brisance
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Dubious reaction
While searching for a procedure to isolate Boron from Borax, I found the following equation in the detritus section:
| Quote: | Originally posted by BromicAcid
7Mg(s) + Na2B4O7 ---> 2Na(g) + 7MgO + 1/3B12
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This post was found here.
How credible is this reaction, and at what temperatures and pressures might it need?
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chemoleo
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It's credible, but not very good if you want to isolate Na or boron.
Essentially you are reducing 2 B2O3 and Na2O simultaneously.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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BromicAcid
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I think that may have been in the sodium book that's now in the library, I've also seen the reaction done with carbon. In any case the
reaction medium has to be quite hot >900C and maintained as such for some time. Your magnesium would melt and sodium vapor would boil off and
eventaully leave you with a hunk of MgO and boron, you'd normally want to dissolve off the MgO with HCl, but in this case you'd have
magnesium borides which make borane with HCl and most likely (if the reaction was allowed to go to completion) a massive quantity of elemental sodium
contamination, now those two would not be happy with acid at all.
Edit: The reaction in the sodium book is the reduction involving carbon:
Na2B4O7 + 7C ---> 2Na + 7CO+ 4B
Stating that the reaction mixture is first heated to 600C to remove water of crystalization and then to 1000C to distill the sodium formed. I have
seen the reaction with aluminum somewhere though I think, possibly in the complete treatise on inorganic chemistry, regardless, 1000C is kind of low
for a carbon reduction, plus you get two useful products, it would be dangerous though, you won't hear me say that much.
[Edited on 12/15/2004 by BromicAcid]
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brisance
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Those temperatures, though reasonable, are out of my range for experimentation. (I have no arc furnace). My ultimate goal is to synthesize diborane,
B2H6; my only source of Boron comes from Borax. Any ideas on how to do this?
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BromicAcid
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Diborane can be made from the reaction of magnesium boride at low temperatures (~0C) with hydrochloric acid. The reaction of borax with magnesium
would be very energetic, once initiated it would probably go to near completion, whichever products those might be without the need for external
heating (I imagine this being very violent, ejecting sodium vapor as well, the reactoin vessel would be fun to design). An excess of magnesium in the
above reaction would favor this reaction:
3Na2B4O7 + 29Mg ---> 6Na + 21MgO + 4Mg2B3
Reacting this with HCl would be dangerous as I stated before due to sodium, but there has been a whole host of work one on the reaction of magnesium
boride (Which I've also seen written MgB2) with HCl to produce boron hydrides (Others will be produced). Just remember they're pyrophoric.
Note that diborane reacts with water and therefore its residence time in the generation flask should be minimised and also note that diborane is
supposedly very toxic. There is some more information on this method online somewhere but a reference escapes me.
BTW, what was your method to make diborane from elemental boron? There are only a few methods I have seen that I can think of to start from elemental
boron, the industrial process:
2BF3 + 2NaH ---> B2H6 + 6NaF
Coming to mind but working with boron triflouride never appealed to me.
[Edited on 12/15/2004 by BromicAcid]
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