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metalresearcher
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Bromine from KBr, MnO2 and hydrochloric acid
My second attempt for making elemental Br2 from these chemicals was rather succesful.
However, according to the stoichiometric ratios
2 KBr + 4 HCl + MnO2 => 2KCl + MnCl2 + 2H2O + Br2
240 146 86 => 160
14.4g 8.8g 5.2g => 9.6g == 3ml Br2
8.8g equals to 24ml 36% conc. HCl acid.
but after some time the Br2 generation stopped, while the liquid in the round flask was still dark brownish red.
The setup for distilling with a mushroom distiller.
The bromine collecting in the water cooled erlenmeyer flask.
<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/NBg0AfKkKQw" frameborder="0" allowfullscreen></iframe>
[Edited on 2012-11-18 by metalresearcher]
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Endimion17
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Unless you work in a deep freezer or Antarctica, your setup won't give great yields. You simply can't use such primitive cooling methods for bromine.
Liebig or vertical spiral cooler with ice water are essential.
At least simple distillation kits aren't that expensive anymore.
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blogfast25
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It would help a LOT to just put an icepack on your mushroom condenser and its outlet tube: it's clear your bromine vapours (BP = 59 C) have trouble
condensing...
And I was fearing to see your camera lens catch fire or possibly melt any time!
[Edited on 18-11-2012 by blogfast25]
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mr.crow
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Haha I love the mushroom condenser!
KMnO4 can also oxidize HCl to Cl2, which works but can form impurities if in excess. You also need good stirring.
Your HCl should really be in a glass bottle, not plastic. It leaks out and can rust everything in your lab.
Double, double toil and trouble; Fire burn, and caldron bubble
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AJKOER
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I think this synthesis is a bit too dangerous as you are, in fact, generating Chlorine (via MnO2 + HCl) and inviting the possible formation of
Bromine monchloride (see http://www.sciencemadness.org/talk/viewthread.php?tid=1091 ). The creation of any BrCl not only reduces yield, but requires the use of a fume hood
if you want to keep your lungs functional.
My suggestion: treat aqueous KBr with an acid (forming HBr) and then react with some chlorate:
KClO3 + 6 HBr --> 3 Br2 + 3 H2O + KCl
For this purpose, a Chlorate/chloride solution can easily be formed by warming a solution of an unstable hypochlorite (includes Magnesium or Copper
hypochlorite), or the more stable variety (like KClO or NaClO or Ca(ClO)2).
[EDIT] Note working via an acidified hypochlorite reaction is essentially a chlorine path akin to your original synthesis.
[Edited on 19-11-2012 by AJKOER]
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blogfast25
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Quote: Originally posted by mr.crow  | | Your HCl should really be in a glass bottle, not plastic. It leaks out and can rust everything in your lab. |
HDPE or PP are perfectly resistant to most mineral acids, even 70 % HNO3 and 95 % H2SO4. Conc. HCl is almost always sold in hydrocarbon polymer
bottles.
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blogfast25
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| Quote: Originally posted by AJKOER | My suggestion: treat aqueous KBr with an acid (forming HBr) and then react with some chlorate:
KClO3 + 6 HBr --> 3 Br2 + 3 H2O + KCl
For this purpose, a Chlorate/chloride solution can easily be formed by warming a solution of an unstable hypochlorite (includes Magnesium or Copper
hypochlorite), or the more stable variety (like KClO or NaClO or Ca(ClO)2).
[EDIT] Note working via an acidified hypochlorite reaction is essentially a chlorine path akin to your original synthesis.
[Edited on 19-11-2012 by AJKOER] |
KClO3 + acid is a recipe for (potentially explosive) ClO2, unless you know EXACTLY what you're doing. And chlorates are fairly expensive anyway.
See for instance:
http://www.sciencemadness.org/talk/viewthread.php?tid=17940
Chilled H2O2 is probably safest, with reported yields of over 90 % and no interhalogens possible.
Perhaps most importantly, the choice of acid (HCl) was unfortunate but as an oxidiser MnO2 would work well with H2SO4 as an acid,
then no Cl2 (or BrCl) can form. I assume the poster didn’t have any sulphuric acid or didn’t consider it.
[Edited on 19-11-2012 by blogfast25]
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elementcollector1
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Wouldn't the chlorine produced react with the bromide first, and then when all bromide was converted to free bromine start making BrCl? I'm planning a
similar setup for my eventual bromine distillation, and I'm not using sulfuric acid. (I'm certainly using sulfuric acid to dry the product, however).
