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Author: Subject: Bromine Source and Synthesis
PainKilla
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[*] posted on 5-1-2007 at 12:52


Trichloroisocyanuric acid is a most excellent source of chlorine, and I found that this process works quite well for generating bromine: (I kept in moles for easier adjusting of ratios etc)

.5 mol C3Cl3N3O3 (crushed up very finely)
2.75 mol NaBr in ~300ml H2O
~275ml 20% HCl

In a 1L round bottom flask set up for distillation and equipped with an addition funnel containing the HCl, add NaBr solution. Add TCCA to this solution. With stirring, begin to heat the solution (to ~55C) while very slowly adding the HCl. The bromine will begin to gradually distill over. Continue addition of HCl and distill until no more bromine is carried over.

Yields should be near quantitive (~1.25mol Br2)


The rate of bromine generation depends on HCl addition, so if your condensor is less than adequate, adding the HCl slowly works well as compensation. The procedure works very well, some other things to note are that the TCCA must be finely crushed, otherwise it takes a long time to react and results in a buildup of Br2. It's also quite a bit easier to stir when fine. It is also very important to have good stirring because without it, the bromine forms a layer in the reaction flask and once heat is applied, you begin to have an extreme amount of bromine evaporating that the condensor can't handle (well mine can't anyway). Other than that, this is a very straightforward procedure.

Some things I have yet to test is adding H2SO4 to the receiving flask in order to dry the bromine and keep it at least somewhat less volatile. I should be retrying the procedure soon and will report with more accurate measures.

EDIT: Forgot to put in yield. EDIT2: Fixed error.



[Edited on 7-1-2007 by PainKilla]




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[*] posted on 5-1-2007 at 15:59


I wonder how pure that Br2 would be, though. As well as oxidizing Br- to Br2, the Cl2 could also result in the formation of BrCl, and oxidize further to BrCl3 or the BrCl4- anion.
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[*] posted on 5-1-2007 at 16:18


And what would be the solubility of chlorine in bromine? I can imagine that some chlorine would bubble out and dissolve in the condensor.



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[*] posted on 7-1-2007 at 03:56


Quote:
Originally posted by PainKilla
.5 mol C3Cl3N3O3 (crushed up very finely)
1.25 mol NaBr in ~300ml H2O
~275ml 20% HCl


What is the point in using such an enormous excess of trichloroisocyanuric acid (TCCA)?

The redox reaction for the oxidation of NaBr with TCCA is:
TCCA + 6NaBr + 3H(+) => cyanuric acid + 3Br2 + 3Cl(-) + 6Na(+)

So you used more than a double excess of TCCA which quite possibly caused the formation of lots of BrCl and Cl2. I recommend using a 5 to 10% excess of NaBr instead. This would efficiently prevent any interhalogen compounds distilling over. There is no need to use so much HCl as the acid for the reaction. Use just a bit more than the required amount (~0.6 equivalent in relation to NaBr instead of ~1.65 that you used). Using a non volatile acid like H2SO4 would also be preferred to avoid HCl contamination of the distillate. Mind that only water is easily removed from the Br2 distillate with a conc. H2SO4 wash, but removing BrCl, Cl2, HCl and such is not easy (so preventing contamination is wiser than repairing what is already done).
Also, as I already said several posts above, using 1-bromo-3-chloro-5,5-dimethylhydantoin as the oxidant is more rational as you get to use the Br equivalent from it as well (and not only from NaBr). Otherwise such methods have no advantage over simply using H2O2/H2SO4 as the oxidant (except maybe if H2O2 is getting difficult to acquire).




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[*] posted on 7-1-2007 at 07:25


I actually like the method of Painkilla (with your modification of using a little excess NaBr), because TCCA is very cheap and easy to obtain. Over here in Europe, 1-bromo-3-chloro-5,5-dimethylhydantoin is not easy to obtain, swimming pools never are brominated over here (in NL it even is forbidden).



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[*] posted on 7-1-2007 at 10:43


Quote:
Originally posted by PainKilla
Trichloroisocyanuric acid is a most excellent source of chlorine, and I found that this process works quite well for generating bromine: (I kept in moles for easier adjusting of ratios etc)

.5 mol C3Cl3N3O3 (crushed up very finely)
1.25 mol NaBr in ~300ml H2O
~275ml 20% HCl

In a 1L round bottom flask set up for distillation and equipped with an addition funnel containing the HCl, add NaBr solution. Add TCCA to this solution. With stirring, begin to heat the solution (to ~55C) while very slowly adding the HCl. The bromine will begin to gradually distill over. Continue addition of HCl and distill until no more bromine is carried over.

Yields should be near quantitive (~1.25mol Br2)


The rate of bromine generation depends on HCl addition, so if your condensor is less than adequate, adding the HCl slowly works well as compensation. The procedure works very well, some other things to note are that the TCCA must be finely crushed, otherwise it takes a long time to react and results in a buildup of Br2. It's also quite a bit easier to stir when fine. It is also very important to have good stirring because without it, the bromine forms a layer in the reaction flask and once heat is applied, you begin to have an extreme amount of bromine evaporating that the condensor can't handle (well mine can't anyway). Other than that, this is a very straightforward procedure.

