Synthesis of potassium bromate from potassium bromide

[woelen]

I have made some KBrO3 from KBr and this synth was quite succesful. I used this for my oscillating reaction experiment, and also for some other energetic materials experiments. The synth is described here:

 

http://woelen.scheikunde.net/science/chem/exps/KBrO3_synth/index.html

 

Have fun, but be careful. KBrO3 is a possible human carcinogen. It also can react very energetically with some reductors.

[Gilded]

Nice! I might try this at some point, as rather coincidentally I ordered 100g of KBr a while ago for no particular reason.

[encipher]

How well would this work with iodates? Obviously using KI instead of KBrO3 ?

[YT2095]

I`ve done it with Sodium Iodide/ate and it worked quite well, although with carbon electrodes the crystals never turn out the color they`re suposed to be, they turn a sort of Chocolate color, it`s the nature of the crystal formation, it traps in a lot of impurities esp coloidal carbon.

 

never tried with KI though, it`s too expensive IMO, so I used NaOH and I2 crystals instead, and then electrolysed it.

 

it`s solubility is quite low also, so in that respect it`s a pleasure to work with.

[encipher]

hmm.. that's an Idea. I just recently bought half a kilogram of KI (not cheap) and im pretty much out of iodate. So I would probably use half of it to make KIO3, since I can't get a hold of it due to all the restrictions nowadays on oxidizers.

 

Think NaOH and I2 is a more viable route in the synthesis of Iodate?

[YT2095]

it works great, infact well over half the material will be iodate before it even sees an electrode

[encipher]

If you are referring to NaOH and I2..

 

Wouldn't that also produce Sodium Iodide ? Not pure Iodate? That means the percent yeild would be pretty bad?

[YT2095]

it does produce a little iodide too, as I said however over half will be iodate, and from there you can electrolyse, you already have a head start though

 

it was never mentioned that adding the 2 was the Entire synth.

[encipher]

Ah, I apologize, misread what you wrote. Right, I'll give it a shot then.

[woelen]

it does produce a little iodide too, as I said however over half will be iodate, and from there you can electrolyse, you already have a head start though

 

it was never mentioned that adding the 2 was the Entire synth.

YT, I wish it were true what you are saying here, but unfortunately things are not that good. Only 1/6 becomes iodate, the rest becomes iodide:

 

3 I2 + 6 NaOH ---> 5 NaI + NaIO3 + 3 H2O

 

To my opinion it is cheaper to use KI as a starting point, I2 also is an expensive reagent. Using KIO3 also results in formation of less soluble KIO3, which separates from solution, if a concentrated solution of KI is used as a starting point.

I plan to do such an electrolysis with KI next weekend. I'll dissolve 20 grams of KI in as little as possible of water (I expect this will be 30 ml or so) and then proceed as with my KBr synth. I'll let you know how things are going if I've done the experiment.

 

In the past I already made some KIO3, but that material is beige/brown, and I want a nice white chemical, so I'll retry again, now with more experience from my KBrO3 synthesis.

[YT2095]

Hmm... I`m probably mistaken then. I seem to remember a while ago, making some NaI as a plant food suplement for my asparagus, and learning that it made NaIO3 also (toxic to plants) and being rather disappointed.

I was under the impression that the quantity was greater than just 1/6`th.

 

not to worry though, it`s still saved an hour or so in the iodate cell as head start.

 

Woelen, are you going to try using your Pt electrodes this time? IIRC the last time you made some with carbon, you got the same beige brown result that I did, your Pt should make a much cleaner product

if you can, try grow some large(ish) crystals of it and take a close-up picture, if they`re like mine, ther have a Very strange structure indeed, and seem almost silver/waxy (if you can ignore the brown contamination).

[woelen]

I indeed intend to use my Pt-electrodes for making KIO3. My previous sample is brown/yellow and has a fairly strong smell of iodine. I hope to get a better result this time. I'm not sure whether this is due to the use of carbon rods, but using platinum electrodes always is very neat, the result is really clean.

[woelen]

I have done the synthesis of KIO3 from KI.

 

I dissolved approximately 10 grams of KI in a little over 10 ml of water, giving a total of appr. 20 ml of liquid. First I did the electrolysis with 2 A current, using a platinum anode and a titanium cathode. After 5 hours, the yield was only 1 gram. Pathetic! The liquid become really hot, almost boiling.