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AJKOER
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by AJKOER | My suggestion: treat aqueous KBr with an acid (forming HBr) and then react with some chlorate:
KClO3 + 6 HBr --> 3 Br2 + 3 H2O + KCl
For this purpose, a Chlorate/chloride solution can easily be formed by warming a solution of an unstable hypochlorite (includes Magnesium or Copper
hypochlorite), or the more stable variety (like KClO or NaClO or Ca(ClO)2).
[EDIT] Note working via an acidified hypochlorite reaction is essentially a chlorine path akin to your original synthesis.
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KClO3 + acid is a recipe for (potentially explosive) ClO2, unless you know EXACTLY what you're doing. And chlorates are fairly expensive anyway.
See for instance:
http://www.sciencemadness.org/talk/viewthread.php?tid=17940
Chilled H2O2 is probably safest, with reported yields of over 90 % and no interhalogens possible.
Perhaps most importantly, the choice of acid (HCl) was unfortunate but as an oxidiser MnO2 would work well with H2SO4 as an acid,
then no Cl2 (or BrCl) can form. I assume the poster didn’t have any sulphuric acid or didn’t consider it.
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Actually, while I agree with Blogfast25 sentiments, if one mistakenly somehow prepares concentrated HClO3, it is probably a greater risk. The reason I
would down play the ClO2 in my current suggested synthesis in the presence of sufficient HBr is based on the reaction quoted in Mellor for Iodide,
page 289, http://books.google.com/books?id=AnnVAAAAMAAJ&pg=PA289&a... to quote:
"Iodine separates from an acidified soln. of potassium iodide: 2Cl02+10HI=2HCl+4H20+5I2; in neutral soln.: 6Cl02+10KI=4KI03 +6KCl+3I2; and in the
bicarbonate soln.: 2Cl02+2KI=2KCl02+I2, whereby 80 per cent, of the chlorine dioxide is converted into the chlorite."
So for an acidified KBr solution, I would similarly expect:
2 Cl02 +10 HBr --> 2 HCl + 4 H20 + 5 Br2
so any Chlorine dioxide created oxidizes the HBr (or, the HBr presence would reduce any ClO2 formed), so it is important to have sufficient (or an
excess) of HBr present to address any ClO2 formation. Also, any Chlorate formed by my suggested disproportionation of a dilute hypochlorite is not
likely to result in an unstable concentration of Chloric acid.
----------------------------------------------------------------
Also, one does not need H2O2 if one has access to concentrated H2SO4 as per one source (see Equation #7 at http://wenku.baidu.com/view/bf135124a5e9856a5612602a.html ):
2 NaBr + 2 H2SO4 (Conc) --> Na2SO4 + Br2 + SO2 (g) + 2 H2O
[Edited on 20-11-2012 by AJKOER]
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woelen
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The latter is a very bad way of making Br2. Only a small part of the bromide reacts to bromine, the main part reacts to HBr. Besides this, you get
Br2, contaminated with SO2. On contact with water this mix IMMEDIATELY reverts back to HBr and H2SO4.
Mixing H2SO4 with solid bromides is a bad way for making Br2 and it is a bad way for making HBr. This reaction simply is not useful at all for
synthetic purposes.
Any reaction in which chlorine is present as well (either as element, or as oxidizer, or as chloride) is suboptimal. Indeed, as AJKOER writes, you can
assure that only Br2 is formed if there is enough bromide in the mix. In order to be sure, you need excess bromide. The bad thing, however, of having
excess bromide in the mix, is that you loose bromine as bromide, and even worse, the bromide also fairly strongly keeps bromine in solution as Br3(-)
ions. This makes the method of simply pipetting away bromine from under the aqueous layer less attractive, because a lot of bromine remains in
solution.
If there is insufficient bromide, then you get BrCl and you loose bromine as well, through formation of bromate ions (hydrolysis of BrCl yields Br2,
bromate and HCl). If you have a large excess amount of oxidizer, then you'll see that all bromine disappears again. It all will go in solution as
HBrO3 and you will not be able to separate this from the liquid.
Best is to use an oxidizer like H2O2 and dilute H2SO4 or dilute HNO3 as acid. MnO2 or KMnO4 also works. I myself make bromine by means of electrolysis
of a solution of a bromide, such that 1/6 of the bromide is converted to bromate and then I acidify this solution with dilute H2SO4.
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AJKOER
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OK, a route I would be interesting in testing out is as follows.
