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Author: Subject: Zn-Hg amalgam safety
Monoamine
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[*] posted on 11-7-2021 at 11:31
Zn-Hg amalgam safety


I've been looking into reducing a ketone to an alkane. Scouring the literature, the classical way to do this seems to be via the so called Clemmensen reduction (see reference). The reaction depends upon a zinc-mercury amalgam, which sounds slightly scary, since I really don't want to fuck with anything containing mercury. Mercury (and especially their salts scare the crap out of me tbh...).

On top of that I also don't know how to to properly dispose of it. For organic solvents I just bring them to the local waste collection site for disposal so hopefully they also take mercury waste...

The main question I have is basically on how to use this reagent safely and to remove all Hg contaminants from the final product.

Has anyone used this reagent before and knows what the correct safety precautions are that have to be taken when using this compound ?

Thanks.

References:
THE CLEMMENSEN REDUCTION
Martin, E. L. React. 1942, 1, 155
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Monoamine
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smile.gif posted on 11-7-2021 at 18:17
Answer:


According to this product safety sheet

(Zn-Hg amalgam safety)

It actually seem to be fairly safe to handle without and isn't considered hazardous.
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[*] posted on 11-7-2021 at 21:15


WTF?
Zinc mercury amalgam is 50% zinc and 50% water?????

What about the mercury?

It's been a while, but I'm pretty sure I'd make that stuff up by either treating Zinc with mercuric chloride solution, or by agitating mossy zinc in a mixture of mercury and concentrated HCL.(Just a little HCl)

Geez, am I missing something when I read that MSDS?

I feel like I'm taking crazy pills.

Well, actually I am sorta doing that, so feel free to set me straight.

Disclaimer:

I do have a prescription.


[Edited on 12-7-2021 by SWIM]




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Oxy
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[*] posted on 11-7-2021 at 21:45


It must be a mistake, there should be a mercury.
Maybe they want to sell a greener alternative for amalgam... Who knows.

Regarding the toxicity, it is toxic as hell and it's better to avoid any contact and breathing.
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12-7-2021 at 05:23
Jenks
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[*] posted on 12-7-2021 at 07:32


Isn't zinc-mercury amalgam what was used for dental fillings? Probably not very toxic in bulk form then, when not stored in one's mouth, at least until the zinc is dissolved out.
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[*] posted on 12-7-2021 at 07:56


Quote: Originally posted by Jenks  
Isn't zinc-mercury amalgam what was used for dental fillings? Probably not very toxic in bulk form then, when not stored in one's mouth, at least until the zinc is dissolved out.


No, that was silver-mercury amalgam.




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Mateo_swe
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[*] posted on 12-7-2021 at 16:15


Hmm, when doing Al-Hg the Mercury(II)chloride is removing the oxide layer of the Al making it very reactive.
Can it be something similar but they removed all traces of Hg in some way after it removed the oxide layer of the Zn?
If not, i dont understand that MSDS, very strange.
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Oxy
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[*] posted on 12-7-2021 at 23:12


Mercury amalgam is an alloy, it does much more than removing oxide layer. Once amalgamated the metal and mercury forms metallic bonds.
Once mercury is removed it shouldn't be named as Zinc-Mercury amalgam as there is no mercury there.
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[*] posted on 13-7-2021 at 10:11


I know the mercury is still present in the Al-Hg but i thought the main working reaction was to remove the Al oxide layer making the Al very reactive.
Good to know there are more going on in that reaction, i look up the details of how it works.

That MSDS (link in monoamine´s post above) must be plain wrong and maybe very dangerous if there is Hg present.
And if there isnt any Hg present it should be removed as it is in that case incorrect or at least change the name to "Zinc metal in water".
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Monoamine
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[*] posted on 25-8-2021 at 21:30


Oh jeez... Well, good thing I haven't dragged any on shore yet.

Does make me wonder about that safety sheet. But this goes to show that just because something's written on a nice sheet of paper doesn't make it true.

Thank you for the warnings!

Reading this sheet again though it looks like what they call zinc mercury amalgam doesn't actually contain any mercury. It seems to only contain zinc and water. Maybe they called it this to scare noobs like me off playing with it.

Kinds: Don't listen to rap-mercury amalgam, it'll damage your nerves!

[Edited on 26-8-2021 by Monoamine]
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[*] posted on 26-8-2021 at 08:33


Quote: Originally posted by DraconicAcid  
Quote: Originally posted by Jenks  
Isn't zinc-mercury amalgam what was used for dental fillings? Probably not very toxic in bulk form then, when not stored in one's mouth, at least until the zinc is dissolved out.


No, that was silver-mercury amalgam.


Low-copper amalgam commonly consists of mercury (50%), silver (~22–32%), tin (~14%), zinc (~8%) and other trace metals.




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macckone
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[*] posted on 27-8-2021 at 07:28


You can substitute gallium for mercury in a lot of amalgam type reactions.
Or you can ditch the mercury entirely if you use it with HCl.
If your reactants and products are not acid sensitive then you can use HCl and skip the mercury.
If you are reducing nitrates, you can use devarda's alloy.
Without more information on the exact reaction it is hard to suggest an alternative reagent.

There are a LOT of reducing agents that don't contain mercury.
LiAlH4, LiH, Sodium Metal in liquid ammonia, DiBAl, BAlH, NaBH4, etc
Obviously some are hard to get but others not so much.
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