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Runningbear
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Drying IPA - easiest method
I want to dry IPA (91% ethanol) using a drying agent. Preferably something I can heat or buy dry, that can be added to the bottle and will store OK in
the bottle for use at a later date.
And I want to be relatively certain I have about 99% pure ethanol.
Can anyone suggest the best drying agent(s) to use for this purpose? Is 99% purity realistic without distillation and drying combined?
There are plenty of threads on drying agents here but none address my specific requirements.
thanks in advance,
Runningbear
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JohnWW
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It is not clear whether what you have is isopropyl alcohol or ethanol.
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Runningbear
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Sorry, I said ethanol but it is in fact C3H8O.
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Skyjumper
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IPA = Isopropyl alcohol (:
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entropy51
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You sure about
that, bear?
Quote: Originally posted by leu  | JACS 54 1445 (1932)
Note on the Preparation of Absolute Isopropanol
BY LEWIS E. GILSON
During several years of biochemical research the writer has found many instances where isopropanol could be substituted for ethanol in laboratory
work. It is cheap and there are no restrictions governing its use; nor is it likely to be an object of theft. The commercial 91% azeotropic mixture
was used instead of 95% ethanol and found to be fully equal or superior to the latter as a solvent or extracting medium. Absolute isopropanol was used
in place of absolute ethanol.
Absolute isopropanol is easily prepared. The 91% grade is shaken with 10% of its weight of commercial flake sodium hydroxide, separated from the
aqueous layer which forms, then shaken with a little more sodium hydroxide, decanted and distilled. The product obtained mixes with eight volumes of
carbon disulfide, xylene or petroleum ether without the slightest trace of turbidity.
Dilute isopropanol can be concentrated by shaking with dry sodium chloride. Water is removed as a saturated layer of brine. The upper layer contains
about 87% isopropanol and 2-3% of sodium chloride. While distilling, an additional quantity of brine separates. The distillate has so nearly the
composition of the 91% azeotropic mixture that it can be used as such without further treatment. Or, after shaking the dilute isopropanol with sodium
chloride and separating, it can be treated directly with sodium hydroxide and the absolute grade prepared.
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Runningbear
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thanks entropy51, much appreciated.
[Edited on 19-4-2010 by Runningbear]
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redox
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2-propanol forms an low-boiling ternary azeotrope with water and methyl ethyl ketone.
An alternate way of drying IPA would be through adding MEK to 91% IPA and distilling until anhydrous.
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ChemProdigy808
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"it is not clear whether it is alcohol or ethanol"
If you don't understand that ethanol is an alcohol hence "ol" then I wouldn't recommend carrying out process.
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Pulverulescent
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If you can't even read a post correctly, then I . . .
P
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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AirCowPeaCock
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| Quote: Originally posted by redox | 2-propanol forms an low-boiling ternary azeotrope with water and methyl ethyl ketone.
An alternate way of drying IPA would be through adding MEK to 91% IPA and distilling until anhydrous. |
How do you intend to separate the MEK from isopropanol? If he doesn't want to distil, I doubt he has an apparti for such, let alone for fractal
distillation.
BOLD
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DougTheMapper
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Jesus, how many times does this topic have to come up? Throw a bunch of NaCl into it and wait for it to layer out. Extract layer of iPrOH, dry over
anhydrous MgSO4, CaCl2, whatever; filter out the desiccant.
This iPrOH will be quite dry, well over the 99% spec you're shooting for. The distillation part is recommended to remove the tiny amounts of dissolved
desiccants. However, considering your definition of 1% impurities as 'good enough', the amount of dissolved solids should be more than tolerable in
your situation.
So, breaking out the spoon:
-Throw a bunch of rock salt into the 91% isopropanol container. Shake vigorously, let it stand for a couple hours to separate into layers.
-Use a syringe, syphon, etc. to remove isopropanol form the saturated NaCl solution.
