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longtermmadscientist
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Bromine from NaBr
I've been thinking of a simple way of producing a few ml of elemental bromine using sodium bromide. Could conc. HNO3 be used on NaBr solid or
solution? I've been researching up on this, and there's a lot of talk of H2SO4 but it seems it's not a strong enough oxidant to produce Br2 in good
yield, and you get a lot of HBr.
My concern is that I will produce a lot of NO2, which, being the same colour as Br2, could lead to some confusion as to how much Br2 has been
produced. Also, I'd like to know whether the bromine would contain more that a trace of NO2. Water impurity can be extracted by conc. H2SO4, but what
about removing the NO2, if this turns out to be an issue?
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simba
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Why don't you just use sulfuric acid? You said you need only a few ml, so yields are not important right?
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elementcollector1
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I would recommend 98% H2SO4, added slowly to very cold NaBr solid. If you really wanted to go the extra mile, you could use dry ice so that any
bromine formed is frozen, not likely to sublimate. At least, I think that would work (hint: don't use glass. Go for ceramic.), but it might end up
that the solid bromine formed would prevent further reaction, etc.
Alternative: Trap reaction inside a corked gigantic flask (large enough for the bromine gas to spread out without increasing pressure to dangerous
levels and add the H2SO4 through a one-way funnel (or add it quickly and stopper it off).
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longtermmadscientist
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Quote: Originally posted by simba  | | Why don't you just use sulfuric acid? You said you need only a few ml, so yields are not important right? |
I'm dealing with a small quantity of NaBr, using a small vessel, as is necessary due to limited resources. I plan on using a pipette to draw- off the
bromine from the underlayer (which I'm hoping will form, as Br is denser than HNO3). What I don't want to happen to get so little bromine that I can't
pipette more than miniscule quantities of it up without scooping up water with it. I'm guessing, and only guessing, here, that HNO3 would give a
higher yield than H2SO4, but there's very little info out there, it seems, on using the former acid for producing Bromine from bromide.
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longtermmadscientist
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| Quote: Originally posted by elementcollector1 | I would recommend 98% H2SO4, added slowly to very cold NaBr solid. If you really wanted to go the extra mile, you could use dry ice so that any
bromine formed is frozen, not likely to sublimate. At least, I think that would work (hint: don't use glass. Go for ceramic.), but it might end up
that the solid bromine formed would prevent further reaction, etc.
Alternative: Trap reaction inside a corked gigantic flask (large enough for the bromine gas to spread out without increasing pressure to dangerous
levels and add the H2SO4 through a one-way funnel (or add it quickly and stopper it off). |
Thanks, refridgeration is definitely something I'll be looking into, due to the exothermic nature of this reaction, or a similar reaction using HNO3.
Do you get a good yield with the method you suggested here?
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elementcollector1
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I have no idea, I just got it from a youtube video.
http://www.youtube.com/watch?v=QkTu7yKSyzg
You can clearly see the enormous amount of bromine lost as vapor as the reaction predictably heats up.
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AJKOER
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Actually if one doesn't have 98% H2SO4, I would argue that Bromine can be released by the action of NaOCl and vinegar (in place of HOAc, one can also
use dilute or concentrated HCl), which forms dilute HOCl (or Cl2 with conc HCl), on NaBr.
Some chemistry (pardon the complexity):
NaOCl + HOAc --> NaOAc + HOCl
HOCl + NaBr --> HOBr + NaCl
3 HOBr --> HBrO3 + 2 HBr
Or:
5 HOBr ---> HBrO3 + 2 Br2 + 2 H2O (on heating, low pH)
As:
HBr + HOBr <--> Br2 + H2O (the reverse reaction is much slower than occurs with chlorine)
On net we have therefore approximately:
NaOCl + HOAc + NaBr ---> NaOAc + NaCl + 1/5 HBrO3 + 2/5 Br2 + 2/5 H2O
Approximately owing to the minor secondary reaction:
2 HOBr --> 2 HBr + O2 (g)
and the post reaction additional of H2O2 may remove any free HBr:
2 HBr + H2O2 --> Br2 + 2 H2O
(Source: https://docs.google.com/viewer?a=v&q=cache:5FnZ5VbTCUAJ:... )
Note, at this point in the reaction with acetic acid or dilute HCl, some the Bromine is locked away as bromate. With strong HCl, the reaction of
Chlorine gas on aqueous NaBr proceeds much more simply as:
2NaBr + Cl2 → Br2 + 2NaCl
Here is a patent that references these reactions and add more detail on the reaction of Bromine in water and the influence of pH:
http://www.patentstorm.us/patents/5516501/description.html
Here is a YouTube video on the NaOCl/HCl/NaBr path to Bromine:
http://www.youtube.com/watch?v=BdrM9oj-Cyc&feature=relat...
