[baochun]

why benzoic acid is soluble both in water and methylene chloride?
the only thing i can figure out is benzoic acid has hydroxyl group can form H bond with water molecule, but how about in methylene chloride(CH2Cl2) ?

[movies]

The organic part of benzoic acid is going to be soluble in organic solvents.

[paperclip]

Could you please explain how hydrophobic interactions actually come about? Why would it exclude polar interactions?

[movies]

Well, polar molecules have a "built-in" energy problem, namely there is a charge separation.  Remember that opposite charges will be attracted to one another.  Within a polar molecule the partially charged ends are mechanically held apart, right?  So in order to stabilize that charge separation the polar ends like to "stick" to other polar molecules so they can get oppositely charged ends closer together.

When you put a polar molecule in a non-polar solvent, the solvent can't provide these stabilizing intermolecular interactions, so the polar molecule has to "find" another polar molecule and when it does, they will clump together in order to stabilize one another.  Since there is very minimal stabilization from the surrounding non-polar molecules, there is no energetic incentive for the two to mix to an appreciable amount.

[sandal]

i was prepared schiff base.
                       but results are not correct
please sent ma a procedure