-Bake epsom salts (MgSO4) or calcium chloride ice melter in the oven on high for a couple hours, let cool, crush.
-Mix isopropanol with the desiccant, shake, wait, repeat for a few hours.
-Filter out the desiccant. Distill (optional) to remove any dissolved desiccant which will be much less than 1% by weight.
Also, UTFSE! http://tinyurl.com/drying-isopropanol
[Edited on 15-2-2012 by DougTheMapper]
Victor Grignard is a methylated spirit.
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Bot0nist
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| Quote: Originally posted by DougTheMapper | Jesus, how many times does this topic have to come up? Throw a bunch of NaCl into it and wait for it to layer out. Extract layer of iPrOH, dry over
anhydrous MgSO4, CaCl2, whatever; filter out the desiccant.
This iPrOH will be quite dry, well over the 99% spec you're shooting for. The distillation part is recommended to remove the tiny amounts of dissolved
desiccants. However, considering your definition of 1% impurities as 'good enough', the amount of dissolved solids should be more than tolerable in
your situation.
So, breaking out the spoon:
-Throw a bunch of rock salt into the 91% isopropanol container. Shake vigorously, let it stand for a couple hours to separate into layers.
-Use a syringe, syphon, etc. to remove isopropanol form the saturated NaCl solution.
-Bake epsom salts (MgSO4) or calcium chloride ice melter in the oven on high for a couple hours, let cool, crush.
-Mix isopropanol with the desiccant, shake, wait, repeat for a few hours.
-Filter out the desiccant. Distill (optional) to remove any dissolved desiccant which will be much less than 1% by weight.
Also, UTFSE! http://tinyurl.com/drying-isopropanol
[Edited on 15-2-2012 by DougTheMapper] |
Ummm, IIRC, calcium chloride is not a suitable desiccant for alcohols.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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DougTheMapper
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| Quote: | | Ummm, IIRC, calcium chloride is not a suitable desiccant for alcohols. |
The halogenation of alkanes using a chloride salt is an SN1 reaction and does not proceed at an appreciable rate with primary and secondary alcohols.
Isopropyl chloride is usually prepared by refluxing isopropanol in HCl with ZnCl2 as a catalyst. At room temperature, simply mixing isopropanol with
anhydrous CaCl2 is not going to give any appreciable yield since CaCl2 has a much stronger ionic bond than ZnCl2 and no strongly acidic conditions are
present to protonate the alcohol.
I wouldn't dry tert-butanol with it, but this method works fine for ethanol and isopropanol in my experience. If anything, you have to deal with
increased solubility over MgSO4.
EDIT: Here's a JACS article about making absolute ethanol with CaCl2 and CaO: http://pubs.acs.org/doi/abs/10.1021/ja01656a048
[Edited on 17-2-2012 by DougTheMapper]
Victor Grignard is a methylated spirit.
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Lambda-Eyde
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That's not what Bot0nist refers to. Calcium chloride forms complexes with simple alcohols.
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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DougTheMapper
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o_O
Yikes, I didn't know that. Perhaps my alcohols aren't as dry as I thought...
Victor Grignard is a methylated spirit.
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Mr. Wizard
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Been there, done that 
"It's what you learn after you know it all that counts. "
John Wooden
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killswitch
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What about drying isopropanol with anhydrous copper sulfate? Would that be too acidic? I ask because copper sulfate (unlike magnesium sulfate) offers
an obvious indicator by way of color change for when it has fully hydrated, and would perhaps be less soluble in alcohol than magnesium sulfate.
[Edited on 31-3-2012 by killswitch]
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subsecret
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If you do decide to distill IPA, please be careful as it can form peroxides.
Fear is what you get when caution wasn't enough.
