Sciencemadness Discussion Board

Getting the Bromine from BCDMH

un0me2 - 7-2-2010 at 02:10

My only realistic bromine source is the OTC 1-Bromo-3-Chloro-5,5-dimethylhydantoin, which on treatment with HCl will give a mixture of chlorine and bromine.

To separate these is the issue

I was thinking, pass the mixture of halides into aqueous SO2/H2O, thereby forming HCl & HBr gasses.

Pass those into a solution of either KOH or NaOH and get a mixture of KCl:KBr and NaCl:NaBr... Treat that mixture with HCl gas (which will not react with the KCl/NaCl) will give HBr and KCl/NaCl

Anyone see any issues?:)

Picric-A - 7-2-2010 at 03:59

There are thousands of threads on this including pictures of previous members experinces at this. UTFSE!

blogfast25 - 7-2-2010 at 09:25

Quote: Originally posted by un0me2  
My only realistic bromine source is the OTC 1-Bromo-3-Chloro-5,5-dimethylhydantoin, which on treatment with HCl will give a mixture of chlorine and bromine.



You call BCDMH 'your only realistic source of bromine'????

How about KBr or NaBr? Treat solution with Cl2 to obtain Br2. With enough bromide it will actually sink to the bottom to siphon it off.

What's OTC about BCDMH, what's its normal use?

crazyboy - 7-2-2010 at 09:44

Quote:

What's OTC about BCDMH, what's its normal use?


If you UTFSE you would find it is a common spa and pool brominator.

woelen - 7-2-2010 at 09:55

Only in certain countries it is a common spa and pool brominator. Where I live it cannot be purchased, nowhere at all. Bromination of pools is forbidden over here. Actually, we don't have any really OTC source of bromine. KBr and NaBr can be purchased over here (e.g. as photography supply) and we also can buy KBrO3 and NaBrO3, so making bromine is not a problem at all, but you must keep in mind that what is common in one country is not common at all in other countries.

Picric-A - 7-2-2010 at 10:32

It has been said but in the UK BCDMH is used instead of K/NaBr, infact i find it quite hard to get a cheap source of NaBr, the only thing i have found is a dilute solution of NaBr used as a drilling fluid.

crazyboy - 7-2-2010 at 10:45

Well considering that I have a large bucket of BCDMH tablets and I live in the US and Picric-A has confirmed it is also the predominant brominator in the UK I think it's fair to say it's common even if it doesn't appear in the Netherlands.

un0me2 - 7-2-2010 at 12:46

I cannot purchase NaBr/KBr whereas BCDMH is ALL I can buy. I believe there are numerous pictures of people using the route from NaBr/KBr to Br, but I have not, in the past several years (nor in the archives I have been able to find) actually seen a single picture of anyone getting the Br in a pure form from BCDMH. I have used the FSE, matter of fact I use it a lot more than most people.

PS Just treating the solution with HCl will give Cl+Br+BrCl+all the permutations of the halogenated halogens. In order to purify it, it is necessary to work out HOW to purify it, as both Cl and Br will oxidize SO2 to SO3 (actually H2SO3 to H2SO4) and HCl and HBr, and both of those can be neutralized with either Sodium Hydroxide or Sodium Carbonate/bicarbonate (use the latter for a visible endpoint), that would be the shortest route I can think of to a mixture of the Bromide and Chloride salts. As the Bromide salt will react with HCl and the Chloride salt will not, careful addition of HCl to the mixture should give ONLY HBr in solution (I need PURE chemicals, not kinda sorta pure).

[Edited on 7-2-2010 by un0me2]

blogfast25 - 7-2-2010 at 12:51

Quote: Originally posted by Picric-A  
It has been said but in the UK BCDMH is used instead of K/NaBr, infact i find it quite hard to get a cheap source of NaBr, the only thing i have found is a dilute solution of NaBr used as a drilling fluid.


