The Chemistry Shack
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Drying 90% Ethanol with Magnesium Sulfate?
Edit: I have reposted this in the organic chemistry section
I have looked through all of the ethanol and solvent drying threads, but haven't found a definitive answer to this. I distilled some 70% ethanol, and
testing the density of the distillate, I found it to be 90% ethanol and 10% water. If this is repeatedly dried with anhydrous MgSO4, will the
resulting ethanol need to be distilled? Or will simply filtering off the MgSO4 work well enough (and then storing the product in a parafilm-wrapped
bottle to prevent moisture absorption)?
P.S. I don't need completely anhydrous ethanol (If I did I would just reflux over magnesium), but I do want to obtain ethanol above the 96.5%
EtOH/4.5% water azeotrope concentration.
[Edited on 6-7-2015 by The Chemistry Shack]
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diggafromdover
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Or, you can buy absolute ethanol:
http://nh.craigslist.org/grq/5086621619.html
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The Chemistry Shack
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That stuff is $80 per gallon, or $21 per liter. The stuff I bought cost $12 and will give me 1.32 L of ethanol, which is a unit cost of $9 per L. So I
save a lot of money by distilling the 70% ethanol (also, I dont have to pay shipping, as the local pharmacy has it).
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The Chemistry Shack
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Drying 90 Ethanol with anhydrous MgSO4?
I have looked through all of the ethanol and solvent drying threads, but haven't found a definitive answer to this. I distilled some 70% ethanol, and
testing the density of the distillate, I found it to be 90% ethanol and 10% water. If this is repeatedly dried with anhydrous MgSO4, will the
resulting product be close to 99% ethanol? Or do I need to fractionally distill the ethanol first up to 96% (I know it would be best to do a
fractional distillation anyway, but I want to try and avoid it if I can).
P.S. I don't need completely anhydrous ethanol (If I did I would just reflux over magnesium), but I do want to obtain ethanol above the 96.5%
EtOH/4.5% water azeotrope concentration.
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Deathunter88
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I have had mixed results with using magnesium sulfate drying ethanol. I added about 250grams of anhydrous magnesium sulfate to 500ml of 95% ethanol.
I shook the bottle and let it stand for 20 minutes. After that I distilled it over and tested it with anhydrous copper chloride. I was disappointed as
the copper chloride turned green on contact. It might be that I needed to leave it for longer, or copper chloride is too sensitive to test ethanol for
water at say ~98-99% ethanol.
[Edited on 6-7-2015 by Deathunter88]
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byko3y
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AFAIK, ethanol solvates the MgSO4.
Suitable drying agents are CuSO4, KOH, CaO, 3Å molecular sieves - those can be easily filtered off even without a need for redistillation (KOH
creates some amount of KOEt in the alcohol though).
And of course I forgot about azeotropic distilation with something like benzene.
Deathunter88, did you remove the MgSO4 precipitate after drying but before distillation?
[Edited on 6-7-2015 by byko3y]
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blogfast25
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CaO (quicklime) is used to dehydrate azeo EtOH.
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Tsjerk
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Above the azeotrope is perfectly doable with just magnesiumsulfate, I think you can go to at least 99%. You only need more of the sulfate if there is
more water in there, plus a way to get your ethanol out of the salt. Do you have means to do a vacuum filtration? That always worked great for me.
[Edited on 6-7-2015 by Tsjerk]
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The Chemistry Shack
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Yes I can do a vacuum filtration
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The Chemistry Shack
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Quote: Originally posted by Deathunter88  | I have had mixed results with using magnesium sulfate drying ethanol. I added about 250grams of anhydrous magnesium sulfate to 500ml of 95% ethanol.
I shook the bottle and let it stand for 20 minutes. After that I distilled it over and tested it with anhydrous copper chloride. I was disappointed as
the copper chloride turned green on contact. It might be that I needed to leave it for longer, or copper chloride is too sensitive to test ethanol for
water at say ~98-99% ethanol.
[Edited on 6-7-2015 by Deathunter88] |
Since MgSO4 absorbs water in a reversible process:
MgSO4 + 7H2) <-> MgSO4*7H2O
You have to filter it off first before distilling, so that's probably why it didn't work.
