because the soles did not stick to the floor when wet with DCM.

IIRC, it is not metabolized to yield phosgene, in-vivo, like chloroform.

This was in '95-96.

Although I cannot rule out very long term effects, it appears that I can still slap myself on the ass with both hands.

Ether, on the other hand, can be iffy even in a laboratory setting. I have seen it "just go". In one case, the roof and flashing near the hood outlet was hot enough to cause ignition of the vapor, which flashed-back though the hood an blew up the whole damn lab. Nevermind peroxides.

The vapors are heavier than air, and will creep along the ground. If that vapor encounters an ignition source, you will have a flash-fire.

Unless the application absolutely requires ether (e.g. extracting phenols/phenolic acids at acidic pH, where DCM selectivity is left severely wanting, complexing solvent, etc.), I'd use DCM.

For me, problem-wise: slightly poisoned << badly Burnt.

DCM recycles easily as well, without peroxide formation. This greatly minimizes the expense.

For these reasons, DCM (if it will work for the application) is probably my favorite low-boiling non-polar solvent. EtOAc isn't bad, either. Don't forget about mixtures such as EtOAc-DCM.

Cheers,

O3


[Edited on 30-8-2008 by Ozone]




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[*] posted on 30-8-2008 at 20:05


Thank you for your comment, I think I agree with you and stick to DCM.

It is also more versatil as a reaction solvent than Et2O, for which THF substitiutes well or even better (organometallics).
I still have an unopened 2.5L bottle of Et2O I will open the day I really need the solvent, but until then I will keep it stored I guess.

Indeed, if a fire starts in my garage, health effect in 10 years will be the least of my thoughts :) i suppose I could just wear my gas mask when handling DCM as long as my fume hood is not finished.

I wouldn't have liked to work in your lab 10 years ago! :) Floor wet with DCM?! :o

Also another good aspect with DCM is that it can be dried more easily than ether (P2O5, no need of Na or ketyl stills), and is less hygroscopic.




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[*] posted on 30-8-2008 at 21:09


I think you should do some more research before coming to your conclusion; as it doesn't seem that you have based it on much research.

There is a lot of good information about methylene chloride toxicity; while your interpretation of this information may differ from mine, It seems to me that if you can smell it you are putting yourself at an unnecessary risk. I very infrequently smell methylene chloride when working with it, I guess this is because I work in a cold basement.

Methylene Chloride Hazard summary (EPA)

I am not saying don't use methylene chloride though I think chronic exposure to any chemical should be thoroughly considered. Also consider engineering controls (ventelation, chilling the solvent etc) to reduce your exposure.

In regard to ether; while it is true that it has wide flammability limits, its lower flammability limit is ~2%. Of course vapors of ether will collect on the floor and counter top, but unless you are being reckless I think a 2% concentration is hard to achieve save maybe right on the surface of the counter top next to the flask.

It might be worthwhile to try some flammability tests with small amounts of ether; it is one thing to read about it, another thing to see it. In my experience the only time there are problems with ether are when there is open flame or spark, on the same counter top or surface that ether is on. Even then; once ether starts burning; it doesn't act much differently than a gasoline or ethanol fire.

Also remember, when working with ether, that our noses are many more times more sensitive to the smell of ether than to other solvents. So keep that in mind when comparing to DCM. Also of note the MAC (loosely: the minimum conc. to produce anaesthesia) for ether is 1.92%.

I use both; but I use ether much more frequently. I am admittedly paranoid about toxicity because I am so many times more afraid of this hobby making me die of cancer than in a fire.
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[*] posted on 31-8-2008 at 00:12


Quote:
Originally posted by Ozone
Ether, on the other hand, can be iffy even in a laboratory setting. I have seen it "just go". In one case, the roof and flashing near the hood outlet was hot enough to cause ignition of the vapor, which flashed-back though the hood an blew up the whole damn lab.


Well, one thing to consider: If you end up with DCM covering your floor (!), something is going very, very wrong.