-----------------------------------------
Now, before someone attempts to criticize the HOCl synthesis over the possible loss of some of the Bromine to Bromate, one may be able to recover the
loss by adding more NaBr and an excess of acid paralleling the reaction with Iodine and Iodate. In particular, per "Synthetic inorganic chemistry: a
course of laboratory and classroom study ...", by Arthur Alphonzo Blanchard, Joseph Warren Phelan, page 232:
"Iodate and iodide ions alone have no action on each other, but with hydrogen ions present a mutual oxidation and reduction of the iodine takes place.
6H+ + 5 I- + IO3- -> 3H2O + 3 I2
No oxidation or reduction of the hydrogen occurs, but the hydrogen ion is used up, which explains why the presence of acid is necessary to make the
reaction take place." where I would assume a similar reaction based on Bromine. Link:
http://books.google.com/books?ei=E1ewT5P1IOaR6gHf9fnWAQ&...
EDIT: Found a related equation for Bromine reference. To cite two reactions from "White's Handbook of Chlorination and Alternative Disinfectants" by
Geo. Clifford White, page 860:
KBrO3 + 2 KBr + 6 HCl --> 3 BrCl + 3 KCl + 3 H2O
and: BrCl + H2O --> HOBr + HCl
Link: http://books.google.com/books?id=9_2idzksARMC&pg=PA859&a...
[Edited on 14-5-2012 by AJKOER]
[Edited on 14-5-2012 by AJKOER]
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woelen
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All methods, described above are utter crap for making Br2.
I myself tried adding HNO3 to solid NaBr. It does not work. The reaction at first does not seem to start at all, you must have some NO2 in the mix
already to get it started. That can be done by adding a small pinch of Na2SO3 or NaNO2. Once this is added you get bromine, but also copious amounts
of NO2 and I think that the bromine will be heavily contaminated with this. I only obtained a few small droplets of Br2 from this reaction though. One
of the big problems is that NaBr hardly dissolves in conc. HNO3, it becomes covered by an insolutable layer of NaNO3, which prevents further reaction.
Adding conc. H2SO4 to solid NaBr is even worse. The stuff starts foaming a lot and you get HBr-gas, which is contaminated with Br2 and SO2. But the
yield of Br2 is so low, that you hardly can speak of more than serious contamination. No visible liquid droplets of bromine are formed, you only see
gaseous Br2.
Adding bleach to NaBr does give Br2, but it is so dilute that it does not separate from the aqueous solution. Vinegar as acid is equally bad, it
dilutes even more and this acid is weak.
-------------------------------------------------------
Some decent ways of making Br2:
- Electrolysis of a concentrated solution of NaBr, such that 1/6-th part of the bromide is converted to bromate and then adding a slight excess of 50%
H2SO4 or saturated solution of NaHSO4. I did this myself. It works very well. You need a graphite anode and unfortunately, you need a pinch of
chromate or dichromate in order to have a decent current efficiency. Here follows the write-up:
http://woelen.homescience.net/science/chem/exps/OTC_bromine/...
Another option:
- Make a concentrated solution of NaBr and for each mole of NaBr add well over 1 mole of appr. 50% HNO3. Allow mixing of the solution and allow
crystals of NaNO3 to separate from the liquid. This can occur if the acid is too concentrated. Instead of using HNO3 you can also use HCl. In that
case use at least 30% HCl, otherwise the solution is too dilute. Do not use H2SO4, that will lead to a terrible mud of insoluble CaSO4 in the
following step of the process!
