Amalgamated aluminium cathode
Most of you knows about reductive aminations using Al/Hg or eletrolytical reductions using platinium or palladium cathodes in a divided cells.
But how about taking the best from both worlds? A divided cell using an amalgamated aluminium cathode.. I myself have never herd or read about that
anywhere. Maybe its just because it wont work, but I find that a little hard to beleve. I meen if NaOH can be used to multiply the speed of an Al/Hg
reduction using a minimum of mercury to pretty large amounts of aluminium by weight, then do think this can be done.
disadvantages:
Amalgams when used in electrolytical cells tends to overreduce the product. Fx benzene to hexane ect.. But I think its only a matter of adjusting the
voltage pr cm2.
This paper is pure speculations!
Benefits:
The cathode can be used over and over again.
No hard-to-get-rid-of poisonous Hg waste product.
When not used, the cathode is stored under heptane, octane or other similar solvent to prevent erosion.
As little as 1 mg HgCl can be used to amalgamate an Al cathode surface of 60 cm2.
The Al cathode wont erode nether in action or when stored properbly.
Elemental mercury is cheap and easy to get.
To compare, one gram of PdCl2 will cost you around 100 US dollars.
You should be able to get a mercury thermometer containing two grams of elemental mercury to around 10 dollars. Meaning that you can cover an area of
12 square metres surface.
When done reduction there should not be as little as nothing of Hg in the product or solvent.
There should be no greyish wasteproducts like in normal Al/Hg reductions such as NaAlO2 contaminated with mercury.
As long as the cathode is keept under solvent you wont be exposed to mercury vapors.
Because the mercury is attached to the cathode as an alloy it cant, and will never find its way into the batch you are cooking.
1 mg HgCl to 60 cm2 surface area seems a little bit too little but it works in normal Al/Hg reductions when NaOH is used.
Amalgamation of the cathode
If you want to be 99.9% sure you are not flushing any HgCl into the sewers, I suggest you use a cell. Run an undivided cell using a graphit rod as
anode and the wanted size of cathode in demineralized H2O together with the estimated amount of HgCl. An electrolyte most likely also will have to be
added, such as a little H2SO4 or aq. HCl. Dont use alkali salts such as NaCl or NH4Cl as they will form amalgams to.
Or
You could of course also just clean the cathode from oxides using 5-10% aq. HCl and then place it in a jar with the estimated amount of HgCl in
demineralized H2O and then let it sit until you asume most of the HgCl have reacted with the aluminium cathode. Small hydrogen bubbles evolving from
the cathode is a good indicator to show that amalgam layer has formed. when they appears let it sit a little longer to clean the H2O as much as
possible from HgCl, and then you are ready to go.
Now.. It would be fun to hear your opinions. Confirm or disconfirm. New inputs, please share.
[Edited on 12-10-2011 by noche]
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