KemiRockarFett
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calcium amide
The acetylide anion reacts nicely with water forming the hydroxide salt of Calcium and the gas acetyhlen is formed. In ammonia, NH3(l), we have the
autoprotolys reaction
2 NH3 -><- NH2- + NH4+. Ammonia have quite high pKa value but in the solid states the gitterentahphies are a strong driving foce. I wonder if
its possible to produce the amidsalt by ammonolys of Calcium carbide to form ethyn gas and calcium amide. If its possible what will be the result if
we introduce N2O to this melt? Can we form azides in that way ?
It may be a bad idea overall, it seems that a way to produce pure CaC2 is to have pure Ca in ammonia and introduce C2H2 to this.
The energi of the lattice must be high for CaC2. I have not calculated it but this does not exclude that other salt like carbides can form amides from
ammonia. The carbide ion should be quite basic also. One pathway is if its more basic than the amide ion but I think its around 25 and amide is around
38, maybee wrong.
[Edited on 22-10-2004 by KemiRockarFett]
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Jome
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With "gitterentahpies" you probably meant "lattice enthalpies".
I dont quite get what kind of reaction you mean, adding CaC2 to liquid ammonia? What is molten, you talk about a melt.
When a carbide of an "alkaline earth metal" is heated with nitrogen present, it forms a cyanamide like CaCN2.
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Theoretic
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You could probably use calcium oxide instead, this would give you calcium amide and calcium hydroxide.
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chemoleo
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Jeez, Theoretic, what are you talking about? A reaction of CaO with 2NH3 to form Ca(NH2)2 and H2O? Nice in theory, but I bet my shoes (which are old
anyway) this has not a chance on earth to work... unless you fuse it under super extreme conditions or something. H-NH2 is an extremely weak acid (in
other words a base, NH3), while H-OH is a much stronger acid. Do you see why this would make it difficult to displace the oxygen to replace it with
NH2?
Besides... NaNH2 is prepared by reacting sodium metal with NH3, but never ever sodium oxide!!!! What makes you think this would work with calcium
oxide? 
Anyway - again, reacting CaC2 with NH3 would require the NH3 to be a stronger acid (i.e. a stronger tendency to give up a proton) than acetylene.
Whether this is the case, I do not know, but I am sure there are some tables on that, i.e. the pK values. Otherwise, jsut try?
Crush some CaC2, and flow dry ammonia gas across it - if a change occurs, then the reaction has probably worked.
Testing for acetylene gas should be relatively easy, i.e. look for precipitates with various salt solutions, such as CuC2, AgNO3, etc. Or simply do
the burn test, a yellow smoky flame is expected. However do make sure the ammonia is VERY dry.
In fact, I was wondering this before with other reagents - how about reacting it with chlorinated hydrocarbons?
Also, dry alcohols for instance should definitely yield calcium alcoholates, at great yields.
[Edited on 5-11-2004 by chemoleo]
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vulture
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I think some people here are mixing up calciumamide, Ca(NH<sub>2</sub> <sub>2</sub>, with calciumcyanamide, CaCN<sub>2</sub>...
[Edited on 5-11-2004 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Theoretic
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Oh, WHAT? 
"A reaction of CaO with 2NH3 to form Ca(NH2)2 and H2O?"
Not water, but calcium hydroxide:
NH3 + O-- => NH2- + OH-
The oxide ion abstracts a proton from the ammonia molecule.
"Besides... NaNH2 is prepared by reacting sodium metal with NH3, but never ever sodium oxide!!!! What makes you think this would work with
calcium oxide?"
Sodium oxide IS in fact used to make sodium amide.
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chemoleo
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Now, before this goes any further, maybe it might be good to provide a reference to your claims. NH3 reacting with CaO, to form Ca(OH)2 and Ca(NH2)2.
Or from Na2O to form NaNH2. And please not a reaction that produces a few micrograms of it, with 99% the hydroxide or somethign.
Besides, I just checked Brauer, and no such mention of such a process is made.
But I will happily be educated. It would make the production of metal amides a hell of a lot simpler.
So - reference please.
[Edited on 5-11-2004 by chemoleo]
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vulture
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There's an old thread somewhere about sodiumamide I started. The general consensus there was that amides can not be made from oxides, because
this produces water and this reacts immediatly with the amide (violently).
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Theoretic
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The old "Preparing alkali amides" thread has several members sharing my viewpoint, also a reference to Chemistry of the Elements (the person
said page 525, it's actually page 425).
