Sciencemadness Discussion Board

XeF2 for making Perbromate

Tdep - 26-6-2021 at 21:00


Xenon difluoride, 1 gram! I'm really interested what you are going to do with that. That's a really special reagent!

From another thread, I thought I might discuss it here. I've got 1 gram of XeF2 on the way, which may or may not make it... but regardless, any suggestions of experiments?

Mostly, I'm going to be aiming to make some perbromates. It wont make very much and the perbromates aren't some super wild oxidiser, but it is a very interesting compound in its difficulty to make, requiring such extreme reagents such as F2 gas or XeF2 to make.

From "Synthesis of perbromates", 1968


To make a relatively large quantity of perbromate, several hundred milligrams of XeF2 was stirred with 4 ml of 0.4 M NaBrOs until the XeF2 had all reacted.
The resulting solution was 0.07 M in perbromate. Bromate was removed from this solution by precipitation with excess AgF at 0 C. Then the ice-cold supernatant solution was made 0.5 M in RbF, and the rubidium perbromate precipitate was isolated, washed with a little ice water, and dissolved to make 5 ml of solution.

I'm hoping that RbCl can be used in the place of RbF? But I forgot that I also need AgF... so I will either have to source that or think of an alternative.

The perbromate synthesis will use up most of my XeF2, which leaves me a few hundred mgs to use for another experiment/demo, any thoughts Sciencemadness hivemind? Will use it up rather than keeping it around.

[Edited on 27-6-2021 by Tdep]

Tdep - 26-6-2021 at 21:22

Quote: Originally posted by Tdep  

But I forgot that I also need AgF... so I will either have to source that or think of an alternative.

Could I just use silver nitrate? All it is doing is acting as a soluble silver source to precipitate out silver bromate...
AgF + NaBrO3 --> AgBrO3(s) + NaF
AgNO3 + NaBrO3 --> AgBrO3(s) + NaNO3

Sure, there's a solubility drop from the fluoride salts to the nitrates, but they're still pretty soluble, so seem to check out for me

Bedlasky - 26-6-2021 at 22:01

What about Au2F10?


Krypton difluoride can also oxidise gold to the +5 oxidation state:[4]

7KrF2(g) + 2Au(s) → 2KrF+AuF6-(s) + 5 Kr(g)

KrF+AuF6- decomposes at 60 °C into gold(V) fluoride and gaseous krypton and fluorine:[5]

2KrF+AuF6-(s) → Au2F10(s) + 2Kr(g) + 2F2(g)

Maybe it is also possible with XeF2???

Anyway good luck with perbromate synthesis! I also want to try to make some perbromate. I prepared some sodium diperiodatonickelate(IV), it should oxidize bromate to perbromate. But I am not sure if it will work. If doesn't, I'll probably try some Pr(IV) or Tb(IV) based oxidiser.

[Edited on 27-6-2021 by Bedlasky]

Tdep - 26-6-2021 at 22:29

Interesting thought!

Yeah I prepared some sodium diperiodatonickelate(IV) too, but the paper that describes the formation of perbromate using it does seem pretty dubious... and even so, how are you meant to isolate the perbromate from the reaction mix?? Seems messy and I couldn't work out a way to pull it off.

Edit on the Gold(V) fluoride, it doesn't seem water stable (or stable to much at all!). I think it's best for me to only stick to aqueous reactions, there's enough going on without me having to worry about anhydrous stuff and protection from the air etc

[Edited on 27-6-2021 by Tdep]

Fery - 27-6-2021 at 01:43

here synthesis of perbromates with more available chemicals (hypobromite + bromate)
they did not separate perbromate, just determined its concentration

Attachment: pisarenko2011.pdf (1.4MB)
This file has been downloaded 66 times

Bedlasky - 27-6-2021 at 08:11

Tdep: I'll try to add 20% of diperiodatonickelate(IV) needed for full conversion of bromate to perbromate. Heat it and wait if brown solution turn green. If it will work, I'll add stoichiometric amount of sodium persulfate to oxidise Ni(II) back to Ni(IV). So in the end if you keep alkaline conditions, diperiodatonickelate(IV) stays in the solution while only compound which precipitate out is KBrO4 (both KClO4 and KIO4 are insoluble, so KBrO4 should also be insoluble). Diperiodatonickelate(IV) can be crushed out by neutralisation of solution. So you also recover most of your oxidiser.

woelen - 28-6-2021 at 12:24

This is really cool. It would be very nice if you could isolate a little amount of some perbromate salt. I simply would keep it around as a proof of your achievements.

One way to separate it from excess bromate may be to add HBr. HBr can be obtained relatively cheaply from S3-chemicals (I ordered 500 ml of water clear 48% HBr for EUR 35 or so). With BrO3(-) this instantly gives Br2, which can easily be driven off. It might be that BrO4(-) is inert in solution (like ClO4(-)), and that this does not react with bromide at low pH. I once used a similar method for purification of perchlorate (made by heating KClO3 carefully until the molten salt solidifies again). The molten mix contains KClO4, KCl, but also some left over KClO3. On addition of HCl, the KClO3 quickly is destroyed, while only KCl and KClO4 remain behind. The big difference in solubility in cold water can be used to purify the KClO4 easily. Maybe the bromine analog of this purification reaction can be used as well.

The people, who made perbromate in 1968 used AgF for precipitating AgBrO3. I see no reason why AgNO3 cannot be used. The only issue is that it adds another ion to the mix. With XeF2 as oxidizer, your mix only only will contain F(-), BrO3(-) and BrO4(-) and with AgF no new ion is added. This makes purification easier. The nitrate ion is annoying in combination with Rb-ions (and also with K-ions). RbNO3 and KNO3 dissolve very well in hot water, while only moderately well in cold water. This same characteristic exists for perbromate, so separating the perbromate from nitrate might be cumbersome.

I would try to find to selectively find a method for destroying bromate, while keeping the perbromate. Perbromate is less reactive than bromate (just as perchlorate is less reactive than chlorate), but I do not know how much less reactive.

EDIT: I see that the paper, posted by Fery, mentions the selective reduction of bromate with sulfite. I can imagine that this allows you to remove bromate, by bubbling SO2 through the solution, until all bromate is destroyed. The process leads to formation of acid, sulfate ions and Br2 (if excess SO2 is used, the Br2 is reduced further to Br(-)). This will leave you with the task of separating perbromate from sulfate and fluoride. Sulfate can be removed with BaCl2, leaving only chloride, fluoride and perbromate in solution. At neutral or alkaline pH, these ions do not react with perbromate, not even at near boiling temperatures and this should allow you to separate KBrO4 or RbBrO4 or CsBrO4 (which all are sparingly soluble in cold water) from the fluoride and chloride.

[Edited on 28-6-21 by woelen]

woelen - 28-6-2021 at 12:46

Some interesting ideas: