# Is the conjugate base of every polyprotic acid amphoteric?

Since all compounds with an accessable free lone pair can act as a Brønsted-Lowry base, I was wondering if there was any specific example of a substance that when it loses a proton, it cannot accept a proton but can donate another proton.

Please note that I am not considering something like sulfuric acid which is a strong diprotic acid, as $$\ce{HSO^{-}_{4}}$$ still accepts a proton even if its to a limited extent.

• What you ask for is a contradiction in terms. If your hypothetical acid exists in the protonated form in the first place, then of course it get protonated after being deprotonated. There is no going around it. True, superacids might be pretty reluctant to protonate, but what I said above still applies. – Ivan Neretin Mar 25 at 7:39
• I thought there might be a compound that upon deprotonation forms a base that is very unstable and breaks down into something else in a very one way manner? – sab hoque Mar 25 at 7:47
• If there were cooperativity you could imagine a case where the acid loses two protons or none, but not one. I don’t know of such a case. sciencedirect.com/science/article/abs/pii/… – Karsten Theis Mar 25 at 11:19
• @sabhoque That felse like a different thing than what is asked in the question. You may want to look for anionic rearrangements. I think that one could design a molecule from which two hydrogens could theoretically be abstracted, but after the first one, it undergoes rapid rearrangement, possibly preventing the second from being abstracted. – TAR86 Mar 25 at 17:28