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hardik22
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How to get Hydrobromic acid (HBr) from Br2
I want to get HBr 48% w/w from Br2 ...
what is the procedure or method for it?
Attachment: HBr Gas Generation PFD.pdf (14kB)
This file has been downloaded 459 times
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hardik22
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the pdf is HBr gas generation from 48% w/w HBr solution
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woelen
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Why use (expensive and valuable) Br2 for this? Get some KBr or NaBr, available at kilo quantities from eBay. With H3PO4 you can make HBr-gas, which
you can pass through water. You can also use H2SO4, but then you have to use somewhat dilute acid and distill over HBr and water together, otherwise
you will have partial oxidation and a mix of HBr, Br2 and SO2 will go over, leading to impure HBr.
I even think that you can use NaHSO4, NaBr and some water. First allow Na2SO4 to crystallize and then decant the liquid, which is distilled.
Really, don't use Br2 for making HBr. It is much more risky, much more expensive, and also much harder to get a usefully pure product.
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Melgar
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That being said, if you wanted to do it anyway, you could add Br2 to elemental sulfur and water. The sulfur would oxidize to sulfuric acid, so this
reaction is often used if you have Br2 and want to use it to make alkyl bromides from alcohols. The reaction between Br2 and S isn't very vigorous
and takes a while. I think it gets stuck at S2Br2 for a while. Elemental phosphorus reacts with bromine much faster, but it tends to cause
explosions and fires.
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hardik22
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Thank you, I appreciate your answer.
but can i use NaOH solution with Br2 and convert into NaBr ? after then can i get HBr from NaBr?
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Melgar
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Quote: Originally posted by hardik22  |
Thank you, I appreciate your answer.
but can i use NaOH solution with Br2 and convert into NaBr ? after then can i get HBr from NaBr? |
That'll give you sodium hypobromite, which will disproportionate into sodium bromide and sodium bromate. If you have Br2 and want to somehow form HBr
with it, you have to reduce the Br2 somehow, by using the Br2 to oxidize something. That way, it'll accept an electron and be Br-. Sulfur and water
is probably the best way to go in this case, just because it'll form sulfuric acid, and doesn't go very fast.
woelen is just telling you that sodium bromide is so much easier to get than elemental bromine, that he doesn't think you should waste that.
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DJF90
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There is a reliable procedure in OrgSyn using the reduction of bromine with sulfur dioxide, followed by (double) distillation:
http://www.orgsyn.org/demo.aspx?prep=CV1P0025
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woelen
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If you really want to spoil your Br2, then add it to a solution of NaOH and then heat the solution to dryness and then to a read heat. The NaBrO3 then
decomposes to NaBr and O2. The NaBr then can be used to make HBr.
But again, it really is insane to use bromine for making HBr, unless you have some large scale industrial process in which Br2 is isolated from some
dilute solutions (e.g. by bubbling Cl2 and hot air through brine with a tiny amount of NaBr in it) and you want to concentrate it again in NaBr. In a
lab-setting, however, you never use Br2 for making a dull chemical like NaBr.
[Edited on 19-1-18 by woelen]
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Chemi Pharma
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Better then all the options that have been posted until now, is the reaction of bromine with tetralin, giving anhydrous HBr, what is a must for the
major reactions envolving HBr, cause not always 48% HBr works well to give the desired product, and must to be concentrated to do that.
From PrepChem:
3) Preparation of hydrobromic acid from tetrahydronaphthalene and bromine:
If anhydrous hydrogen bromide is desired, the procedure is carried out in the absence of water, using dry reagents.
Preparation of hydrobromic acid from tetrahydronaphthalene and bromine:
Thirty-five grams of tetrahydronaphthalene (tetralin) are placed in the flask with either 200 ml of water, depending on the desired concentration of
the acid. At first the flask is cooled in ice while 50 ml of bromine are slowly added drop-wise ; about one gram of iron filings catalyzes the
bromination. As the reaction proceeds, the flask may be allowed to warm up to room temperature. After all the bromine has been added the flask should
be shaken for some time; the aqueous layer should be colorless. The acid layer is then separated from the organic material and worked up as in
“Preparation of hydrobromic acid directly from hydrogen and bromine“.
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unionised
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IIRC the industrial reduction of bromine to bromide uses scrap iron.
On a lab scale I think steel wool would be a sensible option.However you would probably need to add soda to convert it to ferrous hydroxide/carbonate
and NaBr before adding H3PO4 and distilling.
Ferrous phosphate isn't very soluble, so it would be a pig to remove from the still pot.
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Melgar
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Adding hydrazine sulfate to liquid bromine might work, releasing N2 and HBr. But don't do this without looking for a source first, since neither of
those substances are ones you want to be careless with.
