Fractionating the Br2 should leave no impurities in the bromine afaik.
a) How would that look practically ? Like what length of a coloumn/type of filling would be needed ? Has anyone got an actual written protocol ?
b) I think fractionation would mainly be done to get rid of the azeotrope of water and HBr, boiling at 122°C. If one used an excess of oxidizing agent, there should be no HBr left - right ? Then you could do a normal distillation at 58°C collecting wet bromine.
Which leads to my next thought: extrapolating the facts given in
https://www.thevespiary.org/rhodium/Rhodium/chemistry/tma2.vanillin.html
1L CHCl
3 dissolves (at least) 1248,5g / 400,3 mL / 7.8125 mol Br
2. But only 9ml H
2 are miscible with 1L chloroform. So, catching the wet bromine vapor in CHCl
3 has two advantages: no need for critical cooling in the receiving flask, easy separation of the bromine from water.
separation of Br2 from CHCl3
I dont think that is possible without distillation.
What about this: If you took your bromine saturated chloroform and cooled it to -10°C the bromine (mp -7.2°C) would turn into a solid, the chloroform (mp -63°C)would remain a liquid and could be decanted.
The gaseous bromine will escape to wherever it can go to
Have you heard of 'catching bromine under sulfuric acid' ? Seems like Br2 vapor bubbled into H2SO4 gives a bottom layer of liquid bromine. Purification from there on remains in question.
And as for the propanoic acid bromination, perhaps it would bee nice to brominate the propanoic acid "in situ" using for example H-Br/H2O2 ?
You definately cannot mix propanoic acid, P2O5, H3PO4, H2O2 and HBr to get the bromopropanoic acid, as the water would destroy the polyphosphoric acid, generated from P2O5 and H3PO4, which is the essential ingredient to let the bromination happen at the position next to the -COOH group, not the -CH3 at the end of the chain.
However, maybe you could just bubble Br2 gas into the polyphosphoric acid/propanoic acid mix as it is liberated from whatever bromide oxidation reaction mixture. Maybe minor impurities don't fuck it all up.
Thanks for the answers so far!
--psyloxy--