I got KBr and KI from Silverprint (UK)

woelen - 7-2-2010 at 13:14

Quote: Originally posted by un0me2  
I cannot purchase NaBr/KBr whereas BCDMH is ALL I can buy. I believe there are numerous pictures of people using the route from NaBr/KBr to Br, but I have not, in the past several years (nor in the archives I have been able to find) actually seen a single picture of anyone getting the Br in a pure form from BCDMH. I have used the FSE, matter of fact I use it a lot more than most people.

PS Just treating the solution with HCl will give Cl+Br+BrCl+all the permutations of the halogenated halogens. In order to purify it, it is necessary to work out HOW to purify it, as both Cl and Br will oxidize SO2 to SO3 (actually H2SO3 to H2SO4) and HCl and HBr, and both of those can be neutralized with either Sodium Hydroxide or Sodium Carbonate/bicarbonate (use the latter for a visible endpoint), that would be the shortest route I can think of to a mixture of the Bromide and Chloride salts. As the Bromide salt will react with HCl and the Chloride salt will not, careful addition of HCl to the mixture should give ONLY HBr in solution (I need PURE chemicals, not kinda sorta pure).

[Edited on 7-2-2010 by un0me2]

Adding HCl to a mix of chloride and bromide salts certainly will not give you pure HBr when the stuff is heated. You will end up with a mix of HBr and HCl and also a mix of bromide and chloride remains behind in the liquid. Adding HCl to a mix of bromide and chloride just dilutes the bromide.

What can be done to make pure bromine is the following:
- Add HCl to your pool bominator. This gives a mix of Br2, Cl2 and BrCl. Heat until all of the halogenmix is driven out and collect this mix in a solution of acidified Na2SO3. If the color of the halogen mix does not disappear in the collecting solution, then add a little more acidified Na2SO3. Always assure that just enough Na2SO3 is added, do not add large excess amounts.
- Now you have a mix of bromide, chloride and sulfate (and excess acid) in solution.
- Determine how much bromide is in solution. You can derive that from the starting amount of pool brominator.
- Make a chlorine generator, using pool chlorine and HCl. Bubble chlorine gas through the solution of bromide and chloride. Bromide is oxidized to bromine. As long as you do not bubble too much chlorine through the solution you will have bromine only and no chlorine. Your liquid then contains free bromine, chloride and sulfate (and acid).
- You need a glass distillation setup to isolate the bromine from the solution. This can be done fairly easily, because of the big difference of boiling point of Br2 and water. HCl will hardly come over, because this forms an azeotrope with water, which boils at 110 C.

I have done this distillation from a KBrO3/NaBr mix, but yours will not be really different. Try to keep your solutions as concentrated as possible. Use Na2S2O5 (metabilsulfite instead of sulfite, this allows getting a higher concentration).

The practical distillation setup is described here: http://woelen.homescience.net/science/chem/exps/raw_material...

[Edited on 7-2-10 by woelen]

Polverone - 7-2-2010 at 13:27

A few months ago len1 described in some detail the liberation of bromine from this product. See near the last page of this thread: https://www.sciencemadness.org/whisper/viewthread.php?tid=69...

entropy51 - 7-2-2010 at 13:32

Quote: Originally posted by Nicodem  
You would need to reduce 1-Bromo-3-Chloro-5,5-dimethylhydantoin with KBr, NaBr or other bromides in the presence of an acid in order to efficiently use it as a bromine source:

1-Bromo-3-Chloro-5,5-dimethylhydantoin(s) + 3KBr(aq) + H2SO4(aq) => 2Br2(l) + K2SO4(aq) + KCl(aq) + 5,5-dimethylhydantoin(s)

Using this exact stoichiometry is very important else you get other pathways reduce the yield of Br2.
If you want only the Br in 1-Bromo-3-Chloro-5,5-dimethylhydantoin you could reduce it with other reductants instead of bromides, but then you would obtain only half mol Br2 per one mol 1-Bromo-3-Chloro-5,5-dimethylhydantoin. For example, like you did with NaNO2, forming NaCl, NaNO3 and Br2. Sulfites and similar reducing agents would also work. However, like I said, it would be a waste of the oxidative power to do so while the reagent can be used to oxidize bromides instead.



