Polar compounds that are insoluble in water

[CrimpJiggler]

I'm a bit confused about how polar molecules can be insoluble in water. Polar means they have a permanent dipole so I would have assumed that they would solvate water. An example of a polar insoluble compound is pyrantel embonate. Its used to treat hookworm and pinworm infections in the GI tract. Its low water solubility and high polarity mean it can't travel to other areas or bypass membranes very well and consequently, it gets localized to its site of action. Again though, I don't understand how a polar molecule can be insoluble in water.

 

[chemisttree]

That compound has two ortho hydroxy aromatic carboxylic acids. They are pretty acidic and form hydrogen bonds intramolecularly. It looks pretty bulky too. I'm not surprised that it isn't water soluble. You need enough hydrogen bonding with the solvent to get something into solution and this compound looks fairly limited in that regard.