Sciencemadness Discussion Board - Elemental bromine isolation

Elemental bromine isolation

madscientist - 21-1-2003 at 18:16

I was thinking of several methods of isolating elemental bromine without distillation. This is the idea I tested:

2KMnO₄ + 10NaBr + 16H₂SO₄ ----> 2KHSO₄*H₂O + 2Mn(HSO₄)₂*H₂O + 10NaHSO₄*H₂O + 5Br2

I mixed 3.2g of granulated KMnO₄ with 10.3g granulated NaBr. I then proceded to add 9.5mL of concentrated sulfuric acid. There was slight bubbling, then the mix turned brown, and suddenly began spewing bromine gas. After a few more seconds, it began crackling, and I saw red flashes within the reaction beaker. After about two minutes, visible quantities of bromine were no longer visible. I looked at the remaining solid, and noted that it was slightly purplish (likely because sulfuric acid was participating in the oxidation of HBr, causing not all of the KMnO₄ to be used). I was hoping that the reaction would be a tad less violent, meaning that the reaction would have yielded liquid bromine instead of gaseous bromine.

This is what I plan to try next:

2NaNO₃ + 10NaBr + 12H₂SO₄ ----> 6NaHSO₄ + 6NaHSO₄*H₂O + 5Br₂ + N₂

That reaction should be much less violent. Hopefully, I'll just be able to pour off the bromine.

a_bab - 21-1-2003 at 22:18

I see no point in your desire to obtain directly liquid bromine. The byproducts will impurify your bromine and there is no way to filter it in the usual, way, as is VERY volatile. You can distill it by the simple means of two testubes and a glass tube: one as reactor vessel and one testube to collect and condense the bromine vapors. The second testube should be ofcourse kept in some cold bath. It's much simpler and there will be no nasty stinks.

I have played quite a lot with bromine and it's a nasty stuff. I got burned (it was horrible), and the vapors are very irritable too...Not talking about the things you can get with it: bromacetone, benzyl bromide, etc.

fluffy bunny - 21-1-2003 at 22:36

Madscientist, you do realise sulphuric acid reacts with KMnO4 to produce manganese septoxide don't you!! No wonder you had a very violent reaction, manganese septoxide is some nasty shit, it spontaneously ignites, with almost any organic material.
I strongly reccomend you don't have any mixture with KMnO4 and H2SO4 in it together.
I've made very small amounts of this stuff and its really nasty.
Once a tiny drop landed on the bench without me noticing. There was a lighter there and, and it ate straight through the plastic causing it to explode!

Nick F - 22-1-2003 at 03:17

I'd just bubble chlorine through a strong NaBr solution. I think there'd be less chance of any side reactions, you'd get some bromine chlorides but the amounts of these would be insignificant unless you used a massive excess of chlorine.
NaOCl could probably be used too, like when preparing iodine from that tincture you can get in pharmacies. There'd be less chance of getting chlorides with this.
Or, melt it down and electrolyse it. Condense the bromine and collect the sodium! Ahh, if only it was that simple eh?

madscientist - 22-1-2003 at 11:55

I think that passing dry chlorine over NaBr should yield dry bromine without the bromine chlorides - if the temperature is kept over 10C (BrCl decomposes with evolution of Cl₂ at 10C).

I wasn't worried about Mn₂O₇ (yes, I have worked with it before) because it was created and destroyed in small amounts (due to there being only small grains of KMnO₄ in a mix of NaBr).

With the second process I suggested in the first post of this thread, it should be easy enough to separate the bromine with a separation funnel, considering that the density of liquid Br₂ is 3.1g/cm³, while the density of NaHSO₄ is 2.74g/cm³, the density of NaNO₃ is 2.27g/cm³, and the density of H₂SO₄ is 1.84g/cm³. Everything that's not bromine that's left after the reaction should float on it. The main problem that potentially could plague the reaction would be HBr gas escaping before it's oxidized.

Darkfire - 22-1-2003 at 14:02

Try my method

I think the safest and best way would be to use NaBr MnO2 and H2SO4.

CTR

I am a fish - 23-1-2003 at 12:59

Nick, how do you get the bromine out of the resulting mixture?

Do you extract it with a non-polar solvent? If so what?

Chris

Bromine? Oxidation!

