yankeex
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Ether drying, amount of Na needed?
I have 2 liters of diethyl ether which contain azeotropic amount of water, or about 0.4%. Can I calculate directly that this amount is about 8 grams
and I need equivalent amount of sodium metal to remove it? What happens to the hydrogen gas evolved, if I close the container, wont it explode upon
pressure buildup? I understood I would need to use silica stacked gas dryer with rbflask to dry this out?
And of course, how long would the drying take?
[Edited on 2-2-2013 by yankeex]
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Nicodem
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Thread Moved
2-2-2013 at 02:56 |
kavu
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Well 8 grams of water will produce in STP some 5 litres of hydrogen. I suggest using a CaCl2 drying tube to vent off the gas. As for the amount I
would prefer a slight excess. Even if you press the sodium into a wire (maximize the surface area that is) only the surface can be used to actively
dry the ether. There will naturally be some sodium left intact under the oxide/hydroxide layer.
[Edited on 2-2-2013 by kavu]
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vmelkon
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You need 0.444 mol (10.2 g) of sodium.
You would have to take into consideration the surface area of the sodium pieces. The reaction forms NaOH and it is insoluble. I guess you need sodium
foil.
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garage chemist
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You should pre-dry the ether by stirring with anhydrous CaCl2 overnight. Then let it settle, decant and apply your sodium as either very thin slices
or wire. Reflux the ether for several hours until the surface of the sodium no longer produces bubbles. Put a CaCl2 drying tube on top of the reflux
condenser. This lets the hydrogen escape without letting in aerial moisture.
[Edited on 2-2-2013 by garage chemist]
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Mercedesbenzene
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If you have peroxide free ether, molecular sieves will probably achieve better results than sodium. Not to mention it's probably safer and less effort
intensive.
http://www.slu.edu/~rmccull2/resources/JOC-Drying-Solvents.p...
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UnintentionalChaos
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You can use sodium-lead alloy to dry the ether, which is very brittle and can be ground to powder in a mortar and pestle. It reacts less vigorously,
but reportedly (given time) just as completely with water as pure sodium metal. Same with the air.
Just melt together ~1.05eq of sodium metal and 9eq of lead in a small metal crucible with some aluminum foil over the top to exclude air. Somewhere
around 200C, a reaction kicks in, the temperature spikes, and it all becomes a homogenous melt. Let cool covered and remove from the crucible by
smacking the bottom with a hammer until it falls out in chunks that look a lot like polycrystalline antimony and tarnish within a minute or two. Store
in an airtight jar as large chunks. Grind immediately before use (preferably in low humidity or under some of the solvent to be dried) and transfer
quickly before it starts to stick and clump from NaOH formation in the fine powder.
The leftovers can be quenched with water or alcohol easily. The sodium as an alloy does not ball up and pop/explode like plain sodium, though a
hydrogen explosion could still be possible.
[Edited on 2-5-13 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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paulr1234
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You need to think about your end use, some reactions are very finicky. Having dried your ether, remember that it will immediately start to take up
atmospheric moisture and oxygen again.
Sodium stills are definitely to be avoided. 3 angstrom MS seem to be a good choice but be sure of your sources, as recycling/drying them may not yield
dependable results
Distilling solvents with sodium does offer the advantage of being able to use benzophenone as an indicator. In the most sophisticated of set-ups, the
solvent is distilled under a dry inert gas at slightly reduced pressure. The dried solvent is distilled using a schlenk apparatus yielding moisture,
oxygen and stabilizer free product.
http://commons.wikimedia.org/wiki/File istillation_of_dry_and_oxygen-free_toluene.jpg
Sodium wire is generally best but you are going to have to make it and then safely dispose of it afterwards.
Eventually it will just ball up at the bottom of your still and will lose surface area. I was interested by the lead alloy idea.
Even getting a sodium press is tough, I found one single supplier in India still making them (and willing to ship to me). You might try one of these:
http://www.amazon.com/gp/product/B004VY6PJG/ref=pd_lpo_k2_dp...
Be careful.
Disposal tips here: http://delloyd.50megs.com/moreinfo/drying2.html
Again, be careful... boiling mixtures of ether and sodium can quickly lead to many years of painful reconstructive surgery.
More stuff: http://curlyarrow.blogspot.com/search?q=drying+solvents
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zed
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Sodium is a lame way to dry ether.
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Damitwhy
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I've found that when making Diethyl Ether via Sulfuric Acid Catalyst and ethanol, after twice distilling product last time with fractionating column
there is still enough ethanol left in ether to react with sodium wire upon bottling... so i guess either i must filter the ether next and/or distill
again once the sodium wire shows no signs of activity... alot of messing around for dry ether me thinks...
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UnintentionalChaos
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Quote: Originally posted by Damitwhy  | | I've found that when making Diethyl Ether via Sulfuric Acid Catalyst and ethanol, after twice distilling product last time with fractionating column
there is still enough ethanol left in ether to react with sodium wire upon bottling... so i guess either i must filter the ether next and/or distill
again once the sodium wire shows no signs of activity... alot of messing around for dry ether me thinks... |
You know, that reaction produces water as well. you probably just fractionated out the azeotrope with water. Sodium forms a hydroxide skin that is not
immediately obvious, but stops reaction. Fresh sodium with continue to react if you add some. Last time I cleaned up ether, I rough dried it overnight
with a huge excess of anhydrous MgSO4 and then stirred it with NaPb dust for 6 hours until new additions produced little, if any gas. Then it was
distilled into the reaction vessel I was going to use. It made EtMgBr enthusiastically.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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DraconicAcid
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Another vote for pre-drying your ether. We always used calcium sulphate to dry it first, IIRC, and then added it to the still with
sodium/benzophenone (but it's been a long time since I did that).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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