Like smuv is saying, ether IS very flammable, but to actually ignite it, it takes quite some sloppy lab practice. I've seen people smoking next to ether distillations, which is kinda silly, but they went away with it.

How do you make enough ether escape from your work space to make for an explosive atmosphere?




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[*] posted on 31-8-2008 at 01:33


http://toxnet.nlm.nih.gov/

Oh please. Of course there is some dangerous toxicology to DCM. Don't use it as aromatherapy.

OSHA has no problems letting us use all the DCM we want at work, the smell gets pretty strong. Not that they are all-knowing or all-caring.
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[*] posted on 31-8-2008 at 03:45


Having similar issues with my workspace being located next to a gas powered water heater I tend to stay away from ether considering its flamability. DCM has its hazards, but when properly used it shouldn't be too much of an issues especially if you have good ventilation. Were I work we use DCM by the 55 gallon drum without any problems at all. Of coarse all the work is done under large fume hoods, but I would imagine in an open garage you would have to many problems with fume build up. Plus as a bonus DCM is very easy to recycle since it forms very few azeotropes with anything, and has such a low B.P it easily separated from any waste gunk. Just my two cents.



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[*] posted on 31-8-2008 at 05:05


For extractions I tend to use AcOEt. I have DCM and have used that also but my choice is based purely on what the text recommends OR what I have at hand and what I have most of. Pet Ether is useful also esp a low boiling one like 40/60. DCM I have always considered to be less toxic than chloroform and carbon tetrachloride. Ether and THF are mainly used in organo-metallic work I do and almost always THF over Et2O! A solvent which may be nicer than DCM (not quite so low boiling) maybe 1,1,1-trichloroethane although it can be expensive if you can find it.

If the temperature is frequently over 30*C I would imagine DCM and Et2O would generate quite some vapours, even my older texts recommend ether preps not be performed on hot days unless condenser water is precooled with ice and the collection flask chilled too and mention the flammable limits (although the book is aimed at teaching classes so are expecting multiple distillations by students etc.)

I'd say working with Et2O on a desk, by a boiler with a flame at ground level, on a hot day in a garage is a bad BAD idea. More vapours, not removed from the desk will roll off onto floor by boiler unless you ventilate well at ground level. You could go outside to do Et2O extractions?

I'd stick with DCM, AcOEt maybe investigate Pet Ether and 1,1,1-TCE




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[*] posted on 31-8-2008 at 07:23


I always am very cautious about toxicity of chemicals, especially long term effects.

A direct risk like fire or explosion is something which can be handled by a carefully engineered environment. Long-term exposure to low concentrations of possibly carcinogenic chemicals is a much more dangerous thing in my opinion.

In the case of Klute, I would consider buying a table-top fan (one which does not spark!!) and blowing air along a setup, which contains ether. If some ether escapes, it will be diluted at once. Your nose also is very sensitive to ether and if you smell it, you still are well below the flammability level, but at that point you can take some measures before concentration builds up too much. So, I would go for ether. I hate 'ghost-like' risks, where the punishment comes from mistakes I made 10 years ago. I prefer the direct risks, which I have to take care of now!




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[*] posted on 31-8-2008 at 07:42


Sometimes you cannot avoid usind DCM. I participated in a multi-kg -78 deg oxidation & subsequent ozonoloysis of a diterpene that could only be run in that solvent. The starting material was a diterpene that had the physical properties of pine sap. It would cling to the glassware & the only way to remove it was with DCM. Acetone had no effect.



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[*] posted on 31-8-2008 at 08:25


Well, lot's of diverging opinions :)

I did search around for toxicity data on DCM, but to be honest, this doesn't help me judge how dangerous it is. Of course it has ba dhealth effects, but so most of the chemicals ramdomly used. I find it very hard to quantify the toxicity under work conditions. Comparing LD in rats (often injected or exposed to very concentrated atmospher is hardly enlighting IMHO.

So I really on the interpreations of others, which perhaps more knowledge on the subject, people that have been in contact with sanitary people that can really give an assement of the threat, etc

And that's one reason for this thread.