Step 1. Prepare HBr from heating NaBr and aqueous NaHSO4 and condensing the vapor.
Step 2. Prepare HOCl. Start by adding a weak acid (Boric, Acetic, Critic or very dilute H2SO4, HNO3,..) to Bleach and distilling half the volume to
form HOCl for immediate use. Adding a small amount of alkali metal silicate may increase the stability of the HOCl (see Patent EP 0 892 042 A1 and
comment "Silicate is said to prevent decomposition of hypochlorite and corrosion by hypochlorite" at https://data.epo.org/publication-server/html-document?PN=EP0... .
Step 3. Combine HBr and HOCl in an hourglass like container set on ice. The volume of the lower part of the hourglass should correspond closely to the
expected yield of Br2. Target reaction:
2 HBr + HOCl --> Br2 + H2O + HCl
Side reactions:
Br2 + H2O <---> H[+] + Br[-] + HOBr
and the presence of H[+] from the HCl should push the equilibrium to the left. Also important for limiting:
3 HOBr --> 2 HBr + HBrO3
Now, hopefully the hourglass vessel shape may limit the surface area contact of any separated Bromine and solution which is important for the
undesirable reaction:
Br2 + Br- --> Br3-
Step 4. Now apply the method of pipetting away the bromine from under the aqueous layer.
Now, in comparison to the HBr plus H2O2 method:
2 HBr + H2O2 --> Br2 + 2 H2O
my suggested synthesis produces less water at a better (meaning more acidic) pH to hopefully relatively reduce the formation of HBrO3.
------------------------------------------------------------
[EDIT] After coming across a good source that comments that the reaction between an Iodide and HOCl does form an intermediary of ICl (see "Kinetics of
hydrolysis of iodine monochloride measured by the pulsed-accelerated-flow method" by Yi Lai Wang , Julius C. Nagy , Dale W. Margerum, published in J.
Am. Chem. Soc., 1989, 111 (20), pp 7838–7844 at http://pubs.acs.org/doi/abs/10.1021/ja00202a026 ), and that the final product in the hydrolysis of ICl in an acid is given by:
5 ICl (aq) + 3 H2O <--> HIO3 + 2 I2 + 5 HCl
Base:
3 ICl(aq) + 6 NaOH <--> NaIO3 + 2 NaI + 3 NaCl + 3 H2O
I would now suspect similarly that the action of HOCl on a Bromide would also produce BrCl and with further hydrolysis a Bromate (see http://cat.inist.fr/?aModele=afficheN&cpsidt=1007184 ). As such, I would not be surprised if this suggested HOCl route does not result in a
significantly better yield over the H2O2 approach.
[Edited on 21-11-2012 by AJKOER]
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SM2
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My suggestion, go to an Ace Hardware store or a small, local hardware store, where everything costs a little more then Home Depot. Get Rooto brand
H2S04, and proceed as if you are trying to make hydrobromic acid too quickly. Post reaction chamber, DO HAVE a west condenser circulating a freezing
cold, liquid brine solution, stored in a simple polystyrene disposable cooler. Also, insulate condenser, especially at top. Have a short path, yet
enough head space so that no solid NaBr or dilute aq HBr comes over. The trick to making bromine it to know what your doing, AND to do it quickly.
It doesn't smell deadly, like Cl2, but is has a strange fecal nose, along with the chlorine irritation. Wear double nitrile gloves, I told you so!
If you have an organic (activated charcoal) mask, use it, or buy one from the big hardware stores or big auto body paint shops. This is a practical
way to bromine for the home chemist.
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woelen
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I strongly advice against both two methods, presented in the last two posts. Maybe of academical interest, but not of any preparative value!
Distilling HOCl, just for making Br2? Why do it the difficult way if it can also be done easily  ?
As I wrote before, mixing H2SO4 and a bromide is not useful for preparative purposes. Too many impurities, too many losses, a pain in the ass.
There are quite a few threads on making Br2, please have a look at those, there are quite a few practical ways of making Br2 and to my opinion the
subject of making and isolating Br2 is resolved long ago already.
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blogfast25
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Woelen:
Amen to that.
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elementcollector1
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I'm trying to decide between a few things:
I don't have the heat setup for distillation of bromine, so could I;
-Pre-produce the bromine in solution (NaOCl, HCl and NaBr) and suck out the water with concentrated (Rooto, 96%) sulfuric acid?
-If I do get the heat setup, should I use the bleach + HCl method to avoid the potential hazards of a chlorine generator (instead forming in-situ
chlorine)?
I might borrow a hot plate from a teacher fairly soon, but I wanted to know if there was a bit of a faster way.
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woelen
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Bleach + HCl + bromide makes bromine, but the bromine will be very dilute. Isolating the bromine from all the water and acid will be hard without a
proper distillation setup. Adding conc. H2SO4 does not help, because bromine also dissolves to some extent in H2SO4.
If you don't have a distillation setup, then you need a highly concentrated oxidizer. Best is calcium hypochlorite, added in nearly stoichiometric
amount to NaBr or KBr. Add the bromide to some conc. HCl and then add the hypochlorite, in small steps and swirl each time. When all is added, quite
some liquid bromine will settle at the bottom and you can pipette away the bromine. In this way, yields of appr. 70% are feasible. It is important to
have the reagents in stoichiometric ratios, best to have slight excess amount of bromine, otherwise you get impure Br2, which contains BrCl.
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elementcollector1
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Never mind, it turns out my parents had a hotplate of sorts lying around! It's got a coil for a surface, and only a rudimentary temperature control,
but it should work perfectly. Now all I need is a 10/18 glass stopper for my distillation adapter and I'm all set!
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metalresearcher
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Here a new attempt with another distillation bridge and the Br2 received in an ice cold round bottom flask.
<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/VuMsnKx2ZuE" frameborder="0" allowfullscreen></iframe>
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Endimion17
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It seems your fume hood is so powerful you don't have to fear any poisoning so the paper plug at the end is not necessary. The fan sound like a jet
engine. 
To increase yields, use a salt-water-ice bath for the receiver.
If you don't have running water for the cooler, improvise using an elevated bucket filled with water and chunks of ice. Syphon the water into a lower
bucket and occasionally transfer it back up. That's what I used before I started using recirculating pumps. It's efficient, but you have to monitor
the water level.
Also, avoid using open flame when working with glassware. Yes, it's a small flask and it's round bottomed, and the flame is not "oxidizing blue", but
nevertheless, it's a good practice to use a heating bath for a steady supply of evenly distributed heat. Boiling water is probably enough. If you
don't want a steady supply, wrap it with two layers of iron net.
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sbbspartan
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Woelen, you mentioned that you make bromine via electrolysis of a solution of potassium bromide. How exactly does this work? Does the potassium
bromate react with the sulfuric acid to make the bromine, which then sinks to the bottom and you harvest? On your website, it looked like there was
some bromine produced even before you added acid. Did this then dissipear as the bromate was produced? Would there be some excess bromate then so the
bromine does not dissolve in the sulfuric acid and you lose your product? How is the yield? Is there any contamination from the potassium dichromate
used in the electrolysis, or is it pretty pure? This seems like a pretty easy and safe way to make bromine. Pretty cheap too.
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woelen
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The electrolysis process indeed first makes bromine, which however is not easily separated. I just keep it in the liquid and allow it to react with
the hydroxide, formed at the cathode. This process gives bromate ions:
3Br2 + 6OH(-) --> BrO3(-) + 5Br(-) + 3H2O (through intermediate step of BrO(-))
Electrolysis is continued, such that 1/6 of all bromide ions is converted to bromate ion and then acid is added. In the page to which I posted a link
it is described how long you need to perform electrolysis. Not too short and not too long, in both cases you loose bromine, but too short is much
worse than too long.
The dichromate does not cause any contamination of the bromine.
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elementcollector1
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How does this method compare to bubbling chlorine in, in terms of percent yield?
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woelen
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The yield depends on how accurately you are able to perform just enough electrolysis. The process, however, is very forgiving when the solution is
somewhat electrolysed too much. Even electrolysis of 50% too much leads only to a loss of 10%. The process, however, is extremely sensitive to
electrolysing too little. Just a few percent too little of electrolysis leads to huge losses. So, be sure to have sufficiently long electrolysis
times. Better 50% too long than 5% too short!
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Lambda-Eyde
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You don't have running water in your condenser? What was your yield?
This just in: 95,5 % of the world population lives outside the USA
You should really listen to ABBAPlease drop by our IRC channel: #sciencemadness @ irc.efnet.org
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elementcollector1
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Checked your website, and I'm liking the setup so far. It doesn't matter if I use sulfuric or even hydrochloric acid, right? I don't have access to
bisulfate.
I'm off to do the stoichiometry equations for the amount of NaBr I have.
[Edited on 14-12-2012 by elementcollector1]
[Edited on 14-12-2012 by elementcollector1]
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