 

The next day, I added approximately 50 mg of K2Cr2O7, dissolved in 1 ml of water, and continued the experiment. With this K2Cr2O7 added, the result was amazing. After 2 hours, I already had a nice thick crop of KIO3. The liquid again becomes VERY hot. I have had this running for 4 hours total, and that has given me a nice amount of KIO3 (appr. 7 grams). I rinsed 5 times with 15 ml of cold distilled water, the 5th time, the rinsing liquid is not yellow anymore. The powder is very light beige, almost white, but not 100% purely white.

 

I did a test with 1 M H2SO4. A small spatula full, added to 1 M H2SO4 does not result in a brown color, the solution becomes colorless. This means that the iodate is free of iodide, and that even without recrystallization. Just a 5 times rinse! I am very content with this synth and I'll do further experiments with this KIO3, most notably the Briggs-Rausch reaction, mentioned by Encipher.

[YT2095]

Nice work!

 

Do take some pics of these crystals though, I`de love to compare them to My samples.

[woelen]

I don't have crystals, but a very fine powder. A picture of that is not interesting, it just is a fluffy off-white powder.

 

Today I did some further tests with it, and despite the off-white color (most likely due to tiny traces of I2 in it), it is remarkably pure. I cannot find any traces of iodide in it (tested with Pb(2+), no yellow precipitate of PbI2), it also seems to be free of periodate, because I do not obtain a precipitate with copper (II) sulfate. Copper (II) gives a green/yellow precipitate with periodate, but I could not obtain such a precipitate with my sample.

[lavenatti]

I tried the potassium bromide to bromate experiment described on woelens website. (great site by the way!) The experiment worked wonderfully and I loved watching the red bromine run down off the anode and accumulate in the bottom of the vessel.

 

Would this also work with ammonium bromide? I know ammonium bromate is pretty soluble so seperating the reaction products may be difficult but are there any problems or dangers (beyond those of using KBr) I should be aware of before I try?

[YT2095]

there`s not much on the net about it, I tried the MSDS also.

 

I did find this though: http://www.myregs.com/dotrspa/goto.asp?ref=CFR49_HM215G_A

scroll down to it.

 

I know the Chlorate is Very dangerous and should be avoided at all costs (it`s a Nasty material), and it seems the Bromate is in the same catagory.

 

I personally wouldn`t even Try to make it.

 

http://www.chem.ubc.ca/safety/PEC_sorted.pdf

[lavenatti]

Thanks,

I did search the net and found little besides shipping restrictions. I did find several suppliers who sell it (chinese) although none had an MSDS available.

 

I am, of course, more curious about it now and will continue to look for info. I'm not going to make it without researching a bit more. Don't need to blow my ass up.

[YT2095]

I`m not sure, but a safer way to make a small sample rather than use electrolysis, is to make some Barium Bromate, and then dissolve that as soln A and then dissolve Ammonium Sulphate to make Soln B.

mix the 2 (A and B) and BaSO4 should ppt out leaving ammonium bromate soln.

 

you can pipette a little of this soln out of the test tube and test it that way.

[lavenatti]

http://books.google.com/books?id=uTmc-BeVbZoC&pg=PA116&lpg=PA116&dq=%22ammonium+bromate%22&source=web&ots=OrOFQN2fVo&sig=_OQeo5I5TMQ4LtGkQ0fErgpjQQg#PPA1,M1

 

Describes Ammonium Bromate as "spontaneously decomposing".

 

I like your method, I don't need to be indoors or using electricity to try it. I do believe I'm going to let this one go as a bad idea however. It just seems a little to unpredictable.

[YT2095]

it`s like Am Chlorate then, reasonably stable in soln, but unpredictably dangerous if anywhere towards being a solid.

 

I think you`ve made the right choice

[sivas54]

The electrolysis could ne carried out in a undivided cell having TSIAnode (Titanium substrate Insolube ANode- CECRI(CSIR)-INDIA)/ or DSA and Titanium or MS cathode. There would not be any appearance of brown colour if the electrolyte around the cathode is buffered (pH: 6.6) properly using K2Cr2O7 (2 gpl). If K2Cr2O7 is present in the electrolyte, there is a great loss of current efficiency. Morover, if we allow formation of brown colured bromine at anode, the anode will get damaged due to the reaction of nascent bromine with the precious metal oxide (Ru, Ir ) catalysts coated on the anodes. The diiference in solubility of KBrO3 at room temeperature and at the cell temperature (60'C) could be used crystallise out the KBrO3. The KBrO3 will be white crystalline salt.

---

Merged post follows:

Consecutive posts merged

Correction: 'If K2Cr2O7 is present in the electrolyte, there is a great loss of current efficiency' should be read as "If K2Cr2O7 is not present in the electrolyte, there is a great loss of current efficiency". bear with me please.- sivas54