Nosferatu
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H2S from aluminum and sulfur?
Hi!
Has anyone thought or maybe tried the possibility to make this precious reducing agent by burning aluminium in sulfur and the adding acid to the Al2S3
to free H2S? I know this works with zinc, but aluminium is a bit more otc...
Grof Orlock
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chemoleo
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Well, it should be possible in principle. It might be too violent, however, for you to be able to collect any Al2S3 - i.e. the resulting Al2S3 may
burn in the atmosphere straight on to Al2O3 and SO2.
I thought that sulphides are most easily obtained by burning iron powder with sulphur?
Have done that, and it works nicely, and not too violently. Then add HCl dropwise to liberate H2S.
Alternatively... boil NaOH(aq) with sulphur, it reacts to form NaSx, which will also liberate H2S to a smaller extent (next to sulphur powder) when
subjected to an acid.
PS whats so precious about it? My prrecccioussssss 
[Edited on 9-12-2004 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Nosferatu
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Thanks for imput, the NaOH idea sounds pretty fair to me, might try it tmrw..
| Quote: | Originally posted by chemoleo
PS whats so precious about it? My prrecccioussssss
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A good reducing agen. You can use it to make HI, with HI you can cleave aromatic ethers, you can make alkylhaliedes from alcohols, and use them to
alkylate. You can also use H2S to make NaSH, to reduce aromatic nitro functions selecively to amines for sandmeyer, in presence of other
sensitive-to-reduction functionalities elsewhere... Among other things, that's why it find it precious...
[Edited on 9-12-2004 by Nosferatu]
Grof Orlock
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chemoleo
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Ah, I see. You were referring to what could be done with H2S, not as much as the difficulty in making H2S 
I wouldnt rely on the NaOH/S thing though - it's by far not as good as FeS.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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hodges
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I often use a mixture of powdered aluminum and powdered sulfur to ignite thermite. It is a hot, somewhat violent reaction, but it does leave behind
aluminum sulfide. Aluminum sulfide produces hydrogen sulfide on contact with water (such as when cleaning up).
I doubt you will be able to get aluminum foil or other non-powdered aluminum to burn in sulfur, though.
If you have NaOH and sulfur you can add the aluminum to that to get some sort of complex sulfides. Adding an acid to this produces much more H2S than
just adding it to NaOH/S solution.
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Organikum
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| Quote: |
I doubt you will be able to get aluminum foil or other non-powdered aluminum to burn in sulfur, though.
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Use the microwave.
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Protium
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H2S can be formed from dripping HCl onto fool's gold.
H2S will kill you if you breath it. But before it kills you, it will deaden your ability to smell it, allowing you to think it's ok.
It just depends on how you look at it...
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Theoretic
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The NaOH/S trick won't work, as you'll have Na2SO3 formed as well as Na2S. this will make SO2 on acidification, and that will react with H2S
to form elemental sulfur and water. Maybe slow addition of acid to preferentially displace H2S from the sulfide (it's a weaker acid than H2SO3)
or addition of an acid weaker than H2SO3 but stronger than H2S will work. Even NaHCO3 might be strong enough (or if it's not, then you can heat
the whole thing to 60 C, at which temperature it decomposes into Na2CO3 and carbonic acid, which is stronger than H2S but weaker than H2SO3)!
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BromicAcid
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| Quote: | | H2S can be formed from dripping HCl onto fool's gold. |
If it's true then it happens at such a rate that it does not produce enough H2S to bubble or smell. I once tried this and after three days the
HCl had not canged appearance and the pyrite was still in the form it was origionally, i.e., shrap chips where I broke the pieces apart, pieces as far
as I could tell the same size. Whereas my H2S generation with FeS is definately noticable after a few seconds of being in contact with the acid. The
difference between FeS2 and FeS is therefore more then noticable, not only in physical properties but reactivities.
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JohnWW
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FeS occurs naturally as the mineral troilite, although unlike Iron Pyrites, FeS2, it is found almost exclusively in iron-containing meteorites. FeS2
is a solid solution of S in FeS.
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BromicAcid
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It's a solution of sulfur in ferrous sulfide? I'd thought that it contained iron in the +2 state with a disulfide molecule.
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JohnWW
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Because FeS2, iron pyrites (cubic), and marcasite (orthorhombic, formed at lower temperatures), are opaque with metallic-level reflectivity, and are
electrically conducting, it is clearly a compound of a low valence of Fe, not of Fe(IV), with metal-metal bonds and with a substantial proportion of
its valence electrons lying in the conduction band. I remember reading somewhere years ago that the extra S is in solid solution; but this is
contradicted by http://mineral.gly.bris.ac.uk/Mineralogy/18.sulfides.pdf which says (page 4) the S is present as disulfide, S2--, with the Fe(II) being low-spin
(instead of having 4 unpaired electrons) which would be consistent with metal-metal bonding.
Other variants of it are arsenopyrite, FeAsS, and bravoite, (Fe, Ni, Co)S2. There is also a range of compositions containing Cu as well as Fe and S,
particularly chalcopyrite, CuFeS2 (see the above PDF for the ternary phase diagram).
Although called "fool's gold", it sometimes does contain Au and Ag in solid solution, especially where chalcopyrite is also present, or
where some or all of the S is replaced with As, Se or Te.
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