For my research project I synthesized some 3,5-difluoro-4-hydroxybenzenesulfonic acid from 2,6-difluorophenol using fuming Sulfuric Acid at high
temperature (110 C). However because of the high polarity of this molecule it has proven very difficult to extract from the H20, H2SO4 solution that
it is now in.
I have attempted to extract it using Ether, followed by NaHCO3 and Brine. However Ether proved to be insufficient at extracting any product. I later
tried a continuous extraction using Ethyl Acetate, followed by crystallization. This too proved unsuccessful.
Turning the solution into its Sodium salts wont work as acidifying it will yield exactly what I started with. So my Product requires a highly polar
solvent to extract. I decided to try Nitro-methane as a means to extract my product from H2O however because NM is miscible in water and have similar
boiling points I am not sure what the best method for separating the two is. Should I just try using excess NM, as water can absorb 10% of its own
volume of NM; I think? Or is there a better method that won’t be as wasteful and grant me a higher yield?
I have 150ml of my aqueous solution with (best guess) aprox. 2g of product dissolved in it. I ultimately want to isolate my product.12AX7 - 17-8-2007 at 14:53
Can't you evaporate the water? I suppose evaporating the H2SO4 would be kinda hard, but you might crystallize it as NaHSO4.
Timnot_important - 17-8-2007 at 16:16
Quote:
Originally posted by Eldor
...
Turning the solution into its Sodium salts wont work as acidifying it will yield exactly what I started with. ...
That solution is pretty dilute to extract from.
Add barium chloride to remove the free sulfuric acid as BaSO4, then neutralise with Na2CO3. Filter off the BaCO3, evaporate the filtrate until mushy.
Treat that with cold concentrated hydrochloric acid, in severalfold excess of you product - say 5X mole ration. Add EtOH to dissolve the free
sulfonic acid, leaving most of the NaCl as a precipitate. Evaporate, then dissolve in and recrystallise from a fairly non-polar solvent to clean up
the remaining NaCl.
Removing the H2SO4 means you'll only be faced with the volatile HCl in the later stages, much easy to removed from the sulfonic acid.Eldor - 17-8-2007 at 22:14
Quote:
Add EtOH to dissolve the free sulfonic acid, leaving most of the NaCl as a precipitate. Evaporate, then dissolve in and recrystallise from a fairly
non-polar solvent to clean up the remaining NaCl.
I assume that I filter out the NaCl, and then the non-polar solvent will hold the remaining NaCl as I recrystallize my product?not_important - 18-8-2007 at 05:22
Yes, filter out NaCl, evaporate, dissolve in the less polar solvent leaving the remaining NaCl as a solid. You should be able to find solubility info
on the target or a closely related compound to help pick a solvent. Remember that the free acid is fairly strong.
Isopropanol could be used in place of ethanol, which would do a bit better job of leaving NaCl behind, which would mean less chance of the NaCl +
ArSO3H <=> HCl + ArSO3Na interchange.
