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plante1999
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The most funny mistake I ever saw
A user of sciencemadness had a runaway during a reaction and asked my questions. It was about making bromine from sodium bromide using potassium
permanganate and sulphuric acid.
He told me about a runnaway, condenser not working properly, suckback and bromine fumes everywhere.
At first from what he say, I had tough he add used conc sulphuric acid and potassium permanganate and bromide mix. Obviously sulphuric acid would
react with the bromide to make bromine and SO2. Also manganese heptoxide would have bean made, and used as the oxidizer in the reaction. This was
worthy of AnderHoverland pathway to simple chemical.
But then he told me he used bromide solution and added the sulphuric acid to it, I asked for a picture or a drawing, and he gave me this:
Obviously there is a problem with the setup. It was the first time I saw a sep. funnel at this place in a ground glass set-up.
So what do you think of this?
I never asked for this.
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elementcollector1
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That's... certainly interesting. I use a small, cone-shaped sep. funnel, so i can't imagine using mine for the same purpose (it has no sidearm)...
Oh, and see that thermometer? I'm guessing that was attached with rubber. Bad idea.
Is that an erlenmeyer at the receiving end? Why on earth is he using an erlenmeyer and not a RB flask?
Still, if this worked it would certainly be an extraordinarily good setup. Few joints, simple... Not me. I'm going to bubble chlorine through my hot
sodium bromide solution (requiring a ton of stoppers and adapters and such).
Congrats to your friend for the novel attempted use of the sep. funnel, but he might want to work a little on optimizing it. ;P
Elements Collected:52/87
Latest Acquired: Cl
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kristofvagyok
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After the first explosion -if survived- the chemist is usually more careful.
I have a blog where I post my pictures from my work: http://labphoto.tumblr.com/
-Pictures from chemistry, check it out(:
"You can’t become a chemist and expect to live forever." |
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elementcollector1
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I must not be 'usual', then. XD
Elements Collected:52/87
Latest Acquired: Cl
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Magpie
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That's not a separatory funnel but a pressure-equalizing funnel. I don't see why that wouldn't work if the H2SO4 was added slowly. Biggest problem
is that it does not have a vent. You should always have one.
That's not to say that I would recommend that set-up, however.
[Edited on 9-12-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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smaerd
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Yikes! Hopefully they were working on a 10mmol scale! More importantly I hope they review some literature and didn't have a hard time cleaning up.
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UnintentionalChaos
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The NaBr/KMnO4 mix with sulfuric acid added is my preferred method of making bromine. It generally goes very smoothly unless you were to somehow dump
all the H2SO4 in at once due to the severe exotherm, but that apparatus is baffling.
[Edited on 12-9-12 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Pyro
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Hello.
I will own up  it was me. I was trying out UC's prep. My claisen has NS14 joints
at the top. and my addition funnel is NS29. i dont have an adapter for that yet, so i put it between the two.
It is a thermometer with teflon ring, so it isn't so bad.
and it is an erlenmeyer, I have ground glass erlenmeyers as wel as RBF's (All nice schott ones)
what happened was that my cooling pump failed and i didn't nitice till my scrubber started bubbling frantically. at that moment i stopped H2SO4
addition, but forgot about suckback.
You can only use a funnel like that if its pressure equalized, I had a big arument with plante as he said that the pressure of the Br2 being formed
forced more H2SO4 into the flask. this isn't so according to Pascal's law (though that's physics, not chem) the only problem was my cooling pump.
Kristof, I did learn  tomorrow i will fix my water pump, swap reciever and get
all the Br2 as to not waste the NaBr
@UC i dripped it in slowly, all went well until the condenser warmed up!
It was not a small scale! the flask was 1l, funnel 500ml, condenser 400mm,...
[Edited on 9-12-2012 by Pyro]
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smaerd
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Always start with small scale first pyro, especially when abusing glass-ware like a red-headed step-child on a new reaction. I'm not a pro, but that's
something I have learned along the way.
Two neck flask seems to make a lot more sense?
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Pyro
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red headed step child? i dont get that one!
I don't have a smaller add. funnel! and I don't have a reasonable sized 2-neck flask.
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cyanureeves
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pyro not even if the red headed child stood out like a sore thumb among brunette parents? by the way do fumes travel up that side arm and pass the
sulfuric acid and condense into the erlenmeyer? is heat involved in this set up? so is this a proper set up or not?