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S.C. Wack
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Losing half the bromine forever can't be better.
Sulfur was a better plan.
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Melgar
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Here's a patent, if you need a procedure for making HBr from Br2 and S:
https://www.google.com/patents/US3145079
Of course, nobody's mentioned the easiest way yet: add Br2 to a sodium metabisulfite solution, then distill from that. You may need to add a strong
mineral acid (H2SO4 or H3PO4) before distilling for best yields though.
[Edited on 1/20/18 by Melgar]
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S.C. Wack
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Schlessinger's Inorg. Lab. Prep. has an S process among others. The patent speaks of problems they compensate for, but naturally they operate in a way
causing problems only they can fix.
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Boffis
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What's wrong with the Nurdrage video method using sodium bromide and sodium hydrogen sulphate? Simple and easy to acquire reagents?
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clearly_not_atara
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Titanium metal might work as an alternative to phosphorus or sulfur. But you have to activate it first somehow. One advantage is that the byproduct
TiO2 is easily separated by filtration.
[Edited on 04-20-1969 by clearly_not_atara]
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unionised
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I suspect that titanium burns well in bromine...
Some reactions really are "too good".
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clearly_not_atara
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I definitely meant to react titanium with bromine water... not liquid bromine!
[Edited on 04-20-1969 by clearly_not_atara]
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j_sum1
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I dunno. That sounds kinda fun. At least as much fun as aluminium and bromine.
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AJKOER
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More interesting than turning Br2 into HBr is converting it into 5 HBr + HBrO3:
At pH 6-8: 3 Br2 + 3 H2O = 5 HBr + HBrO3
See comments at https://books.google.com/books?id=T-20PBkl51IC&pg=PA76&a...
[Edited on 24-1-2018 by AJKOER]
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Dope Amine
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To get HBr/acetic acid I just add NaBr and phosphoric acid to acetic acid. Worked great for cleaving aryl methyl ethers. No Br2 produced
upon heating like is the the case when using sulfuric acid.
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Monoamine
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Interesting method!
| Quote: Originally posted by Dope Amine | | To get HBr/acetic acid I just add NaBr and phosphoric acid to acetic acid. Worked great for cleaving aryl methyl ethers. No Br2 produced
upon heating like is the the case when using sulfuric acid. |
Two questions: 1) Does it have to be phosphoric acid (maybe because it's a weaker acid? Or could H2SO4 work too as long as you include acidic acid?
2) Did you per-chance post your synthesis somewhere? I'm always short of HBr and the "standard" method I use never seems to give me HBr that is more
than about 20% by weight. Distilling off some of the water helps, but its still not fully concentrate, and even when distilling just about
100oC some acid still seems to distill of too, so you loose some in the process. Maybe fractional distillation?
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Monoamine
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Any thoughts on whether the following might work?
Generate Br2 by dripping H2SO4 into NaBr (or KBr) (not in solution, just the dry salt).
If you are not using conc. H2SO4, then begin distilling at around 120oC since you'll probably directly form some HBr in the reaction flask,
if it is concentrated 60oC should be enough.
Submerge the other end of the condenser in a solution containing some reducing agent (vitamin C may not be best here, since the HBr would probably
react with the OHs in it... Some reducing agent that will precipitate out should be best, or at the very least does not react with the HBr so you can
remove it (HBr) by distillation. (Question would good old sodium thiosulfate do the trick??)
After you're done, rinse the glassware with a reducing agent solution and collect the run off (carefully! Since this will be acidic).
An advantage of this method may be that it allows you to control the amount of of H2O exactly, so you can make any concentration that's physically
possible.
Sorry for the bad doodle, I just included the drawing of the apparatus for clarity...
And bear in mind, I haven't actually tried this, so it may all go horribly HORRIBLY wrong....
[Edited on 20-6-2021 by Monoamine]
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S.C. Wack
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HBr can be made with sulfuric acid if the acid is not concentrated and the addition to KBr does not get hot. In many cases it does not need to be
distilled, e.g. n-butyl bromide in Vogel.
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draculic acid69
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| Quote: Originally posted by Melgar | Here's a patent, if you need a procedure for making HBr from Br2 and S:
https://www.google.com/patents/US3145079
Of course, nobody's mentioned the easiest way yet: add Br2 to a sodium metabisulfite solution, then distill from that. You may need to add a strong
mineral acid (H2SO4 or H3PO4) before distilling for best yields though.
[Edited on 1/20/18 by Melgar] |
While metabisulfite will form hbr from br2 I'd be very concerned about so2 contamination.
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