[Edited on 7-2-2010 by entropy51]

len2 - 7-2-2010 at 17:37

Ah yeah, well as I wrote this formula is wrong because the chlorine in BCDMH does not get reduced.

By the above I mean by S2O52- as posted in that thread. With HCl it does get reduced and you get a mixture of BrCl, Br2, Cl2. Depending on how quickly the reaction goes some/most the BrCl,Cl2, gets reduced by the bromide to Cl-, but unless done very slowly there will always be some Cl in the evolved gases - using S2O5 is superior in that regard.

[Edited on 8-2-2010 by len2]

unome - 8-2-2010 at 03:17

Sorry Polverone and of course, Len:( I thought I had read most of that thread, but it was some time ago I must confess

So what, I add the BCDMH to a solution of sodium metabisulfite, and heat? Then heat again with an ice condenser to get the Cl out of the mixture? OK Seems we've got similar suppliers on the pool chem front:D

woelen - 8-2-2010 at 03:39

Don't add the BCDMH to a solution of sodium metabisulfite. That will give a mix of chloride, bromide, organic stuff and acid. I can imagine that this results in a nasty slurry, which is hard to boil without excessive bumping.

unome - 8-2-2010 at 03:58

From Len (@ the link above):
Quote:
So the main reaction is

4RBrCl + Na2S2O5 + 3H2O -> 2NaHSO4 + 2Br2 + 4RClH

1/4 of the moles of metabisulphite are required, which is very efficient.

Take 120 gms (0.5 mole) BCDMH place in a 1 liter three neck flask with thermometer, distilation head, droping funnel. The distilation head leads to a west condenser at 30-45 degrees fed with 0-10C water from a recirculating pump. Add 40-50mls H2O and mix by shaking to a thick slurry. Add 10ml conc HCl. Place 80ml metabisulphite solution made by dissolving 160gms Na2S2O5 in water to 500ml in funnel. Adjust drip rate so the drops are just too fast to count (about 3 per second). The entire flask will soon turn a deep red and the contents will boil, with temperature rising to 83-87C. The addition rate is such that bromine essentially boils off as soon as its formed. After all reducer has been added wait for boiling to subside and turn on heater raising temperature to about 97-99C until gas in flask loses red colour (becomes orange due to BrCl). Yield 30gms bromine phase, + about 1 gm in water phase. Note that insufficient reducer added for anything but a) to occur substantially.

Interestingly small amount of HCl raises yield somewhat.


I had it back to front, but still, a slurry is what you will get...

[Edited on 8-2-2010 by unome]

len2 - 8-2-2010 at 15:13

Right, I did the experiment, got essentially pure bromine, recorded the results. but apparently if you you should get an intractable 'slurry'. Next time Ill save myself the trouble of confronting nature and go directly to Wilco!

un0me2 - 9-2-2010 at 04:40

I wasn't taking the piss out of you Len... Damn, I try and add some levity when "I" fuck up and people get all touchy... I honestly didn't see the latest input on that thread and just "assumed" (yeah, I know, mother of all fuckups)* that it hadn't gone further...


* Although it isn't an excuse, from the 6-9/11 I was in a propofol induced coma while the skin was removed from my arms, so your posts around that date probably weren't read by me...:(

Magpie - 9-2-2010 at 15:44

Do you live in the US, un0me2? NaBr is available in the US but is becoming increasingly hard to find, except possibly those little 2 oz packs where they want ~ $1.65/oz. I understand it is being replaced by tablets (BCDMH?) for the spas. When I saw your post I checked my inventory of NaBr and went into a mild panic when I saw that I had <100g. Fortunately I quickly found a local source and have now built back my stock to 5 pounds. At this scale it was $0.53/oz.

entropy51 - 9-2-2010 at 16:04

Quote:
Damn, I try and add some levity when "I" fuck up and people get all touchy
Recognizing humor is not our strong suit. We are very good at touchy, however:(. I hope you are recovering well from your serious burns.