Author Topic: Anhydrous amines and different salts of amines  (Read 90 times)

fishinabottle

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Anhydrous amines and different salts of amines
« on: April 05, 2012, 09:22:43 AM »
 :'(  It is most probably just wasted time to write this for latest tomorrow five people will repeat what they read at Rhodiums or similar as if better ways don´t exist.

But for the hope that one or two listen and profit here it is:

Anhydrous ammonia, methylamine and hydroxylamine as gas or in situ for an alcoholic solution or direct in reaction.

Ammonia and methylamine: Dropping conc. solution of NaOH onto the salt calls is ok in small batches but if one wants some more it gets pretty fast to wet and yields suffer as dryness. The addition of lime CaO prevents this and gives superior results.
(courtesy lugh, who a long time ago posted the correct procedure for anhydrous ammonia which got long forgotten since).

Note by Enkidu: NaOH + NH4Cl --> NaCl + NH3 + H2O. NH3 + H2O <---> NH4OH. 
2CaO + 2NH4Cl --> Ca(OH)2 + CaCl2 + 2NH3, i.e., the end of the water problems.

In situ, to generate an alcoholic solution of ammonia, methylamine or hydroxylamine (and many others I suspect), one uses not the hydrochloride but the sulfate and preferable the phosphate. The salt is slowly added to a suspension of CaO in the alcohol (ethyl, methyl issoprop...) with stirring, a dash of NaOH in water may be necessary to initiate the reaction. Cooling and patience. Filter and voila: Quantitative amine in alc, no tedious weighing is necessary afterwards, you calculate this beforehand.
Also in a reaction CaO can be used instead of NaOH to genrate the base from the salt. (procedure was adapted from a reference where hydroxylamine sulfate was wanted to form an imine with a ketone and the sulfate salt was used accordingly with 95% yields claimed).

Anyways, it seems to have been forgotten that there are other salts except the hydrochloride. In special when the salt is not the final product but an intermediate for further reaction or for purification the sulfate or even more so the phosphate are superior in formation and handling.
All phosphate salts I encountered drop out of cold water and are just filtered off and dried in a matter of minutes. They are freed with lime into most organic solvents plus alcohols without contamination by water. The Ca(OH)2 is removed by decanting the solvent more then filtration to get around clogging, but it is easy.

Thats not the quick, quick, hurry, hurry way to do it, but the relaxed one without hassle, stress and problems. Just relax, CaO may take its time to react - not exceedingly though. But as there is no need to babysit anything it really does not matter at all.

Preparing the phosphate (with H3PO4 of course) has another advantage: Being non-oxidizing one can hardly scorch the amine, something what with HCl happens much to often to some extent and what is one of the main reasons of final product with strange properties.


After 17 years as a regular on this kind of boards and curse with a very good memory I am getting tired. The Rhodium archive which once was helpful has become a bane with its myth of validity. Someone has to tell ppl that most of it is misleading, plain wrong, wishthinking or at least byzantine. The better parts are almost correct but often not up to date anymore.

It is high time somebody makes a new compilation, if not for the sake of education but for the sake of the boards not getting cluttered with this stuff anymore. To have the possibility to tell ppl: Go there read that and then ask again (instead of telling them to search what actually mostly will turn up the same nonsense for it getting repeated over and over again...).

my 3 cents (€)
/ORG
« Last Edit: April 23, 2012, 04:15:36 AM by Enkidu »

no1uno

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Re: Anhydrous amines and different salts of amines
« Reply #1 on: April 09, 2012, 02:46:22 AM »
With ammonia at least, the phosphate salts can be purchased in massive  bulk (monoammonium & diammonium phosphate fertilizers). That is the starting point, expect to spend some time recrystallizing that shit (don't try and put too much in at the start unless filtering fine mud is something you enjoy).

Once you have pure crystals, they are incredibly soluble in water so purification is easy if rather a long task, heat will give virtually anhydrous ammonia and polyphosphoric acid. Adding water to the polyphosphoric acid will give some fairly pure (you are gonna have to wait) phosphoric acid.

One thing I have seen (actually seen - not read on rhodium) is that the addition of povidone-iodine causes the clear polyphosphoric acid glass to dissolve really fucking rapidly (instead of taking days), a brown tar is produced as well as an iodine "type" smell. I wonder what would happen with I2 or Br2?

Someone should perhaps register some accounts at sciencemadness.org and associate them with youtube accounts in the same names. Then perhaps a couple of people, with time and interest, could do some basic chemistry and provide some actual illustrated procedures. As a matter of fact, there are some rather interesting ones on youtube already - I2 from Povidone, GAA from sodium acetate + sodium hydrogen sulfate, etc. There are some absolutely shit ones as well, a webpage/wikipedia-type arrangement (I vote for a webpage - terms & conditions of use would not be really easy to stay inside of).
« Last Edit: April 09, 2012, 02:59:08 AM by no1uno »
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