Sidmadra - 24-8-2018 at 07:51
Long story short I had an accident when refining my PdCl2, broken beaker, PdCl2 liquid spilled onto hotplate surface and jack, removing some of the
Aluminum, which I'm assuming based on the visible plating reaction I saw take place of bubbly silvery metal.
The Problem: If I had to guess, I have about 23g of PdCl2 that is polluted with maybe no more than 1g, maybe 2g of Aluminum/Aluminum
Salts. With what I could recover, I boiled it to dryness in aq. HCl. Is there any way I can purify this without having to go through the reduction and
extraction process? I know I could easily extract the Aluminum with HCl if both are in the reduced state, but I'd like to avoid this tedious process.
My issue here is I don't know what sort of reaction the PdCl2 liquid had with the Aluminum, nor am I familiar with how Aluminum salts behave since I
don't work with them.
One idea I had is to form Sodium tetrachloropalladate and extract that, since that is the form I will inevitably use it as, but I am not sure if this
would also help the Aluminum dissolve in solution. If I had to guess, the result of boiling off a solution with AlCl3 / AlOH3 would result in the
hydroxide remaining being what remains? Is that likely to dissolve in a salt solution like PdCl2 would?
clearly_not_atara - 24-8-2018 at 10:53
There are three reagents which selectively precipitate palladium.
Dimethylglyoxime
The most well-known way is to selectively precipitate Pd from solution by forming the complex with dimethylglyoxime:
https://link.springer.com/article/10.1134%2FS002016851314007...
The full prep of DMGO, using only MEK, sodium bisulfite, sodium nitrite, ethanol and sulfuric acid, is on Orgsyn:
http://www.orgsyn.org/demo.aspx?prep=cv2p0204
Alternatively, dimethylglyoxime can be purchased from Sigma-Aldrich for relatively cheap (much cheaper than Pd!).
Once the complex is isolated, Pd can be recovered easily, now that there are no other metals to get in the way.
If MEK is unavailable, it can be obtained by decarboxylation of levulinic acid, prepared by hydrolysis of sugar with hydrochloric acid -- possibly,
the levulinate salt can be distilled immediately after basifying+evaporating the reaction mixture:
http://en.wikipedia.org/wiki/Levulinic_acid
Salicylhydrazide
Alternatively, another precipitation reagent for palladium can be obtained by the reaction of salicylic acid esters and hydrazine:
https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-S...
Ethyl salicylate is used, but I would also expect good results with the much more common ester methyl salicylate, aka "oil of wintergreen". Hydrazine
is a bit annoying.
Beta-furfuraldoxime
If both of these methods are too much trouble, yet another method to precipitate palladium is to use beta-furfuraldoxime:
https://pubs.acs.org/doi/abs/10.1021/i560106a017?journalCode...
Now, the prefix "beta-" refers to one of the two possible chiral configurations of the oxime, which usually doesn't matter, but here it does. IIRC o
ximes formed by the reaction of a carbonyl compound with hydroxylamine tend to be mixed, but racemic furfuraldoxime should work fine here - you just
have to use a little extra.
Furfural is not a common chemical, but Orgsyn says it can be made from corn cobs (!):
http://www.orgsyn.org/demo.aspx?prep=cv1p0280
If corn cobs are not available, possibly another source of cellulose might be substituted, perhaps including e.g. cotton, although to be honest, I
don't know of any place where corn cobs are not available.
So yes, there are a lot of ways to precipitate palladium.
[Edited on 24-8-2018 by clearly_not_atara]
unionised - 25-8-2018 at 05:26
A few points
"Furfural may be obtained by the acid catalyzed dehydration of 5-carbon sugars (pentoses), particularly xylose.[10]"
From
https://en.wikipedia.org/wiki/Furfural
rules out poly hexoses like cellulose.
Re. "Now, the prefix "beta-" refers to one of the two possible chiral configurations of the oxime, which usually doesn't matter, but here it does.
IIRC o ximes formed by the reaction of a carbonyl compound with hydroxylamine tend to be mixed, but racemic furfuraldoxime should work fine here - you
just have to use a little extra. "
It's not a chiral isomerism, it's more like cis/trans.
Treatment of the material with a strong base like NaOH will dissolve Al as sodium aluminate.
I'm fairly sure it will not dissolve the Pd
NaOH may be easier to get than the oxime reagents.
Sidmadra - 26-8-2018 at 13:03
These are good suggestions, but I think I'm just going to reduce the solution with borohydride and reextract it. It's much less work intensive than
going through the process of making and purifying an unfamiliar reagent. Once I reduce the solution, hydrochloric acid should be able to rapidly
dissolve the Aluminum particles while leaving the palladium, from which point I can reconvert he palladium with aqua regia.
I was just hoping to avoid this because the palladium nanoparticles that form on reduction stay suspended in solution for over 24 hours before
settling, and are nigh impossible to filter. The process of removing the salts from the water involves repeated decanting and diluting over a period
of multiple days until salt concentration is adequately low enough. It's tedious but straight forward.
[Edited on 26-8-2018 by Sidmadra]