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Author: Subject: Storage of PBr5
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[*] posted on 1-7-2008 at 11:29
Storage of PBr5


Hi

I looking for safe manner to storage PBr5. A glass pot containing PBr5 with joint in air fuming HBr and leading to decompose of PBr5. This compound is very rapidly react with traces of water in air and when i close tight jar a pressure of HBr in container increase ... May be is simple method to preserve PBr5.


[Edited on 1-7-2008 by Inorganic]
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[*] posted on 1-7-2008 at 12:47


You should try flushing the jar with a dry, inert gas such as argon or nitrogen, fitting a tight teflon screw lid with parafilm around the closed neck, and keeping the jar in a baggie with CaSO47 or another suitable dessicant. Works for most moisture sensitive compounds (LiALH4, TsCl, etc)



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[*] posted on 2-7-2008 at 11:28


Now I keep PBr5 in desiccator over anhydrous CaCl2 but fumes of liberated HBr opening a lid. When I used silicon grease ([Me2SiO]n) to seal a desiccator a gaseous HBr react with lubricant merging both part of vessel very hard :mad:. Decomposition product looks something like "SiO2" .
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[*] posted on 2-7-2008 at 14:22


I think CaCl2 isn't efficient enough then, the water partial pressure is still high enough to form HBr, and "dry" the CaCl2 -water consumed, relative humidity becomes lower than that provided by Cacl2 alone, so the CaCl2 release some of the water absorbed, etc etc. I guess you are "drying" your CaCl2 in the most expensive way :).
I would try P2O5 or conc. H2SO4 (both less practical than CaCl, try absorbing them on vermiculite). But if sealed well enough, it shouldn't be a problem. Is the PBr5 is it's original recipient?




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[*] posted on 2-7-2008 at 14:52


P2O5 would be best choice for dessicant.

Another option would be to not store it at all. Store PBr3 and Br2 seperately in premeasured charges and form PBr5 as needed from these, in an inert, dry atmosphere. Argon better than N2.




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[*] posted on 2-7-2008 at 16:24


I take it PBr3 is much less reactive/unstable than PBr5 (never used any of them)?

But in any case he needs to store the amount he has now. I can imagine HBr fumes everywhere you leave the bottle must be pretty annoying...
If using dry inert gas, and the bottle is sealed properly, the formed HBr should be minimal or non-existant. A few layers of parafilm might be better suited than a desicator in this case (in a can with vermiculite and thiosulfate?)




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[*] posted on 2-7-2008 at 19:28


CaCl2 and other neutral or acidic desiccants are worthless in this case!
He wants something that not only binds water, but also binds the HBr vapors, to keep them from accumulating and creating pressure in the desiccator!

I am storing my bottle of PCl3 in an airtight wide-mouth screw jar (pickle jar) with Ca(OH)2 on the bottom. It has kept fine for over three years now, without any pressure buildup or hydrolysis of the substance!

I recommend the same for the PBr5 bottle- put it in an airtight jar with a substance that binds the HBr, NOT just a desiccant.
KOH would be a good choice for example. CaO too.
I like to use Ca(OH)2, as my jar is airtight and I don't need to bind moisture.




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[*] posted on 2-7-2008 at 22:32


I have similar problems with storage of SOCl2, SO2Cl2 and CH3COCl. I ampouled the bigger amount of these chemicals and I left 20 ml or so in small bottles. These three bottles I put in a big plastic jar with a screw cap, and inside this jar, I also have a small open bottle with NaOH. This method of storage works very well. The only thing is that I should not keep this bigger jar tilted, otherwise I have granules of NaOH spread around in the big plastic jar (but not in the precious reagents).



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