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Antwain
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@Nicodem- Oh my god. How could I possibly have not known about that. For 5 years I have been miscalculating my KOH requirements, this explains a few
things that have happened in the past. How dare they call it an analytical reagent. My most impure home-prepared reagents would never be put in my
cupboard with 15% impurity. However it also says >85%, so I don't even know how much water is there. I would estimate that I added an additional 3g
of KOH for a total of ~31.5g If not too much HCl came across then that is a good yield. Also, by the end of the distillation I would colourimetrically
estimate that there was less than 1/20 atm partial pressure of bromine above the distillation flask @ ~80*C, and probably a lot less than that.
I may reduce the distillate to bromide and then feed that to some more BCDMH, but I will wait for that.
Also does anyone know why the solution is yellow? It went the kind of yellow you get in bleach at first, then to a pale yellow. This makes sense I
guess, hypohalite and all, but since bromide and bromate are both white... why is it still yellow after being heated to 90*C for an hour?
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Jdurg
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From my own personal experience, once Bromine has been in something it NEVER goes away. It will permanently stain everything and attack almost
everything as well. It's a little devil of an element and it took a great deal of glass and acrylic resin to keep it from leaching out. I've used
tubing that appeared very clean and clear, heated it up in a flame and seen liquid bromine leach out from it. There's a good chance that you have
very dilute amounts of Br2, or BrCl that is giving that very faint color.
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
requires wiping afterwards.\"
http://maddox.xmission.com. |
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Antwain
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not in alkaline solution.
I should elaborate... When there was bromine dissolved in the solution and it was orange. Upon addition of more alkali and stirring this colour faded
immediately. Further, the disproportination of OBr- takes place much more readily than OCl-, so I do not believe it is possible that after boiling it
anything but KBr and KBrO3 should remain....
yet it is yellow  and I don't know why. But I would bet my last dollar against
it being bromine
[Edited on 21-10-2007 by Antwain]
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woelen
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I agree with you it is no bromine, but most likely, it must be some contaminant, which is discolored by the bromine.
I have a very similar experience, but in strong acid. I once made a solution of KBr, very concentrated, and added concentrated H2SO4, in order to
obtain HBr (with sulfate and potassium contamination). This liquid was light yellow/brown, due to partial oxidation of bromide to bromine, and
subsequent loss of SO2. The yellow/brown color remained.
Later, I took some of this liquid, and added Na2SO3 in order to make it colorless. But to my surprise, it did not become completely colorless, no
matter how much Na2SO3 I added, and even when there was a strong pungent smell of SO2, it still remained light yellow. For me, this never was
resolved. I don't have the liquid anymore, I used it up in all kinds of experiments (mainly for making drops of bromine with KBrO3).
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ProfessorMolly
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The method i have been using to get my bromine would be bubbling chlorine gas into a fully saturated sodium bromide solution, but the problem i have
been having is the yeilds i get are awful, out of several runs and in total from 1lb NaBr i got about 60ml of Br2.
I believe that its because Br2 is soluble in water and when the gas tears it out of the solution it is still being dissolved into the water, and the
actual dark bromine you get it just the amount left over that the water can't take any more of. So i have been looking for a different route to get
this, and what sparked my interest was the H2O2, H2SO4, and NaBr route, now i understand that the purity of the H2O2 would be 35% but the questions
that i had that i could not find answered here were, what ratios should be used (as in amounts of H2O2, H2SO4, and NaBr) and from what i read the NaBr
is dissolved into the H2O2 and then H2SO4 is added somewhat slowly and Br2 is released, i jsut wanted to make sure of these things before wasting my
time and/or money, also i had to ask, the final product , will it be a layer on the bottom of the solution that i can take off easily, or does it
require distilling? its not that i don't have the equipment, its just id rather not, but if i must then i will,
If you guys could help me out with these questions id highly appreciate it, Thanks
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roamingnome
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Ive been trying to generate a useable amount of bromine by electrolysis because it seems so simple. Well the first trial mainly just produced bromine
water.
So I had white gas and extracted the orange bromine water and the bromine associated with the white gas. But I came back 2 days later to see that the
density of the bromine or something caused it to fall out of the top layer back into the water.
Now im building a custom cell that has a DCM water interface. The electrode will be as close to the dcm as possible and the bromine will fall of the
electrode into the clutches of the DCM which can be tapped of the bottom. It will be slow but consistent process…
Anyways im not sure where all your bromine went but a DCM extraction of the water will surely not hurt.
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StevenRS
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I have made bromine before with HCl, H2O2, and NaBr, and have yet found a way to store it. It always leaks out of my glass stoppered flasks! Could I
seal it with Teflon tape, maybe?
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woelen
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Storing bromine in a bottle with teflon tape around the rim and a thick teflon liner in the cap works exceptionally well for me. I simply don't smell
any bromine near the cap of the bottle.
Below follows a picture of what I mean:
This is the bottle with its cap.
The white cap is a modified cap. These caps contain some foam material, when purchased. I replaced that with a thick teflon liner (more than 1 mm
thickness). The teflon tape really must be there. Without the teflon tape, I can smell the bromine, even when the cap is screwed on the bottle very
firmly.
Btw, I store this bromine in a plastic bag, with 1 kilo of Na2S2O3.5H2O outside the bag, and another bag around these two chemicals. This Na2S2O3.5H2O
works as a safety filler, which absorbs bromine in a controlled manner, just in case the bottle breaks.
[Edited on 5-2-08 by woelen]
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StevenRS
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Hmm... I wonder, can I melt Teflon plumbers tape without it decomposing? That could open up a lot of possibilities....
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12AX7
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Not really. It can be formed more easily when hot, but it doesn't melt (gooify) like thermoplastics. Consider your nonstick frying pan (the Teflon
one, not the cast iron one*), which is pretty solid up to perhaps 400-500°F, then gives off toxic fumes any hotter.
*Any cook who knows anything (which, okay, need not necessarily include any chemistry geek -- but I can always hope!), knows that well oiled and
seasoned cast iron pans work just as well as any Teflon-coated pan. Technical progress? Yup -- they figured it out centuries ago! 
Tim
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MagicJigPipe
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I would like to add that I have attempted to melt PTFE tape before. It "melts" very slightly before decomposing into a brown tinged mass at around
330*C. Definitely not good for molding at all.
I use the technique that woelen mentioned above for pretty much all of my volatile chemicals. It works very well. During the winter time, keeping
Br2 outside (in the garage or shop) seems to help, also.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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StevenRS
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I tried to coat a glass stopper in it to achieve a better fit, and in never seemed to work, and if it did, it was single use only. I recently tried
melting (or heating) the teflon tape covered stopper, then inserting it into the flask, and it seemed to work a lot better.
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skippy
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I did a little bromine synthesis tonight. I don't have any fancy ground glassware so I made my apparatus from two erlenmeyer flasks connected by
tubes and stoppers I cast and lathed out of lead. The stoppers were covered with teflon tape. I put a small cooling jacket on but I didn't end up
using it as I did the reaction outside where it is very cold right now ;-). I don't have yields yet, I think I may have lost a bit through the
stoppers, and my peroxide was old too so I'm not sure what strength it was, so maybe there was still bromide unoxidized. Or maybe I over did it
thinking it was weakened (can peroxide oxidize bromine?).
The bromide was from a liquid spa solution, the sulfuric acid was "liquid lightning" and the the hydrogen peroxide was hydroponic 30%. I slowly
added all the peroxide at bottle concentration and didn't have any significant distillate until I applied heat to the large reaction flask. I'll
put up some pictures of the product soon - its an nice little bit of bromine.
Nothing too revolutionary about the reaction, but I thought maybe someone would find my construction method interesting. The castings were made
in wood molds lined with foil. The stopper molds were made by drilling a hole with a forstner bit into wood. The stoppers were cast then drilled and
a rod threaded into them so they could be turned on a lathe until they would fit the flasks. The pipe was made by casting lead around a steel mandrel
in a piece of wood I cut a trough in with a router. The steel mandrel was tightly wrapped with a strip of aluminum foil to make removal easy.
The pipes were rasped untill they would fit into holes drilled in the stoppers. The pipes were flared into the stopper holes and then soldered with
a tin-lead solder for mechanical strength. No tin solder was visible on the inside of tube stopper interface. I may try this reaction again soon
with some fresh peroxide.
[Edited on by skippy]
[Edited on by skippy]
[Edited on by skippy]
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a_bab
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Bromine for everyone: (found this interesting to share): http://www.perekopbromine.com/main.php?lang=eng&page=pro...
Now these are ALOT of bottles...
Also an idea about safely storing it (as somebody said before, with Na thiosulphate in a metal container instead of perlite)
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LSD25
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| Quote: | Originally posted by BromicAcid
To avoid the cholorine gas all together I usually dissolve my sodium bromide in water and add calcium hypochlorite then once the two are mixed I add a
bit of hydrochloric acid. The mix instantly turns red from bromine liberation and if the concentration is high enough you get some rewarding drops of
dark red in the bottom of the reaction mixture. Then the bromine can be distilled off of course. |
So, with the latest incarnation of the constant battle to keep bromine away from those who want to isolate it being to mix sodium bromide with
hypochlorite, all that is necessary is to add HCl to liberate the bromine?
(the mix as sold has a considerable excess of calcium hypochlorite (s), around 750-800g/kg IIRC while the NaBr content is around 150g/Kg).a
You know, I was just about to post a question asking if anyone had any bright ideas on how to separate the two, kinda lucky I read the WHOLE thread,
ain't it?
I was actually thinking of feeding it something to oxidise (like aluminium), same way you get iodine from KI when you add too much OCl after HCl... It
really is the same thing, aint it?
Whhhoooppps, that sure didn't work
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Bohrium
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Just finished distilling...
Today I obtained 180g (60ml, an 80% yield) of bromine by distilling 400g of DBDMH with 200ml of water while slowly adding 250ml of concentrated HCl.
Here is the apparatus:
After about 75 ml of acid had been added:
And here is a portion of the final product:
Edit:
DBDMH = 1,3-Dibromo-5,5-dimethylhydantoin
[Edited on 9-1-2009 by Bohrium]
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Lambda-Eyde
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That's a wonderful setup. I really envy you. 
Is there any specific reason to why you chose to use DBDMH? Is it readily available? It sounds like a rather exotic compound to me. Did I miss
anything?
[Edited on 9-1-2009 by Lambda-Eyde]
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woelen
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DBDMH is not exotic at all. It is a swimming pool brominating agent and in countries where bromination of swimming pools is allowed this is as common
as TCCA for chlorinating swimming pools.
Unfortunately, in NL the bromination of swimming pools is forbidden en for this reason this compound is not available here. Here we only have TCCA,
Na-DCCA and calcium hypochlorite, no bromine-containing chemicals.
Did you assess the purity of the bromine? Water and remains of acid easily can be removed from the bromine, but I still think it is rather impure, due
to the presence of elementary chlorine. In the process with DBDMH besides formation of bromine, there also is formation of chlorine, which reacts with
bromine to BrCl, which dissolves in Br2 exceptionally well and cannot be removed easily by distillation, unlike the water and remains of acid.
[Edited on 9-1-09 by woelen]
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Bohrium
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| Quote: | Originally posted by woelen
DBDMH is not exotic at all. It is a swimming pool brominating agent and in countries where bromination of swimming pools is allowed this is as common
as TCCA for chlorinating swimming pools.
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Exactly.
I was able to obtain 5lbs of it for $14.
| Quote: |
Did you assess the purity of the bromine?
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I was unable to do so yesterday, but I'll measure its density later today. Will the BrCl evaporate out if the bromine is left to stand around 5
degrees C? I don't believe much could have condensed, because my condenser coolant was at around 10 degrees.
[Edited on 9-1-2009 by Bohrium]
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woelen
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I would not simply leave the bromine in an open bottle at 5 C. You will loose way too much bromine as well. BrCl dissolves in bromine exceptionally
well and is not easily removed by non-chemicals means.
There is a good way to get rid of the BrCl, but this step requires a second distillation of all the bromine. The BrCl is destroyed chemically instead
of physically removed.
Prepare a solution of NaBr or KBr. In your situation with appr. 200 grams of bromine I would take 25 ml of water, dissolve 2 gram of KBr or NaBr in
the water and add this solution to your bromine. Shake well and then let the bromine settle at the bottom. If you do not have NaBr or KBr, then you
can sarifice some of your current bromine to make a solution of a bromide (see end of post).
Separate the bromine from the aqueous layer as good as possible. If you have a separating funnel then that is most conveniently used, otherwise
pipette away the bromine from under the aqueous layer.
Next, take 10 ml of concentrated sulphuric acid and add the bromine to this. Shake well again. Any water, left over in the bromine, now is bound to
the sulphuric acid.
Distill this liquid and what goes over is very pure and dry bromine.
The treatment with KBr/NaBr destroys any BrCl: BrCl + Br(-) --> Br2 + Cl(-)
The Cl(-) goes in the aqueous layer.
