Color of potassium nitronate

[woelen]

I'm playing around with salts of the nitronate ion. All experiments I do point in the direction of a dark brown/red ion, but from a chemistry expert, I understood that nitronate ion is colorless. The expert, however, does not have personal experience with nitronate salts.

 

I prepared the nitronate salt by adding a solution of KOH to a solution of nitromethane.

 

Nitromethane, when dissolved in water, is converted to nitronic acid (the so-called aci-form of nitromethane):

 

H3C-NO2 <----> H2C=N(O)OH

 

The H-atom at the right is the acidic one. When hydroxide is present in solution, then the liquid turns red/brown. According to literature the following reaction occurs:

 

H2C=N(O)OH + OH(-) ----> H2C=NO2(-) + H2O

 

I originally thought that nitronate ion is colorless, but my experiments show a deep red/brown color. The solid can be isolated as a dark brown water-soluble powder.

 

The reagents I use are very pure (99.9+% nitromethane and reagent grade KOH in distilled water). Still I get the dark brown stuff.

 

So my question is: is nitronate brown? or is there a side reaction, which produces a brown compound?

[akcapr]

im sure somehow related to NO2 being brown, some how... lol its the most i can contribute

[woelen]

im sure somehow related to NO2 being brown, some how... lol its the most i can contribute

The fact that there is 'NO2' in it does not mean that it is brown. This way of reasoning does not hold.

 

For example, NaNO2 contains 'NO2', but not as molecule, but as ion. The compound is not brown, but white/colorless or very pale yellow if finely divided.

 

Another example is nitromethane, which contains 'NO2' as nitrogroup: H3C-NO2. This is a colorless liquid, like water.

There also is an isomer H3C-O-NO, it also contains 'NO2', but now one of the O-atoms is between the C and the N. This is the colorless gas methylnitrite, which I have prepared some time ago from acidified methanol and sodium nitrite.

 

You see, the fact that a certain group or set of atoms is in a molecule does not say anything about the color. If nitronate ion is brown, then it is a pure coincidence that this seems to match with the color of NO2.

 

So, anyone out there, who knows the real answer?

[akcapr]

well, u see my reasoning