Sciencemadness Discussion Board

recover ethylene diamine from its dihydrochloride salt

NeonPulse - 24-10-2013 at 00:49

HI, i was wondering if anyone could help me with the procedure to convert ethylene diamine back to a liquid state from its dihydrochloride salt? i have looked around a bit on this site and other places but i cant seem to find a definate process to do this. there is plenty of info on how to make ethylene diamine dihydrochloride from the liquid using HCI. i have only found a few small references on using NaOH as a possible way to do this but not many.there was also a mention of converting aniline back to liquid from its hydrochloride form. could this method be used with ethylene diamine also? any help on the procedure or a point in the right direction as to where i would find how out would be greatly appreciated. thanks. NP

sonogashira - 24-10-2013 at 02:25

You shouldn't be messing with chemicals if you need to ask that.

NeonPulse - 24-10-2013 at 05:40

I know. Electronics is
more my specialty. I'm still learning when it comes to chemistry.

Random - 24-10-2013 at 11:22

Electronics as in making a spark to detonate something?

woelen - 24-10-2013 at 11:55

Quote: Originally posted by sonogashira  
You shouldn't be messing with chemicals if you need to ask that.
Why this answer? I unfortunately notice a change of atmosphere on sciencemadness the last few months. The place seems to become less friendly. This is just one example of such a type of response, I do not want to put you, sonogashira, in the spotlight, I use your response as just an example of this type of responses.

This may sound like a beginner's question, but the extraction of the free amine can be less straightforward than one thinks of at first glance. The reaction itself is straightforward, just add enough NaOH and then a slight excess amount to have all of the ethylenediamine released from the ion. But the isolation of this compound from the water is not that trivial. The amine has a boiling point, close to the boiling point of water. That is one complication. Another issue is that if you want all of the amine to be released, then you need to use excess NaOH, but if you distill such solutions and if you want all of the amine to be expelled from the solution, then you need to distill off nearly all liquid. This is very hard on your glassware. It might even be that you need copperware instead of glassware. I know of a similar problem with distilling hydrazine from solutions of N2H4.H2SO4 which are neutralized with NaOH. Because of the excess NaOH needed, you need to distill in copper apparatus if you value your glassware.

Maybe extraction in some organic solvent which does not mix with water is an option, but someone with experience in organics may be of more help in this.

deltaH - 24-10-2013 at 12:30

Well said woelen, even the simplest of processes can be an art to fine tune and get working well.

NeonPulse, another route could be to pass a solution of your salt through a column filled with a strong base type ion exchange resin in it's 'free base' form. From the bottom will come a solution of relatively pure ethylene diamine in water until the column becomes saturated with chloride which happens from the top down. You then regenerate the column by flushing with NaOH solution that yields, separately, a NaCl solution.

Solvent extraction followed by distillation can then be used to get the ethylenediamine back into a concentrated form from the water ethylenediamine solution and regenerate your organic solvent.

[Edited on 24-10-2013 by deltaH]

NeonPulse - 24-10-2013 at 18:51

Thanks woelen and deltah, these were the kind of answers I was looking for.I knew it was not going to be as simple as it sounds and there was bound to be thee problem of the amine and waters similar BP.

Tsjerk - 25-10-2013 at 04:14

@Woelen; Couldn't the corrosive effect of NaOH on glass be avoided by using a little less NaOH? You would have a little lower yield ethylendiamine but it will be less bad for your precious round bottom or Erlenmeyer.

woelen - 25-10-2013 at 04:29

It might be that if you use an amount of NaOH just insufficient to convert all ethylenediamineH(+) ions to free ethylenediamine that the effect on the glass is much less severe. On the other hand, I expect that you need to heat more strongly to het the last free amount of ethylenediamine from the slurry of solid/liquid mix at the end of the distillation. This will cause a lot of bumping and splattering at the end of the distillation. But it might be worth a shot.

deltaH - 25-10-2013 at 04:42

This is very interesting... I also found this patent:

"Method for recovering ethylenediamine from an aqueous ethylenediamine solution"

That describes how to do extractive distillation to break the ethylenediamine/water azeotrope. Looks like all you need is a glycol or monoethanolamine(MEA)... I'd certainly prefer to work with the glycol myself!

The route I propose now is (i)ion exchange to make ethylenediamine free base in water then (ii) extractive distillation using added propylene glycol to break the water/ethylenediamine azeotrope.

While the patent is for a continuous extractive distillation column, there is certainly nothing stopping you from carrying this out batch wise.

[Edited on 25-10-2013 by deltaH]

DraconicAcid - 25-10-2013 at 09:36

You could also use carbonate to deprotonate the ethylaminediamine (pKa of HCO3- is 10.3, pKa of H2NCH2CH2NH3+ is 9.9). It might even be possible to do this reaction in dry methanol, and let excess sodium carbonate absorb any water...

Why do you want to isolate the ethylenediamine? If you want to use it as a ligand, you can usually make it and use it in situ...