T_FLeX
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Magnesium Oxide
I'm trying to obtain some magnesium oxide, and was thinking of some different ideas. Is it practical to just buy a magnesium strip and burn it?
This will give me pure magnesium oxide right? Or is there some easier way? Maybe a trick using milk of magnesia or Epson salt? Any help would be
appreciated.
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unionised
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Burning magnesium in air usually produces at least some nitride.
You could get magnesium oxide from milk of magnesia (the hydroxide IIRC) or epsom salts and it would probably be cheaper that way (less fun though).
Roasting the hydroxide or carbonate will give the oxide. You can get the carbonate from the sulphate by precititation with washing soda (sodium
carbonate).
Magnesium oxide is pretty uninteresting stuff; what do you want it for?
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T_FLeX
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Could sodium bicarbonate be substituted with sodium carbonate?, are these two always interchangeable? Thanks for the info!
I'm trying to isolate caffeine,
Procedure
100 g finely powdered tea are placed in a Soxhlet extractor or similar extraction apparatus and extracted for 3 hours with 400 ml ethanol. The extract
is transferred to a porcelain dish containing 50g magnesium oxide in 300ml water, and the whole is evaporated to dryness, with frequent stirring, on a
steam bath. The residue is boiled once with 500 ml water and then twice with 250 ml water and filtered hot on a Buchner funnel. 50 mllO % sulfuric
acid are added to the combined filtrates which are then concentrated in vacuo to about one third of the original volume. The solu- tion is filtered
hot to remove the flocculent precipitate which occasionally forms and then extracted with five 30-ml portions of chloroform. The pale yellow
chloroform solution is decolorized by shaking with a few milliliters of I % sodium hydroxide solution, then with the same volume of water. The
chloroform is evaporated, and the residue of crude caffeine is recrystallized from a very small volume of hot water. Yield, 2-2.5 g soft, silky
needles containing one molecule of water of crystallization, m.p. 235°. Crude caffeine can also be purified by sublimation at 180-200°.
I got this from "Natural Products" by raphael Ikan, a book I found in my local Library. The book is kinda old, but I wanted to try this
method anyway. I'm not sure if there is an easier method, but I didn't find other information that wasn't way too complicated for me.
I haven't taken organic chem yet, and I am still trying to learn.
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Mumbles
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Would MgO react with the water it is put in? Similar elements do. Perhaps just substituting the stoiciometrical equivalent of
Mg(OH)<sub>2</sub> would be acceptable.
I also believe that any base would work. The Magnesiums have the ability to be filtered easily due to the low solubility. I believe the alkaloid you
want is soluble in basic solution, and that is the reason for the MgO.
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unionised
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The trouble with cafeine is that, unlike most alkaloids,it is soluble in aqueous alkalies. If you use a base like magnesium oxide, which is barely
soluble you don't lose much of the product into the aqueous phase during the work up.
Actually, this is a bit over the top; this is how I did it.
Extract the tea with water then extract the aqueous solution with DCM (or chloroform if you like but DCM is less toxic and easier to get hold of).
Dry off the DCM and you get fairly clean cafeine. You cna do the ususal tricks of recrystalising it to clean it up (a bit of charcoal helps). If you
want to remove the theobromine you can make use of its greater solubillity in alkalies (IIRC) .
Another notable thing about cafeine is that it sublimes quite well so you can purify it that way (I know you said that, it's just that it's
unusual so, it's worth saying twice).
[Edited on 16-11-2003 by unionised]
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theh0ser
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obtaining magnesium oxide
you dont need to do all that stuff...jus open up an alkaline battery (flashlight size) and collect all the black stuff around the core. let the black
stuff sit out in the sun or under a lamp for a couple of hours and crush it up. there ya have it-magnesium oxide...p.s if you mix it with hdrogen
peroxide, it creates alot of oxygen, good for pressure bombs
hoser
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BromicAcid
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| Quote: |
jus open up an alkaline battery (flashlight size) and collect all the black stuff around the core.
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That's mainly manganese dioxide and carbon black and some other things, depending on if the battery was a new one or a dead one.
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Mumbles
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You could not know how many times I've heard this before. There must be a misprint(what a suprise) in the ACB or something. Manganese is not
the same as Magnesium. They do have spelling realitivly similar though.
On the plus side at least he knows the reaction. I've heard that Hydrogen is released byt the reaction so many times too.
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unionised
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Please note that the black stuff is not the same as the white stuff.
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guaguanco
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I've done this extraction; it works!
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Mumbles
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Did you purify the Manganese (IV) Oxide? I did it once, but it was mostly just for the hell of it.
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guaguanco
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| Quote: | Originally posted by unionised
The trouble with cafeine is that, unlike most alkaloids,it is soluble in aqueous alkalies. If you use a base like magnesium oxide, which is barely
soluble you don't lose much of the product into the aqueous phase during the work up.
[Edited on 16-11-2003 by unionised] |
I suspect that another advantage of using MgO is that it binds with the tannins in the tea, but it's been a while since I looked at any of this
stuff.
[Edited on 10-12-2003 by guaguanco]
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unionised
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The tannins are fairly acidic so any base would bind them. If they happen to form insoluble Mg salts that would help too.
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guaguanco
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| Quote: | Originally posted by unionised
The tannins are fairly acidic so any base would bind them. If they happen to form insoluble Mg salts that would help too. |
That's exactly what happens. It makes a nice insoluble precipitate from what I remember.
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T_FLeX
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Ok I have been able to form magnesium hydroxide by
NaOH + MgSO4 ---> NaSo4 + MgOH
I have been trying to filter off the precipitate but this stuff is a hard as hell, it keeps clogging up my filter paper (paper towels). Anyone got
some advice?
Also, by dehydrating Mg(OH)2 it will give MgO right?
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Magpie
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isolating Mg(OH)2
Here's some ideas:
1) If you have access to a lab centrifuge that would likely work. Successive washings (with water) then centrifuging would clean up the product.
2) It could likely be filtered by mixing with DE (diatomaceous earth), but then I don't know how you would separate the two.
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I am a fish
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| Quote: | Originally posted by T_FLeX
I have been trying to filter off the precipitate but this stuff is a hard as hell, it keeps clogging up my filter paper (paper towels). Anyone got
some advice?
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Don't use paper towels. Filter papers of reasonable quality can be bought from brewing/winemaking suppliers.
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