Polar compounds that are insoluble in water

In summary, polar molecules can be insoluble in water despite having a permanent dipole, as seen in the example of pyrantel embonate. This compound's low water solubility and high polarity prevent it from effectively traveling through membranes and instead localizes to its site of action. This is due to the compound's acidic nature and limited ability to form hydrogen bonds with the solvent.
  • #1
CrimpJiggler
149
1
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.
 
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  • #2
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.
 

1. What are polar compounds?

Polar compounds are molecules that have a positive and negative charge, known as a dipole, due to unequal sharing of electrons between atoms. This results in one end of the molecule being slightly positive and the other end being slightly negative.

2. Why are polar compounds insoluble in water?

Polar compounds are insoluble in water because water is a polar molecule itself and therefore can only dissolve other polar molecules. Nonpolar compounds are unable to form hydrogen bonds with water molecules and are thus unable to dissolve.

3. Can polar compounds ever be soluble in water?

Yes, some polar compounds can be soluble in water if they have functional groups that can participate in hydrogen bonding with water. Examples include alcohols, amines, and carboxylic acids.

4. How do polar compounds behave in water?

In water, polar compounds will interact with the water molecules and become surrounded by them, with the positive ends of the polar molecules attracted to the negative oxygen atoms of water and vice versa. This is known as hydration and stabilizes the polar molecules in the water.

5. Are there any exceptions to the rule that polar compounds are insoluble in water?

Yes, there are some exceptions to this rule. For example, some polar compounds may have a very large non-polar portion that makes them more soluble in nonpolar solvents, such as benzene or ether. Additionally, some polar compounds may be able to form micelles in water, where the nonpolar portions of the molecules cluster together to avoid contact with water molecules, making them more soluble.

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