Author Topic: Basics of a/b extraction (Q&A pm)  (Read 3907 times)

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Basics of a/b extraction (Q&A pm)
« on: December 31, 2002, 11:46:00 AM »
this is a couple of questions aurelius received from a fellow bee, just thought this might help put some basics in front of the newbees.  forgive any obvious errors and keep in mind this isn't meant to be an authoritative piece.  just help.

In reply to:
Here's a question that I'm still trying to understand but not getting cuz so far swim's every dreams previous has been a nightmare.

When you have a solution with your epheds within it.  You add a np layer equal to that so that when you basify the water layer the epheds have a new layer to migrate to.  Now... Then using a separatory funnel you drain the water based layer.    all the red above is correct

Then you add "hot" dh2o to clean the np layer that might have NaOH residues or other binders.  Then you dump the water layer again.   in the green you mention using "hot" dH2O, don't!  if you use hot water, the freebase is more soluble in hot dH2O than cold.  and NaOH is plenty soluble in any temperature.  So, use cold to minimize your losses of ephedrine into the water wash while the NaOH is washed out completely in two or three COLD (can be RT) dH2O washes. 

Now my question is, you add dh2o at the very last then you acidify back to 7 so that the epheds in the np can go back down to the water layer.  The dh2o is supposed to have a PH of 7 already.  So which layer is supposed to go down to 7 in this case?  I thought np layer is not supposed to have a PH.  in the blue, well this is more explaining.  at a neutral pH (at pH 7), the ephedrine is still actually a freebase and therefore more soluble in the np than water.  however, the more acid you add (aqueous acid- which means acid in water because HCl is actually a gas which is commonly dissolved in water to give what most people consider HCl at a concentration of 37% by mass, aurelius thinks it's by mass anyway) the more acid you add the more the pH drops (goes towards 0) the more ephedrine freebase reacts with the HCl to form its salt which is soluble in polar solvents (like water or acidic water).  because HCl is a strong acid, is dissolved/dissociates COMPLETELY is water.  that means it breaks into H+ and Cl- ions completely. there is theoretically no HCl as a combined species/molecule.  because of the this the water has more ions in it than dH20 which almost no ions at all (theoretically none- at least for this application).  because of the excess of ions, the water becomes more ionic AND more polar, this means the ephedrine salt will be even more soluble in the water.  this means, IF YOU WANT, you can add aqueous HCl (HCl acid solution) to your np layer with the E freebase dissolved in it, and extract the ephedrine as it's HCl (hydrochloride) salt.  now you have E-HCl in your water and very near no ephedrine at all in the np (which can be thrown away or re-distilled for use later)  the np has no pH, (at least for this application, np's do have a pH but that's a bit above where you are at right now- maybe later we'll discuss this)  just pay close attention to the pH of your water layer at all times.  if the water is basic (red litmus paper turns blue when dipped in the water) then the ephedrine is a freebase and almost completely insoluble in the water layer (some will dissolve but only about a gram or two per every couple hundred milliliters of water).  this means the freebase will be in the np layer.  now, if the water is acidic (blue litmus will turn red), the ephedrine freebase will be turned into it's acid salt (if HCl is used you get a hydrochloride, if sulfuric acid (H2SO4) is used, you get the sulfate salt) and the salt will go to the water layer almost completely.  the reason for saying ALMOST completely is that there is always some amount that stays behind, but is usually so negligible that it's not worth worrying about. 

now if you hear someone say to isolate the freebase, you extract your salt (the form that's in pills) from the pills using whatever method you choose to (check TFSE for MANY different ways)  once you have your salt, dissolve it in dH2O and add NaOH or another similar base until the pH is somewhere around 8-11.  for newbees without great equipment to check the pH accurately, just use red litmus, it should turn blue.  now add your np and stir/shake.  wait for the emulsion to settle- overnight is usually best, then separate the np off and SAVE IT.  repeat this last step of extraction/shake/separate with fresh/unused np.  save this also.  add both np fractions (portions) together.  now, evaporate the np off of the ephedrine freebase that is dissolved in it.  use VERY LOW HEAT.  yes, it's a pain in the ass to have to be so patient but it's worth not burning your product.  the alternative (for more fortunate bees) is to do a low temp vac distillation.   in any case, DCM (dichloromethane) is an ideal solvent (NP) because it evaps/boils at a low temperature so the evap is quicker and the low temp means you are less likely to burn your E.  It also has the added bonus of being non-flammable (good for newbees) once the np is gone, you should have some nice water crystals- ephedrine freebase.  two acetone washes should be done on the freebase to remove impurities. 

to isolate the salt, do the extraction to the point of having your freebase dissolved in the np layer (if this method is chosen, toluene is an ideal solvent) and separate off your water layer.  discard the water.  now dry the np layer (UTFSE for methods of drying).  once dry, pass dry HCl gas through (like blowing bubbles through your pop with your straw).  (USTSE or Rhodium's site for ideas on a HCl gas generator)  continue to pass HCl through your solution of freebase and np until no more Ephedrine hydrochloride falls out of solution ( the white snow-like crystals that form).  filter off the crystals and perform two acetone washses to remove impurities. 

this is not all inclusive, there is much more to talk about, however, it does cover a lot of the basic knowledge necessary for beginner's understanding of what is going on in the flasks.


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« Reply #1 on: January 01, 2003, 02:43:00 PM »


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« Reply #2 on: January 01, 2003, 04:22:00 PM »
NP- non-polar.  basically (for our purposes) this means that an organic solvent, such as tolune, xylene, DCM (dichloromethane), hexane(s), heptane, naptha, coleman's white fuel is used as a second phase.  (phases = layers) the organic phase will almost always be on top (DCM sits on bottom when used with water.)

you can pm other Q's to aurelius.