Distilled water with different synthetic dissolved salt in it.

Question

Hello
I have a liquid mixture in a bottle containing different synthetic substances dissolved from their salt forms (i.e. lidocaine hydrochloride, anhydrous caffeine). These compounds are dissolved in distilled water.
So the question is: How can I separate the dissolved solids from the aqueous solution? Can I do it by forming a hydrochloride precipitate by adding some hydrochloric acid? Or, say the sulfate salt by adding sulfuric acid, etc.?
Thanks in advance

Answer 1

If these are both amines (which they seem to be) and they are dissolved as the HCl salts, the reason they are dissolved is because they ARE the salts and they are ionic compounds.  Otherwise, the original molecules (fairly large organic amines) would not be very soluble in water. 

 

The way to get these is to use an "organic" solvent like ether to extract the organic amines from the water.  But they will stay in the water as long as they are the salts of the acids.  So you need to add some base like NaOH to the aqueous phase, making the pH too high for the amines to be protonated.  Then they will turn into the regular amines and be WAY less soluble in water - they will prefer to be dissolved in the ether phase.

 

You can extract these compounds from the water using ether in a separatory funnel, add enough NaOH solution to change the pH of the aqueous phase to basic and they will go into the ether.  Then you can easily evaporate the ether, since it's very volatile.

Answer 2

Do you want to separate each individual compound from each other, or just separate the compounds from the water.  If the latter, simply evaporate the water and you'll be left with the solid mixture of the compounds.  If you want the individual compounds separated, then it is more complicated, but certainly adding HCl will NOT be effective. In fact, the lidocaine is already the HCl salt, and making caffeine into the HCl salt will only increase its solubility.  Also, what other compounds are present besides the lidocaine and caffeine?  Separation of organic compounds is a complex issue and requires special equipment.