| Pages:
1
2
3
4
5
..
13 |
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
The reason my experiment failed was that I didn't know the exact molatity of hypochlorite in the bleach and therefore couldn't get the
quantity of other reagents just right. It is true chemically that the redox reactions are similar, but in practice the bubbling method works much
better.
[Edited on 10-12-2004 by neutrino]
|
|
|
psychokitty
Harmless
Posts: 10
Registered: 5-12-2004
Member Is Offline
Mood: No Mood
|
|
And?
You likely didn't know the exact molality of hypochlorite formed by the addition of Cl2 to water but that didn't seem interfere with the
progress of your oxidation of NaBr to Br2.
There must be some other explanation as to why your first few hypochlorite experiments failed.
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
What Cl<sub>2</sub>? The whole point of the one-pot reaction was to avoid having to use chlorine gas. What exactly are you getting at?
|
|
|
BromicAcid
International Hazard
Posts: 3245
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
Too much hypochlorite and the experiment may fail, too little and it will fail, just right and added too fast or too slow and it will fail. One main
side reaction eats up yields:
Br2 + 2OCl- ---> 2OBr- + Cl2
Solution has to be acidified afterward to recover the bulk of the bromine, the activity series is reversed for oxo halogen compounds. With stright
chlorine this is adverted however inner halogen compounds are more likely to form, though they usually have short half lifes in aqueous mediums.
|
|
|
psychokitty
Harmless
Posts: 10
Registered: 5-12-2004
Member Is Offline
Mood: No Mood
|
|
The Cl2 you bubbled in . . .
Cl2 bubbled into an aqueous solution of NaBr = Br2 and NaCl in water, assuming, of course, exact stoichiometric amounts; however, too much Cl2 in
solution will form hypochlorous acid. Thus, you're back where you started as far as the problems you had using sodium hypochlorite as an
oxidizer in this reaction.
The only difference between sodium hypochlorite and Cl2 in water is that one is basic and one is not. Got it?
Damn . . .
|
|
|
BromicAcid
International Hazard
Posts: 3245
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
Yeah, hypochlorous acid is formed if an excess of chlorine is added, however as long as the solution is not basic (which it wouldn't be) then
less then 2 g of chlorine will be solvated in the equilibrium:
Cl2 + H2O <---> HCl + HOCl
At any time, therefore the hypochlorite problem is largely eliminated.
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
Ah, you’re referring to my recent experiment. The hypochlorite reaction isn’t really that much of a problem. For the most part, the hypochlorous
acid would form near the surface, as the chlorine is bubbled about halfway down into the solution, while the bromine collects in a pool at the bottom.
Aside from that, I discontinued the chlorine when the color of the atmosphere began to change, indicating completion of the reaction.
This process is interesting: while bubbling in the chlorine at a medium-fast pace with a crappy bubbler (end of a Pasteur pipette), large bubbles kept
breaking the surface of the shallow solution, yet little bromine vapor seemed to escape, except when my chlorine source generated too much chlorine in
one big blow.
|
|
|
enima
Hazard to Self
Posts: 98
Registered: 1-12-2004
Member Is Offline
Mood: No Mood
|
|
Oxone and a bromine salt will yield elemental bromine, I'm not sure your purpose for its usage, if you are using it for aromatic halogenation
I'd recommend using ammonium bromide in an acetic acid solvent, dripping 30% peroxide onto the solution (containing your aromatic of course)
stir for 5-6 hours and you should have a nice brominated product..
If it is another use, you can try forming the HBr with sulfuric acid (So2 is produced too) and then you can drip peroxide onto that, (keep it cool at
0C when doing the h2o2 dripping) this should yield bromine.
You can purify it via distillation, although IMO its best to keep away from elemental bromine whenever possible.
|
|
|
Nick F
Hazard to Others
Posts: 439
Registered: 7-9-2002
Member Is Offline
Mood: No Mood
|
|
Ah, I can't wait to get my NaBr! Lots of things I want to try...