- For each gram of NaBr take half a gram of calcium hypochlorite with 70% chlorine content (for swimming pools). If the chlorine content is less or
more, then adjust the computation. Do not use more than half a gram of less than half a gram. Both excess and too little will result in loss of
bromine.
- Carefully add the solid to the solution of NaBr/HNO3. Do this in small increments!!! When all of it is added, bromine will settle at the bottom.
I like the electrolysis process most. The bromine, produced in this way is very pure. The bromine, made with hypochlorite almost certainly contains
some chlorine in the form of BrCl. This is invisible though. For fun energetic experiments with bromine, or when the bromine is stored as a sample in
an ampoule this chlorine content is no issue. If the bromine is used for bromination in organic syntheses, then the presence of the chlorine may be
disturbing.
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weiming1998
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What about bubbling Cl2 using a simple gas generator through concentrated NaBr solution? Bromine has a limited solubility in water, and after some
time, a layer of liquid bromine will form at the bottom, which you can then purify by distillation, then chilling with a cold ice bath.
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woelen
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Yes, reacting Cl2 with a solution of NaBr also works, but I found the practical setup for this rather cumbersome. Simply bubbling Cl2 through a
solution did not work very well for me. The Cl2 reacts too slowly, a lot of it just bubbles through the solution and some Br2 is drawn out of solution
as well. I used a normal beaker and that was not a great success. Maybe if you use a long thin glass bottle or a longdrink glass and insert the
bubbles of Cl2 at the bottom and disperse these bubbles as very fine bubbles you might have better results.
Another option might be to use an inverted funnel and put its rim just under the liquid surface. Initially, air will be driven away and bubbles of air
escape along the rim of the funnel, but as the concentration of Cl2 is rising, more and more Br2 will form at the surface of the liquid under the
funnel and the Br2 will sink to the bottom. Generation of Cl2 should be slow though in this setup. If generation of Cl2 becomes too slow, then liquid
will be sucked up in the funnel, but this causes the liquid level to go down and if the funnel is put at such a height that it looses contact with the
surface of the liquid when it is sucked half full, then you will not experience suck-back of liquid into your chlorine gas generator.
I'm sure that with some experimenting you will get it working, but I never bothered after my initial bad experiences with it. The other methods worked
more easily for me and I felt no need to try again. I know of other people over here, who succesfully applied the bubbling of Cl2 through bromide
solution, so it can be done.
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Endimion17
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woelen, what about concentrated hydrogen peroxide and sulphuric acid with concentrated solution of alkali bromide? It works quite well.
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woelen
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Yes, the latter also works quite well. Actually, there are so many methods of making bromine which work quite well. Any decent oxidizer, combined with
a strong acid and a soluble bromide does the job. The only thing is that you need solid chemicals or at least highly concentrated solutions if you
want to have bromine separate from the aqueous layer.
I made Br2 with H2O2, KMnO4, Ca(ClO)2, NaClO3, KBrO3 as oxidizer. Electrolysis is another option, as written above. The following are not suitable and
do not work at all or only marginally: nitrates, perchlorates, conc. H2SO4, persulfates. These oxidizers are not strong enough or react too
sluggishly. TCCA also is not really suitable, due to the formation of a mud of insoluble cyanuric acid. I expect that dichromates also work reasonably
well, but some heating or patience may be needed with them.
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Zan Divine
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All factors considered, I favor a warm, stirred mixture of NaBr & KMnO4, treated dropwise with conc. H2SO4, which will quickly warm to a temp
above the bp of Br2. The vapors are condensed, washed, dried over NaBr & distilled.
There are no interhalogens as with Cl2. This is operationally simple and it is considerably cheaper than H2O2, which is important for larger batches.
Look at Wiki under bromine for the stoichiometry.
[Edited on 14-5-2012 by Zan Divine]
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barley81
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Has anyone tried manganese dioxide? In <a
href="http://books.google.com/books?id=OkUAAAAAYAAJ&printsec=frontcover#v=onepage&q=bromine&f=false">this book</a>, there is a
procedure which uses manganese dioxide on page 124. Since manganese dioxide can be used to make chlorine gas, and since bromine is less volatile than
chlorine and is not as good an oxidizer, this might be a good method.