Some things I have yet to test is adding H2SO4 to the receiving flask in order to dry the bromine and keep it at least somewhat less volatile. I should be retrying the procedure soon and will report with more accurate measures.

EDIT: Forgot to put in yield.


[Edited on 5-1-2007 by PainKilla]


As much as time takes the reaction?
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[*] posted on 7-1-2007 at 10:55


Sorry everyone, Nicodem is right, I actually messed up in writing out the procedure. The proper amounts should be a slight excess of TCCA, but only by .25mol less of NaBr. In other words, 2.75mol NaBr. I use the slight excess of TCCA because I want to ensure that all of the NaBr is used up (harder for me to get NaBr than TCCA).

As far as contamination goes, isn't BrCl unstable at those temperatures? All of the other contamination is solved without problem by redistilling the bromine, and I have noticed no problems in using the bromine for synthesis.

It may be true that other methods aren't any more or less effective but this is a very quick and easy procedure to do and generates large amounts of bromine without any sort of effort, and for those in the US, the chemicals are fairly easy to obtain (and cheap).



[Edited on 7-1-2007 by PainKilla]




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[*] posted on 7-1-2007 at 13:28


Using excess NaBr leads to double loss of bromine. The excess bromide is not reacted, but the excess bromide also keeps behind quite some bromine, due to formation of the complex ion [Br2.Br](-), the so-called tribromide ion. Bromine dissolves MUCH better in solutions of a bromide, than in plain water.

On the other hand, BrCl is not that unstable. If it is formed, then it certainly will be in the bromine, it simply is dissolved in the bromine. It will be hard to remove, once you have it in the bromine.

So, whether you take excess bromide or excess TCCA depends on what you want to do with the bromine. In the past I have made bromine several times, but I always used it for somewhat more spectacular experiments, such as reacting it with Al, Mg, Na and red P. For all those experiments, the presence of some BrCl is not an issue at all.

But if you want to use the Br2 for synthetic purposes (e.g. brominating some organic), then you do not want the BrCl, because that always will lead to very hard to remove impurities of chlorinated compounds. BrCl chemically speaking resembles Br2 very much, but it is somewhat more reactive.




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[*] posted on 7-1-2007 at 18:54


good
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[*] posted on 7-1-2007 at 20:11


Since I have an old photocopy of a relevant 1 page article - "Methods for preparing aqueous solutions of chlorine and bromine for halogen displacement reactions", where a saturated solution of bromine is made from TCCA in that way, among other things - here it is, even though I think that most will pass on this as a preparative method.

Attachment: jce_64_156_1987.pdf (58kB)
This file has been downloaded 1749 times

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[*] posted on 11-1-2007 at 06:16


I just followed a synth Woelen gave me, using KBr + KBrO3 + HCl as a "one pot" reaction, I had an instant reaction and bromine was created, although it wasn`t until it spent a short time in the fridge cooling that I actualy got a blob of Br2 at the bottom (about match head sized).
I`ve had a read through this thread and distilation use etc... and also Bromine water.
I decided to make Bromine water with the gas given off, so using a double boiler I heated the rxn vessel and caught the gas under water, naturaly it changed color, but then eventualy droplets of Br2 were falling to the bottom, cut a long story short I now have a 4mm blob of Br2 in the bottom of a test tube with about 2cm of bromine water over it.
also I did the RP rxn with the spent vessel as there was still a little Br2 gas in there, RP instantly ignites on contact with it, the same as with Cl2 gas.
it`s also a nice way to clean your vessels afterwards :)

Thnx for the synth woelen and the extra data I needed from the rest that have posted in this thread, on behalf of myself and my Element collection ;)




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[*] posted on 11-1-2007 at 06:26


A slight excess of NaBr in the TCCA reaction does of course keep some of the bromine in solution as the tribromide, but this does not matter if the bromine is distilled out of the mix, as one must always do if any useful yield of bromine is to be achieved.
Extracting the blob of liquid bromine that frequently forms under the mix and discarding the aqueous layer is essentially the same as dumping half of your NaBr down the drain.
Bromine does dissolve in water to a degree that cannot be neglected, even if bromide ions are absent. Distillation is always necessary for any serious preparation of bromine.

However, maybe it isn't that bad an idea to not use an excess of NaBr and get BrCl- containing bromine as the first product.
BrCl and dissolved chlorine in the crude bromine can be removed completely by dissolving it in NaBr solution and distilling the bromine out of it. Cl and BrCl react with NaBr to form additional bromine.
The NaBr solution can be used again and again for this purpose as long as it still contains bromide (test with HCl + H2O2).
This would give an overall better yield of bromine since all of the bromine in the NaBr gets extracted in the first step.

