I'm reading Bard's Electrochemical Methods. He cites the oxidation of p-aminophenol in acid solution. I haven't taken organic chemistry in a while and don't understand why oxidation takes place in acid. The pKa's of the amine and alcohol are 5 and 10, respectively. If you have a solution, say pH 1, wouldn't both moieties remain protonated and nothing happen? Thank you.
You can read about the quinhydrone electrode here: https://en.wikipedia.org/wiki/Quinhydrone_electrode
This electrode reaction is similar to the oxidation of Para-aminophenol and is measurably reversible over a pH range of about 2-10. It would be reasonable that the aminophenol coupled with the acid requirements of the oxidant would have an optimum pH [range] for the redox reaction.
Standard electrode potentials are when all activities are at unit levels. Some reactions can actually be measured under those conditions but sometimes the standard potentials must be calculated from other thermodynamic data. [Imagine trying to measure the standard potential of sodium metal immersed in one normal acid!] Research is needed to determine what is going on here.
About " and nothing happen.", Acid-base reactions in water involving proton transfers are very fast and frequent; something is always happening [sometimes catalysis is helpful].
You are right in your assumption that in a solution with an acidic pH nothing would happen as is. But the example is considering a redox reaction.
If a suitable oxidant oxidises the p-aminophenol first, the resulting positively charged p-aminophenol will have drastically different pKa values because of the positive charge. The pKa might be low enough, that the deprotonation can even happen in acidic solution.
Alternatively, the reaction might also proceed via a concerted mechanism, where both a proton and an electron are transfered at the same time. In that case, pKa values don't apply anymore.