When refluxing and/or distilling DCM, i always use 5-10°C water, and keep the reciever immersed in ice-water, which uses quite alot of ice, and during the hottests days use a scrubber with cold acetone or AcOET to absorb any DCM vapors. I also have small fans working on the bench, sending the vapors to the biggest opening of the garage, but when doing extarction, opening the bottle (pfffit), pouring some in a graduated cylinder, then int he seperating funnel, opening the funnel after extarcting (pffit), and all the different handling before fianl drying and removing the solvent, a certain amount of vapors evolve, enough for me to smell it on several occasions.

Concerning ether, I also have trouble judging the fire hazard it's use represents. I don't really have an idea when 2% concentration is reached, and that boiler is only 2-3 meters away from my workbench, in the less ventialted corner or the garage.. I can totally imagine the vapors generated from the extarction process I described (pffiit :) ) crawling to meet the flamme. Having over a certain amount of solvents stocked in the garage, I don't want to take a chance at a fire starting off. The cabinets they are in are not meant to be flamme proof, they are ventilated though.

AcOEt has defiantively became my favourite solvent for extarctiosn now. It is very cheap (8euros 5L), very efficient, practically harmless if I trust what I have read and heard, and easily removed with a little vacuum. It can also be recylcled somewhat easily (hard to remove other solvents with simialr bps, no strong base or acid traemtment to remove any impurities possible though). When the aqueous is very basic or acidic, I use toluene instead.

Pet ether I use alot for chromatography or recrystallizations, but never with extarctions. Itis just too non-polar, and doesn't dissolve much of anything (hence the use for recrystns).

I think the final work is that I really should finish my fume hood, and only use DCM under it. Ether I will limit myself to the case where it is really needed, if the toxicity aspect can be avoided, I prefer avoiding any concern about peroxides (even I think it is quite exagerrated, from my experience with THF). Until then, i will keep my gas mask on when handling it.

Thank you all for expressing your opinions!




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[*] posted on 10-9-2008 at 15:31


If AcOEt is substituted for DCM/Chloroform in a biphasic NaOCl oxidation system would significant amounts of chloroacetate be formed?
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[*] posted on 10-9-2008 at 22:22


I have already seen AcOEt been used in biphasic systems with NaOCl. But depending on the reaction times and concentration of the hypochlorite,, I would perhaps feel safer using toluene, if it substitutes well (might need a PTC for better contact).

EDIT: This document uses NaOCL and AcOEt up to 24h:
Oxidation of limonene catalyzed by metal(Salen) complexes


[Edited on 11-9-2008 by Klute]




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[*] posted on 12-9-2008 at 00:36


i agree with woelen.
I think anything that can be used in methylenation reactions
like DCM should be considered to be highly dangerous over
prolonged exposure.

each time you get methylenated your taking a gamble
with cancer.




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[*] posted on 12-9-2008 at 00:45


Quote:
Originally posted by Ephoton
each time you get methylenated your taking a gamble
with cancer.

It is the methylation of nucleic acids that is dangerous in regard to cancer, not methylenation. N-methylenation of primary amines leads to the Shiff bases of formaldehyde (R-N=CH2 or its trimers) which are highly labile in biological environments and usually regenerate the amine back as it was. There is however always a small chance that the imine can be reduced by some enzymatic process before being hydrolyzed, but this does not appear to be of great concern or else even formaldehyde would be considerably carcinogenic (more so than just speculatively).




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[*] posted on 12-9-2008 at 04:41


Well, seeing the conditions required to methylenated very nucleophilic phenolates, I doubt any peptides are going to get methylenated on the spot by a few ppm'sDCM... But I'm no biologist. I just think DCM toxicity must be du to other things.



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[*] posted on 12-9-2008 at 04:50


One thing about the solvents, what about heptane as a solvent for extractions it is really apolair so it doesn't mix with water "at all".
What are your thoughts about heptane?
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[*] posted on 12-9-2008 at 04:54


Nah, such hydrocarbons are too non-poalr for an efefctive extraction, except for really non-polar compounds (terpenes?) etc.
I can be usefullw hen mixed with more polar solvents for selective extarctions, I think this is used for extracting complex plant material..




