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Author: Subject: Salting out alcohols
beeludwig
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[*] posted on 7-5-2019 at 06:59
Salting out alcohols


I'm trying to salt out alcohols either a 50:50 mix of ethanol or isopropanol and neither is working. It is one of the simplest procedures in chemistry and I'm not sure what's going wrong.

I created a 1:1 ratio of anhydrous ethanol and tap water and mixed them together. Then I added table salt until no more would dissolve. Then I mixed them up but there's been no separation of layers. Is there something in the tap water or in the table salt that's interfering? But I can't think of any reason for it. One time I tried making a saturated salt solution first and then mixing, but the salt precipitate out instead of the ethanol. I feel like I'm missing something blindingly obvious. Any ideas?
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woelen
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[*] posted on 7-5-2019 at 07:19


I think that NaCl is not sufficiently soluble. Try with adding NaOH. E.g. take 5 ml of isopropanol, 5 ml of water, mix, and then add solid NaOH. Probably you salt out some of the isopropanol.



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happyfooddance
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[*] posted on 7-5-2019 at 08:22


For ethanol, use potassium cation salt (K2CO3, KCl).

For isopropanol, use sodium cation salt (NaOH, NaCl).

With a 50/50 etOH/water you will need to use a very large proportion of salt, and it will be well worth your time to powder it finely.
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MrHomeScientist
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[*] posted on 7-5-2019 at 08:23


NaOH has worked for me. To dehydrate 91% isopropanol (IPA), I added in a good amount of NaOH (10's of grams to a regular store-bought bottle of IPA) and shook for a few minutes. The hydroxide pulls out almost all of the water into a separate layer that can be easily removed. You then have to distill the IPA to get rid of the NaOH, and the result is very pure and very dry alcohol.
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