Making KBrO3 using Ca(OCl)2 and bromide.

Quote: Originally posted by theAngryLittleBunny

KBrO3 is a very interesting and useful salt, being a stronger oxidizer then even chlorates and providing a very convenient way to make bromine without destillation. I found a quite easy way to make it using calcium hypochlorite and a bromide salt which might be interesting to anyone who doesn't wanna deal with the black woodoo called electrochemistry. I'll first explain the chemistry, so hypochlorite in solution reacts with bromide forming chloride and hypobromite (ClO- + Br- -> Cl- + BrO-). You can easily see this, because when you dissolve a bromide salt in a hypochlorite solution (like bleach for instance) it will quickly turn orange, which is hypobromite. Hypobromite is much less stabile then hypochlorite and quickly disproportionates into bromate and bromide at room temperature, which is what we want here. So I first dissolved calcium hypochlorite in a minimum amount of water and added over maybe 10 minutes a 1/3rd molar equivalent of sodium bromide based on hypochlorite to it. The hypochlorite oxidizes the bromide to hypobromite which then turns into bromate and more bromide which gets oxidized again until all the bromide is turned into bromate. Ca(ClO)2 + 2 NaBr -> CaCl2 + 2 NaOBr 3 NaOBr -> NaBrO3 + 2 NaBr Overall: 3 Ca(ClO)2 + 2 NaBr -> 3 CaCl2 + 2 NaBrO3 After all the bromide is added I heat it up in boiling hot water for maybe 30 minutes while slowly and carefully adding HCl until the solution is slightly acidic (around pH 3 to 4), since commercial calcium hypochlorite contains a lot of calcium hydroxide/ carbonate. Obviously this produces a bit of chlorine and should be done outside or with good ventilation. The solution has to be a bit acidic, otherwise the yield will be very poor. After that I filter it, (the calcium hypochlorite contains impurities that won't dissolve) add a molar equivalent of a potassium salt to the bromide and cool it in the fridge to crystallize out some nice white KBrO3. The yield was about 50% when the solution was made slightly acidic and about 15 to 20% when it was neutral/ slightly basic. The 50% yield was from my first try, so I'm sure it could be optimized. Probably 15% of the KBrO3 is lost in solution since it still has a solubility of about 30g/L at 0°C. The theoretical yield is about 54g of KBrO3 for every 100g of 70% Ca(ClO)2, which means in practice at least 27g for 100g. And since Ca(ClO)2 is rather cheap (8 to 10 euro per Kg) you could make 1Kg for KBrO3 for less then 40 euros. The KBrO3 from that seems to be quite pure too, I used it to make bromine by dissolving it together with 5 molar equivalent of NaBr and acidifying it with 6 molar equivalent H2SO4 and it worked perfectly (it's important not to use HCl, since the chloride will form a chlorodibromide (Br2Cl-) ion with bromine keeping it dissolved. 5Br- + BrO3- + 6H+ -> 3Br2 + 3H2O I hope this is helpful and if anyone is able to optimize this method to increase the yield I'd love to hear about it. Considering the KBrO3 that's just lost in solution it should still be possible to get up to 40g KBrO3 per 100g Ca(ClO)2.

Hi, I find very attractive bromates Ba(BrO3)2 and Sr(BrO3)2 when crystallized from an aqueous solution there are small lightning bolts, miniature electrical discharges. I'm going to try it...!

Quote: Originally posted by Admagistr

Hi, I find very attractive bromates Ba(BrO3)2 and Sr(BrO3)2 when crystallized from an aqueous solution there are small lightning bolts, miniature electrical discharges. I'm going to try it...!

Quote: Originally posted by theAngryLittleBunny

Quote: Originally posted by Admagistr   Hi, I find very attractive bromates Ba(BrO3)2 and Sr(BrO3)2 when crystallized from an aqueous solution there are small lightning bolts, miniature electrical discharges. I'm going to try it...! Cool, but how do you wanna make Sr(BrO3)2? It has a solubility of about 300g per liter at room temperature, which is much higher then KBrO3. One way would be to make AgBrO3 which has a rather low solubility in water (I think less then 1g/L) and then mix that with a solution of SrCl2 to get AgCl as a precipitate leaving Sr(BrO3)2 in solution. Anyway, let me know how it goes.

