Sciencemadness Discussion Board

hexahydrate to monohydrate - what could I use ?

chemguy5000 - 24-11-2012 at 10:32

My dear science friends,
I have a question about - propably a stupid question, but I*m just a Biotechnician:

I have a substance in the hexahydrate formular and I want to get rid of all the H20 to get the monohydrate form. I read people do this by distilling with absolute ethanol. We only have 96 vol% Eth-OH. Would this work ?
In this forum I came across some information that I could use some other "drying chemicals" - which I don't have.......

What should I do?

Thanks

CG

Mailinmypocket - 24-11-2012 at 10:43

Quote: Originally posted by chemguy5000  
My dear science friends,
I have a question about - propably a stupid question, but I*m just a Biotechnician:

I have a substance in the hexahydrate formular and I want to get rid of all the H20 to get the monohydrate form. I read people do this by distilling with absolute ethanol. We only have 96 vol% Eth-OH. Would this work ?
In this forum I came across some information that I could use some other "drying chemicals" - which I don't have.......

What should I do?

Thanks

CG


And the hydrated chemical is...?

Fossil - 24-11-2012 at 19:09

Removing all of the H2O will not give you the mono-hydrate, but the anhydrous.

To make an accurate prediction, we would need to know what the compound is.

chemguy5000 - 25-11-2012 at 03:03

Thanks for the answers so far - the compound is: piperazine hexahydrate from sigma aldrich...
That I'll get the anhydrous - didn't think about that that all the cristall-water will be removed from the substance or at least most of it. The yield will be also not so good because of the only 96 % Eth-OH - right?

turd - 25-11-2012 at 05:12

Could it be that you misunderstood the procedure to benzylpiperazine (https://www.erowid.org/archive/rhodium/chemistry/bzp.html)? They are mixing equivalent amounts of the freebase and the dihydrochloride to get the monohydrochloride.

turd - 27-11-2012 at 13:44

The mystery was cleared up by U2U: The OP indeed wants to transform piperazine hexahydrate to the dihydrochloride monohydrate.

So it seems that the OP missed a few points:
- The reaction is an elementary ionic acid/base reaction, not a dehydration.
- The "dehydration" is just a byproduct of different crystallization behaviour of the freebase and the dihydrochloride.
- The use of absolute ethanol and dry HCl gas is to decrease the solubility of the dihydrochloride in the solvent.
- The same effect can be achieved by diluting with acetone as described in the above document. Thus no need for nasty gaseous HCl.

My recommendations to the OP:
- Read, reread and rereread until you understand the background of what you are doing.
- Always be as exact as possible in your queries. Better too much than too little information.

chemguy5000 - 21-1-2013 at 23:56

Hey there,
it took a while but I've reread and reread all over and I think I got most of the procedure. But the first part I just can't understand:

They claim to add piperazine heahydrate in ethanol and then just Quote: .....22.1g of piperazine dihydrohlride monohydrate.

So there are two substances added to the 50ml of ethanol.

The hexahydrate - that's clear and the piperazine dihydrochloride must be produced in the second step (Note1). But without nasty HCL-Gas I would have to add 0,125 mole) of piperazine heahydrate and add the exact ammount of pure HCL 0.125 mole - Is this correct ?

So I can use (as turd told me) Acetone instead of Ethanol - right?

Is it also possible to use other solvents than dry benzene to wash 1-benzylpiperazine dihydrochloride and an alternative to chloroform to collect the BzP from the basic solutions, like DCM or something?

Thanks,

CG

[Edited on 22-1-2013 by chemguy5000]