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testimento
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When I purified my otc isopropanols I simply poured a pile of salt into the liquid and heated it to boiling. The water layer was not separated within
half an hour after mixing and stirring, but the layer became apparent only after the mixture was brought to boiling temp. I distilled about 90% of the
IPA over and discarded the residues including salt, water and impure leftovers of IPA. Because I used simple distillation, not fractionation, the
purity is probably not nearly 99%, but I only made an experiment then. IPA could be dried with CaCl as well, as mentioned before, it will not form any
appreciable amounts of collateral substances at STP with short exposure times that are required to make it mostly dry.
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Lotus
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If you distill IPA purity of azeotrope will be around 82% max. Easiest is salting out with NaCl then slow distillation to remove salt. MgSO4 is
soluble in iso therefore would not be first choice in to simplify procedure.
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Rich_Insane
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I use sodium hydroxide to dry my isopropanol.... If you need really, really dry IPA, wasn't there something in Vogel about using magnesium metal (or
was it sodium?) to approach >99% concentration of the alcohol (in Vogel, it was ethanol).
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ElectroWin
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| Quote: Originally posted by Rich_Insane | | I use sodium hydroxide to dry my isopropanol.... If you need really, really dry IPA, wasn't there something in Vogel about using magnesium metal (or
was it sodium?) to approach >99% concentration of the alcohol (in Vogel, it was ethanol). |
yeah i seem to recall he used sodium metal to dry ethanol.
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Sublimatus
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The procedure described for "super-dry ethanol" uses magnesium. It's on the 401st page of the fifth edition.
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MrHomeScientist
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| Quote: Originally posted by entropy51 |
Note on the Preparation of Absolute Isopropanol
BY LEWIS E. GILSON
During several years of biochemical research the writer has found many instances where isopropanol could be substituted for ethanol in laboratory
work. It is cheap and there are no restrictions governing its use; nor is it likely to be an object of theft. The commercial 91% azeotropic mixture
was used instead of 95% ethanol and found to be fully equal or superior to the latter as a solvent or extracting medium. Absolute isopropanol was used
in place of absolute ethanol.
Absolute isopropanol is easily prepared. The 91% grade is shaken with 10% of its weight of commercial flake sodium hydroxide, separated from the
aqueous layer which forms, then shaken with a little more sodium hydroxide, decanted and distilled. The product obtained mixes with eight volumes of
carbon disulfide, xylene or petroleum ether without the slightest trace of turbidity.
Dilute isopropanol can be concentrated by shaking with dry sodium chloride. Water is removed as a saturated layer of brine. The upper layer contains
about 87% isopropanol and 2-3% of sodium chloride. While distilling, an additional quantity of brine separates. The distillate has so nearly the
composition of the 91% azeotropic mixture that it can be used as such without further treatment. Or, after shaking the dilute isopropanol with sodium
chloride and separating, it can be treated directly with sodium hydroxide and the absolute grade prepared. |
I'm currently using this method to dry some 91% IPA as much as possible. I poured roughly 100mL (79.1g) into a small bottle and added 10% of its
weight in NaOH (7.9g), capped it, and shook vigorously for a few minutes (venting often). After allowing to settle overnight, there are two very
distinct layers with lots of undissolved NaOH prills. I'm hopeful that beyond pulling the majority of the water into the lower layer, the remaining
prills should dry the IPA even further over a few days of standing. I plan to decant and store the alcohol in another bottle. I don't think
distillation is really necessary for my purposes.
My question now is, how would I go about testing the water content? I'd try sodium but I believe it also reacts with the alcohol, so it might give
false positives.
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Magpie
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Here's a couple methods that were recommended in my 1960s organic lab manual for ethanol. I don't see why they wouldn't be good for IPA also:
1. Place 1 mL of your dried IPA in a small test tube. Add a little CuSO4. If it stays white this would indicate that no water is present. If it
turns blue, it's forming a hydrate.
2. Place 1 mL of your dried IPA in a small test tube. Add a little CaC2 (calcium carbide). If you see tiny bubbles of H2 then that indicates the
presence of water.
The single most important condition for a successful synthesis is good mixing - Nicodem
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