Apparently BrNO2 can be made with Br2 and NaNO2 (damn, or was it NO2 and NaBr? Some red gas and some white powder, I forget which way round it was!
:p), that could be quite fun stuff  .
I also want to use it for making NaOBr solutions to try to make hydrazine with, just because it's easier for me to make lots of bromine than it
is to make lots of chlorine. Concentration of the hypohalite solution seems to play a big role in determining how much hydrazine you get out. I think
it should be easy to make a solution equivalent to >15% NaOCl solution. And sodium bromide leftovers could be easily recovered.... One concern is
adding the sulphuric to ppte the hydrazine - does dil. sulphuric still oxidise HBr? That could destroy your hydrazine real quick....
|
|
|
aludel
Harmless
Posts: 6
Registered: 16-11-2004
Location: holland
Member Is Offline
Mood: No Mood
|
|
First post here after some reading - great forum! My chemistry passion is awakened after 25 years of slumbering... unfortunately I can't set up a
proper lab in my apartment at the moment but I still have some chemicals.
One of my favourites is bromine and I tried to make it a few times using KBr, MnO2 and concentrated H2SO4, distilling it. Bromine was developed
immediately and pretty violently when I poured the H2SO4 in. Being an ignorant fool, I used a lot of rubber tubing the first time, which happily
reacted with the bromine and was destroyed (and consumed most of the Br2). But I got my first glimpse (and smell!) of this beautiful element.
It's difficult to cool it enough, it's very volatile. Another reason for my poor yields.
But I ended up with a few ml of bromine. Hard to store, it evaporates right through plastic screw caps.
I'll never forget the smell, it's getting into your clothes, hair, the whole house! My poor mom 
|
|
|
HNO3
Hazard to Others
Posts: 211
Registered: 10-11-2004
Location: America
Member Is Offline
Mood: No Mood
|
|
I made ~2mL bromine. I started with some bleach (left over from a chloroform reaction). I then added some NaBr. This formed a dark yellow solution. I then added 3mL 31% HCl. there was a barely noticable
reaction, but no bromine was produced. More HCl. More HCl. Still no reaction. So I added some Ca(OCl)2, then some more HCl. No reaction. So, I added
some leftover KMnO4 solution. No reaction. More HCl. No reaction. Aha! I get my sulfuric acid out and add 3mL. That did it. Bromine starts being
formed, and some starts boiling off. I hold my breath and bolt for the door (I'm not too fond of the halogens ). I take a couple breaths and go get my gas mask and put it on. I go back in. I soon discovered that its filters
needed replaced, as it was leaking bromine fumes. Oh well, it wasn't that bad. I dumped the top layer off and poured the bromine and a little bit
of solution above it into a graduated cylinder. I then pipetted the bromine into a home-made glass ampoule. Then I made a neck on the ampoule and
sealed it shut. There is one picture at http://www.geocities.com/stwrt_kck/mypage.html
Another one
\"In the beginning, God...\" Wait a minute, God doesn\'t exist!!!!!!!!!! \"OK, in the beginning, ummm, hydrogen...\" Wait a minute, what about the
laws of thermodynamics? \"OK, in the beginning, ummm.....UMMMMM, what\'s left to choose from?
|
|
|
Theoretic
National Hazard
Posts: 776
Registered: 17-6-2003
Location: London, the Land of Sun, Summer and Snow
Member Is Offline
Mood: eating the souls of dust mites
|
|
"Apparently BrNO2 can be made with Br2 and NaNO2 (damn, or was it NO2 and NaBr? Some red gas and some white powder, I forget which way round it
was! :p), that could be quite fun stuff ."
Both would work I think. No, really, both of these reactions would work:
Br2 + NaNO2 => NaBr + BrNO2
NaBr + 2NO2 => NaNO2 + BrNO2.
