stoichiometric_steve - 16-12-2005 at 15:33
lets say you have your post-reaction mixture which you have already washed with nonpolar solvent and basified. the easiest thing to do with amines is
making sulfates, no doubt. hydrochlorides are just too hygroscopic and phosphates are tricky to make, leaving you with various amounts of amorphous
gunk.
now extract the mix 3 times with toluene, dry the toluene over Na2SO4 and filter it off. calculate the amount of pure H2SO4 you expect to be needed in
the worst case scenario (it has 2 protons, mind that) and carefully add concentrated sulfuric acid to the vigorously stirred amine-toluene solution.
the precipitation of sulfate salt is delayed, so don't be too hasty. if you don't want to filtrate the portion you have just titrated right away, let
it settle and decant supernatant toluene to another beaker in which you continue titration.
filtrate and wash sulfate salt by disconnecting vaccuum, making a slurry of the salt with fresh toluene and continuing filtration several times to
ensure no residual amine is sticking to the crystalline mass.
proceeding slowly in small steps prevents overtitration, while a slight excess (5 drops) of sulfuric acid usually does no harm. just don't try to do
it too fast. optionally, you may want to wash your crystals with a solvent which evaporates faster since toluene likes the crystals so much it sticks
to them for quite a while. ether, acetone or an alcohol (all reasonably anhydrous) are just right- mind that some alcohols may dissolve an amount of
your salt.