I was recycling solvents like usual, but this time needed really pure DCM, so instead of just distilling it, I did the complete purification procedure
(according to Armarego, "Purification of Laboratory Chemicals"):
Quote:
Shake it with portions of conc H2SO4 until the acid layer remains colourless, then wash with water, aqueous 5%
Na2CO3, NaHCO3 or NaOH, then water again. Pre-dry with CaCl2, and distil it from CaSO4, CaH2 or P2O5.
The DCM was very dirty so I distilled it first, observing rise of temperature several degrees over boiling point of DCM (39 °C) by last third of
distillation.
The distillate was clear but conc. sulfuric acid washes turned dark red, then orange, then yellow. Even the fourth wash was still yellowish and I
ended there. I washed with dH2O, then with 5% NaOH (no discoloration) and then with dH2O. The solvent turned cloudy in the process.
Finally, added CaCl2 clumped immediately and the solvent became crystal clear (the clouding was probably water?). However, adding more CaCl2 so that
no more clumping happen gave the solvent a pink tint.
The image shows state the next day. I plan to filter it and fractionally distill again, hoping the pink stuff are higher boiling impurities.
The DCM have been used for eugeon isolation from clove oil, so it seems some volatile components from oil (predominantly eugenol) are the impurities.
This would explain redding of sulfuric acid possibly pulling the oil out of the solvent.
However it seems the purple stuff has settled on bottom overnight so it is likely a precipitate.
Any further ideas?
[Edited on 8-9-2018 by nimgoldman]
Tsjerk - 8-9-2018 at 07:59
I could imaging there are alcohols or ketones there that polymerize due to the sulfuric acid. They usually turn red when that happens. Maybe the red
goo dissolved a bit in the DCM and precipitates when the solvent becomes too dry?
If the colored stuff is composed of polymers you should be able to get rid of them by distillation easily.
Edit ; whatever it is, distillation should help getting rid of it.
[Edited on 8-9-2018 by Tsjerk]macckone - 8-9-2018 at 08:22
That looks like it needs a filtration then redistilled.
I agree with Tsjerk.
Something carried over then polymerized.nimgoldman - 8-9-2018 at 08:38
I filtered it and some of the pink stuff mixed with drying agent stayed on filter (looks like a cotton candy :-) ) and the filtered DCM stays pink.
However I used just an ordinary quantitative filter paper.
I am going to fractionally distill it with temperature control and see.
[Edited on 8-9-2018 by nimgoldman]fusso - 8-9-2018 at 21:32
Can piranha solution destroy DCM? If no then it may be a possible way to purify it.Sulaiman - 9-9-2018 at 00:23
maybe there is a clue in the first line of the procedure;
"Shake it with portions of conc H2SO4 until the acid layer remains colourless"
and your comment;
"Even the fourth wash was still yellowish and I ended there. " nimgoldman - 9-9-2018 at 13:19
maybe there is a clue in the first line of the procedure;
"Shake it with portions of conc H2SO4 until the acid layer remains colourless"
and your comment;
"Even the fourth wash was still yellowish and I ended there. "
Yes, likely, but I spoiled over 200 ml of conc. acid and it was still yellowish though faintly. The purification procedure does not specify how clear
the acid should be as it might never be pristine, even if I spoil entire bottle of H2SO4.
Hence I resorted to less superpure DCM and saving the precious reagent grade acid (the fresh bottle of DCM is actually cheaper than the acid at that
point).
I was just interested what the purple coloring could be since the solution was clear, then white-cloudy, then clear and then it turned purple, which
is interesting considering the only thing turning it purple was addition of an drying agent (pure CaCl2). Even after that it was clear but after
adding excess of CaCl2 to ensure dryness, it turned blue. Like if there is some compound clearless when dissolved in water but purple when forced into
DCM.
[Edited on 9-9-2018 by nimgoldman]MrHomeScientist - 10-9-2018 at 05:39
Shot in the dark: Was your calcium chloride drying agent the indicating type? You mention the solvent turning both pink and blue after adding it,
which are the colors of the cobalt chloride indicator.nimgoldman - 17-9-2018 at 12:50
Shot in the dark: Was your calcium chloride drying agent the indicating type? You mention the solvent turning both pink and blue after adding it,
which are the colors of the cobalt chloride indicator.
No I never observed color change from this particular batch of calcium chloride. It's reagent grade and the bottle does not specify any additives.
I dried DCM with it in the past without this effect so the coloring most likely come from some of the last experiments (e.g. eugenol isolation).macckone - 17-9-2018 at 13:19
If your first distillation was a simple distillation with no column things could definitely carry over. Redistilling with a packed column would be
the way I would go.happyfooddance - 18-9-2018 at 12:23
If your first distillation was a simple distillation with no column things could definitely carry over. Redistilling with a packed column would be
the way I would go.
Also drying it first (over Mg or Na sulfate), will help tremendously. I do a lot recovery of solvents from extractions of essential oils, and this
makes a huge difference for me. And definitely use a suitable column (for DCM you can use a big one) like mentioned.JJay - 18-9-2018 at 13:26
Is it possible that the DCM is leaching dyes out of the cap?Tsjerk - 18-9-2018 at 22:44
I know these caps and they are fine in combination with DCM. They can handle most solvents for at least years.
Edit: they are completely made out of teflon
[Edited on 19-9-2018 by Tsjerk]nimgoldman - 19-9-2018 at 14:14
