Sciencemadness Discussion Board

Ether and DCM, OTC

JJay - 20-10-2015 at 02:35

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.

Dr.Bob - 20-10-2015 at 04:15

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.

JJay - 20-10-2015 at 23:10

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.

Deathunter88 - 20-10-2015 at 23:33

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]

JJay - 30-10-2015 at 03:48

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]

gdflp - 30-10-2015 at 06:07

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.

JJay - 30-10-2015 at 08:19

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.


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.

chemrox - 30-10-2015 at 10:03

[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]

Detonationology - 30-10-2015 at 10:11

Quote:

what is a stabilizer for DCM?

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.

JJay - 30-10-2015 at 10:43

I have discarded the low-boiling substance (just a few drops), but it looks like it was probably 1-pentene.

Rocket89 - 30-10-2015 at 10:47

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?

JJay - 30-10-2015 at 14:20

I think adding EtOH to the final product is a better idea since it allows you to control the concentration of stabilizer.

UC235 - 30-10-2015 at 14:29

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.

gdflp - 30-10-2015 at 14:41

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...

aga - 30-10-2015 at 14:47

Wow ! now there's something else i did not know.

Even DCM arrives impure.

JJay - 30-10-2015 at 14:53

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.

JJay - 30-10-2015 at 17:44

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.

JJay - 30-10-2015 at 17:50

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.

JJay - 30-10-2015 at 23:38

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....

JJay - 1-11-2015 at 22:11

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.

UC235 - 1-11-2015 at 22:42

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?

JJay - 1-11-2015 at 23:31

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.

JJay - 1-11-2015 at 23:42

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.

JJay - 6-11-2015 at 23:06

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....

Deathunter88 - 6-11-2015 at 23:15

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.

JJay - 6-11-2015 at 23:31

Quote: Originally posted by Deathunter88  
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.


Good point... it's looks likely from here (and someone who knows more about calcium chemistry than I do, please feel free to speak up) that dehydration is a competing process and CaCl2 monohydrate may be tremendously less effective at removing methanol than anhydrous CaCl2.

[Edited on 7-11-2015 by JJay]

gdflp - 7-11-2015 at 07:56

Yes, the reason for this is that the calcium chloride is not reacting with water or methanol, rather it is complexing with both of them. If a calcium chloride molecule has already complexed with two water molecules, it is unable to complex with any more molecules of either water or methanol(Technically it does form a hexahydrate, but this is reasonably unstable; I prefer to assume that it can only form a dihydrate when calculating how much drying agent is needed). Alternatively, if a calcium chloride molecule has complexed with two methanol molecules, it is unable to absorb any more water or methanol. I could believe that anhydrous calcium chloride would much more readily absorb methanol molecules than calcium chloride monohydrate.

JJay - 7-11-2015 at 11:16

Perhaps I will try further dehydrating the calcium chloride... that looks like a messy procedure....

JJay - 11-11-2015 at 02:51

Drying the CaCl2 at 300 C produced very little physical change in the CaCl2, but allowing the DCM to stand over a large quantity of CaCl2 for a few days appears to have removed nearly all of the methanol. I'm still waiting on getting some dichromate to perform a more conclusive test.

I've noticed a fairly disturbing trend in that that every time I distill DCM I have a nosebleed the next day, so today I wore a respirator during the smelly parts and added 1% ethanol to the final product.

I'm thinking about distilling some ether as soon as I find a suitable container for storing it.

[Edited on 11-11-2015 by JJay]