bhassi
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query: how to dehydrate iron(III) chloride?
hi all
I have a query and I hope I would get it solved. One year back I purchased Ferric Chloride hexahydrate (FeCl3.6H2O) from Sigma. It was in good
condition..that is..completely dry and free flowing. I used it happiy and then kept it back in the chemical store. Yesterday I needed it again and I took the bottle back from the store..but to much of
my disappointment it was completely hydrated....almost completely converted from solid to solution state owing to the extraordinary hygroscopic nature
of this compound. I am going to screen a large number of lipid samples from natural
sources using ammonium ferrothiocyanate method for lipid quantification which requires absolutely dry salt. I tried for this salt with a few of my
friends but they are all having the same problem.
I was wondering if there is any method of getting the salt back to the original state..that is hexahydrated state besides being completely dry?
I would much appreciate if somebody could give some feedback.
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Vitus_Verdegast
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I would say, evaporate the water from your solution, preferably using light heat and vacuum.
You cannot get it much drier than the hexahydrate stage.
By heating it strongly it will start to decompose, losing HCl.
The only way to go from the hexahydrate --> anhydrous FeCl3 is washing it with SOCl2.
melting point FeCl3.6H2O = around 37°C
Sic transit gloria mundi
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leu
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| Quote: | | The only way to go from the hexahydrate --> anhydrous FeCl3 is washing it with SOCl2. |
That's not the only way, one can probably also heat it in an atmosphere of hydrogen chloride; or as otto posted on a defunct web site one can simply
heat it in the presence of ammonium chloride Another approach is to use the
procedure that was published in US3471250 which is attached, there are some other methods that have been published that can be provided later upon
request 
[Edited on 1-8-2006 by leu]
[Edited on 1-8-2006 by leu]
[Edited on 2-8-2006 by leu]
Attachment: US3471250.pdf (309kB)
This file has been downloaded 1015 times
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Organikum
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I thought the heating with ammonium chloride method works only with magnesium chloride but not for AlCl3 and FeCl3?
/ORG
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leu
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This is what he said:
otto
(Newbee)
03-11-02 20:48
No 280725
Re: Anhydrous ferric chloride FeCl3 MgCl2 SnCl2 NiCl2
yes antoncho,
not about friedel-crafts though. instead of heating in HCl-atmosphere, one can use NH4Cl. so for MgCl2 i know that procedure to work just fine. mix
MgCl2*xH20 with excess of NH4Cl (exact amounts dont know this moment) and heat 'till all NH4Cl has gone.
for AlCl3 this method does not apply.
otto
It's possible that he's wrong, but it seems unlikely
Chemistry is our Covalent Bond
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neutrino
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I've never heard of that method before. How does it work? Something along these lines, maybe?
MCl<sub>X</sub> + H<sub>2</sub>O --> MCl<sub>X-1</sub>OH + HCl
MCl<sub>X-1</sub>OH + NH<sub>4</sub> --> NH<sub>3</sub> + MCl<sub>X-1</sub>
MCl<sub>X-1</sub> + Cl --> MCl<sub>X</sub>
(charges ignored for the sake of simplicity)
[Edited on 1-8-2006 by neutrino]
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leu
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Since that method has never been considered for personal use, the mechanism hasn't been considered either The proposed mechanism seems reasonable, perhaps some member who has the time and means can investigate this reported
reaction to determine if and how it occurs  As far as the method of dehydration
of metallic chlorides by refluxing in thionyl chloride, Inorg. Synth. 28, 321-3 (1990) describes that process:
Attachment: pray.zip (15kB)
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not_important
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The ammonium chloride method works through the diassociation of the salt into ammonia and hydrogen chloride; in effect t is similar to dehydrating in
a stream of HCl. Bothe the HCl and NH3 may associate with the water, helping it along, and the cation - reducing the interaction with the water. And
the HCl certainly surpresses and undoes any hydrolysis.
I first saw this use of ammonium chloride in an early J Inorg Chem, for preparing anhydrous chlorides of the rare earths, which can be done by mixing
their oxides or carbonates with NH4Cl and so on.
The procedure does not work well with fairly volatile chlorides, as they evaporate along with the NH4Cl. Thus it fails with AlCl3, which sublimes
around 180 C, would be gone bofore the NH4Cl starts subliming around 337 C (or even diassociating much). MgCl2 melts at 700 C or so, and boils above
1400, so there's no problem there. ferric chloride would seem to be a borderline case, boiling around the sublimination point of NH4Cl.
I've read of several cases of the bromides being used.
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bhassi
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Thanks all the guys for taking interest in this thread and sparing time to reply with such wonderful ideas.
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cranium
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I would like to know how to dehydrate household ammonia, so that I can get the pure ammonia gas from the solution.
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not_important
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Household ammonia isn't a very good source. Simplest way is to boil the NH3 out of the water, saturating with salt can help get a little more out.
Dry with NaOH or KOH, condense with dry ice. Ammonia really wants to get back with water, it will give you burns and rip your lungs to shreds.
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