Author Topic: The final word on hydrogen bromide...  (Read 1363 times)

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Atropos

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The final word on hydrogen bromide...
« on: June 14, 2003, 11:06:00 AM »
I have seen many mantions of generating HBr gas in the same manner as one would liberate hydrogen chloride from aqueous solution, with the use of H2SO4 and NaCl, and then I have seen many statements that this does not work...

Since I have not seen the liberation of the gas from aqueous solution mentioned in any of the journal articles I have dredged up, and from the various posts saying "nay" I have pretty much come to the conclusion that this does not work, and you must resort to the use of tetralin and bromine.

Am I wrong?  Has anyone ever actually done the procedure using aqueous HBr?  If it does work, would one need to substitute NaBr for NaCl, or is the salt simply a dehydrating agent?  Since HCl is a weaker acid than HBr, I keep having the persistant thought that if NaCl is present, it would react and generate at least some HCl.

If it is not a viable option, would simply reacting equimolar amounts of a bromide salt and H2SO4 in GAA be a viable alternative for anhydrous HBr?

Any help would be greatly appreciated!

El_Zorro

  • Guest
You have to be careful using H2SO4 on any...
« Reply #1 on: June 14, 2003, 03:19:00 PM »
You have to be careful using H2SO4 on any bromide salts, because it has the tendancy to oxidize the brimide to elemental bromine.  It will make HBr, but it will be mixed in with the Br2, with the ratio depening on the reaction temp.

I would guess that just dripping 48% HBr into 96% H2SO4 would generate a fairly dry stream of HBr, but I don't know if it would oxidize the HBr, though.  Maybe a more knowledgable bee can answer that question.

By the way, what reaction needs anhydrous HBr?


Bwiti

  • Guest
Fuck Tetralin & Bromine..
« Reply #2 on: June 14, 2003, 09:21:00 PM »
"Hydrogen bromide and hydrogen iodide can also be made by reaction of the sodium or potassium salt with acid, but phosphoric acid must be used instead of sulfuric acid. Hot concentrated sulfuric acid oxidizes bromide and iodide ions."
-- pg. 978, General Chemistry by Jean B. Umland
----------------------
Also:
US3199953
Process For Production Of Anhydrous Hydrogen Bromide From Lithium Bromide

  "Into a turbomixer having approximately a 100ml capacity was charged 61g benzoic acid and 15g (approximately 0.15M) of lithium bromide. The mixture was heated to a temperature in the range 250-260*C with stirring, and nitrogen gas at a flow rate of 235ml per minute was passed through the heated mixture. After 1 hour at temperature, approximately 80% of the theoretical amount of hydrogen bromide had been evolved. At 2 hours, 89% of the theoretical hydrogen bromide had been evolved. The reaction is substantially complete after 4 hours of reaction time."
8)


Barium

  • Guest
HBr
« Reply #3 on: June 15, 2003, 04:57:00 AM »
Sulfuric acid can be dripped into a mixture of GAA and NaBr or KBr. This will give a solution of HBr in GAA which is a remarkable effective mixture of reactant and solvent. BUT, it's a nightmare to get rid of the Na2SO4 or K2SO4 from the solution. I've tried and I've cursed! The filtration is not a quick one and HBr and GAA are both very hygroscopic.

HBr can be made by dripping sulfuric on NaBr wetted with some water without oxidizing 2 Br- to Br2 if the mixture is kept cold by slow addition and good cooling.


hypo

  • Guest
interesting...
« Reply #4 on: June 15, 2003, 05:41:00 AM »
and the GAA/HBr mixture does not form an azeotrope
like H2O/HBr?  :(