Sciencemadness Discussion Board - Removing BrCl from Bromine

Removing BrCl from Bromine

hacker - 20-12-2018 at 08:48

How do you remove BrCl from Br₂? I have a fractional distillation apparatus. I also have anhydrous sodium bromide.

If I let the contaminated bromine stand overnight over a small amount of NaBr, will fractional distillation remove the BrCl? Is it necessary to filter before the distillation? I'm not filtering Br₂!!

walruslover69 - 20-12-2018 at 11:06

It seems like that could probably work, When you fractionally distill you might consider keeping the temperature below the boiling point of bromine 40-50C so as to just drive off the BrCl without losing too much Br2.

I assume you are determining the BrCl contamination gravimetrically? If so it might be a small problem weighing the bromine and getting the volume with the NaBr in it. I don't think adding or storing it over NaBr is necessary.

DavidJR - 20-12-2018 at 12:39

Personally, I think it's far easier to produce pure bromine in the first place than to try and separate interhalogens.

fusso - 20-12-2018 at 12:46

What experiment did you do to make a mixture of Br2 and BrCl?

12thealchemist - 20-12-2018 at 12:50

Tried to make bromine from BCDMH? (1-Bromo-3-chloro-5,5-dimethylhydantoin, a water sanitation chemical)

hacker - 20-12-2018 at 20:14

I have not yet performed the experiment. I want to make bromine from BCDMH following the procedure of len1: https://www.sciencemadness.org/whisper/viewthread.php?tid=69...

BCDMH is very cheap.

clearly_not_atara - 20-12-2018 at 21:22

Sulfuryl chloride exists, but sulfuryl bromide does not, so maybe you can reduce the BrCl with SO2?

SO2 + 2 BrCl >> SO2Cl2 + Br2 ???

unionised - 21-12-2018 at 02:37

Almost any reducing agent should, in principle, work- use enough to reduce the Br+ to Br.
For example, you could use copper (I'd not use a more reactive metal).
2 BrCl + Cu --> CuCl2 + Br2

Obviously, if you use excess Cu you will lose bromine.

The most satisfactory option is certainly something like NaBr- that way the by-product is also bromine.

Tsjerk - 21-12-2018 at 02:59

Quote: Originally posted by hacker

I'm not filtering Br₂!!

Why don't you use a separatory funnel with a glasswool plug. You can do the reaction overnight in the funnel and after that you can just drain the bromine.

j_sum1 - 22-12-2018 at 23:31

I don't have it on hand, but Len Lerner's book on small s ale prep of lab chemicals describes a procedure for exfracti g Br2 from BCDMH. IIRC, the procedure excludes formation of interhalides.

hacker - 22-12-2018 at 23:53

Quote: Originally posted by j_sum1

I don't have it on hand, but Len Lerner's book on small s ale prep of lab chemicals describes a procedure for exfracti g Br2 from BCDMH. IIRC, the procedure excludes formation of interhalides.

According to the book, the product is 5% chlorine. On a molar basis, that is almost 10% chlorine!! I want less than 1% chlorine in my bromine.

hacker - 23-12-2018 at 00:08

Quote: Originally posted by Tsjerk

Quote: Originally posted by hacker

I'm not filtering Br₂!!

Why don't you use a separatory funnel with a glasswool plug. You can do the reaction overnight in the funnel and after that you can just drain the bromine.

Will the vapor pressure blow the cap out of the funnel? Will the procedure scale?

Quote: Originally posted by clearly_not_atara

Sulfuryl chloride exists, but sulfuryl bromide does not, so maybe you can reduce the BrCl with SO2?

SO2 + 2 BrCl >> SO2Cl2 + Br2 ???

Wow. Do you know the mechanism that liberates bromine from BCDMH and leaves most chlorine behind?

clearly_not_atara - 23-12-2018 at 00:17

unionised has a very good idea about using NaBr as the reducing agent. I think this is the way to go. NaBr should not form a stable tribromide; usually you need Cs+ or a polyatomic cation for that.

