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draculic acid69
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h3po3+br2 then distilling. h3po2 + I2 is extremely exothermic so I'm guessing that it's the same if not worse with br2. h3po3 is a much milder
controlled
rxn.
Red P could also be used but using rare red P + expensive hard/dangerous to handle br2 just to get to hbr or using the br2+sulfur route seems like
going the long expensive difficult & troublesome way to arrive at hbr.br2+acetone will give off lots of hbr gas if you don't mind losing more than
50% of the bromine.again it's the stupidly long troublesome way to get hbr.
[Edited on 20-6-2021 by draculic acid69]
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Monoamine
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Quote: Originally posted by draculic acid69  | | Quote: Originally posted by Melgar | Here's a patent, if you need a procedure for making HBr from Br2 and S:
https://www.google.com/patents/US3145079
Of course, nobody's mentioned the easiest way yet: add Br2 to a sodium metabisulfite solution, then distill from that. You may need to add a strong
mineral acid (H2SO4 or H3PO4) before distilling for best yields though.
[Edited on 1/20/18 by Melgar] |
While metabisulfite will form hbr from br2 I'd be very concerned about so2 contamination. |
An alternative which may be a bit less toxic is Na2S2O3
for which the following reaction occurs:
4 Br2 + Na2S2O3 + 5H2O -> Na2SO4 + H2SO4
+ 8 HBr. Source
So with sodium thiosulfate (Na2S2O3) you should even be able to recover some sulfuric acid for later work.
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Monoamine
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Use sodium thiosulfate (Na2S2O3):
4 Br2 + Na2S2O3 + 5H2O -> Na2SO4 + H2SO4
+ 8 HBr. Source
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Monoamine
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Maybe vitamin C is better for reducing Br2 than sodium thiosulfate after all...
On the other hand sodium thiosulfate (Na2S2O3) may not be the best choice in the end for the following reasons:
It melts at around 48.3oC and actually decomposes at 100oC, which is lower than the boiling point of HBr.
To make matters worse, it reacts with hydrochloric acid as follows:
a2S2O3 + 2HCl -> 2 NaCl + S + SO2 + H2O !!
I would imagine that the same happens with HBr, except that you'd end up with NaBr as one of the products, so you'd be right back where you started.
Also SO2 is pretty toxic, so not really something you want to be making...
Earlier I said that ascorbic acid (C6H8O6)may not be a good choice, but I'm starting to think that it may actually
not be so bad. It reacts with Br2 as follows:
C6H8O6 + Br2 -> 2 HBr + C6H6O6
(C6H6O6 is dehydroascorbic acid)
Both of these vitamin C variants melt at temperatures well above the boiling point of HBr.
The downside is that these "reducing agents" easily decompose, and could react with the HBr via nucleophilic substitution of their OH groups...
However, it might still work, since this is actually used to determine the amount of vitamin C in supplements and then measuring how much HBr is
produced.
This will probably take some trial and error, but I would start by simply trying to distill off the HBr and hope see how concentrated you can get
it...
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clearly_not_atara
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You should consider that bromine is about fifty times as toxic as sulfur dioxide before attempting any of this.
Also, I am pretty sure that the decomposition point you're citing is the dehydration of the hydrate. It's not relevant anyway because the thiosulfate
will be consumed by oxidation before you distill it.
The greater concern would be generating H2S from thiosulfuric acid disproportionation, and dealing with the heat of reaction. This may be partially
managed by dilution.
I like the H3PO3 idea, if phosphites are available. But it's probably more practical + cheaper to just make a bromide and heat it with TsOH or NaHSO4.
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Amos
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You guys are really still responding to a pointless thread, only relevant to one user, that then never returned to look at the answers?
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