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?