Sciencemadness Discussion Board

Dried my DCM and now I have some tiny bubbles on the bottom, are these peroxides?

alking - 3-5-2016 at 18:16

I have some DCM, which has recently been distilled btw so there has not been any real time to form peroxides, but as I was distilling this again I noticed these odd bubbles and became concerned. I've stopped the distillation to make sure I haven't done anything dangerous. It is possible it's just some suspended air, but I don't want to risk it until I get confirmation. I will say that I see nothing when not heated which makes me lean towards that, but I don't recall seeing heavy bubbles like that before.

So I have about 400ml of DCM that has been distilled within a week. It contained some water, methanol, and hcl so I washed it with water to get most of the methanol and hcl out and then dried it over MgSO4 and a bit of NaOH to remove what remained. After drying I filtered off the MgSO4 and began to distill it. Not long after it heated up I noticed a small bubble or two swirling around the bottom (bigger than all of the tiny bubbles formed by boiling though), apparently more dense than the DCM. I can't believe peroxides have formed so quickly, but what else could this be, or if air why the weird behavior? My glasswear was clean and dry, and I have not worked with any solvents heavier than DCM that could float on the bottom anyway. Have I done something I should not have? If this is peroxide formation could I safely filter it through some alumina to remove it or is it too dangerous to even bother handling and if so what should I do with it then?

alking - 3-5-2016 at 18:49

It was just some MgSO4 that formed spherical clear clumps giving the appearance of bubbles; I did not filter well enough : /. Maybe it was in there when it was cool and I just didn't see it then, but I realized because as it sat it started to combine together and it became obvious it was a solid.

macckone - 3-5-2016 at 19:28

DCM does not form peroxides fyi for future reference.

BromicAcid - 4-5-2016 at 03:35

Quote: Originally posted by macckone  
DCM does not form peroxides fyi for future reference.


But it's still worth noting that there are stabilizers present in purchased material, just not to stabilize against peroxides (as far as I know).

j_sum1 - 4-5-2016 at 03:40

AmI the only person who read this as:
Subject: Dried my DCM and now I have some tiny bubbles on my bottom, are these peroxides?

[smirk]

alking - 4-5-2016 at 05:41

Oh, that is good news then. What do the stabilizers protect against? I could swear I've read otherwise but maybe I'm either confused or misinformed.

aga - 4-5-2016 at 07:38

Quote: Originally posted by j_sum1  
Am I the only person who read this as:
Subject: Dried my DCM and now I have some tiny bubbles on my bottom, are these peroxides?

Yes.

The relevant authorities have been informed.

solitanze - 4-5-2016 at 08:28

DCM slowly decomposes to HCl and phosgene (bad!) if I recall correctly, usually it is stored with a few anhydrous potassium carbonate pellets.

Deathunter88 - 4-5-2016 at 10:15

Quote: Originally posted by solitanze  
DCM slowly decomposes to HCl and phosgene (bad!) if I recall correctly, usually it is stored with a few anhydrous potassium carbonate pellets.


I think DCM can only form phosgene and HCl upon combustion or exposure to high heat. You might be thinking of chloroform.

BromicAcid - 4-5-2016 at 13:01

I think the stabilizers are there to protect metal and to prevent the formation of HCl. Can someone chime in on this?

alking - 4-5-2016 at 13:25

Quote: Originally posted by solitanze  
DCM slowly decomposes to HCl and phosgene (bad!) if I recall correctly, usually it is stored with a few anhydrous potassium carbonate pellets.


That does sound familiar actually, I must have misremembered.

Quote: Originally posted by Deathunter88  
Quote: Originally posted by solitanze  
DCM slowly decomposes to HCl and phosgene (bad!) if I recall correctly, usually it is stored with a few anhydrous potassium carbonate pellets.


I think DCM can only form phosgene and HCl upon combustion or exposure to high heat. You might be thinking of chloroform.


What exactly constitutes high heat though? DCM boils at <40c so it doesn't take much, or are we talking further heating in the gaseous stage or from increased pressure?

Deathunter88 - 4-5-2016 at 19:13

I think high heat as in the vapor passed through a flame, or the vapor itself heated to very high temperatures.

Washing Alcohols from Dichloromethane, is it feasible?

alking - 7-5-2016 at 06:42

I posted here months ago now asking how I could clean up my DCM and I have read of others doing so by washing methanol out with water, drying, and then distilling to get pure DCM. I have done it previously and since, but I never really did anything to check the purity. However I just did a solubility test with some 70% isopropanol, 5ml of each, and the results lead me to believe it's really not. Of 10ml total I now have two layers, the bottom one is 8ml and the top one about 2ml. This leads me to believe that the alcohol rather strongly prefers the dcm layer.

I have not tried saturating the water with NaCl yet, but this is already contrary to what I've been lead to believe so I want to get some input. I should still be able to purify the DCM by using a drying agent such as CaCl2 as it will also hold the alcohol I would think. I commonly use CH2Cl2 and alcohols in the lab resulting in cocontamination, so I'd like to find an efficient way to recycle at least the DCM, being the more expensive and less environmentally safe, if not both.

blogfast25 - 7-5-2016 at 07:40

You may be pushing it with IPA.

Just look at the log P values of a few alcohols:

MeOH = - 0.69
EtOH = - 0.16
1-PrOH = + 0.329

The more negative the value, the more the solute tends to accumulate in the water. Remember it's a log scale.

IPA may not be hydrophilic enough to easily extract from a DCM solution with water as the extracting solvent.

And DCM shows some affinity (solubility) to water, it's not as non-polar as octanol.


[Edited on 7-5-2016 by blogfast25]

clearly_not_atara - 7-5-2016 at 08:12

Sodium pyrosulfate should do the trick, I think.

Na2S2O7 + ROH >> NaHSO4 + NaROSO3

Both salts are insoluble in DCM. Sodium pyrosulfate is made by heating sodium bisulfate at 300 C for several hours. There's info on it sonewhere.

I'd suggest distilling, then extracting alcohol with water, distilling again, and finally removing any remaining alcohol with pyrosulfate.

DFliyerz - 13-5-2016 at 11:42

Personally, I think that the best stabilizer choices for DCM are ethanol, methanol, and (if you can get it somehow) amylene.