So NaBr (or NaNO2) can serve as a catalyst for combining bramine and NO2 into nitryl bromide. 
|
|
|
Protium
Harmless
Posts: 27
Registered: 25-12-2004
Location: Point Of Return (Subject To 15% Restocking Fee)
Member Is Offline
Mood: unenlightened
|
|
Bromine Source and Synthesis
I have tried making bromine a few times.
I've tried passing Cl2 through NaBr in H2O solution, then distilling...
didn't work well...
I tried dripping conc. H2SO4 directly onto dry NaBr salt in large RB flask. What ended up happening was that the NaBr formed a solid chunk that
was encapsulated within a shell of NaSO4 so that no further reaction occurred. Some (few ml's) actually distilled over being caught in an
acetone/dry ice cooled falsk. Magnetic stirring did little to break up this chunk of NaBr trapped in NaSO4.
My most recent idea was this...
In a large test tube, one would add a portion of xylene, then adding conc. H2SO4 to the tube while it is tilted so that the H2SO4 would flow
nicely to the bottom of the tube. Then addition of NaBr in small amounts would cause bromine formation.
I tried this because I thought that the bromine would be soluble in the xylene and I could just remove the xylene layer and distill the bromine
directly because of the large difference in bp's of bromine and xylene.
In a trial run, a small amount of NaBr was added to a large test tube as described above, though reactants were previously cooled to about 5
degrees C. Immediately small amounts of gases started to form. A tinge of orange color formed as well. A pH test paper placed across the top of the
tube indicated that some HBr escaped the system without being oxidized by the H2SO4. I added a few more spatula tip-fulls of NaBr and let tube sit for
a while as small amounts of gasses continued to escape into the environment....no fume hood .... It turned out that the bromine had all dissolved in the H2SO4 rather than the xylene that I had thought it would dissolve in.
I have never been able to get a layer of bromine to form on the bottom of any experiment to where I would merely be able to pipette it out.
Should I dilute my H2SO4 with H2O?
I would like to collect around 50mL or so of Br2.
What method would be best for collecting larger amounts?
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
Bromine is insoluble in sulfuric acid, that’s why it’s usually dried in sulfuric acid. How long did you let it sit before giving up on it?
I don’t know why your bubbling experiment failed, mine worked very well. My chlorine was being bubbled about 1cm below the surface of the liquid
(~100mL of NaBr solution in a 500mL round bottom flask) through the end of a Pasteur pipette. The pipette was stuck through a thermometer adapter
(without the rubber part) and loosely plugged with plastic wrap. Even with my archaic bubbler, I still got a good yield.
|
|
|
HNO3
Hazard to Others
Posts: 211
Registered: 10-11-2004
Location: America
Member Is Offline
Mood: No Mood
|
|
I tried passing Cl2 over NaBr before. I was using trashy equipment (plastic bottles, anyone?). The bromine formed colored the plastic orange/brown,
but I didn't get any bromine.
The problem with your NaBr/H2SO4/xylene experiment is that the halogens do a substitution reaction with organics. Br2 + C6H4(CH3)2 -->
C6H3Br(CH3)2 + HBr.
\"In the beginning, God...\" Wait a minute, God doesn\'t exist!!!!!!!!!! \"OK, in the beginning, ummm, hydrogen...\" Wait a minute, what about the
laws of thermodynamics? \"OK, in the beginning, ummm.....UMMMMM, what\'s left to choose from?
|
|
|
psychokitty
Harmless
Posts: 10
Registered: 5-12-2004
Member Is Offline
Mood: No Mood
|
|
p-methylbenzylbromide
The bromine will add to one of the methyl side chains of the xylene. I believe I read somewhere that the product of this reaction,
p-methylbenzylbromide, is a powerful lacrymator. Use another solvent, one that is inert to bromination.