The treatment in turn with conc. H2SO4 is done in order to easily separate from the water. Without the acid, you cannot get your Br2 free of water in
a single distill. At 50 C or so, also quite some water vapor comes over as well. But if you separate as much as possible of the water using a funnel,
then the rest can be tightly bound by the sulphuric acid. Your H2SO4/Br2 mix now can be separated very easily, no water will come over below 150 C,
while the Br2 goes over at 60 C or so. You can distill over all bromine and you stop when only sulphuric acid remains left. Do not continue the
distillation to also get the bromine, dissolved in the H2SO4. That last little bit must be regarded as lost. It will only be a small amount, I think
less than 1 gram if you use 10 ml of concentrated acid.
----------------------------------
In case you have no bromide: Take 10 ml of household ammonia (5% NH3) with NO additives. Mix with 15 ml of water. This makes 25 ml of 2% ammonia, To
this, slowly add 1 ml of bromine while swirling (which is excess of bromine, but you mix with your bromine anyway, so that is OK).
This liquid gives a very clean quantitative reaction with bromine:
8NH3 + 3Br2 --> 6NH4Br + N2
You really have no side reactions. Any BrCl in your bromine immediately reacts to chloride and bromine, so your solution will contain ammonium ions
and bromide ions and a small amount of chloride ions. This can be usded as your solution of NaBr or KBr.
[Edited on 9-1-09 by woelen]
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Jor
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I'm most impressed by your fume hood! Did you buy it or build it yourself? If yes, that's a very neat sash and baffles!
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pHzero
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Sorry to revive an old topic (I don't know how people feel about that here, you get told off for it on some forums) but wouldnt an easy way to make a
high yield of bromine be to bubble HBr (produced by KBr+H2SO4) through a solution of BCDMH or DBDMH?
You can produce bromine by oxidising HBr, or by reducing the HOBr produced by BCDMH, so I'm surprised that noone's suggested oxidising/reducing one
with the other?
Surely HBr+HOBr--->H2O+Br2?
I happen to have some KBr, and I could get BCDMH quite easily.
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woelen
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Yes, this can be done, but it is quite a hassle. It is much simpler to simply dissolve the KBr, add sufficient acid and then add the BCDMH (or any
other suitable oxidizer). Bromine drops out and can easily be distilled (see above).
Bubbling HBr through a liquid containing BCDMH has no advantage over the procedure, given above. You also need to distill bromine.
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pHzero
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Quote: Originally posted by woelen  | Yes, this can be done, but it is quite a hassle. It is much simpler to simply dissolve the KBr, add sufficient acid and then add the BCDMH (or any
other suitable oxidizer). Bromine drops out and can easily be distilled (see above).
Bubbling HBr through a liquid containing BCDMH has no advantage over the procedure, given above. You also need to distill bromine.
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Ah right - I did consider that, but then I thought maybe the K+ or SO4 2- might somehow interfere with the reaction, eg the dissociation of the BCDMH
into HOBr.
But still, thats basically what I meant, using one to oxidise/reduce the other, rather than introducing external oxidisers like H2O2
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len1
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A bottle of Br2 containing some BrCl in solution, will essentially rid itself of the BrCl if let to vent to the atmosphere. BrCl equilibrium is
quickly attained, so the task is to rid of the BrCl while minimizing loss and in fact gaining Br2 in the bottle due to dissociation of the former.
BrCl boils at 5C, taking this and assuming the vent is an efficient reflux at this temperature, (ie time scale of reflux much greater than 2BrCl ->
Br2 + Cl2 equib constant ) the bromine partial pressure is about 0.07. The equib constant is about 0.14
pCl2 pBr2/pBrCl^2 = 0.14
so
pCl2/(0.93-pCl2)^2 = 2 -> pCl2 = 0.45, pBrCl = 0.48
Say there is initially 1 mol Br2 and 1 mol BrCl in the bottle (obviously instantaneosly since this mixture is not in equib).
The 1 mol of atomic chlorine will be lost as 1/3 mole of Cl2 and 1/3 mol of BrCl. In addition about 1/20 mole Br2 will be lost from the bottle. 2/3
mol BrCl would have been converted to 1/3 mol Br2, so the bottle now contains
1 + 1/3 - 1/20 about 1.28mol Br2.
We have gained 0.28 mol.
Experimental test gave me almost spot on this result.
[Edited on 7-11-2009 by len1]
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