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]fritz - 25-4-2004 at 11:32
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!Hermes_Trismegistus - 25-4-2004 at 11:42
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.
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?vulture - 25-4-2004 at 12:16
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)]
From Ullmans.
my mistake....... it was Agent Blue..
Hermes_Trismegistus - 25-4-2004 at 13:29
They dumped so damn much crap on the bush back then it's easy to get mixed up, you'll have to forgive me.
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.chemoleo - 25-4-2004 at 16:19
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!I am a fish - 26-4-2004 at 09:40
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. vulture - 26-4-2004 at 10:30
Couldn't you precipitate it as As2S3 with H2S or a sulfide?chemoleo - 26-4-2004 at 11:18
Quote:
Possibly. However if such a process exists, it would probably produce As2O5 rather than As2O3. Then again, As2O5 is also useful.
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.vulture - 26-4-2004 at 11:21
As2O5 + 3H2O ---> 2H3AsO4
So you have As in a +V oxidation state...chemoleo - 26-4-2004 at 11:23
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
I am a fish - 28-4-2004 at 00:47
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?fritz - 1-5-2004 at 11:33
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.