Quote:

Do you know the mechanism that liberates bromine from BCDMH and leaves most chlorine behind?

AIUI it happens because the Br-N bond is longer than the Cl-N bond which gives it a higher dipole moment. That means that the activation energy for rxn with nucleophilic reducing agents is lower. So you use HSO3- which has right about the desired reducing ability and you work at a temperature which will achieve the activation energy for Br-N cleavage but not for Cl-N cleavage.

Note that the reducibility/oxidizability of substances is affected by pH, so while this reaction leans left:

SO2 + Br2 + 2 H2O << H2SO4 + 2 HBr

this one leans right:

SO2 + Br2 + 4 OH- >> SO4(2-) + 2 Br- + 2 H2O

[Edited on 23-12-2018 by clearly_not_atara]

j_sum1 - 23-12-2018 at 00:56

Quote: Originally posted by hacker

Quote: Originally posted by j_sum1

I don't have it on hand, but Len Lerner's book on small s ale prep of lab chemicals describes a procedure for exfracti g Br2 from BCDMH. IIRC, the procedure excludes formation of interhalides.

According to the book, the product is 5% chlorine. On a molar basis, that is almost 10% chlorine!! I want less than 1% chlorine in my bromine.

Quote:

Page 81-82
It is interesting to note that with a moderate reducing agent chlorine is reduced much more slowly than bromine, presumably due to the stronger N-Cl bond of the halogenated amide, so the reaction with a concentrated solution of Na2S2O5 is rapid, and leads quantitatively and almost exclusively to the reduction of bromine.

I have not done it but I would tend to take Len's word for it here. At least if the procedure is followed exactly.

hacker - 23-12-2018 at 07:19

Quote: Originally posted by j_sum1

Quote:

I have not done it but I would tend to take Len's word for it here. At least if the procedure is followed exactly.

In the second sentence on page 81, Len wrote that the upper bound for chlorine contamination is 5%.

I believe Len, but 5% chlorine contamination is far too much. The question is not whether the bromine contains chlorine. We already know that the bromine is unacceptably impure. The question is how to purify the bromine.

j_sum1 - 23-12-2018 at 11:29

I don't think there is any argument here. And we are both reading from the same source.
It appears that Br2 is extracted preferentially. At a small sacrifice of yield then BrCl production should be eliminated. The claim is if you go to completion then the interhalide is less than 5%.

Like ] said, I have not done this. And my next Br2 production will be from NaBr. But the source suggests high purity is attainable.

XeonTheMGPony - 23-12-2018 at 13:03

https://www.youtube.com/watch?v=HuHceKvSHk0

Best method IMO no secondary halogens used in production.

hacker - 23-12-2018 at 13:31

Quote: Originally posted by j_sum1

I don't think there is any argument here. And we are both reading from the same source.
It appears that Br2 is extracted preferentially. At a small sacrifice of yield then BrCl production should be eliminated. The claim is if you go to completion then the interhalide is less than 5%.

Like ] said, I have not done this. And my next Br2 production will be from NaBr. But the source suggests high purity is attainable.

The source uses different standards for "high purity" than typical. Technical grade bromine is usually 99.5% pure, minimum. 95% is not high purity. 95% is low purity.

Tsjerk - 24-12-2018 at 04:16

Quote: Originally posted by hacker

Quote: Originally posted by Tsjerk

Why don't you use a separatory funnel with a glasswool plug. You can do the reaction overnight in the funnel and after that you can just drain the bromine.

Will the vapor pressure blow the cap out of the funnel? Will the procedure scale?

As long as the bromine has the same temperature as the apparatus and the environment it shouldn't. Only when the surroundings heat up it will pressurise. To be sure loosely put in the stopper, this way it will just vent and not fly out. Or put a clip on the stopper after you reached your temperature equilibrium, separatory funnels can handle quite some pressure in case it would heat up.

[Edited on 24-12-2018 by Tsjerk]