Organikum - 8-2-2003 at 12:12

Any oxidiser does the trick. H2O2 might be the most easy to get.
H2O2 + 2NaBr -> 2NaOH + Br2
H2O2 in diluted (10%) HCl. Purification by sublimation. (I hope this counts as "without distillation")

Every oxidising agent in acidic solution should do the job, bleach, chromiumsalts, MnO2.......

ORG

trinitrotoluene - 12-2-2003 at 20:19

Yesterday I added some NaBr into water until it dissolved. Then added some HCl. After that precipitated it with 30% H2O2. The Br2 is in the soloution it must be distilled to be isolated. Also distillation will also yield O2 as the H2O2 decomposes. I heated it to 60*C and visiable amount of Br2 gas is given off. I had a 20" fan blowing the fumes to my backyard neighbors yard

Organikum - 14-2-2003 at 01:50

this is just a quickshot, I haven´t looked it up (my MERCK index refuses to work).

Freezing? Will Br2 precipate by cooling it down? Perhaps it will be necessary to add something (ethylene glycol?) to lower the freezing point of the solvent...

And sublimation seems possible. Decomposing the H2O2 with a drop of blood

and sublimation over a few days.....

ORG

trinitrotoluene - 30-3-2003 at 17:39

I was wondering if anyone had tried to isolate bromine using this method.
2 KBr+ 2 HNO3= 2 KNO3+ Br2

Mumbles - 30-3-2003 at 18:20

trinitrotoluene, I think that procedure would yield 2HBr. You seem to have forgotten about the Hydrogens from the nitric acid.

Theres a proceedure for creating elemental Br in my chemistry book. I'll type it up as soon as I can find the book and proceedure.

Polverone - 31-3-2003 at 11:14

HBr isn't that hard to oxidize. That is why you can't prepare HBr just by mixing H2SO4 and NaBr/KBr: the H2SO4 will oxidize at least a portion of the HBr to elemental bromine. The nitric acid method is worth trying, at least.

madscientist - 15-4-2003 at 12:16

Oops, I just realized that I forgot to post about the results of my second plan (the one involving nitrate) for preparing elemental bromine. The reaction was violent, evolving considerable amounts of bromine gas, but wasn't quite as exothermic as the first attempt involving permanganate.

the nitrate method

Cat Wrangler - 12-5-2003 at 20:24

I tried NaBr + KNO3 + H2SO4. When mixed together at room temperature, there was little activity from these three materials. Adding a little water soon had Br2 pouring from the flask, but adding a large quantity of water stopped it. Oddly, when quenched with a large quantity of water the solution was a light red, not the deep red-brown that I would have expected of Br2 in water.

Is there some way H2O might participate in the oxidation reaction, or is likely just the heating provided by H2O + H2SO4 that caused the Br2 evolution to start?

sirius_cm - 17-5-2003 at 14:48

How bout the good ole activity series? I mean take some NaBr and add some Cl2, then all you have is Salt on the Bromine. Filter it, and bingo, its all good

liquid bromine

alchemie - 4-6-2003 at 15:41

An interesting trick I read about in an old(1850´s) chemistry book is to distill the bromine from the flask where it is being generated, into another flask containing concentrated H2SO4.
The purpose of the H2SO4 is to dry the bromine while, at the same time, keep it from evaporating, as it forms a layer beneath the lighter acid.
If the Br2 is introduced through a tube(glass, preferably) into the H2SO4 and the flask is chilled with an ice-bath, the Br2 losses should be greatly diminished.

vulture - 5-6-2003 at 13:54

Dry KBr and conc sulfuric acid produces Br2 quite violently and in copious amounts. The sulfuric acid is reduced to SO2. Same goes for KI.

Scorpion - 5-6-2003 at 14:12

But what if the KBr is in a solution with water and not so concentrated. I would also think that in this way some HBr could be formed as an impurity along with elemental Bromine...!!

vulture - 6-6-2003 at 09:36

If the KBr is dissolved, nothing will happen because it's too diluted to keep the redox reaction going and secondly, HBr is a too strong acid to be formed form sulfuric acid in solution.

I also doubt HBr will be formed during the dry reaction.

madscientist - 6-6-2003 at 12:42

NaBr will react with H2SO4 to liberate substantial quantities of elemental bromine, but also significant amounts of HBr (HBr is the initial product; the reason for Br2 being formed is HBr being oxidized by H2SO4.) MnO2 is typically used to help reduce the amount of HBr liberated.

[Edited on 6-6-2003 by madscientist]