[Edited on 11-1-2007 by garage chemist]




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[*] posted on 11-1-2007 at 11:56


I`ve just repeated this synth again, scaled up X10 and now hav a good 6mm of the test tube bottom full of Br2, however, I don`t know what`s happened but it would seem you cannot simple resume where you left off (so to speak), plenty bromone was "spilling" over the sides of the receiver tubs and into the conical flask holding the ice water, much went into the air too and I was forced to put my gas mask on!:o

I have no idea why it went this way at all??? everything was exactly the same as before other than being scaled up, the only Logical thing I can think of is that it overwhellmed the absorbtion capacity (surface area) of the liquid as it was being produced too fast.

all`s good in the Lab now, just my hair and clothes stink of Br2 now! my wife is just gunna LOVE ME in bed 2night! :(




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[*] posted on 11-1-2007 at 12:05


Scaling up of an exothermic reaction usually leads to different results. Speed of transfer of heat grows quadratically (area), while production of heat grows cubically (volume). So, the same reaction will lead to higher internal temperatures in the mix, so I certainly can imagine that you obtained copious amounts of bromine vapor from the warmer mix.



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[*] posted on 14-1-2007 at 04:38


That solubility has in water ClBr?
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[*] posted on 14-1-2007 at 09:36


Similar to that of bromine. It also reacts with water, leading to formation of bromic acid, bromine, and chlorine. There is a fairly complicated equilibrium, BrCl when added to water leads to a complicated mix of different chemicals.



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[*] posted on 15-1-2007 at 01:26


Ok, 7 pages is a lot to sift through, but has electrolysis been brought up?

I know that when electrolyzing a solution of NaCl, H2 forms at the anode, and Cl2 at the cathode, resulting in NaOH in solution. Would the same work with NaBr? Would you get H2 at the anode and Br2 at the cathode? If so, it sounds like a much less messy, and vastly simpler method.




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[*] posted on 15-1-2007 at 04:28


H2 forms at the cathode, not at the anode. Br2 forms at the anode.
But isolating the Br2 from the solution is a real pain. For a home-lab, electrolysis definitely is not the best way to make bromine.

You can use electrolysis indirectly, first make KBrO3 by means of electrolysis (I made another topic on that subject) and then react the KBrO3 with KBr and concentrated acid. That is a very convenient method of making Br2.




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[*] posted on 15-1-2007 at 09:17


what reaction does it produce: NaBrO3 + Cl2 =>?
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[*] posted on 15-1-2007 at 09:46


I expect you`ll get plenty side reactions doing it that way, leaving a messy outcome with a shopping list of products.
don`t forget you`ll need these in a state where they can combine, as Cl2 would be gas the other must be a liquid, and since water would be choice, Messy:(

[Edited on 15-1-2007 by YT2095]




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[*] posted on 15-1-2007 at 11:09


Quote:
Originally posted by Filemon
what reaction does it produce: NaBrO3 + Cl2 =>?

No reaction: bromate does not react with chlorine, not in the solid state, nor when both are dissolved in water.

[Edited on 15-1-07 by woelen]




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[*] posted on 15-1-2007 at 11:22


or of course it do nothing at all like Woelen said :P



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[*] posted on 15-1-2007 at 11:49


It's not likely that chlorine would donate electrons to the Br in the bromate.

Which makes me wonder,

how well would this work with I2?




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[*] posted on 16-1-2007 at 05:19


Bromate can oxidize I2. I2 and bromate can react, giving iodate and Br2. I do not expect this to work well in the solid state, but in solution, certainly when some acid is present I'm quite sure the following happens:

I2 + 2HBrO3 ---> Br2 + 2HIO3

I did not try with my bromate, but what I did do is reacting potassium chlorate in acidic solution with I2. If you do that, then the I2 quickly dissolves and the liquid becomes light green. Chlorine gas is evolved.

[Edited on 16-1-07 by woelen]




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[*] posted on 6-10-2007 at 09:24


Interesting thread. I have 1kg of bromochlorodimethlyhydantoin and want to make bromine from this.

The way I see it my options are throw in NaOH and boil it (slow addition may be better, not sure yet) to make NaCl:NaClO3:NaBr:NaBrO3 = 2:1:2:1. Then slowly add HCl to the solution produced (minus the dimethylhydantoin, solubility 0.1g/100mL) while heating, to produce Br2 with perhaps some BrCl. Or I could just add HCl to the BCDMH and get the bromine and halogens from that. If bromine is liberated first then the amount of HCl added could be tailored so as to not liberate large quantities of chlorine.

Q1. Will concentrated, acidic halogens react with dimethylhydantoin to decrease my yield? ie. do I need to do an alkaline extraction first?

Q2. If the addition of HCl is slow will I be getting *mostly* Br2, BrCl, Cl2 or all of the above? If all of the above, then how the heck do I handle 100g+ of chlorine :(

Q3. Since at least some BrCl will be formed how do I remove this from the Br2? I was thinking that by refluxing it up a column for ages I could let it escape as Cl2, but using tap water to cool the column BrCl will probably be lost too (bp.'s of Cl2, BrCl and Br2 are -34*C, 5*C and 59*C respectively). I am assuming that an equilibrium exists Cl2 + Br2 <---> 2BrCl.

Any help appreciated. ;)

[Edited on 7-10-2007 by Antwain]
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