facetious fontanelle
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Hg2Cl2 as a safe substitute in amalgamation?
Good morning everyone,
as most of you who ever worked with amalgams probably know, the general approach towards amalgamation (at least for usage in organic chemistry) is the
application of Hg2+ salts (e.g. HgCl2, Hg(NO3)2, etc.), dissolved usually in water, in which the metal
which is to be amalgamated is submerged. Hg2+ salts are so prominent in amalgamation because they are highly soluble in water - which is
why they are also very toxic, as the body can easily absorb the contained mercury.
Now, despite having performed quite a number of diverse reactions and having a solid understanding of chemical processes, I consider myself nothing
more than a "recreational" chemist, which means I try to steer clear of using toxic substances whenever possible, even more so when they are
bioaccumulative as mercury is - also since the disposal of such compounds can be troublesome. In addition, Hg2+ salts are sometimes hard to
come by - rightly so, considering their toxicity.
But since aluminum amalgam is a reducing agent not only of high safety (compared to, for example, LAH) but also of diverse applicability (reductive
sulfurization, reductive amination, alkenic reduction, removing water from a solution etc), I'd really really like to make some, and as I happen to
have a goodly amount of Hg2Cl2, I recently wondered whether there is a way to use it in amalgamation despite its low solubility.
I read from a member here that he tried Hg2Cl2 as an amalgamation agent, but there was "zero reaction" with the
aluminium foil he used. I tried some approaches, too, and I have to disagree; with application of some heat to the solution, after about 30 min
amalgamation started - but at an extremely slow rate. The amalgam started to react with the water and hydrogen evolved (again, not even remotely
comparable to any of the violent reactions HgCl2 is said to launch). However, after I removed the water, washed the - alleged - aluminum
amalgam and added it to the final reaction vessel, no reductive process whatsoever occurred. I also tried performing the amalgamation in
situ, just dumping the aluminum and the Hg2Cl2 into the reaction vessel and applying heat for a solid 10 hrs (about 5 times
the recommeded reaction time when using HgCl2), and although the reaction seemed to be nicely (albeit slowly) going, in the end I was
rewarded with a yield that was ridiculously low (about 5%-10% of what it should have been). Also, by amalgamating in situ, one is
presented with the problem of remaining mercury salts in the final product that possibly need filtering out (which wasn't a problem in my particular
case, but could be in other reactions).
I came across a reference in the rhodium vault, where they like to use Al/Hg as a reducing agent for a number of nitrostyrenes etc.; most of the
chemists there are conservatively using HgCl2, but one - only one - synthesis used Hg2Cl2, here's the link.
| Quote: | 14g of Al (Heavy duty Reynolds) was amalgamated in 400mls MeOH and 50mg Hg2Cl2 by heating to reflux. The flask was fitted with a reflux condenser and
was then transferred to a cold stirrer, (etc)
...
Prepared by amalgamation using Hg2Cl2 in refluxing 50%H20/MEOH, followed by MeOH wash and a THF wash. |
To sum it up; Hg2Cl2 amalgamation can work, but I have yet to find the perfect set of variables. It seems that the
amalgamation needs a lot of warmth and time - and I wonder whether using water is a good approach here, since during the slow amalgamation process
already amalgamated pieces will react with water and dissolve. I thought about ethanol as a medium, but I'm not quite sure.
This is all I have found out about the topic, and I'd love to hear your opinions, suggestions or even experiences. I still have about a dozen grams of
Hg2Cl2 and aluminum ready, and I'd gladly try out some new approaches.
With kind regards,
the facetious fontanelle
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zoombafu
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There is plenty of literature on reductive amination with the amalgamation. Look on erowid for more examples of this.
[Edited on 7-9-2012 by zoombafu]
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zed
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I've read some reports of producing Mercury salts, by direct reaction of Mercury with Iodine. Those salts are then used to produce amalgams.
Otherwise, HgCl2 can be generated by the action of Cl2 on Mercury, or possibly the Hg2Cl2 that you already have.
Or, as reported here on this board, one may resort to producing a Gallium/Aluminum amalgam. Gallium is more expensive than Mercury, but it can be
recycled, and it is reported to be non-toxic.
[Edited on 8-9-2012 by zed]
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SM2
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it's cuz calomel is poorely soluble in water, and doesn't take to the Al that well.
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facetious fontanelle
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| Quote: | | it's cuz calomel is poorely soluble in water, and doesn't take to the Al that well. |
Yes I am aware of that,
read "I happen to have a goodly amount of Hg2Cl2, I recently wondered whether there is a way to use it in amalgamation despite
its low solubility."
| Quote: | | There is plenty of literature on reductive amination with the amalgamation. Look on erowid for more examples of this. |
Yes, read "most of the chemists there are conservatively using HgCl2, but one - only one - synthesis used Hg2Cl2, here's the
link." - and that's exactly the problem: Mostly, HgCl2 is used, which is toxic, hence the question.
| Quote: | | I've read some reports of producing Mercury salts, by direct reaction of Mercury with Iodine. Those salts are then used to produce amalgams.
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yes, but then I'd have to find a way to reduce my Hg2+ to Hg, which is toxic again.
| Quote: |
Or, as reported here on this board, one may resort to producing a Gallium/Aluminum amalgam. Gallium is more expensive than Mercury, but it can be
recycled, and it is reported to be non-toxic.
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Thanks a lot for the input! I've never heard of that before, but I looked into gallium and it seems great - readily available on several online
suppliers, neither toxic nor bioaccumulative. Before I start searching, do you happen to have any references on how to make a Al/Ga and do you know
for a fact that it works as a viable reducing agent the way that Al/Hg does, and how to recycle it? I'm very interested.
Also, by the way: I've given up on Hg2Cl2 - it just doesn't work out. Today I have tried out a technique to reduce it to HgCl2,
laid out by Tacho here and now I see why everyone is so fond of HgCl2 - I had yields about 10 to 20 times of what I had with
Hg2Cl2. Absolutely fabulous.
Still, if the gallium alloy is workable with my equip, I'd love to try that out, too.
[Edited on 10-9-2012 by facetious fontanelle]
[Edited on 10-9-2012 by facetious fontanelle]
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zed
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A science madness search, should turn up information on producing a Gallium/Aluminum amalgam.
http://www.sciencemadness.org/talk/viewthread.php?tid=11687#...
There is more out there. Perhaps under reductions.
[Edited on 11-9-2012 by zed]
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facetious fontanelle
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Thanks again, zed. I'll try this out sometime and see how it goes.
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