Nitrite Chemistry (2): Na3[Co(NO2)6] & K2Na[Co(NO2)6].H2O(?)

This is the agent for K+ detection, as the K salt is insoluble while Na salt is extremely soluble.

The whole reaction is rather confusing, and IDK whether HNO2 or O2 is the oxidant, all in all I decided to just follow the Manual, and just reduce the amount a little.

Attempt 1

Our source material of Co is... Tutton's salt (NH4)2[Co(H2O)6](SO4)2 which contains NH4+, and as is known to all this reacts with nitrite, so we should remove it. Also Na2SO4 can be precipitated by ethanol. Converting to acetate as usual is a good choice.

19.75g(0.05mol) salt was dissolved in 150mL water. Containing large crystals, we heated to dissolve them, and then cooled to RT. 6.90g(0.05mol) K2CO3 was dissolved in 20mL water and added to the Co solution with vigorous stirring, filtered and washed carefully with water to give a purple solid of CoCO3. Solution is still slightly colored but large excess of K2CO3 is not allowed as evolved NH3 may attack CoCO3 and resulted [Co(NH3)6]2+ is very easily oxidized.

This solid was dissolved into a solution of 6g(0.10mol) AcOH in ~20mL water. This solution was set aside.

45g(0.65mol) NaNO2 was dissolved in 45mL water. It cannot be all dissolved but this is not a big deal. The Co solution was poured into it. Solution immediately became brown and cold.

Then 7.5g(0.125mol) AcOH was mixed with the same amount of water and then added dropwise into it with vigorous stirring. Gradually, colorless gas with a nauseating smell was generated. IDK what it is. I tried to pump gas into the solution but it was hard to do so for half an hour, so I decided to just let it go. Reason for removing NOx might be: if NO is oxidized into NO2 then dissolved back into the solution, pH would fall.

Few hours have passed, and the evolution of gas has ceased. Solution was filtered(precipitation might be due to trace of K in NaNO2, or some other things like NH4 from reduction). It was perfectly clear and was orange.

EtOH twice of its volume(~200mL) was added. Orange milky precipitation immediately appeared. Leave it there for a few hours to age it.

By the way, since many of its salts are insoluble, a question is how to wash them away. 37% H2SO4, KOH, H2C2O4 all do nothing to it. Only hot KOH can turn it into a brown stuff. However, NH2OH(from its salt and KOH) can quickly reduce it into a black stuff which can dissolve in acid quickly.

The mixture was filtered, and the brown solid washed with EtOH until liquid became colorless, then dried in a sealed box with CaCl2. Filtrate was still colored, and we can do something interesting to it: 1.5mL 10M KOAc was added to it, and yellow precipitation immediately separated, solution became colorless after filtration. Solid was washed with EtOH and collected. Its formula might be the one I showed on the title. Its color is very different from the Na salt. Video

After drying, yield: 13.16g(65.15%) + 0.81g(3.57%).