|
|
|
HNO3
Hazard to Others
Posts: 211
Registered: 10-11-2004
Location: America
Member Is Offline
Mood: No Mood
|
|
I wondered if it wouldn't react with a methyl group, but I wasn't sure, so I went with what I knew.
|
|
|
kryss
Hazard to Self
Posts: 77
Registered: 11-7-2003
Location: N Ireland
Member Is Offline
Mood: No Mood
|
|
The easiest way of making Br2/Cl2/I2 from the halides is by mixing a solution with MnO2, then adding dil H2SO4 and gently warming or distilling. With
KI/NaI you'll get loads of I2 produced quickly and exothermically ( easy to lose control), KB2 is a little less violent and NaCl will give you
loads of Cl2 on warming.
|
|
|
phanchem
Harmless
Posts: 5
Registered: 11-1-2005
Location: Texas, USA
Member Is Offline
Mood: dyspeptic and g
|
|
About handling liquid bromine: I once had to get 10 ml of liquid bromine out of the lab refrigerator. So here I was, pouring out of a half-liter glass
bottle...and the mass of frozen bromine lurking on the bottom of the bottle sloshed about an ounce of the liquid all over my hand once I got past a
certain angle in my pouring. Fortunately, the sodium thiosulfate was nearby, and I could neutralize it in place, the only lasting evidence of the
spill being a brown crust of brominated skin on the back of my left hand that wore off in a week or so. Refrigerator temp was turned too low--profit
from my mistake and don't repeat it.
|
|
|
HRH_Prince_Charles
Hazard to Self
Posts: 92
Registered: 29-6-2004
Location: Clarence House, London
Member Is Offline
Mood: Bombastic
|
|
Would it be impudent of me to suggest wearing gloves?
|
|
|
BromicAcid
International Hazard
Posts: 3245
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
Writeup of today
Premise:
Upon mixing HBr(aq) with KBrO3 a top water layer and a bottom bromine layer was observed, the bromine appeared to be clean, no precipitate, and
appeared in large quantity indicating a good yield. When the reaction is done with NaBr and H2SO4 with KBrO3 dirty bromine (almost a suspension of
bromine with precipitate) appears in the bottom. My attempt today was to make a solution of HBr in situ with NaBr and H2SO4, cool to allow the
sulfate to precipitate, then add the bromate in the cold weather.
Equation:
10NaBr + 2KBrO3 +6H2SO4 ---> 6Br2 + 5Na2SO4 + K2SO4 + 6H2O
Procedure:
To 200 ml of room temperature distilled water in a 1 L Erlenmeyer was added 120 g (~1 mol) NaBr*xH2O, with slight agitation the sodium bromide was
dissolved in 7 minutes. 92 ml (a slight excess) of concentrated H2SO4 was measured out in a graduated cylinder and was added in several portions with
significant swirling to the sodium bromide solution. A slight red color from bromine evolution was observed and the reaction mixture heated to an
estimated 40 C once all the H2SO4 had been added. The mixture was allowed to cool for two hours outside at -10C. Upon inspection of the mixture it
was noted that it was now a slush, the expected precipitate of Na2SO4 had either been over shot or occluded by the mixture freezing entirely, it was
wrong to assume that the Na2SO4 would precipitate out nicely and the rest of the solution would remain liquid due to the freezing point depressive
abilities of the HBr contained therein.
The slush and chunks were broken up to a homogenous consistency and 33.5 g of KBrO3 was weighed out, roughly .2 mol and half of this was added to the
slush mixture. The addition produced a hissing sound and the mixture quickly started to turn red from bromine evolution. After the fist half had
been added a watch glass was placed on top, lifting the mixture drops of bromine were evident on the bottom, at these temperatures the bromine was
significantly less volatile and only small amounts wafted off the top.
The mixture was allowed to cool for twenty minutes further outside. The addition of the second half of the bromate was smoother then the first
addition, no sound or other indicative factors of a fast reaction. The color slightly deepened and bromine was more pronounced at the opening of the
container and little droplets of it clung to the sides at the water line. The top was covered yet again and the mixture was allowed to react to
completion over the course of another 20 minutes.
