ethan_c
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digestion of Rh, Pd, Pt organometallics
This is the most appropriate place to post this, I think.
I have a lot of random assorted organometallic compounds in vials used as research for medicines in the late '80s, I think. The labeling is not at all
clear, but a bunch of them, for example have a Pt or Rh surrounded by Cls and PYs, or PPH3s, or even amine groups. Another one is
[Pt(terpy)Cl]Cl•3H20- all sorts of stuff like this.
Basically, I want to try and extract the metals from the organic groups as best I can, efficiently, since there are MANY types of these things, 50+
vials, but very little of each one.
I think the two best options, at this point, is to either put it all together, and stick it in a furnace in hopes that eventually all the metals are
oxidized and the Cls and Cs and such are driven off…or, just dump all of it into an acid cocktail in hopes of digesting all of it into soluble PGM
compounds, and precipitating from there…might anyone have any advice/guidance?
As must be painfully obvious, I have no background at all in organic chemistry (next semester!)- my education, both formal and informal, has been 98%
inorganic/metals, so I apologize in advance.
Thanks for any help!
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not_important
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Don't mix metal types, workup can be difficult.
Heating in air will result in oxidation of the organic part.
Better might be, if you have the gear, fuse a mixture of sodium or potassium nitrate with Na or K hydroxide or carbonate, if you use the carbonate
you'll have more of a mush than a melt. Do this in a ceramic container, not metal. Slowly add the material to be converted, in small bits. If after
adding much of the organic, the reaction seems to slow down, and some more nitrate. After everything has been added, give it a good heating for a few
more minutes, then pour onto a cool steel/iron plate or stone slab (this is to prevent contraction of the freezing melt from breaking the container).
When cold, knock the frozen melt loose, crush it some, and extract the salts with hot water. The metal will remain behind. The water solution will
have hydroxide, nitrate, halides, phosphates, maybe sulfates if there is sulfur in any of those; not dangerous.
Hmm - after you are done adding the organometallics, you might want to sprinkle in some cheap organic material - sugar or sawdust - to react with
leftover nitrate, adding bits until it looks as if the oxidiser is gone then do the finally heating.
Or you could just mix all of those of one type of metal up with a carbonate and some nitrate and fire then mass at once; enough carbonate to keep the
nitrate reaction from being too exciting. Same sort of workup. You could skip the nitrate, just use hydroxide or carbonate to capture halides and so
on, depend on air oxidation; in that case I'd worry a little about the organics that could cook off so you'd want good ventilation and even better
doing it in a furnace where the offgassing would be pulled through a real hot area - heating in the front of a gas furnace whit the door cracked so a
draft flows across the container back into the flue.
On the acid side, 'piranha solution' - H2SO4 and H2O2 with water will chew up organics, but I'd call it a second choice. Run it hot, again add
organics _very_ slowly in small amouts, giving each addition time to react This isn't as good, as halides might take some of the metal into solution
making for a more complicated workup, plus too much organics in too strong of piranha can lead to explosions.
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Fleaker
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Piranhna solution should be avoided. I've had it decompose on me just while preparing it--ate a large hole in the workbench (as in charred).
To be honest, I do not know if there is enough of the PGMs in all of your 50+ vials to be worthwhile to extract. Remember that in most of those huge
complex ions, the Pt or Pd makes up less than 5% by weight. But maybe not, you haven't said anything quantitative about the concentrations or the
volumes involved. With prices as they are these days, you might have a couple hundred dollars coming to you. Just be careful about heating PGM
chlorides, many are volatile and will gas phase transport (blackish gray smoke for platinum chloride, and deposits a red residue).
Platinum will not be oxidized at the temperatures you would reach in an ordinary furnace, it does not start to oxidize til near its sharp melting
point. Palladium is a different story. Anyway, I like not_important's method of fusing with oxidizing agents, but not in a ceramic container (one
based on aluminosilicate will be destroyed by KOH). I seem to recall that nickel can be used for this. When/if you get the naked metal ions into
solution, post again and/or U2U and I will tell you how I would proceed.
