# Preparation of Mercurous nitrite

I read that Prafulla Chandra Ray prepared Mercurous nitrite for the first time and published a paper.

Both Mercurous ions and nitrite ions are quite stable. So they should readily form the compound.

1. Why is it difficult to prepare it, and how to prepare it?

2. Can it be obtained by simply mixing $\ce {Hg2Cl2}$ and $\ce{AgNO2}$, where $\ce{AgCl}$ will be precipitated?

1.Why is it difficult to prepare it, and how to prepare it?

Prafulla Chandra Ray prepared mercurous nitrite, $\ce{Hg2(NO2)2}$ by reacting metallic mercury with cold, dilute nitrous and nitric acid. According to his paper(1):

Mercurous nitrite is the product of the combined action of nitrous and nitric acids on mercury : $$\ce{2Hg + NO2.H + HO.NO2 -> Hg2(NO2)2 + H2O}$$ Some of the nitrite is decomposed by the nitric acid, the quantity of nitrous acid thus rapidly growing, until mercurous nitrite and nitrate are accumulated in molecular proportions. After some, the nitrous acid remains constant in the solution. It has become the catalytic agent between the nitric acid and the mercury,which now interact in the following manner: $$\ce{4Hg + 4HNO3 -> Hg2(NO2)2 + Hg2(NO3)2 + 2HO}$$

It is difficult to prepare the compound because many mercury-nitrite species is generated in the solution like $\ce{Hg(NO2)2}$, $\ce{Hg2(NO3)2.2H2O}$, $\ce{Hg2(NO3)2.OH.Hg(NO3)2}$ etc. These salts exist in the solution and it is difficult to separate the main salt i.e mercurous nitrite from these salts and isolate in pure solid salts as all salts have similar properties and they tend to impure the solid mercurous nitrite.

2.Can it be obtained by simply mixing $\ce{Hg2Cl2}$ and $\ce{AgNO2}$, where $\ce{AgCl}$ will be precipitated?

Reaction between $\ce{HgCl2}$ and $\ce{AgNO2}$ to yield mercuric nitrite $\ce{Hg(NO2)2}$ has been reported (2) but reaction between $\ce{Hg2Cl2}$ and $\ce{AgNO2}$ to yield mercurous nitrite $\ce{Hg2(NO2)2}$ is yet to be reported.

References

• $4 Hg + 4 HNO_3 -> ... + 2 H_2O$, maybe? – Oscar Lanzi Oct 2 '16 at 9:53
• @Oscar, yeah sorry, i was in a bit of hurry.. – Nilay Ghosh Oct 2 '16 at 13:32
• Any idea why the reaction with $\ce AgNO2$ should not happens? $\ce AgCl$ should simply precipitate, leaving $\ce Hg2(NO2)2$ in the solution. – Archisman Panigrahi Oct 2 '16 at 16:03
• @Archisman, theoritically, the reaction between $\ce{Hg2Cl2}$ and$\ce{AgNO2}$ to yield $\ce{Hg2(NO2)2}$ should occur where $\ce{AgCl}$ is precipitated but it has not been yet performed experimentally. Perhaps, working with mercury salts is quite dangerous. – Nilay Ghosh Oct 2 '16 at 16:34