The Vespiary
The Hive => Chemistry Discourse => Topic started by: stratosphere on October 09, 2003, 05:13:00 PM
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AFOAF wanted to test a EtOH solution which is known to contain piperazine and/or NaOH, ideally far more piperazine then NaOH, a titration will reveal the total concentration of base but will not distinguish which base is present.
so AFOAF was thinking for qualitative results to do a melting point test, but lets say the mix is (molar%) like 10%NaOH, 90%pip., will the NaOH crystallize out when the pip is melted?
i guess this result could be turned quantitative by "hot" filtering, for instance by suspending a fine mesh metal screen loaded with the solid above a beaker, placing in a oven to melt the pip through.
or is there some other easy way to get a qauntitative result?
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Add an equal volume of brine to the solution and extract several times with a low-boiling non-polar solvent to isolate the piperazine in the organic phase and leaving the NaOH behind in the aqueous phase. Then dry the orgaic phase and evaporate the solvent to leave the piperazine behind.
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a 2 layer extraction wouldn't be a bad idea, but from the solubility data i can find on piperazine in the crc, the general trend seems to be that it is only readily soluable in protic solvents.
i suppose this is because it would rather hydrogen bond with itself then go into a non-protic solvent.
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Therefore you need to extract several times with chloroform/DCM or other relatively polar (but still water-immiscible) solvent to get it all out. The good thing is that no matter how many times you extract, no NaOH will dissolve in the organic phase.
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swim observed a strange occurance, which could possibly be used as a different method for purifying piperazine.
after washing some rather dirty piperazine crystals in acetone, swim was drying them in a beaker on hotplate with moderate heat (definitly below the b.p. of piperazine), and noticed what looked like snow flakes rising out of the beaker, swim put a watchglass over the beaker and some rather nice looking crystals condensed on it.
swim still needs to test the melting point of them to ensure that they are indeed piperazine crystals, but swim can't imagine what else they could be.
since piperazine normally doesn't act like this the acetone must somehow be involved.
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You are talking about a sublimation. Why isn't that possible with piperazine?
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piperazine melts at ~100C and boils at ~150C, and this was going straight from solid(moistened but not dissolved in acetone) to "snow"
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Have you checked the mp/bp behavior of both anhydrous piperazine and the many piperazine hydrates (piperazine hexahydrate is pretty common). If neither sublimes, then I dunno...
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i could only find info for "dibasic piperazine", presumbly that means anhydrous.
what my friend had was almost surely hydrated.
i would think the hydrate would have a higher m.p. but less of a chance of subliminating.
but before my friend washed the pip. with acetone there was certainly no sublimination.
i recall distilling acetone out of a NH4Cl/water soltn and the condensor getting a coating of white "frost", perhaps the acetone+NH3<-->imine H20 equilibrium somehow results in sublination, although i guess no imine would form with a secondary amine like pip.
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although i guess no imine would form with a secondary amine like pip
No imine, but perhaps an enamine?
Still the whole thing sounds pretty strange though...