I am using dichloromethane to extract caffeine from a liquid (coke).?

Question

I understand that caffeine is only slightly soluble in water and very soluble in dichloromethane. What I want to know is what intermolecular force attracts the caffeine to the dichloromethane and what atoms are involved in the attraction?

Answer 1

Parts of the caffeine molecule are nonpolar, and disrupt the hydrogen bonding network of water when they dissolve in it. This means that there are fewer ways for the water to set up this network, making solubility less favourable. This is called the "hydrophobic effect", and shows up as an unfavourable entropy of solution.

The intermolecular forces in dichloromethane are much weaker, dichloromethane has a dipole moment, and caffeine does have polar parts,so the caffeine can dissolve in CH2Cl2.

Introductory textbooks discuss solubility in terms of the interactionsof solvent molecules with the solvent. To get the full picture, you need to consider the effect of the presence of solute on solvent-solvent interactions as well.