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