[Edited on 14-5-2012 by barley81]
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Endimion17
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| Quote: Originally posted by woelen | Yes, the latter also works quite well. Actually, there are so many methods of making bromine which work quite well. Any decent oxidizer, combined with
a strong acid and a soluble bromide does the job. The only thing is that you need solid chemicals or at least highly concentrated solutions if you
want to have bromine separate from the aqueous layer.
I made Br2 with H2O2, KMnO4, Ca(ClO)2, NaClO3, KBrO3 as oxidizer. Electrolysis is another option, as written above. The following are not suitable and
do not work at all or only marginally: nitrates, perchlorates, conc. H2SO4, persulfates. These oxidizers are not strong enough or react too
sluggishly. TCCA also is not really suitable, due to the formation of a mud of insoluble cyanuric acid. I expect that dichromates also work reasonably
well, but some heating or patience may be needed with them. |
H2O2 and H2SO4 (both concentrated) represent a quite clean method, wouldn't you agree? The only thing left to remove is water. Bromine can be
pippetted out and water traces removed by some H2SO4 and distillation. IMO, the best option for getting pure bromine suitable for organic synthesis.
Alkali bromide really should be in a concentrated solution because if solid, it won't react completely as a cake of bromide and sulphate is formed.
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longtermmadscientist
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OK, thanks, guys, this has given me a bit to think about. I’m a bit disappointed that HNO3 turns out not to be a strong enough oxidant to do the
job; my reasoning was that if Cl can be produced by adding HNO3 to NaCl, then you should be able to get bromine from NaBr, but I had at the same time
in mind the reluctance of bromine to oxidise (as exemplified by the relative instability of bromic acid as compared to the analogous acids of Cl and
I, although I may be misunderstanding something here), so perhaps the result isn’t entirely surprising. If it isn’t the oxidation potential of
HNO3 that is so much the problem, and precipitation/ relative insolubility of NaNO3 which is ( which surprises me, as from what I can gather the two
have quite similar solubilities), then I may have to dissolve the NaBr before I add the HNO3, which means that then I’d have to add excess HNO3 to
ramp- up the oxidising power of the solution. Adding other oxidants is I’m afraid not possible at the moment, excepting household bleach, and
chlorine impurities are acceptable in small amounts, as I don’t do organic chemistry. My purposes in producing bromine are producing enough of the
element to learn of its chemical and physical properties first hand, and to have some in stock so that I can do further experiments on if need be.
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AJKOER
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Commercial methods (see link below as an example from the Dead Sea plant) for the preparation of Bromine do not use strong acid as an aid in removing
water from Bromine reactant mix (cost factor I would guess). Instead, there is a separation stage process which employs heating a Br2 water solution
with steam and using the physical properties of Bromine (much heavier than water with a limited solubility) to facilitate separation (see page 86).
With respect to chemistry, the reference process attached just uses Cl2 (mentioned in my synthesis) on a bromide although I see more potential value
in an HOCl method via a weak acid (preferably a low cost weak acid). My opinion is that such a method reduces the Cl2 presence (as well as BrCl
formation, a function of moderate temperature, excess Chlorine and low pH), and introduces, instead, a small amount of free Cl2O depending on the
concentration of the HOCl employed. However, to reduce initial dilution, one can simply employ Boric acid in place of Acetic and a high concentration
NaOCl (or use Ca(OCl)2 access permitting). Barring the Chlorine route, the HOCl method, however, appears to suffer some yield loss due to bromate
formation (see my edited thread).
A valid comment of the synthesis I presented is that it is more in line with a current commercial process for the extraction of Bromine than a
laboratory synthesis where a different set of criteria (like percent yield, reagents' cost and reaction speed) are more prominent factors. However,
for garage chemists, reagents' cost and access as well as yield, are likewise important factors.
Link:
http://www.weizmann.ac.il/sci-tea/Brombook/pdf/chapter3.pdf
[Edited on 15-5-2012 by AJKOER]
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elementcollector1
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What of electrolysis: I have a makeshift membrane-separator, can I get Br2 and NaOH out of this like I would from an identical NaCl cell?
