Sciencemadness Discussion Board

Can any other mercury salts be prepared from Hg2(NO3)2?

phendrol - 28-11-2014 at 17:51

Can I prepare any other salts from mercury(I) nitrate?

Zyklon-A - 28-11-2014 at 18:06

Could you not be bothered to check Wikipedia? From the first line: '' It is used in the preparation of other mercury(I) compounds, and, like all other mercury compounds, it is toxic."

careysub - 28-11-2014 at 20:33

Quote: Originally posted by phendrol  
Can I prepare any other salts from mercury(I) nitrate?


Oddly enough I was just working out a "mercury salt supply" scheme to allow maintaining an inexpensive and (relatively) non-toxic mercury feed stock chemical, and to make other compounds as needed in easy efficient procedures.

The scheme I came up with was to use elemental mercury as the stock, and dissolve it in nitric acid to make mercury (I) or (II) nitrate as desired (depending on acid strength), or iodine to make mercury (II) iodide.

HgO, Hg2Cl2, HgCl2 (without involving sublimation), etc. are easily prepared from these. HgO in turn in useful for making other mercury compounds.

It looks like you can make mercury (II) cyanide from HgO and potassium ferrocyanide, which can then be used to prepare sodium cyanoborohydride from sodium borohydride without having to prepare hydrogen cyanide.

forgottenpassword - 28-11-2014 at 22:14

Could you share the reference for the mercury cyanide from oxide and ferrocyanide, please? And the cyanoborohydride preparation too, if it's not too much trouble. Thanks.

[Edited on 29-11-2014 by forgottenpassword]

phendrol - 29-11-2014 at 01:09

The question was silly because it's obvious other salts can be prepared. But can someone share a procedure for preparing any? HgO for an example?

Would adding more diluted nitric acid oxidize it to the (II)nitrate?
Hg2(NO3)2 + 2HNO3 = 2Hg(NO3)2 + 2H ??

[Edited on 29-11-2014 by phendrol]

careysub - 29-11-2014 at 11:02

Quote: Originally posted by forgottenpassword  
Could you share the reference for the mercury cyanide from oxide and ferrocyanide, please? And the cyanoborohydride preparation too, if it's not too much trouble. Thanks.

[Edited on 29-11-2014 by forgottenpassword]


For the first, it is from the following (your great-great-great-grandfather's chemistry):
“Prussian blue is quite insoluble in water and dilute acids.... Boiled with water and mercuric oxide, it yields mercuric cyanide and ferric oxide.”
Miller, W.L. Elements of Chemistry: Organic chemistry, 5th ed. New York: John Wiley & Sons, 1880, p. 100. (Accessed through Google Books).

Prussian blue is [Fe4[Fe(CN)6]3], prepared from potassium ferrocyanide and an iron (III) salt, or with potassium ferricyanide and an iron (II) salt.

And I find the procedure in Brauer (see Sciencemadness library):
One part of HgO is digested for a few hours on a water bath
with one part of Prussian blue and 10 parts of H2O. The crystals
separate on evaporation of the solution.

I like this approach since the ferro and ferricyanides are readily available, this is all aqueous room temperature chemistry, and no free HCN is generated.

For the second - the preparation of cyanoborohydride - this is the method of Györi and Emri (B. Gyori and G. Emri; J. Chem. Soc., Chem. Commun., 1983, 1303):

2 Na[BH4] + Hg(CN)2 → 2Na[BH3 CN] + Hg + H2

The reaction is conducted in THF under reflux for 3 hour . Due to the much greater solubility of Na[BH3 CN] over Na[BH4 ] in THF, the product is easily isolated from the reaction solution. Use stoichometric quantities, add a soln of Hg(CN)2 at a concentration of 1.47 g in 25 mL THF. Yield is quantitative.

[Edited on 29-11-2014 by careysub]

Hawkguy - 29-11-2014 at 11:07

I believe you can make Mercury Thiocyanate, which is awesome.. I think its by doing double replacement with a Mercury Nitrate and Potassium Thiocyanate. That should work, I think with Mercurous Nitrate or whatever ¯\_(ツ)_/¯

careysub - 29-11-2014 at 11:46

Quote: Originally posted by phendrol  
The question was silly because it's obvious other salts can be prepared. But can someone share a procedure for preparing any? HgO for an example?


If you reformulate it as really asking "is this a good strategy for making mercury salts" then it really isn't silly.

As a counter example, if one proposed to always start by making HgCl2, isolated through sublimation, then I would take issue since this would always involve volatilizing a highly soluble (and thus highly toxic) mercury compound.

For preparing HgO from Hg(NO3)2 according to Rosco Bodine heating on a boiling water bath for a few hours accomplishes the decomposition:
http://www.sciencemadness.org/talk/viewthread.php?tid=3842

Patnaik, Pradyot; “Handbook of Inorganic Chemical Compounds”, McGraw-Hill, 2003 supports this:
"Gentle heating of mercury(II) nitrate gives mercury(II) oxide evolving nitrogen and oxygen:
Hg(NO3)2 → HgO + 2NO2 + ½ O2
However, on strong heating, mercury nitrate decomposes to mercury metal:
Hg(NO3)2 → Hg + 2NO2 + O2
When excess alkali hydroxide is added to a solution of mercury(II) nitrate, a yellow precipitate of HgO is obtained."
Quote:
Would adding more diluted nitric acid oxidize it to the (II)nitrate?
Hg2(NO3)2 + 2HNO3 = 2Hg(NO3)2 + 2H ??


