# Ionization of hydrogens in hypophosphorous acid

Does anyone know why the hydrogen atoms bonded with phosphorus in $$\ce{H3PO2}$$ are not ionizable?

I tried looking in high school level books, but they only describe the process, not the real reason. I would appreciate if someone has the answer.

• See, the P-H bond is not all that polar. – Ivan Neretin Nov 23 '19 at 23:08
• Even nitrogen attached hydrogen atom is very difficult to ionize, and phosphorus has almost the same electronegativity as hydrogen. Nonpolar bonds do not get ionized in aqueous solutions. – Poutnik Nov 24 '19 at 10:18

To begin with, removing another proton from anionic species is not very favorable. For example, the monohydrogen phosphate dianion is not very acidic $$(\mathrm{p}K_\mathrm{a}\sim 12)$$ despite it having an $$\ce{OH}$$ group.
In the case of $$\ce{H3PO2},$$ the second and third protons are bonded directly to $$\ce{P},$$ which is much less electronegative than $$\ce{O},$$ and consequently these P-H bonds are much less polarized than an $$\ce{O-H}$$ bond. So these protons are unable to ionize appreciably in aqueous solution.