3
$\begingroup$

So I had an organic chemistry lab where we had to dissolve p-nitrophenol in water, dilute $\ce{NaHCO3}$, dilute $\ce{NaOH}$, and dilute $\ce{HCl}$ to test for solubility.

The p-nitrophenol dissolved in everything but water. I just want to make sure if these results are theoretically correct. From what I understand, the nitrophenol should have also dissolved in water because its a polar substance and it shouldn't have dissolved in $\ce{HCl}$ because I think the Hydrogen in the phenol is itself acidic due to electron withdrawing effects of the benzene.

Can someone please explain what should happen?

$\endgroup$
3
$\begingroup$

p-Nitrophenol is actually modestly soluble in water at neutral pH (16 g/l at 25 °C) because of its weak acidity ($p\mathrm{K_a}=7.16$ at 22 °C) and the formation of intermolecular hydrogen bonds between the phenolic OH group and water molecules. The latter would also explain why the compound dissolves in diluted $\ce{HCl_{aq}}$ despite being protonated at lower pH values. The importance of intermolecular hydrogen bonds is also demonstrated by the significantly lower solubility of the ortho isomer, which forms intramolecular hydrogen bonds and therefore appears to be less polar to the solvent (source):

enter image description here

In basic solutions, p-nitrophenol is deprotonated to p-nitrophenolate. The anion is stabilized by delocalization of the negative charge into the benzene ring and the electron-withdrawing nitro group (only two of the possible resonance structures are shown):

enter image description here

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.