Quote: Originally posted by woelen

HBrO3 is surprisingly stable, as long as you don't get too high a concentration. I have done experiments with it, up to 10% or so, using barium bromate and sulfuric acid. Even boiling the solution does not destroy the acid. Barium bromate can be made quite easily. It is not very soluble in the cold and if you have NaBrO3, then you can make it from a soluble barium salt (e.g. BaCl2) and NaBrO3 and purify it by means of recrystallization. It can even be made from KBrO3 (which is less soluble than NaBrO3). If you want to make a solution with HBrO3, containing only little amounts of metal ions, then you must recrystallize your barium bromate from boiling hot water. Making pure HBrO3 solutions without barium ions or sulfate ions is quite laborious. I proceeded by first preparing an approximately 3M solution of H2SO4. As I did not knbow precisely the concentration of my concentrated H2SO4 (could be anything between 95% and 98%) I decided to roughly make 3M solution and then titrate against NaOH. I have 99+% pure NaOH and very quickly weighed this as it absorbs moisture from air quickly and made a solution of known concentration with this. I think that I could achieve appr. 1% accuracy with this. Weighing Ba(BrO3)2 is accurate, once you have a nice dry product. IIRC it exists as the monohydrate, when crystallized from water. I mixed solutions of acid and a hot solution of barium bromate. I decided to take 1% extra of the acid, preferring a little sulfate as impurity over a little barium as impurity. Getting it exactly matching is cumbersome and requires frequent probing. I did not take the effort to do that. The biggest practical problem I ran into was that on mixing solutions of barium bromate and sulfuric acid, you get a lot of very fine white precipitate, which is not easy to filter. Using paper is not advisable because the strongly acidic and oxidizing solution destroys the filter paper quickly. I decided to boil the solutioin for a while to make the precipitate somewhat more compact and easier to settle and then allowed the precipitate to settle. But settling took a long time and it did not really settle at the bottom. A tick white layer remained. I accepted the loss and pipetted the liquid above the white precipitate. After all this labor I finally had a solution of HBrO3, with a slight impurity of H2SO4. I used my solution for oxidation experiments, but you could use that for making Sr(BrO3)2, by adding Sr(OH)2 or SrCO3 to the acid. Any cloudiness can be allowed to settle (that will be SrSO4) and removed, the Sr(BrO3)2 will remain in solution, if it indeed is soluble at 300 grams per liter.

@WOELEN
Great, thank you for the valuable practical information! Have you tried crystalloluminescence of Ba(BrO3)2 and Sr(BrO3)2?!

Quote: Originally posted by woelen

I did not know at that time of the crystalloluminescence of these compounds. It sounds interesting and I still have Ba(BrO3)2, so I'll give it a try. Is it just a matter of crystallizing Ba(BrO3)2 from water and watching little flashes in the liquid on/around the crystals?

Yes, that's all that needs to be done! I did a similar experiment with a mixture of sodium sulphate and potassium sulphate, and the result was very nice! It's like a thunderstorm in nature, where you never know ahead of time when and where the next lightning will come. Also, if it ever strikes again, or if is over. The crystallization wasn't just flashes and tiny sparks, it was a sound effect too! You just have to have patience and time, sometimes it can take an hour before it starts

Quote: Originally posted by woelen

I did not know at that time of the crystalloluminescence of these compounds. It sounds interesting and I still have Ba(BrO3)2, so I'll give it a try. Is it just a matter of crystallizing Ba(BrO3)2 from water and watching little flashes in the liquid on/around the crystals?

Quote: Originally posted by woelen

As I did not knbow precisely the concentration of my concentrated H2SO4 (could be anything between 95% and 98%) I decided to roughly make 3M solution and then titrate against NaOH. I have 99+% pure NaOH and very quickly weighed this as it absorbs moisture from air quickly and made a solution of known concentration with this. I think that I could achieve appr. 1% accuracy with this.

Quote: Originally posted by Oxy

Quote: Originally posted by woelen   As I did not knbow precisely the concentration of my concentrated H2SO4 (could be anything between 95% and 98%) I decided to roughly make 3M solution and then titrate against NaOH. I have 99+% pure NaOH and very quickly weighed this as it absorbs moisture from air quickly and made a solution of known concentration with this. I think that I could achieve appr. 1% accuracy with this. Besides water there is often a lot of carbonate in NaOH due to reactions with water and carbon dioxide from air. Which means that making a standard solution just by weighting some sodium hydroxide and dissolving in water is actually bad idea. Carbonates have to be removed. Then the concentration of NaOH should be titrated by acidimetry. And only then it may be used for quantitative analysis. Otherwise, you can't be really sure about the concentration when it comes to analytical purposes.

Quote: Originally posted by Admagistr

Quote: Originally posted by theAngryLittleBunny   Quote: Originally posted by Admagistr   Hi, I find very attractive bromates Ba(BrO3)2 and Sr(BrO3)2 when crystallized from an aqueous solution there are small lightning bolts, miniature electrical discharges. I'm going to try it...! Cool, but how do you wanna make Sr(BrO3)2? It has a solubility of about 300g per liter at room temperature, which is much higher then KBrO3. One way would be to make AgBrO3 which has a rather low solubility in water (I think less then 1g/L) and then mix that with a solution of SrCl2 to get AgCl as a precipitate leaving Sr(BrO3)2 in solution. Anyway, let me know how it goes. Here's a link I'm sure you'll be interested in, maybe you already know it? https://illumina-chemie.de/viewtopic.php?f=18&t=4470 It doesn't address the production of Sr(BrO3)2, your idea is interesting but quite laborious and complex, perhaps inefficient to implement in practice...I thought to neutralize HBrO3 by SrCO3, it would probably be easier to implement, but I would have to find out how HBrO3 is stable and explosive/non-explosive...What do you think about it? I bought my Sr(BrO3)2 from Chemcraft in Russia. But I bought it in a small amount because it's not cheap...I'll think about it some more...

