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Chris The Great
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[*] posted on 20-6-2006 at 16:52
Complexing methanol


I read, somewhere on this forum (couldn't find the post by searching) that come anhydrous salts are unsuitable for drying ethanol, as they not only form a complex with water but also form a complex with the ethanol.

I assume the salts would also form a complex with methanol easily if they form one with ethanol.

I would be grateful if anyone could tell me what these salt(s) are.

They would be very useful for removing methanol completely from mixtures where it should not be and cannot be easily distilled from, for example methylene chloride distilled from paint remover which contains a few % methanol afterwards, or methyl nitrate which may contain some residual un-nitrated methanol after washing and drying.
I have both of those and thought of this a little while ago when pondering about further purification of these two chemicals.
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The_Davster
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[*] posted on 20-6-2006 at 17:20


http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/e...
Calcium chloride is the most common. I got a sack of it anhydrous from Rona recently.




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Chris The Great
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[*] posted on 20-6-2006 at 17:25


Thanks a lot :D I'll check next time I'm there.
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chromium
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[*] posted on 20-6-2006 at 22:23


Russian "Spravochnik himika Tom 3, 1965": Has table about solubility of various salts in methanol and about complexes they form when crystallised at particular temperature.

First column contains temperature, secund is solubility ( g/100g ) and third is quantity of methanol molecules that get locked into crystal latice for each salt molecule when compound crystalises out.

You can find there that Ba(NO3)2 does not form complexes with methanol at least if temperature is over 0C and less than 60C, and CaCl2 forms Ca(Cl)2*3CH3OH even at temperatures as high as 170C.

I suppose that these data may or may not hold if other substances are present. Nevertheless this is good basis for experimenting.

Edited for spelling and that solubility is not reported grams for 100ml (as i mistyped earlyer) but as grams for 100g of solvent

[Edited on 21-6-2006 by chromium]

Attachment: methanol.pdf (66kB)
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Chris The Great
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[*] posted on 20-6-2006 at 23:02


I see magnesium sulfate in there... hmmm

I think making a methanol solution in toluene, then adding the salt and sealing it, will work. If the methanol is absorbed, the crystals will get heavier, by a very noticable amount.
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chromium
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[*] posted on 21-6-2006 at 00:03


Quote:
Originally posted by Chris The Great
I see magnesium sulfate in there... hmmm


Look at solubility. Extracting any remarkable quantities of methanol with Mg(SO4)2 should take lot of time.

Edit1: I suppose that if some water is present then this does not occur at all becasue Mg(SO4) gets complexed with water. But i do not know.

Edit2: I now looked at similar table for ethanol. In case of ethanol there are no complexes with Mg(SO4)2



[Edited on 21-6-2006 by chromium]
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agent_entropy
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[*] posted on 2-8-2006 at 10:31


About, using CaCl2 and the like to remove water/methanol from a mixture... In what form must it be used? It seems to me that as a solid it wouldn't be able to form complex ions, but in a solution wouldn't it already be complexed?
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[*] posted on 2-8-2006 at 13:36


Just like using CaCl2 to pull water out of some organic solvent. You get the complex formation at the surface of the solid, which is why you want drying agents in forms that have a good amount of surface area.

If there is only a small amount of the complexing solvent, say H2O or MeOH, it forms solid complex at the surface. If there is a lot, the CaCl2 or whatever goes into solution. A small amount in some DCM will leave a solid mix of CaCl2 + H2O/MeOH, a lot will give a liquid layer of CaCl2 + H2O/MeOH.
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