Sciencemadness Discussion Board

How to get Hydrobromic acid (HBr) from Br2

hardik22 - 18-1-2018 at 22:35

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)
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hardik22 - 18-1-2018 at 22:38

the pdf is HBr gas generation from 48% w/w HBr solution

woelen - 19-1-2018 at 00:01

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.

Melgar - 19-1-2018 at 01:35

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.

hardik22 - 19-1-2018 at 01:41




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?

Melgar - 19-1-2018 at 02:01

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.

DJF90 - 19-1-2018 at 02:16

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

woelen - 19-1-2018 at 10:11

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]

Chemi Pharma - 20-1-2018 at 05:05

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“.


unionised - 20-1-2018 at 05:48

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.

Melgar - 20-1-2018 at 09:14

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.

S.C. Wack - 20-1-2018 at 09:20

Quote: Originally posted by Chemi Pharma  
Better then all the options that have been posted until now, is the reaction of bromine with tetralin


Losing half the bromine forever can't be better.
Quote: Originally posted by Melgar  
Adding hydrazine sulfate to liquid bromine might work


Sulfur was a better plan.

Melgar - 20-1-2018 at 10:34

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]

S.C. Wack - 20-1-2018 at 11:33

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.

Boffis - 20-1-2018 at 14:16

What's wrong with the Nurdrage video method using sodium bromide and sodium hydrogen sulphate? Simple and easy to acquire reagents?

clearly_not_atara - 20-1-2018 at 17:33

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.

unionised - 21-1-2018 at 01:42

I suspect that titanium burns well in bromine...
Some reactions really are "too good".

clearly_not_atara - 21-1-2018 at 13:12

I definitely meant to react titanium with bromine water... not liquid bromine!

j_sum1 - 21-1-2018 at 15:40

Quote: Originally posted by clearly_not_atara  
I definitely meant to react titanium with bromine water... not liquid bromine!

I dunno. That sounds kinda fun. At least as much fun as aluminium and bromine.

AJKOER - 23-1-2018 at 16:05

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]

Dope Amine - 23-1-2018 at 22:02

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.

Interesting method!

Monoamine - 19-6-2021 at 17:19

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?

Any thoughts on whether the following might work?

Monoamine - 19-6-2021 at 17:55

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...


Apparatus.jpg - 2.9MB


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]

S.C. Wack - 19-6-2021 at 19:11

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.

draculic acid69 - 20-6-2021 at 02:40

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.

draculic acid69 - 20-6-2021 at 02:51

h3po3+br2 then distilling. h3po2 + I2 is extremely exothermic so I'm guessing that it's the same if not worse with br2. h3po3 is a much milder controlled
rxn.
Red P could also be used but using rare red P + expensive hard/dangerous to handle br2 just to get to hbr or using the br2+sulfur route seems like going the long expensive difficult & troublesome way to arrive at hbr.br2+acetone will give off lots of hbr gas if you don't mind losing more than 50% of the bromine.again it's the stupidly long troublesome way to get hbr.

[Edited on 20-6-2021 by draculic acid69]

Monoamine - 20-6-2021 at 11:56

Quote: Originally posted by draculic acid69  
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.



An alternative which may be a bit less toxic is Na2S2O3
for which the following reaction occurs:

4 Br2 + Na2S2O3 + 5H2O -> Na2SO4 + H2SO4 + 8 HBr. Source

So with sodium thiosulfate (Na2S2O3) you should even be able to recover some sulfuric acid for later work.

Monoamine - 20-6-2021 at 12:05

Quote: Originally posted by hardik22  
I want to get HBr 48% w/w from Br2 ...
what is the procedure or method for it?



Use sodium thiosulfate (Na2S2O3):

4 Br2 + Na2S2O3 + 5H2O -> Na2SO4 + H2SO4 + 8 HBr. Source

Maybe vitamin C is better for reducing Br2 than sodium thiosulfate after all...

Monoamine - 21-6-2021 at 19:51

On the other hand sodium thiosulfate (Na2S2O3) may not be the best choice in the end for the following reasons:

It melts at around 48.3oC and actually decomposes at 100oC, which is lower than the boiling point of HBr.

To make matters worse, it reacts with hydrochloric acid as follows:

a2S2O3 + 2HCl -> 2 NaCl + S + SO2 + H2O !!

I would imagine that the same happens with HBr, except that you'd end up with NaBr as one of the products, so you'd be right back where you started. Also SO2 is pretty toxic, so not really something you want to be making...

Earlier I said that ascorbic acid (C6H8O6)may not be a good choice, but I'm starting to think that it may actually not be so bad. It reacts with Br2 as follows:

C6H8O6 + Br2 -> 2 HBr + C6H6O6

(C6H6O6 is dehydroascorbic acid)

Both of these vitamin C variants melt at temperatures well above the boiling point of HBr.

The downside is that these "reducing agents" easily decompose, and could react with the HBr via nucleophilic substitution of their OH groups...

However, it might still work, since this is actually used to determine the amount of vitamin C in supplements and then measuring how much HBr is produced.

This will probably take some trial and error, but I would start by simply trying to distill off the HBr and hope see how concentrated you can get it...

clearly_not_atara - 21-6-2021 at 21:01

You should consider that bromine is about fifty times as toxic as sulfur dioxide before attempting any of this.

Also, I am pretty sure that the decomposition point you're citing is the dehydration of the hydrate. It's not relevant anyway because the thiosulfate will be consumed by oxidation before you distill it.

The greater concern would be generating H2S from thiosulfuric acid disproportionation, and dealing with the heat of reaction. This may be partially managed by dilution.

I like the H3PO3 idea, if phosphites are available. But it's probably more practical + cheaper to just make a bromide and heat it with TsOH or NaHSO4.

Amos - 22-6-2021 at 08:53

You guys are really still responding to a pointless thread, only relevant to one user, that then never returned to look at the answers?