Edit: Electrolysis is working beautifully, and my makeshift filter paper membrane is holding up well (the two sides are slightly imbalanced by
volume). So, free NaOH (filled catholyte with pure water) and free Br2 (is sinking to the bottom. Doesn't really seem to be soluble).
[Edited on 15-5-2012 by elementcollector1]
Edit 2: Membrane broke, cell overheated.  Now I have a yellow supernatant liquor,
and a small amount of reddish bromine water. Should I start over, and use H2O2 and HCl to get the desired results?
[Edited on 15-5-2012 by elementcollector1]
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BromicAcid
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For crying out loud, use the search engine:
http://www.sciencemadness.org/talk/viewthread.php?tid=6953
This topic has been discussed ad nauseam. Not only are there several refined procedures but there are less refined procedures using most any
oxidizing agent that you can get your hands on. Please, there is enough practical experience with this to bore anyone to death so armchair chemists
need not apply.
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elementcollector1
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I've been trying to make sodium bromate for the bromate+bromide+acid procedure, I get a yellow solution (the same color when I attempted to make
sodium hydroxide/chlorate). Is this the correct color for the hypobromite? I don't think so, but I have not a clue as to what it really is. I also get
bromine water, which sort of sinks to the bottom but not really a distinct layer as of yet. I have the 2-amp car battery running the electrolysis
overnight, so come morning most to all of the bromine should have been converted into something.
Also, I have NO distillation setup - how do I dry and collect this stuff? Sulfuric acid seems like a good idea, but I'd have to concentrate this
annoying pink 10% stuff I found at a pool store (can't find any better local sources).
I could pass Cl2 into NaBr (I have a lot of MnCl2 I need to make anyway), so tell me: Which works better, bromate/bromide/acid or bromide/chlorine?
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AndersHoveland
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NaBr + sodium bisulfate + dilute H2O2
makes Br2
The procedure is very simple, and works well if one does not need to isolate the bromine from solution.
[Edited on 15-5-2012 by AndersHoveland]
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scatha
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What about this reaction ?
4 NaHSO4 + MnO2 + 2 NaBr -> MnSO4 + 3 Na2SO4 + Br2 + 2 H20
All educts and products are solid, except the produced Br2 and the H2O - maybe this is helpful for your case ?
[Edited on 15-5-2012 by scatha]
[Edited on 15-5-2012 by scatha]
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Vargouille
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Scatha, that would only work in a solvent that isn't water, since MnSO4 and Na2SO4 are both fairly soluble in water. I would have to check on the
solubilities of all of the materials involved to find a good solvent to precipitate out the MnSO4 and the Na2SO4, but if you enjoy a challenge, it
might be possible.
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woelen
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The reaction of Scatha most likely can make Br2, but I'm quite sure some heating is required in order to get the powdered reagents to react.
Solid-solid reactions are not the best ones to work with, so this is not a good idea for practical production of Br2. If some water is added, then it
might work, provided the used MnO2 is not calcined and very inert.
But let's keep BromicAcid's remark in mind. Production of Br2 is discussed many times already and even in this thread we now hve seen a few useful and
suitable methods. Now it is time to take out the glassware and chemicals and try things. Reporting back on your results is strongly encouraged.
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longtermmadscientist
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| Quote: Originally posted by woelen |
But let's keep BromicAcid's remark in mind. Production of Br2 is discussed many times already and even in this thread we now hve seen a few useful and
suitable methods. Now it is time to take out the glassware and chemicals and try things. Reporting back on your results is strongly encouraged.
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Will do, woelen, soon after my NaBr arrives. I thought I’d check out the feasibility of doing this before it arrived, as knowing me I’d probably
have impulsively tried something I’d only just thought of, and using up a lot of my reagents. Thanks for your valuable insights from your own
experiments.
I was unsure about whether to open a new thread on this one, and I did in fact search the forum for “bromine” and “HNO3/nitric acid", but
nothing came up with the two tied closely, so I took the decision to open a new thread. If one of the mods would like to merge this topic with others
on bromine production, then that’s fine, and it would possibly make things tidier.
[Edited on 15-5-2012 by longtermmadscientist]
[Edited on 15-5-2012 by longtermmadscientist]
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