\
Or alternatively, if you don't want to mess with it, you can send them to me.
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not_important
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Carbonates are OK for awhile in ceramics, hydroxides will chew holes but they are slow enough that the CO2, halogens, and phosphorous will have
knocked them down to something less agressive. The container may not be worth much at the end, but it will have done the job.
Problem with a metal container is that it might alloy with the platinum metals even though the temperature is no where near the melting points, The
metals are coming in as single atoms or small clusters, and can diffuse into the nickel (which does work well with fused alkali). Be OK if you were
going to sacrifice the container to recover all of the metals.
No matter what the container, unless it's an exotic like zirconium or tantalum, some of it will end up in the melt. I'd rather deal with
Si-Al-Ca-mg-Na-K than with metals.
For high halogen content compounds, if adding to a melt, it might be best to grind them with several times their bulk of Na2CO3 or K2CO3, and add
that. I've never done fusion recovery on halogen containing PMG compounds, just on CONPHS; or done wet recovery for halides or high halogen inorganic
complexes; I'm not certain on the volatility issue so making sure there's plenty of base around is belt-and-suspenders.
The fusion mix may leave the PGM as the metal or the oxide. When washing the solids remaining from treating the cold melt with water, use a 1%
solution of sodiium or potassium nitrate to keep down the formation of colloids.
I've never had problems with piranha, but I use 50% acid and only a small amount of H2O2, adding more as needed. It was the only method that worked to
salvage a batch of fritted glass filter funnals I got cheap; they were full of some coloured goop that didn't dissolve in any solvent I could lay
hands on and shrugged off KMnO4 and boiling nitric acid.
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Nicodem
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I just wanted to add, to be careful of not to destroy some precious catalyst with enantiomeric ligands that is worth hundreds of dollars per gram only
to obtain palladium or other noble metals for only a couple of dollars. That would not be just ironic but also pretty stupid. The chloride and
triphenylphosphine lignaded ones are relatively cheap (even as low as about 30$ for Pd complexes), though they are obviously still more expensive than
the noble metals they contain. But the enantimeric catalysts can be very expensive. For example, even the most common ones, like (-) or (+)-BINAP, go
for >300$ per gram. Generally, enantiomericaly pure ligands are way more expensive than the noble metals, so check the price before destroying
them.
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ethan_c
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| Quote: | Originally posted by Nicodem
I just wanted to add, to be careful of not to destroy some precious catalyst with enantiomeric ligands that is worth hundreds of dollars per gram only
to obtain palladium or other noble metals for only a couple of dollars. That would not be just ironic but also pretty stupid. The chloride and
triphenylphosphine lignaded ones are relatively cheap (even as low as about 30$ for Pd complexes), though they are obviously still more expensive than
the noble metals they contain. But the enantimeric catalysts can be very expensive. For example, even the most common ones, like (-) or (+)-BINAP, go
for >300$ per gram. Generally, enantiomericaly pure ligands are way more expensive than the noble metals, so check the price before destroying
them. |
Actually, I have somewhere close to 5g of Wilkinson's Catalyst and somewhere around a gram of potassium trichloro(ethylene)platinate. They're packaged
questionable since they haven't been used since the '80s, but if anyone wants 'em, let me know! No enantiomers, I don't think…
What I shall do, I think, is divide out all the random compounds by particular metal, and see how much I have of each to see if its worth trying to
sell or recover the metal, or just play around with.
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ethan_c
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Okay, I went through and its almost all Rh compounds- 5.40g, to be exact  . Maybe
I'll weigh the Pt and Pd ones later.
EDIT: why did I write 'to be exact' twice? Probably because it was written with about 3 hours sleep, but ich
[Edited on 24-9-2006 by ethan_c]
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