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Author: Subject: Questions regarding the recycling of DCM
Klute
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[*] posted on 8-1-2010 at 05:34
Questions regarding the recycling of DCM


Like any concerned home-chemist should, I recycle my solvents.

My recuperation bottle of DCM is now full, so it's time for recycling. Unfortunaly, at one point I worked with sulfur compounds. The whole bottle stinks when open, of that so peculiar sulfide smell.. Now this DCM comes from destillations only, no washes, so it means the sulfides have gone through one distillation already, so I guess I'm not going to get rid of them by simple reflux over CaH2 and destillation... Even with a colum, there going to be enough in there to bare the smell..

So any ideas on how to remove them? I was thinking of a 20% NaOH wash, cold, or conc. H2SO4 as I recall it's used to remove sulfur compounds from toluene..

Any less wastefull ideas?




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[*] posted on 8-1-2010 at 06:14


Maybe a dumb idea but for some reason activated carbon came to mind.
A huge advantage of dcm would be that it is quite inert.
One should be able to treat it rough.

Maybe chlorination or strong oxidiser.


[Edited on 8-1-2010 by User]




What a fine day for chemistry this is.
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Klute
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[*] posted on 8-1-2010 at 07:16


oh yes, hypochlorite.. Even reflux over caclium hypochlorite? The CaCO3 might get dry enough also..

Well, anyway, I did a wash of 750mL of DCM with 250ml 80% H2SO4, but there was still the smell, though less, followed by 250mL 15% NaOH, which seemed to take off much more smell. Finally it's refluxing over CaH2, which should reduce all disulfides to thiols, and all thiols to non-volatil thiolates.. Distillation over CaH2 should give good enough DCM, which will only be used for extractions anyway.. Another 1, 750mL to go..




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smuv
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[*] posted on 8-1-2010 at 08:04


I am surprised you are using CaH2 to remove the disulfides (I didn't even know CaH2 was enough of a reducing agent to do this). Seems it would be more economical to just let it stir with some nitric acid or bleach followed by a water wash or two.

Now that you say it, its about time for me to reclaim my waste solvents...




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mr.crow
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[*] posted on 8-1-2010 at 12:18


How about using mercury to remove sulfides? I think it can break disulfides bonds.

Ok mercury is a bad idea. How about silver?
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Picric-A
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[*] posted on 8-1-2010 at 12:32


Sodium amalgam is good at removing organo-sulphides, we got shown it once as a demo in school

Edit- It was liquid Na amalgam so i guess ~ 5-10% Na.

[Edited on 8-1-2010 by Picric-A]
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DJF90
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[*] posted on 8-1-2010 at 12:39


Klute: I too am suprised at your use of CaH2 to "reduce" the disulfides; As I understand it the hydride ion H(-) is very hard and acts only as a base (i.e. it has no reducing capability unlike the complex hydrides). Something you might want to try if you are sure that the stench is due only to disulfides is to add some acetone/cyclohexanone and NaOH; the enolate that forms reacts with the disulfide to form a sulfide. Using cyclohexanone will be your best bet as the product will boil at a much higher temperature than the DCM. If you still have problems with it distilling over, oxidise the produced sulfide to the sulfoxide/sulfone.
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sonogashira
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[*] posted on 8-1-2010 at 14:20


I believe zinc is good at reducing sulfides, but whether it is useful in this case I would not say for sure.

Or magnesium perhaps? It is known that grignard in DCM is possible, so perhaps one can use magnesium as the reducing agent - if it you feel it is better to do this than oxidation.
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[*] posted on 8-1-2010 at 14:49


Metal powders and halogenated hydrocarbons have been used as rocket fuel. Proceed with caution.
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[*] posted on 8-1-2010 at 14:52


Zinc should be fairly safe in this context, as diiodomethane is required for reaction with Zn (see simmons-smith cyclopropanation). However I didnt realise zinc would reduce sulfides; any idea what the product is Sonogashira? Klute: Any idea exactly what is causing the smell? I recall you doing some work on thiophenols/diphenyldisulfides; could this be the culprit?
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Klute
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[*] posted on 9-1-2010 at 05:36


Well, it worked out just fine, no more smell whatsoever in the distilled DCM.. I'm pretty sure thiols were the problem, with possibly dissolved H2S.. Now these could have oxidized to disulfides, but it seems CaH2 got rid of everything. The NaOH washes whee the most efficient, calcium hypochlorite formed a monstrous emulsion beacuse of all the undissolved fine solids..

I just used CaH2 because that's what we use at work to dry DCM, and I have 100g of it.. Indeed it's more a base than a reducer though..

Any ideas regarding stabilizing the DCM? I was thinking of methanol because I don't have any BHT.. What % would be efficient?

Thanks for the replies, guys (and gals?)

EDIT:

Yeah, it's from the time I worked with S2Cl2 and thiophenols/disulfides.. Contaminated the whole bottle (2,5L) of recycled DCM.. I'ev finally finisehd the last portion of DCM, happily refluxing over CaH2, and tada 2,5L of fresh DCM for free! The damn suppliers sell these bottles at 40e.. Hopefully, I found a source for very cheap solvants, though you need a SIRET number to order from them.. 5L DCM for 10e whouhou!

[Edited on 9-1-2010 by Klute]




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[*] posted on 9-1-2010 at 07:04


Why would you stabilise dichloromethane? DCM does not need to be stabilised, chloroform does.

Oh and have you started home chemistry again? :P
I see you are also buying new chems. Ethyl bromoacetate? That will make you cry like there is no tomorrow :(

[Edited on 9-1-2010 by Jor]
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Klute
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[*] posted on 9-1-2010 at 08:08


I imagine it does as all the bottles at work are either stabilized by amylene or methanol..

And yes, I'm back in the south, and setting the lab back up :P

Hopefully pretty soon there will be more reports of the synthesis of various synthetic aromas from me!! ;)




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DJF90
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[*] posted on 9-1-2010 at 09:48


I dont think I've ever seen DCM stabilised! Interesting though...
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Klute
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[*] posted on 9-1-2010 at 09:57


That's curious, I don't think I've ever seen DCM not stabilized! :)



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[*] posted on 9-1-2010 at 11:43


Well I'll be damned! Upon looking a Sigma Aldrich, it appears it IS stabilised! I've never noticed it written on the bottle though, but I've never had to use the stock bottle in the lab. Very intriguing... Any idea what its stabilised FOR?

http://www.sigmaaldrich.com/chemistry/solvents/dichlorometha...
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