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[*] posted on 12-9-2008 at 05:51


Indeed, petroleum ether (hexanes, heptanes, etc.) can be used for extractions out of (moist) methanol since methanol does not mix with them in all proportions. This way it is possible to remove wax material, lipids, terpenes and similar nonpolar plant products from the rest, or extract these away from chlorophyl and other more polar constituents (depending on what you are after and what you want to remove). But at the last stage most extractions of plant constituents require chromatographic methods to obtain a specific compound in its pure state.



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[*] posted on 14-9-2008 at 04:45


Why don't you switch to methyl tert-butyl ether (MTBE)? This is a perfect solvent for extractions. I virtually never use Et2O, because it's too volatile and expensive. MTBE boils at 55 oC, as for toxicity and extracting ability it's comparable to Et2O. I prefer MTBE even to DCM, as DCM extracts too much tars and aliquation with DCM procceds much slower than with ethers.



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[*] posted on 14-9-2008 at 05:09


Fair point. I checked the prices, it hardly above DCM.

Unfortuanly, the suppier where I get all my cheap, technical solvents doesn't sell it, so I will have to go with the "usual suspects" (as Sauron would call them), but that"s the same with diethyl ether and DCM anyway..

IIRC, MTBE doesn't pose any peroxide hazard?




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[*] posted on 14-9-2008 at 05:42


http://www.sciencemadness.org/talk/viewthread.php?tid=10398&...
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[*] posted on 14-9-2008 at 11:58


Well, I don't know about peroxide from MTBE, but if it really doesn't form it, this fact can be rationalized - methyl forms radical fairly, while t-Bu doesn't at all.
Anyway, I actually don't understand these fears about ethers peroxides. I never heard from colleagues about explosions or something like that. We just use freshly supplied solvents and that's all. I think most chemists do the same.
As for MTBE at all, I think you should seek it somewhere else - it is a very popular antidetonator additive to gasoline. For example, we couldn't find it among solvent suppliers for years and finally bought it from petrochemical supplier.




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[*] posted on 26-9-2008 at 01:21


So heptane would only be usefull for TLC eluent but not for extracting small organic compounds like phenylnitrostyrenes and phenylalkylamines from reaction mixtures.
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[*] posted on 26-9-2008 at 02:27


You would need truely large amoutn sof solvents.... It can be used to selectivly extract some aldehdyes (for example) from some polymeric mess (Shulgin does that after a Vilsmeyer all the time), but immediatly on cooling the product cristillzes. So it really wouldn't be a good way to extarct these compounds from aqueous. Actually, the amine sin particuliar might even be more soluble in water than in low alkanes...

On the other hand, they can be used in certain Friedel-Crafts reactions, BuLi, etc and especialyl in column chromatography mixed in portions with more polar solvents (AcOEt, DCM for my favourite eluants).
I also use them very regularily for recrysatllizations, adding pet etehr slowly to a solution of you rproduct in a more polar solvent, and leaving ti diffuse: often get beautifull large crysatls, and very little left-overs. This trick can cause problems for mixture containing tarry material (as it often crashes out when enough pet ether is added), but in that case a premilary recrystn from a more polar system gets rid of the tar and the second one removes all the traces of impurities and forms large crystals..
Mixture like IPA/Pet ether, MeOH/Pet ether (use dry alcohol and small amounts, as they can seperate in two layers!) or even AcOEt/Pet ether work often very well for recrysatllizing amine salts (the last one is suitable for oxalates, not that much for inorganic salts unless some alcohol is added)

Considering they relative inertness, and often low boiling point, they cna often be seperated from traces of other solvents by some treatments: refluxing with aq. NaOh to remove traces of AcOEt, con. NaOh for DCM, aq. CaCl2 to remove IPA, etc and so make good candidates for easy recyling.

So low boiling alkanes are very usefull int he lab, but not that much for extarctions :)




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