Probably. To make mercury (I) nitrate Patnaik says an excess of mercury is required. Adding more nitric acid to the (I) nitrate would probably drive the reaction that way.

According to Patnaik mercury (II) nitrate is obtained from mercury (I) nitrate by straight decomposition (or disproportionation), forming elemental mercury.

"[mercury (II) nitrate] is obtained by boiling a solution of mercury(I) nitrate or by the action of light on mercury(I) nitrate:"
Hg2(NO3)2 → Hg + Hg(NO3)2

Other preps from the (II) nitrate (also from Patnaik):
Addition of potassium thiocyanate solution forms a white precipitate of mercury(II) thiocyanate:
Hg2+ + 2SCN¯ → Hg(SCN)2
Addition of a small amount of alkali iodide to mercury(II) nitrate solution precipitates mercury(II) iodide:
Hg2+ + 2I¯ → HgI2
Similarly, mercury(II) cyanide precipitates upon the addition of potassium cyanide to mercury(II) nitrate solution:
Hg2+ + 2CN¯ → Hg(CN)2



[Edited on 29-11-2014 by careysub]

Mercury Sulfate and Mercury Cyanide

careysub - 29-11-2014 at 12:33

Since we are on the topic of working up mercury salts:

Another route to making mercury cyanide that does not use Prussian blue is to use mercury (II) sulfate and potassium ferrocyanide:
K4[Fe(CN)6] + 3 HgSO4 → 3 Hg(CN)2 + 2 K2SO4 + FeSO4

Question is now, how best to prepare mercury sulfate?

This is usually done by reacting elemental Hg (or HgO) with conc. H2SO4:
Hg + 2 H2SO4 → HgSO4 + SO2 + 2 H2O

The "Zygoat" procedure:
https://www.erowid.org/archive/rhodium/chemistry/mercurychlo...
which has been discussed on this site before has a couple of unsatisfactory loose ends. Part of the HgSO4 precipitates out (so far so good - but he does not say how much) and part stays in solution.

But what to do with the solution? Can the mercury sulfate be efficiently recovered from it? The issue of efficiency is important because:
1. Mercury isn't cheap.
But more importantly:
2. It is really toxic. You don't want to be pouring this stuff down the drain.

Patnaik actually says: "The solution is evaporated repeatedly to yield anhydrous salt as white leaftlets." But AFAIK H2SO4 does not evaporate very much. It boils at a very high 337 C, and I'll bet the mercury sulfate suffers decomposition at that temperature also.

I suspect that the best route is simply to neutralize the acid solution and recover the dissolved mercury as the oxide, which can be used to rerun the procedure.

S.C. Wack - 29-11-2014 at 13:38

I'm not sure that the mercuric sulfate ever goes in the hot hot conc. acid, and don't recall whether neutralizing the acid with NaOH gives anything but sodium sulfate. It's a crystalline mass under the acid once cooled and all the Hg is gone. This isn't the thread to discuss the Zygoat, although it is nice of Erowid to mention that it may in fact be bullshit, which it totally is.

[Edited on 29-11-2014 by S.C. Wack]

careysub - 29-11-2014 at 14:06

Quote: Originally posted by S.C. Wack  
I'm not sure that the mercuric sulfate ever goes in the hot hot conc. acid, and don't recall whether neutralizing the acid with NaOH gives anything but sodium sulfate. It's a crystalline mass under the acid once cooled and all the Hg is gone. This isn't the thread to discuss the Zygoat, although it is nice of Erowid to mention that it may in fact be bullshit, which it totally is.

[Edited on 29-11-2014 by S.C. Wack]


The complete text of Patnaik's comments on preparation:
"Mercury(II) sulfate is prepared by heating mercury with an excess of concentrated sulfuric acid; or by dissolving mercury(II) oxide in concentrated sulfuric acid. The solution is evaporated repeatedly to yield anhydrous salt as white leaftlets. However, in the presence of a small amount of water, the
monohydrate of the salt, HgSO4•H2O crystallizes as a colorless rhombic prism. Hydrolysis occurs in the presence of a large amount of water, forming a yellow basic sulfate, HgSO4•2HgO.

The compound also is prepared by treating alkali sulfate, such as sodium or potassium sulfate with a solution of mercury(II) nitrate."

By multiple sources it does dissolve in hot dilute sulfuric acid.

If it has any solubility at all in the concentrated H2SO4 after reaction I would want to remove it before disposal.

Patnaik's summary leaves a number of open questions, but I haven't found a reliable procedure description, nor enough data about the compound to infer my own.

[Edited on 29-11-2014 by careysub]