Quote: Originally posted by Boffis

@Angrylittlebunny; what an interesting idea! Well done. Did you find this reaction somewhere or invent it?

Quote: Originally posted by theAngryLittleBunny

Quote: Originally posted by Admagistr   Quote: Originally posted by theAngryLittleBunny   Quote: Originally posted by Admagistr   Hi, I find very attractive bromates Ba(BrO3)2 and Sr(BrO3)2 when crystallized from an aqueous solution there are small lightning bolts, miniature electrical discharges. I'm going to try it...! Cool, but how do you wanna make Sr(BrO3)2? It has a solubility of about 300g per liter at room temperature, which is much higher then KBrO3. One way would be to make AgBrO3 which has a rather low solubility in water (I think less then 1g/L) and then mix that with a solution of SrCl2 to get AgCl as a precipitate leaving Sr(BrO3)2 in solution. Anyway, let me know how it goes. Here's a link I'm sure you'll be interested in, maybe you already know it? https://illumina-chemie.de/viewtopic.php?f=18&t=4470 It doesn't address the production of Sr(BrO3)2, your idea is interesting but quite laborious and complex, perhaps inefficient to implement in practice...I thought to neutralize HBrO3 by SrCO3, it would probably be easier to implement, but I would have to find out how HBrO3 is stable and explosive/non-explosive...What do you think about it? I bought my Sr(BrO3)2 from Chemcraft in Russia. But I bought it in a small amount because it's not cheap...I'll think about it some more... HBrO3 is only stabile in a solution of I think below 20%, the silver bromate methode seems easy because you recover the silver as just silver chloride which can be easily turned into silver metal. 100g of silver costs I think 40 dollars and doing one run with this would in theory yield 159g of Sr(BrO3)2, and you will get most likely a close to theoretical yield. And thanks, I'll take a look.

Thank you, I'll try it!

Quote: Originally posted by Admagistr

Well that's true, NaOH and KOH mostly contain water and carbonates, I read that their content can be as much as 10% of water and carbonates! Unless my memory deceives me... If the such hydroxides were packaged in a vacuum, or in dry argon, they would be free of this problem...

Quote: Originally posted by woelen

Quote: Originally posted by Admagistr   Well that's true, NaOH and KOH mostly contain water and carbonates, I read that their content can be as much as 10% of water and carbonates! Unless my memory deceives me... If the such hydroxides were packaged in a vacuum, or in dry argon, they would be free of this problem... Well-packaged NaOH, which has not been exposed to air too much, actually can be fairly pure. In my titration, I certainly did not have significant quantities of Na2CO3 in my NaOH. My NaOH does not produce any bubbles, when added to dilute acids. Commercial general lab grade NaOH (e.g. from laboratoriumdiscounter.nl) is sold as 99% NaOH and I think that is a reasonable claim. I know that NaOH is not a good standard for titration, but in my experiments I did not need utmost accuracy, but an acceptable result. And I think that using my 99% NaOH would be more accurate than using H2SO4 of somewhat unknown concentration as a standard. But I agree that for good accuracy, other standards must be used. NaOH also usually does not contain much water, as opposed to KOH. With KOH you can have as much as 15% by weight of water (pellets or flakes). The little granules of NaOH contain less water. [Edited on 9-12-21 by woelen]

Quote: Originally posted by Antiswat

interesting, interesting. TCCA, trichlorocyanuric acid and NaOH forms NaClO, concentrated now, dump KBr into that and you have some neat yields i suppose they still sell out TCCA? this is especially interesting as KBrO3 acts like KClO3 in many ways, but may give very sensitive compositions, with red phosphorus is almost ignites on contact what about copper bromate? copper chromate is insoluble in water and lets not forget about lead bromate, whats neat about lead salts is how heavy they are, super easy decantation action. on second thought, it also drops out chlorides, and with copper- hydroxides can be turned into copper oxide with a bit of heating

Quote: Originally posted by Antiswat

how doable is it to make calcium hypochlorite yourself? they dont sell it in europe

Quote: Originally posted by Boffis

Well; once I had got the orange coloured cake into solution, in 50ml of hot water, nothing crystallised on cooling. The solution was mixed with an equal volume of saturated KCl solution but still nothing crystallised out, even after 24hours at 5 C. When a small parts was mixed with a little dilute sulphuric acid a little bromine separated so some bromate was present but not enough to ppt KBrO3. This should not be taken as an indication that the technique doesn't work since I am pretty sure that I grossly overheated the mixture during evaporation. The viscous calcium chloride filtrate was also treated with 25ml of saturated potassium chloride solution as mentioned above and about 1.1g of crude K bromate slowly crystallised out. I am going to try this again using the OP method using a direct ppt of KBrO3 with saturated Potassium chloride solution and also with barium chloride solution to get the sparingly soluble barium bromate. [Edited on 16-12-2021 by Boffis]

Quote: Originally posted by Antiswat

thats the kind of yield you should write into a note on achievements how doable is it to make calcium hypochlorite yourself? they dont sell it in europe