[HelloItsGoodbye]

I performed an experiment where I added 4-Aminophenol to a solution of Sodium Nitroprusside + Sodium Carbonate, which after 30 minutes turned blue. The issue is I'm having trouble figuring out the exact reaction mechanism, or what is the molecule which results in the blue colour in the first place?

The two "answers" I've found so far are:
1) The Carbonate ion deprotonates the Phenol group to form a Phenoxide group on the 4-aminophenol, which then substitutes the Neutral Nitroxyl Ligand from the Nitroprusside Ion (Unsure what kind of Ligand Substitution), forming a transition metal complex which reflects blue light(?).

2) 4-Aminophenol, Sodium Nitroprusside and Sodium Carbonate reacts to form some 4-aminophenol indophenol derivative?

I feel the 1st answer makes more sense to me, but I found some papers which mention that the reaction is well documented to form 4AP Indophenol Deriviatives, and they don't get into detail what exactly the reaction is. (https://www.sciencedirect.com/science/article/abs/pii/S0039914002004216#:~:text=The%20manual%20pharmacopeial%20limit%20tests,intensely%20coloured%2C%20blue%2C%20indophenol%20derivative)

The issue I've found with the 1st answer, however, is that Sodium Carbonate is not a strong enough base to deprotonate the Phenol, which means the whole reaction scheme breaks down? Unless the deprotonation step is unimportant, in which case I'm not sure what is the role of Carbonate ions in the solution other than it being slightly basic.

I've scoured many different sources but nothing I've found has been definitive enough for me. Can anyone help me out or point me to some credible sources I can refer to on this?

[rolnor]

Nitroprusside is used in the Simons reagent and gives a blue color with amines, its not exactly what yoy have but maybe worth looking into.

https://en.wikipedia.org/wiki/Simon%27s_reagent

[HelloItsGoodbye]

Nitroprusside is used in the Simons reagent and gives a blue color with amines, its not exactly what yoy have but maybe worth looking into.

https://en.wikipedia.org/wiki/Simon%27s_reagent

I've looked into this already, the main difference between Simon's Reagent and the test I conducted is the presence of Acetyldehyde, and that Simon's test is 2 step, while mine was only 1 step. Furthermore while Simon's test results in very rapid colour change, the reaction took more than 30 minutes for the colour to develop.

I'm uncertain if the reaction that takes place without acetyldehyde is the same as with it, so if anyone could help to clarify on this, that would be great <3

[rolnor]

Yes, its not the same. Its not easy to say what you got, I know that you can make Berliner Blue with hexacyanoferrate so there are colors formed by this type of reagent. I did this pigment in my basement lab as a kid. Did you want to make something special or is it more like a improvised experiment?

https://en.wikipedia.org/wiki/Prussian_blue

[HelloItsGoodbye]

Yes, its not the same. Its not easy to say what you got, I know that you can make Berliner Blue with hexacyanoferrate so there are colors formed by this type of reagent. I did this pigment in my basement lab as a kid. Did you want to make something special or is it more like a improvised experiment?

https://en.wikipedia.org/wiki/Prussian_blue

It was an experiment to study the tests outlined in the British Pharmacopoeia Paracetamol monograph. One of the tests was a Limit test of 4-Aminophenol. I'm trying to understand the mechanism of how the colour change occurs. It seems to be gradual, as the reaction takes 30 minutes to complete, and the intensity of the blue is proportional to the concentration of 4-Aminophenol...

Now I'm looking into whether the Sodium Nitroprusside could be a catalyst, similar to in Berthelot's Reaction, where the final product is a 4AP Indophenol Derivative, which would be blueish in colour... But Berthelot's reaction also seems different from the reaction I've got here...
https://de.wikipedia.org/wiki/Berthelot-Reaktion

[Babcock_Hall]

Why do you believe that sodium carbonate is not strong enough to deprotonate a phenolic hydroxyl group?