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The Chemistry Shack
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Really? I thought MgSO4 was nearly insoluble in ethanol
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byko3y
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The Chemistry Shack, I don't have specific number, but I can tell that it's 1% soluble even in diethyl ether, and also:
"Freely soluble in water; freely (and slowly) soluble in glycerin; very soluble in boiling water; sparingly soluble in alcohol."
It has probably something like 3% solubility in 95% ethanol. But anyway it's a shitty dessicant, because magnesium sulfate draws a lot of water into
the ethanol.
While CuSO4 is "slightly soluble in ethanol" and 1% soluble in methanol, and this means that you'll get something like 0.5-1% of residual water after
drying the ethanol with CuSO4.
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Bert
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Threads Merged
6-7-2015 at 16:37 |
The Chemistry Shack
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| Quote: Originally posted by byko3y |
While CuSO4 is "slightly soluble in ethanol" and 1% soluble in methanol, and this means that you'll get something like 0.5-1% of residual water after
drying the ethanol with CuSO4. |
My lab oven only goes up to 450 F, so I can't dehydrate my CuSO4 all the way (it turns into a very faintly blue powder), and I don't want to use the
oven in my kitchen to dehydrate it fully.
I'm assuming it will still work as a desiccant, and Ill just have to use more--or will CuSO4 work only if it is fully dehydrated?
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blogfast25
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| Quote: Originally posted by byko3y |
It has probably something like 3% solubility in 95% ethanol. But anyway it's a shitty dessicant, because magnesium sulfate draws a lot of water into
the ethanol.
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Really? How can anhydrous MgSO<sub>4</sub> 'draw lots of water into the ethanol'?
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Tsjerk
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There is absolutely nothing shitty about magnesium sulfate as long as you use it in the right way.
Solvated magnesium sulfate does not hold any water, hence; dry with a lot of sulfate (it is cheap and recyclable), filter, distill. This way the solid
sulfate holds the water, and you get rid of any salts through the distillation.
As The Chemistry Shack says, MgSO4 loses water at the boiling temperature of ethanol.
I once tried to further dry the ethanol obtained this way with fresh (shiny) magnesium turnings, after weeks they where still shiny, not a trace of
dullness.
@ The Chemistry Shack; Why don't you use a flame to dry CuSO4? In minutes it goes to complete dryness.
[Edited on 7-7-2015 by Tsjerk]
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byko3y
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Tsjerk, I don't know how to tell ya, but... anhydrous ethanol actually reacts with magnesium forming magnesium ethoxide. The reason why it did not
react is because THERE'S FEW PERCENTS OF WATER IN YOUR ETHANOL.
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Molecular Manipulations
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Which is why it is used to dry ethanol. It won't react until nearly all of the water is gone.
[Edited on 8-7-2015 by Molecular Manipulations]
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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byko3y
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You should read you books once again, because magnesium is never used to dry ethanol, but magnesium ethoxide is.
First you mix anhydrous ethanol, magnesium and iodine to make magnesium ethoxide, than you add the ethanol you need to dehydrate.
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blogfast25
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| Quote: Originally posted by byko3y | You should read you books once again, because magnesium is never used to dry ethanol, but magnesium ethoxide is.
First you mix anhydrous ethanol, magnesium and iodine to make magnesium ethoxide, than you add the ethanol you need to dehydrate.
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Yeah, like anyone actually does it that way. Maybe in Dumbass, I mean Donbas... You're a weirdo and always will be.
[Edited on 8-7-2015 by blogfast25]
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Mychemlife
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Wow name calling. Great way to articulate your point.
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Mychemlife
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I use 3-A sieves. They are re-usable and fairly inexpensive on ebay but be cautious with who you buy them from as some are a mix of 3-A and 4-A. Get
them from a reputable seller.
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zed
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Quicklime used to be a standard. Quicklime sadly, is no longer either cheap or readily available. Expensive and hard to find. Also, not easy to
have shipped.
Gotta make yer own.
The reaction of Magnesium with Methanol is vigorous. With Ethanol...heating to reflux may be required to kick off the reaction. Some suggest, that
drying Ethanol via easily produced Magnesium Methoxide, is a good way to go.
Though to me, it seems that the anhydrous Ethanol produced, must thereafter be contaminated by residual methanol. Quite possibly, a dangerous
outcome.
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