Here's a quote:
M`2O + NH3 => MNH2 + H2 (M` meaning an alkali metal).
Also, in the same book reactions in liquid ammonia which produce the oxide ion have it written as an unstable intermediate, as in [O--].
No water is actually produced during the reaction between the oxide ion and ammonia, the oxide ion just abstracting a proton off the ammonia molecule.
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vulture
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| Quote: |
M`2O + NH3 => MNH2 + H2 (M` meaning an alkali metal).
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Where does the oxygen go?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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S.C. Wack
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Na2O + 2NH3 = 2Na2NH2 + H2O.
So - reference please.
Mellor gives as reference A.W. Titherley, J. Chem. Soc. 65, 504 (1894):
...A. W. Titherley also made the amide by heating sodium oxide in a current of
armnonia...
Of course this says nothing of its preparative value, if you have everything on hand.
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chemoleo
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Ok, maybe, if someone has access, could look up the detailed reference (and post it?)? I would be really interested (and so would many others I
reckon) to see whether this would be feasible to do at home.
I still dont understand though how this would work - of course theoretically this is possible, but I just don't understand how the [NH2]- ion
could be displacing the oxygen, and further how the H2O would be prevented from backreacting with the NaNH2, forming NaOH and NH3 once again. I am
talking in terms of an energetically favourable reaction.
Also, why do industrial processes not make use of this method, since Na2O is much cheaper to come by than Na itself?
I really don't understand 
PS I am not ready to give away my shoes yet
[Edited on 6-11-2004 by chemoleo]
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KemiRockarFett
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Due to the fact that the amid ion probably is a much stronger base than carbide ion, think the first is around 38 and the other 25. This means,
forming an amide is to form a stronger base, thats not favorable. But thats not the right way to think in the solid state. The most important thing is
if you can form a more stabile lattice and even if you can increase the entropy. If you put carbide in water you got a strong driving force related to
three things, both that you get a weaker base and form gas, meaning that you have more states to put energy in, and that you got a very stabile
lattice in the product Ca(OH)2.
The other suggestion was to use CaO and ammonia to form hydroxide and amide. So first check pKa for the oxide, I think its rather high ! So that is
maybee possible. But here we have a big drivingforce in forming the Ca(OH)2 which is much more stable than CaO, so this can work.
Sombody wrote about Na2O and way not use it industrially ? If it works with Na2O the reason is that its not easy to get it. Way? Thats bacause sodium
and pottassium forms peroxides instead of oxides, Na2O2 and K2O2 have got much more stable lattices than the oxides.
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Theoretic
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"Where does the oxygen go?"
Damn me, what a brain fart.  I mixed up two reactions, there was also the
reaction of a hydride with ammonia, that did produce hydrogen gas. The correct equation for the reaction of an alkali oxide and ammonia is:
M2O + NH3 => MNH2 + MOH
"I still dont understand though how this would work - of course theoretically this is possible, but I just don't understand how the [NH2]-
ion could be displacing the oxygen, and further how the H2O would be prevented from backreacting with the NaNH2, forming NaOH and NH3 once again. I am
talking in terms of an energetically favourable reaction."
It's not complicated, the oxide ion, being a very strong base, abstracts a proton off the ammonia molecule like so:
O-- + NH3 => NH2- + OH-
There's no water produced in this reaction, maybe you've been confused by the mistake in the equation I provided earlier (you could have
assumed I intended to write "H2O" instead of "H2" or something).
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S.C. Wack
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Was at the library today (Na triacetoxyborohydride rocks!) and looked up the ref that I mentioned before. Page 504 is the start of the article, this
is from pp. 510-511. The article is about making the amides of Li, Na, and K from the metals. This was the result of failed experiments to make the
hypothetical Na2NH:
"When NH3 is passed over gently heated Na2O, a violent reaction takes place, accompanied by incandescence, the solid quickly fusing to a frothing
mass, and if the temperature is kept at 200-300, nothing remains but NaOH. If, however, the heating be discontinued immediately the mass has commenced
to grow incandescent, and the whole quickly cooled, a white semi-fused product remains, which, on examination, is found to consist of a mixture of
NaNH2 and NaOH, there being nothing to point to the existence of a substituted ammonia other than sodamide. The change may be expressed thus-
Na2O + 2 NH3 -> 2 NaNH2 + H2O
The water at once decomposes the amide, forming NaOH and NH3, unless the action is stopped at once, in which case the secondary decomposition is only
partial."
And that is all. I thought that I wrote some run-on sentences.
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