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JJay
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Ether and DCM, OTC
I have most of the reagents I need for a project that I've been wanting to do for a long time, but I don't have any ether or DCM.
I believe that distilling DCM from OTC sources should be fairly straightforward. I figure I'll fractionally distill it slowly, with a column. I'll
probably get some methanol too. I should add 1% ethanol to the DCM for storage, correct? Do I need to take any stabilization measures with the
methanol?
I think distilling ether is going to be a little trickier. Is it safe to distill ether in air, or should I do it in nitrogen (I can get nitrogen, but
it's a PITA)? I think I should store the ether on molecular sieves (I have 3A) with a piece of copper, but I'm not sure if the copper is necessary.
Does ether need to be stored with copper if it is stored with molecular sieves?
I am pretty sure I'll get some n-heptane too. I think that can be stored without any special stabilization.
I plan to double or triple distill each solvent and avoid distilling any of these solvents to dryness, discarding the front part of each run. I figure
I'll store them in metal cans (except for the methanol - plastic is ok for it).
Comments and advice are appreciated.
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Dr.Bob
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Sounds like a good plan. DCM does best with a stabilizer for long storage. Ether mostly needs storage avoiding water and oxygen, you could distill
under air, but better to do under N2 if you plan to store it. Don't normally see copper in ether. N-heptane ansd other hydrocarbons are find
without any stabilizers. And methanol is quite stable, and most plastics are fine for it.
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JJay
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It looks like maybe I should avoid storing ether.. I think I can just use DCM for my current project, but I have one planned that will require
ether... I don't expect to get to it for a few months, so maybe I'll just hold off on the ether for now.
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Deathunter88
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Quote: Originally posted by JJay  | | It looks like maybe I should avoid storing ether.. I think I can just use DCM for my current project, but I have one planned that will require
ether... I don't expect to get to it for a few months, so maybe I'll just hold off on the ether for now. |
Buy and store the ether, you don't know when you will find it useful. Add a few pellets of sodium or potassium hydroxide and no more peroxide worries.
Also removes the water so it is a win-win.
[Edited on 21-10-2015 by Deathunter88]
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JJay
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I ran my first distillation to separate DCM from paint stripper. A few drops of an unknown substance came over at around 30 C; the substance appears
to be a petroleum distillate (floats on water), but no petroleum distillate products appear on the label (just DCM and methanol).... Most of the
distillate came over at around 36 C; all liquids that distilled between 36 C and 46 C were collected. I don't have a distilling receiver, so I simply
used a separation funnel to collect the fractions, opening and closing the stopcock when changing the flask connected to it.
Quite a bit of wax left in the boiling flask when the distillation was completed... it wasn't easy to remove, but I managed to clean it out with
solvents, heat, and scrubbing.
The next step will be to wash the DCM with water to try to remove methanol, and then I plan to dry the DCM over MgSO4 (previously dehydrated) and
distill. If the distillation rate indicates that the product is relatively pure, I will store it over molecular sieves. Otherwise, I will repeat the
final washing/distillation steps.
[Edited on 30-10-2015 by JJay]
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gdflp
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Several recommendations. Firstly, dry the DCM over CaCl<sub>2</sub> instead of MgSO<sub>4</sub> since it complexes with lower
alcohols and will remove any methanol remaining after the water wash as well as removing water. Then some ethanol or pentene should be added to the
DCM since it will photocatalytically oxidize to phosgene over extended periods of time. The ethanol or pentene will react with the phosgene to
produce harmless products. Storing over molecular sieves is a good idea, though unnecessary if you're only using the DCM for extractions.
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JJay
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| Quote: Originally posted by gdflp | | Several recommendations. Firstly, dry the DCM over CaCl<sub>2</sub> instead of MgSO<sub>4</sub> since it complexes with lower
alcohols and will remove any methanol remaining after the water wash as well as removing water. Then some ethanol or pentene should be added to the
DCM since it will photocatalytically oxidize to phosgene over extended periods of time. The ethanol or pentene will react with the phosgene to
produce harmless products. Storing over molecular sieves is a good idea, though unnecessary if you're only using the DCM for extractions.
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Sounds good. I have a large quantity of CaCl<sub>2</sub>, and unlike MgSO<sub>4</sub>, it doesn't require any special
preparation. I will add 0.5% (or whatever ACS grade calls for) ethanol to the DCM for storage.
I have an abundance of molecular sieves, and I think that keeping the DCM completely anhydrous could prevent rust from forming in the storage
container, so I will use them.
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chemrox
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[rquote=/]Sounds like a good plan. DCM does best with a stabilizer for long storage. Ether mostly needs storage avoiding water and oxygen, you
could distill under air, but better to do under N2 if you plan to store it. Don't normally see copper in ether. N-heptane ansd other hydrocarbons
are find without any stabilizers. And methanol is quite stable, and most plastics are fine for it.[/rquote]
Bob, what is a stabilizer for DCM?
