Sciencemadness Discussion Board

Anhydrous metal chlorides with NH4Cl?

Polverone - 26-12-2002 at 16:16

Many metallic chlorides cannot be prepared in an anhydrous state from their hydrates without some (or much) decomposition, forming hydroxides. So one can't always dump a metal or basic salt of a metal in hydrochloric acid, apply heat, and hope to end up with the pure, anhydrous chloride. Anhydrous metallic chlorides are often prepared with the aid of hot, dry hydrogen chloride or chlorine gas, sometimes thionyl chloride or hot carbon tetrachloride vapor. None of those materials particularly appeal to me - thionyl chloride or CCl4 because of the trouble of acquiring them, hydrogen chloride or chlorine because of the difficulty in generating, drying, and delivering the gasses across multiple vessels. I think that ammonium chloride can be made anhydrous merely by the application of heat; can someone confirm this? If so, it seems that (for instance) Zn + 2 NH4Cl -> 2 NH3 + H2 + ZnCl2 would be a viable method of preparation that wouldn't introduce any water into the system. The one difficult part might be separation of the metallic chloride from remaining ammonium chloride, and the tendency of (for example) AlCl3 to sublime, but in some uses I don't think that NH4Cl contamination would matter. Comments? Suggestions? I will be trying this once Christmas vacation is over and I'm back to my chemicals, equipment, and references. Anhydrous metallic chlorides might be used without ever exposing them to moisture-containing air if subsequent reactions were performed in the same vessel.

Nick F - 1-1-2003 at 11:35

"I think that ammonium chloride can be made anhydrous merely by the application of heat; can someone confirm this?"

Dessication with H2SO4 etc would be better I think, since it sublimes so easily. I don't know what temperature you would have to heat it to in order to totally dehydrate it (it doesn't seem very hygroscopic..), but you might get some sublimation.
Most of the chlorides produced could easily be seperated by sublimation of the ammonium chloride, except AlCl3. I'm sure there are a few more too but I can't remember them (BeCl2 probably). Maybe not.
I don't think the reaction would be very fast unless done in a sealed chamber at a high temperature, which would obviously make things a lot more complicated.

Unless - - that ball mill method maybe?

Hmmm.... what is the solubility of NH4Cl like in ethanol or methanol, do you suppose? If you used a metal alkoxide (easily prepared with the alcohol, a base (like oxide, carbonate, hydroxide) and a dessicant) then you'd produce the chloride, an alcohol and ammonia, and the alcohol could be boiled off.
But if NH4Cl is soluble in alcohols then this would solve the problem of solid-solid reactions being slow, at least to some extent.

madscientist - 1-1-2003 at 11:40

Ammonium chloride is slightly soluble in alcohol.

NH4Cl dries easily

blazter - 1-1-2003 at 12:01

I have produced NH4Cl by neutralizing household ammonia with HCl and evaporating the water. It formed a nice and dry cake on the bottom of the pan and seemed to dry well. The crystals were quite interesting looking as i recall but im not exactly the shape they formed... anyways i'll stop rambling i gotta sleep off this hangover

Rhadon - 1-1-2003 at 13:18

Blazter, did you also test your NH4Cl for hydrate water? If a substance looks dry it can still be a hydrate.


blazter - 2-1-2003 at 16:32

I really didn't need it to be anhydrous, because i ended up just putting it into an ammonia generator with NaOH. I wasnt even aware that there were tests to determine if it was anhydrous. I imagine that it could be purified by sublimation if worst comes to worst. At high temps. i think it sublimates before it decomposes.

Rhadon - 2-1-2003 at 19:25

Oh, I think I misunderstood you. I thought that you wanted to tell us that the CH4Cl you got was anhydrous. My mistake.

Subliming and re-subliming the NH4Cl should not work: It sublimes at 338 °C, whereby it is decomposed to HCl and NH3 (which at once reacts back to form NH4Cl). Since at this temperature the water is also vaporized, it will immediately form the hydrate again.

Organikum - 19-12-2003 at 15:29

Ammoniumchloride is told to work for magnesiumchloride but not for other metal chlorides like AlCl3.
Dont know.

But perhaps TTT, trichloroisocyanyric acid might be a suitable "in situ" source of chlorine to do the job.

DCM or perchlorethylene, TTT and Al-wire pieces - perhaps a drop water to start the reaction - the water will be scavenged by the formed AlCl3 and should be no real problem.

LIGHT will be needed - a UV lamp would be perfect but a halogene lamp should work also. This could be used for reaction control also.

Solubility is no question, just stirring the shit out of the broth...... :D
Does AlCl3 react with the TTT?

unionised - 19-12-2003 at 16:09

NH4Cl crystalises as such, not as a hydrate.
Some metal chloride (eg CuCl2, FeCl3) would be reduced by NH3 at high temperatures.
A lot of metal chlorides form addition compounds with ammonia in much the same way as they form hydrates.

blip - 22-12-2003 at 22:14

Ammoniumchloride is told to work for magnesiumchloride but not for other metal chlorides like AlCl3.

Maybe because AlCl<sub>3</sub> acts as a Lewis acid and binds to NH<sub>3</sub>, just like BF<sub>3</sub> would be expected to... but I bet you already knew that. :)

<tt>&nbsp;&nbsp;H&nbsp;&nbsp;&nbsp;&nbsp;Cl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb sp;&nbsp;&nbsp;&nbsp;H&nbsp;&nbsp;Cl
&nbsp;&nbsp;|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;|+&nbsp;&nbsp;|-
&nbsp;&nbsp;|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;&nbsp;|
&nbsp;&nbsp;H&nbsp;&nbsp;&nbsp;&nbsp;Cl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb sp;&nbsp;&nbsp;H&nbsp;&nbsp;Cl</tt>