organicchemist25
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ACS grade 200 proof Ethyl Alcohol
I have done some searching, and would still like to know if 200 proof ethyl alcohol will absorb moisture from the air?
I know about alcohol and H2O's azeotrope, but will 200 proof just absorb moisture from the air to obtain the natural azeotrope with alcohol and the
H2O?
The test date on my gallon of 200 proof EA is 2016.
I just want to know if its a major concern or not, since the 200 proof EA is so expensive.
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UnintentionalChaos
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Yes, anhydrous ethanol is agressively hygroscopic and will absorb water from the air rapidly.
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'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Nickdul
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I'm not sure if anhydrous copper sulfate can be used to detect water in minute quantities; but is a quick way to ensure that it has not absorbed a lot
of water. Maybe cobalt chloride?
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Tsjerk
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Have a look at this article: I don't know if you have access from where you are now, I don't at least, but the abstract looks good.
http://onlinelibrary.wiley.com/doi/10.1002/jccs.200700089/ab...
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ZIGZIGLAR
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"Water can be qualitatively detected down to 500 ppm by the formation of a precipitate when
aluminum ethoxide in benzene is added to a sample of the ethanol . Quantitative determination of water is carried out by Karl Fischer titration. An
automated coulometric Karl Fischer titration has been described (ref. 2) that has a limit of determination of 5 ppm. Some
corrmercial instruments have by now an even better performance."
REFS:
1. Anon., Merck Standards, Merck, Daxmstadt, 1971.
2. A. S. Lavrenova, I. P. Ogloblina, V .A. Fedorov, N.P. Kuznetsova, Metody Anal. Khim.
Reaktivov Prep., 18, 39 (1971); C.A. 77, 147 319 j.
Anhydrous absolute ethanol will most likely reduce to around 99.5% purity if exposed to the atmosphere. I think it's best to store it on 3A molecular
sieves with minimal headspace in the reagent bottle and obviously best to transfer under inert gas where possible. If not, you might as well buy 99.5%
grade and save some money.
[Edited on 19-2-2014 by ZIGZIGLAR] Had to correct some spelling errors from a bad OCR conversion, sorry.
[Edited on 19-2-2014 by ZIGZIGLAR] http://en.wikipedia.org/wiki/Karl_Fischer_titration
[Edited on 19-2-2014 by ZIGZIGLAR]
[Edited on 19-2-2014 by ZIGZIGLAR]
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feacetech
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Or keep some sodium wire in the bottle to keep the ethanol dry
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TheChemiKid
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That would not work in the slightest. Sodium reacts with ethanol!
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subsecret
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Keeping elemental sodium in ethanol will form sodium ethoxide, IIRC.
2 CH3-CH2-OH + 2 Na -> 2 CH3-CH2-ONa + H2
Vogel's Practical Organic Chemistry states that MgSO4 and CaSO4 are drying agents well-suited for alcohols.
Speaking of which, here's a table of drying agents...
Fear is what you get when caution wasn't enough.
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ZIGZIGLAR
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As listed above, quicklime or CaO is the most widely used dessicant for Ethanol, but, for storage purposes, you want something that isn't miscible,
like molecular sieves. Ethoxide is pretty useful, but not when you actually want anhydrous ethanol for impurity sensitive reactions.
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