I am a fish
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Arsenic(III) oxide from cacodylic acid.
Cacodylic acid (dimethylarsinic acid, (CH3)2AsOOH) is probably the easiest arsenic compound for an amateur to obtain.
Solutions of it are available as a broad spectrum herbicide under names such as Ansar 138, Arsan, Bolls-Eye, Broadside, Check-Mate, Cotton Aide HC,
Dilic, Moncide, Montar, Phytar, Phytar 138, Phytar 600, Rad-E-Cate 25, Silvisar 510 and Sylvicor.
It is also widely used in biochemistry and so (in comparison to other arsenic compounds) is relatively easy to obtain.
Needless to say, I should be getting hold of some soon and I would like to make arsenic(III) oxide from it. Would heating it strongly in air work?
2(CH3)2AsOOH + 7O2 --> As2O3 + 4CO2 + 7H2O
[Edited to fix incorrect formula]
[Edited on 26-4-2004 by I am a fish]
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fritz
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simple heating may be dangerous because As2O3 sublimes at 193°C. Maybe you could use some kind of strong reagent for decomposing organic materials
(e.g. aqua regia, H2SO4/K2Cr2O7 or HNO3) to destroy the compound. But I don´t know if there are any violent reactions with the reagents I suggested!
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Hermes_Trismegistus
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| Quote: | Originally posted by I am a fish
Cacodylic acid (dimethylarsinic acid, (CH3)2AsOOH) is probably the easiest arsenic compound for an amateur to obtain.
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Jesus Christ, that's agent orange!
How easy did you say it was to obtain, because all I got on a search was a bunch of old MSDS sheets for these old herbicides not in use for many
years.
What is a common use for largeish quantities in biochem?
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vulture
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No, that is not agent orange.
| Quote: |
Most of the spraying was with Agent Orange [i.e., a 1 : 1 mixture of (2,4-dichlorophenoxy)acetic acid (2,4-D) and (2,4,5-trichlorophenoxy)acetic acid
(2,4,5-T)]
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From Ullmans.
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Hermes_Trismegistus
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my mistake....... it was Agent Blue..
They dumped so damn much crap on the bush back then it's easy to get mixed up, you'll have to forgive me.
For a concise index.... http://cybersarges.tripod.com/aochem.html
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The_Davster
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I think that strongly heating it would work. Remember navarone's Iodine extraction from povidone? it is similar to that. Heat the Cacodylic
acid to decomposition in a RBF with a (preferably long)condenser attached vertically on top. The arsenic(III) oxide should collect on the inside of
the condenser which could then be pushed out with a rod of some kind.
Never the less, I would make sure to do this outside on a windy day with some sort of remote controlled heat source. Arsenic scares me.
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chemoleo
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Cacodylic acid is used in biochemistry as a crystallisation additive, proteins often tend to crystallise better in its presence.
I just checked Brauer, it appears that once you get As2O3, one can reduce it with Zr to get extremely clean As - however this involves sublimation,
but As sublimes at >815 deg C... so not much chance there!
With free As, one can make all sorts of fun compounds, such as AsCl3. AsCl3 can also be made according to As2O3 + 6 HC1 -> 2 AsCl3 + 3 H2O, meaning
that the OXIDE is enough for this.
Also, this reaction is possible too :
2 AsCl3 + 3 H2O -> As2O3 + 6 HC1
i.e. for cleaning up the As2O3. As2O3 precipitates.
Arsenic acid can be made according to
As2O3 + 2 HNO3 + 3 H2O -> N2O3 - 2 H3AsO4 • 1/2 H2O.
NOTE the formation of N2O3!!! This is normally fed into conc. H2SO4, which then forms the nitrosylhydrogensulphates. Awesome route to this!
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I am a fish
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| Quote: | Originally posted by fritz
simple heating may be dangerous because As2O3 sublimes at 193°C. |
Damn it! It's bad enough as a solid, let alone as a gas!
| Quote: | | Maybe you could use some kind of strong reagent for decomposing organic materials (e.g. aqua regia, H2SO4/K2Cr2O7 or HNO3) to destroy the compound.
But I don´t know if there are any violent reactions with the reagents I suggested! |
Possibly. However if such a process exists, it would probably produce As2O5 rather than As2O3. Then again, As2O5 is also useful.
| Quote: | Originally posted by rogue chemist
Heat the Cacodylic acid to decomposition in a RBF with a (preferably long)condenser attached vertically on top. The arsenic(III) oxide should collect
on the inside of the condenser... |
I don't think I'll be doing that. I like being alive.
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vulture
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Couldn't you precipitate it as As2S3 with H2S or a sulfide?
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chemoleo
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| Quote: |
Possibly. However if such a process exists, it would probably produce As2O5 rather than As2O3. Then again, As2O5 is also useful.
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Well according to the reference literature, this reaction (of dissolving cacodylic acid in strong HNO3) should yield not As2O5, but H3AsO4, according
to As2O3 + 2 HNO3 + 3 H2O -> N2O3 - 2 H3AsO4 • 1/2 H2O. This of course assumes that strong HNO3 does attack cacodylic acid.
I don't see why you just try it. Aqua regia + cacodylic acid, heat for a bit (outside of course, with the wind blowing away from you), and see
what you get!
Once you get some salt/precipitate, it shouldnt be too hard to work out what you have.
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vulture
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As2O5 + 3H2O ---> 2H3AsO4
So you have As in a +V oxidation state...
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chemoleo
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yepp... I realised that?!? where's the contradiction? Just pointing out the route of oxidation. Also, the cacodylic acid is in +V to start with
Never Stop to Begin, and Never Begin to Stop...
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I am a fish
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| Quote: | Originally posted by chemoleo
As2O3 + 2 HNO3 + 3 H2O -> N2O3 - 2 H3AsO4 • 1/2 H2O |
Interesting. I've been interested in making exotic nitrogen oxides for quite a while now. Would the reaction work with (the much safer) Sb2O3,
or is it arsenic specific?
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fritz
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to vulture:
yes of course it may be precipiated as sulfide but it has to be in the form of As3+/As5+! As2S3 may be converted to (AsO4)3- with NH3/H2O2
to I am fish (little off topic):
I read something about producing N2O3 by heating HNO3 with simple starch. And I guess all you need is a moderate(!) reducing agent. Maybe if you are
able to handle measured amounts of gases
NO2 + NO -> N2O3(cooling!!)
should be possible.
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