[Edited on 12-9-2012 by cyanureeves]
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elementcollector1
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Quote: Originally posted by cyanureeves  | pyro not even if the red headed child stood out like a sore thumb among brunette parents? by the way do fumes travel up that side arm and pass the
sulfuric acid and condense into the erlenmeyer? is heat involved in this set up? so is this a proper set up or not?
[Edited on 12-9-2012 by cyanureeves] |
This is not a proper setup, but a rather unorthodox one. And yes, that is what should happen to the bromine fumes.
Elements Collected:52/87
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Endimion17
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Pyro, if you don't want to put the pressure equalizing funnel above the Claisen adapter, just buy the damn two necked flask... A considerable amount
of bromine will end wasted inside sulphuric acid in this setup. I don't understand the neccessity of this design, nor its usefulness. I think there is
none.
For the sake of this expensive and dangerous liquid, don't do experiments with large scale amount of reactants. Experiments are for solving
problems, demonstration experiments are for teaching.
When you want to produce raw material, it's not an experiment anymore. It's production, and production is something you do when you know how
small scale and large scale experiments work.
If you don't do these things properly, you'll end up dead. I'm not joking. You'll end up with a pulmonary oedema in that non-ventilated basement of
yours.
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neptunium
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i dont know why everybody likes the H2SO4 method of producing Br2....i drop conc. NaClO (pool bleach 10% $7 a gal at walmart) in a heated HCl and
saturated NaBr sol.
Bromine just flows nicely towards the cold trap where it remains solid (mostly) untill i need it!
all the chemicals are cheap and plentifull no need to waste precious sulfuric...
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Siggebo
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| Quote: Originally posted by neptunium | i dont know why everybody likes the H2SO4 method of producing Br2....i drop conc. NaClO (pool bleach 10% $7 a gal at walmart) in a heated HCl and
saturated NaBr sol.
Bromine just flows nicely towards the cold trap where it remains solid (mostly) untill i need it!
all the chemicals are cheap and plentifull no need to waste precious sulfuric... |
Usually, as far as I've understood it, because of the risk of interhalogen formation!
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unionised
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| Quote: Originally posted by Magpie | Biggest problem is that it does not have a vent. You should always have one.
[Edited on 9-12-2012 by Magpie] |
Yes it has.
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neptunium
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Siggebo the chlorine is form and used instantly in my set up(or within milliseconds), it ends up in NaCl right anway and cant distill out of the
reaction mix...
Granted there will be some Cl in my bromine but trace amount
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AndersHoveland
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Even without KMnO4, when many ignorant chemists attempt to make anhydrous HBr they discover that their sulfuric acid has oxidized much of their
bromide to elemental bromine. This usually only happens when the sulfuric acid is concentrated, or heated.
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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neptunium
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everybody has its favorite, i just hate to use conc. sulfuric acid when i have gallons of NaClO and HCl ... note that i dont even bubble the Cl2 its
all happening in the mix! ...ignorance? maybe ..this just works fine for me
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Pyro
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Endimion, I already mentioned why I didn't put it on my claisen, the top openings are 14/20 and my add. funnel is 29/42.
I don't see how any Br2 would be lost in the H2SO4 as its all going into the solution eventually. my problem was suckback.
Cyanureeves, almost all the Br2 formed goes up the arm and into the condenser, and only a tiny bit condensed into the funnel and of course the Br2
sank under the H2SO4 and went right back to the flask
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Pyro
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I think i'm on to something! there is green stuff on my hotplate where the flask was touching it.
It was a 1l Laboy flask, maybe it cracked, the mix in it was too dark to see anything though.
I will let you know what i discover
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Fleaker
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Just an aside, I really wish people who want bromine would give the H2SO4 + NaBrO3 + NaBrO3 route--it's very effective and almost quantitative. It is
still necessary to de-water the bromine (after it cools!!!!) with conc. sulfuric acid in a sep funnel. If chloride contamination is tolerable, HCl and
even chlorate can be used as the oxidizers.
I'm making some bromate this weekend (more useful to me than bromine).
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Pyro
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NaBrO3 is expensive! over here its over 15 times the cost!
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smaerd
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When I choose to generate bromine which I surely will, I am going to use woelen's electrochemical method. Electrons are cheap and theres no
decontamination of glass-ware. He also has an electro-synthesis of potassium bromate on his website.
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Nicodem
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Pyro, if you don't have the correct glassware to put the addition funnel out of the distillation pathway, then do the reaction in an ice bath first,
by slow addition of sulfuric acid to keep the temperature under control. Only then change the addition funnel for the claisen adapter and do the
distillation with a normal setup.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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