Sciencemadness Discussion Board

The most funny mistake I ever saw

plante1999 - 8-12-2012 at 16:29

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?

elementcollector1 - 8-12-2012 at 16:41

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

kristofvagyok - 8-12-2012 at 16:44

After the first explosion -if survived- the chemist is usually more careful.

elementcollector1 - 8-12-2012 at 16:48

Quote: Originally posted by kristofvagyok  
After the first explosion -if survived- the chemist is usually more careful.

I must not be 'usual', then. XD

Magpie - 8-12-2012 at 16:50

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]

smaerd - 8-12-2012 at 16:51

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.

UnintentionalChaos - 8-12-2012 at 16:52

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]

Pyro - 8-12-2012 at 16:53

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 :D 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]

smaerd - 8-12-2012 at 17:03

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?

Pyro - 8-12-2012 at 17:06

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.

cyanureeves - 8-12-2012 at 17:53

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]

elementcollector1 - 8-12-2012 at 18:24

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.

Endimion17 - 8-12-2012 at 18:59

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.

neptunium - 8-12-2012 at 19:22

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...

Siggebo - 9-12-2012 at 01:32

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!

unionised - 9-12-2012 at 02:18

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.

neptunium - 9-12-2012 at 04:12

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

AndersHoveland - 9-12-2012 at 05:12

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.

neptunium - 9-12-2012 at 05:44

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

Pyro - 9-12-2012 at 06:12

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

Pyro - 9-12-2012 at 10:19

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

Fleaker - 14-12-2012 at 05:15

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).

Pyro - 14-12-2012 at 06:22

NaBrO3 is expensive! over here its over 15 times the cost!

smaerd - 14-12-2012 at 07:42

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.

Nicodem - 14-12-2012 at 08:08

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.

Pyro - 14-12-2012 at 14:35

hey,
you can't blame me for trying something new! It would have worked if I had thought of a suckback trap!
I have ordered the adapter, but shipping takes a long time.
(PS:I only have a claisen, I find it a lot more economical than a normal three way and a claisen as well)

cyanureeves - 15-12-2012 at 10:04

pyro i used an ahlin condensor instead of a liebig because i thought the bubbles in the glass would diissipate heat better than a straight tube.after i bought the ahlin i noticed that everybody just used it right on the boiling vessel and so i bought a liebig.i dont get it,it seems the bubbles would be better than just a straight tube. maybe liebig himself first used his glass as a fancy cold finger or smoke cooler for his bong.my ahlin is pretty though.

Pyro - 15-12-2012 at 13:40

lol,
the disadvantage of an allihn is that the bubbles can pool liquid unless you position it at a perfect angle. though its perfect for refluxing and such