[Edited on 30-10-2015 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Detonationology
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| Quote: |
what is a stabilizer for DCM?
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Lower alcohols (MeOH, EtOH, and I think IPA) added 1-3% by weight to DCM and chloroform will prevent the formation of phosgene over time. I also
recommend to store it in a dark bottle in the fridge if you can.
“There are no differences but differences of degree between different degrees of difference and no difference.” ― William James
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JJay
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I have discarded the low-boiling substance (just a few drops), but it looks like it was probably 1-pentene.
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Rocket89
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So if lower alcohols stabilize DCM, would it be beneficial to NOT remove all of the MeOH? Instead of, say, washing with dH2O, and separating, followed
by addition of a % by weight amount of High proof EtOH (Everclear and Spirytus <-- readily available for me) to the mix with CaCl2?
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JJay
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I think adding EtOH to the final product is a better idea since it allows you to control the concentration of stabilizer.
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UC235
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If DCM needs a stabilizer, I've never seen one added. Chloroform and ether absolutely need one. I'd keep it in dark glass and in a cool spot and don't
sweat it too hard.
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gdflp
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Every grade of DCM which Sigma sells contains 50ppm amylene as a stabilizer, I think that the fact that it needs one is simply less popular knowledge
than the fact that chloroform needs one. http://www.sigmaaldrich.com/chemistry/solvents/dichlorometha...
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aga
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Wow ! now there's something else i did not know.
Even DCM arrives impure.
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JJay
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Amylene is less likely to interfere with the various uses of DCM than EtOH, but I didn't know what it was... if I ever see any more amylene
(1-pentene), I'm going to keep it to use as a stabilizer.
The stripper was Klean Strip Premium Sprayable Stripper.
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JJay
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The azeotropic methanol is proving to be a little harder to remove than I expected. I washed the DCM 5x with 200 mL water. During the first wash, the
DCM took on a cloudy appearance that diminished with each successive wash. I then dried it over CaCl2. So far, about 200 mL of distillate have come
over, and it all came over at 37 C, meaning that it's a 7% methanol azeotrope....
Nile Red claimed to be able to remove the methanol. The only thing I can see that he did differently that might make a difference involved the use of
brine to break an emulsion.
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JJay
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Also, my molecular sieves are 3A, so they won't remove methanol. 4A can, but it would take a lot of sieves to do that, and most people don't have
sieves anyway.
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JJay
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I stirred the DCM with brine for a while and am letting it stand overnight on CaCl<sub>2</sub>. Hopefully it will distill sans methanol
tomorrow. Now I am vacuum distilling glycerine....
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JJay
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I had no luck removing the methanol with brine and CaCl<sub>2</sub>. I tried some more water rinses, and the DCM is still distilling at
just under 38 C. Short of using 4A sieves to remove the methanol, I'm running out of ideas.
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UC235
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Have you considered the possibility that you are distilling the water azeotrope and/or that an inaccurate thermometer, improper placement in the
stillhead (or improper immersion length), and variable atmospheric pressure can all change a b.p. a degree or two one way or another?
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JJay
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I've calibrated the thermometer; it's not very precise, but it is highly accurate. It's a partial immersion thermometer. I've positioned it a few
places within the still head, and if anything, the temperature where it is now would be too high. The thermometer only has graduations every two
degrees, but the mercury is 3/4 of the way above 36 (so the temperature is 37.5 C really, but that's just too many significant digits for the humble
manufacturer of this quality thermometer).
Air pressure here is barely below 760 mm Hg. I did dry the DCM over CaCl<sub>2</sub> prior to distilling. I think it's pretty dry.
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JJay
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I might try obtaining some sodium dichromate and doing an alcohol test... but considering the temperature of the distillation, I am pretty darn sure I
know what the results would be.
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JJay
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Well, I'm still waiting for my dichromate order to arrive, but I did have a breakthrough - I let the DCM sit for a few days on a larger quantity of
CaCl2 than I usually use, and the tail end of the run came over at just under 40 C - so it looks like dehydrating it does work for removing the
methanol... my CaCl2 is likely not completely anhydrous....
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Deathunter88
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| Quote: Originally posted by JJay | | Well, I'm still waiting for my dichromate order to arrive, but I did have a breakthrough - I let the DCM sit for a few days on a larger quantity of
CaCl2 than I usually use, and the tail end of the run came over at just under 40 C - so it looks like dehydrating it does work for removing the
methanol... my CaCl2 is likely not completely anhydrous.... |
That is not the CaCl2 dehydrating the alcohol out of the DCM, it is more that CaCl2 is reacting with the alcohol.
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