The bromine at the bottom was heavily contaminated with precipitate, separation may have been accomplished by straining through glass wool however due
to the temperature outside I was ready to call it quits so I had to find something to store it in. The entire mixture was poured into a glass reagent
bottle which was accompanied by significant fuming. After the bottom precipitate layer was poured in there was sediment left in the container,
shaking the flask the sediment sounded distinctly like stones in the flask, removing one and prodding it with a glass stirring rod they were found to
be very hard, their composition is unknown.
In the smaller reagent bottle the bromine at the bottom seems to be divided into layers, a top green/red layer, a bottom bromine/sediment layer, if
this separation persists through the winter actions will be taken to ascertain the identity of the layer constituents. Theoretically roughly 80 grams
of bromine (26 ml), although not measured directly the container appears to contain at least 20 ml of bromine, which would be quite good considering
the bromine lost to evaporation and solvated in the water above.
Conclusion:
HBr should be previously purified to give a somewhat pure bromine product in one shot. Filtration through glass frit/wool should be considered if
taking this on following this procedure to remove suspended particulate, distillation is always an option. Unlike a previous attempt, bromine
hydrate was not a problem. Overall this reaction quickly gave quantities of bromine in a high yield without the need for distillation, if a pipette
were to have glass wool inserted into the intake then the filtration may be accomplished by simply withdrawing the bromine from the container.
After sitting for 15 hours or so the bromine has separated into a distinct phase, the particulate has frozen into a layer above it and does not travel
with the bromine. It is now believed the solid rock like pieces left in the reaction flask are pieces of bromate that went into the mixture too
quickly and formed an inert crust. I plan on just suctioning off the bromine only a thin sheet of ice stands in my way, the mixture is for the most
part slushy. The above container has a volume of 450 ml.
[Edited on 1/17/2005 by BromicAcid]
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Where do you get so much KBrO3?
You seem to use lots of it...
Did you buy it or make it?
It is rather carcinogenic after all.
Maybe we should open a thread on the production of bromates.
Nice bromine synthesis by the way.
|
|
|
BromicAcid
International Hazard
Posts: 3245
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
KBrO3 is used in baking as a levening agent or something of that extent, I was in a bakery store and they sold KBrO3 by the pound for $2.75 so I
bought a few pounds, although my frequent use of it has reduced my stock so I must once again go to a bakery store. I wonder what they think I need
that much KBrO3 for? I don't think bakery stores get warned that one of their chemicals can function as an oxidizer and they should watch the
people that buy it.
Edit: Ahhh.. here it is; "Maturing agent in flour, dough conditioner, food additive."
[Edited on 1/16/2005 by BromicAcid]
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Wow, very interesting!
But I never saw KBrO3 on the list of the allowed food additives (the "E-numbers".
I'm quite sure it isn't allowed in Europe.
Anyway, what kind of bakery did you visit?
Some professional, large scale industrial bakery?
BTW, E252 is KNO3, so you could ask for this ,if you needed it ( only in Europe of course).
"I'd like to have some E252" sounds much less suspect than "I'd like to have some potassium nitrate".
[Edited on 16-1-2005 by garage chemist]
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
"Causes irritation to the gastrointestinal tract. Symptoms may include nausea, vomiting and diarrhea. May cause abdominal pain, reduced urinary
output, low blood pressure, methemoglobinemia, convulsions, liver and kidney damage, and coma. Cyanosis may occur as a later symptom. Death may occur
from renal failure, within 1 to 2 weeks. Estimated lethal dose is 4 grams."
Sounds like something really great to have in food products.  The MSDS must be
exagerating...
Source:
http://www.jtbaker.com/msds/englishhtml/p5576.htm
|
|
|
| Pages:
1
2
3
4
5
..
13 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
