Author Topic: Crystallisation questions  (Read 1979 times)

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  • Guest
Crystallisation questions
« on: October 14, 2004, 09:48:00 AM »

SWIM has been using this method to make salt:

Post 107417 (missing)

(Osmium: "Re: MDMA HCL/MDMA sulphate -> ?", Methods Discourse)

It is wonderful that when the IPA solution is added to ther ether, salt forms. What has the water from HCL become now? Does distilling the ether solution to obtain ether reuseable? SWIM tried but the distilled ether could not form salt the second time. What can be done to make it re-cycleable?:)


  • Guest
SWIM is thinking using 3A mol sieves to remove
« Reply #1 on: October 14, 2004, 12:55:00 PM »
SWIM is thinking using 3A mol sieves to remove H20 in the IPA solution before forming salts in cold ether, will this be ok?:) This will help to reduce the amount of ether used(20 times the volume of amine).


  • Guest
sieves are not acid-resistant
« Reply #2 on: October 14, 2004, 06:21:00 PM »
The sieves consist of Ca or Mg ions (don't know exactly), and therefore are ACID-SENSITIVE! You cannot make anhydrous IPA/HCl or IPA/H2SO4 with it, it's gonna partially dissolve and give Ca/Mg salt contamination...

Better try dissolving your freebase and the appropriate amount of aequous acid (HCl 37%? Because H2SO4 can be had in 99% conc., no water present, no drying needed.. 8) ) in toluene, remove water by distillation using a dean-stark separator (or simple still setup, and returning the non-aequous layer to the dist. flask continuously), and cover the remaining yellow/range melt with at least 5x its own volume of anhydrous, cold 9:1 ether/acetone mixture and let sit in freezer for one day. Sparkling little beauties (that is, if you used HCl - sulfate hardly gives crystals).




  • Guest
Thanks, [/b]indole_amine[b], for the reply.
« Reply #3 on: October 22, 2004, 01:43:00 AM »
Thanks, [/b]indole_amine,

for the reply.

The sieves consist of Ca or Mg ions (don't know exactly), and therefore are ACID-SENSITIVE!

so, can SWIM use 3A mol sieves when the pH is above 7? When pH is above 7, the acid could have all reacted with the amine right, leaving no acid behind. Is this logic correct?

Meaning, when HCL or other acid is added till pH 8, SWIM would stir the hell out of it and then add the mol sieves to absorb the H2O under non-acidic condition. After stirring for a while, then filter the mol sieves away. Is this method ok?:)


  • Guest
« Reply #4 on: October 22, 2004, 02:35:00 AM »
Buffering the acid with amine freebase, so it can't hurt the sieves... so to say.

Yes, it should work, if you UTFSE for Bandils posts you will find exactly such a crystallization method... ;)



  • Guest
Hi, indole_amine, Thanks for the reply.
« Reply #5 on: October 22, 2004, 11:39:00 PM »
Hi, indole_amine,

Thanks for the reply.

SWIM has read about Bandil, the good guy's post about this. However, he used 4A mol sieves which could withstand strong acid, whereas in SWIM's case, 3A one is used. Thus the questioning here. SWIM recently distilled some freebase and got only 61%(w/w) of salt obtained using Osium method. This has prompted SWIM to try to reduce the amount of H20 present during crystal formation.

There was no problem when 1 mol scale was done, but when multi mols, it was not too efficient on using ether to transform H20 to other liquid(which SWIM does not know what is it).


  • Guest
sieves and acids = bad, generally
« Reply #6 on: October 23, 2004, 12:42:00 AM »
Both 4A and 3A sieves can not withstand strong acids - but the basic amine prevents the sieves from being attacked by the H+, as long as you don't add too much acid (which is bad, it would cause CaCl2/MgCl2 impurities)...

Their difference is their absorption capabilities (3A excludes everything besides water and ammonia, whereas 4A will also soak up straight chain hydrocarbons or even plain ethanol.

But for water removal during (re-)crystallizations, both are interchangeable.

I am not familiar with "Osmium's crystallization method": is it titrating a np solution with d.H2O and HCl 37% until slightly acidic, then evaporate the water?

Or a dual-solvent crystallization with water and acetone?

Like neutralize the amine freebase with HCl 37%, concentrate in vacuo and pour remainder into 1 liter of dried, pre-chilled acetone, chill and wait, then filter crystals?

I am really curious to learn about what is referred to as the "Osmium method"...



  • Guest
Again, thank you
« Reply #7 on: October 23, 2004, 02:04:00 AM »
Hi indole_amine,

Thanks again for the reply.:)

Osmium's method,

- Measure volume of freebase
- dissolve 5x volume(of freebase) of dry IPA into freebase
- add 37% HCL into the IPA solution, while stirring
- stop adding HCL until it is slightly acidic
- Prepare 20x volume of freebase of cooled ether
- While stirring the ether, slowly drip the IPA solution into the ether. Salt forms.
- keep on stirring for a while
- filter the salt
- distill the ether to recover remaining salt/freebase

SWIM does not know what the H20 has become when it is mixed with the ether. And can the ether be reused after distill? SWIM tried to reuse the ether in a rush experiment, but failed to crystalise.... :-[



  • Guest
triple solvent crystallization ;^)
« Reply #8 on: October 23, 2004, 07:59:00 AM »
The ether is capable of holding a certain limited amount of water but dissolves no HCl salt at all, while the alcohol can hold a certain limited amount of HCl salt, and tends to become water-immiscible when saturated with salts. So the water will slowly migrate to the ethereal solvent part when enough ether was used, and the HCl salt will be pushed into the alcohol, where it slowly precipitates. Acetone can be used instead of ether BTW.

In fact, you partition the HCl salt/water (derived from neutralizing your freebase) between the ethereal and alcoholic part of your solvent mixture... :)

But this method is not very good (no flame Os!): you have to use *much* ether, and even then a small amount of HCl salt will remain dissolved in the water/alcohol after filtration. If you use ether anyway, you could try to add 37% HCl to some ether, then add enough NaCl to saturate the water layer, and some of the HCl (not all) will exit the water layer and dissolve in the ether. Separate the acidic ether and add slowly to your fb/IPA solution until slightly acidic, then carefully heat until most of the ether has evapped, and add dry acetone and chill for several hours to precipitate the hydrochloride. Recrystallize from IPA/acetone to get rid of eventual NaCl impurities.

(not tried yet; but it *should* work fine -  and it is always better to use as little water as possible when crystallizing hygroscopic salts... :P )

Or maybe it would help to evaporate almost all the IPA/water after neutralizing the fb, and then add dried ether? I'm sure it would work better than leaving those 63% water in there!

Theoretically, the ether could be reused: but unfortunately it forms azeotropes with both water and alcohols, and in this case it contains also the excess HCl from your previous run - thorough purification is advised...  :)