Bromine help

mannich_depression · Mon Feb 07, 2005 5:01 pm

I've been tring to make a sample of br2 without any success,
Are there any ways to make it besides using NaBr or CaBr?

It is hard to get where I come from,

My photography needs require about 2ml of Bromine,

Any Ideas

Cheers in Advance,
P.s. Good luck with the new board, Idea

moecat · Tue Feb 08, 2005 6:50 am

java · Consumer

.........source Vogel's 5th edition "A Text Book of Practical Chemistry", page 422

Guest · Mon Feb 14, 2005 7:24 am

this should solve alot of problems,

Many, many different methods

syn

zara · Guest

IndoleAmine · Dreamreader Deluxe

-ggg-

Vitriodor · Fri Mar 11, 2005 2:17 am

Nice set-up you have there I_A....Is the reaction proceeding smoothly or can one expect a "huge" cloud of Br2 once the HBr is added? Would it be a good idea to cool the receiving flask ?

Vit

Nicodem · Sat Mar 12, 2005 10:17 pm

When I need Br2 for bromination of PEA-like compounds, I always prepare it in the addition funnel just before use. This way you skip the dangers involved in using pure Br2.

Example 1:
In a 50ml addition funnel there was added 4ml methylenechloride, 15ml water, 8ml of 35% sulphuric acid and 1.2g of KBr (9.5mmol). When the solid dissolved and the mixture cooled to the room temperature I slowly added 1.07g of KBrO3 (1.9mmol) in 10ml of warm water. The precipitated bromine was extracted in the lower organic phase by shaking. This dark red Br2/DCM phase was then added to the reaction mixture containing 4.95mmol of a certain methoxyamphetamine hydrochloride in acetic acid. This must be done carefully in order to stop the addition before the upper water phase comes into the reaction mixture. Then a further 3ml of DCM was added, the funnel shaken and the addition repeated. A third 2ml DCM portion might be needed if you want to fully extract the Br2 from the water phase, but not really necessary. The yield of the product was 84%.

Example 2:
Same as above, except that 30% H2O2 is used instead of KBrO3. The molar ratio of KBr : H2O2 must consequently be different, that is 2 : 1.

Example 3, 4..:
Instead of KBr, you can of course also use NaBr, NH4Br, CaBr2 etc.

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Additional information:

Other suitable oxidants are KMnO4, MnO2, (NH4)2SO5 and NaBO3×4H2O just to name a few OTC ones. I never used any other than KBrO3 or H2O2 though, but this was only a matter of convenience, not because it would only work with these others. Don’t forget to change the molar ratio appropriately to the relevant redox equation though. The ratio must always be exactly the one you need to oxidize the bromide into bromine. Not enough will result in excess of bromide therefore some bromine will remain in the water phase (Br2 is soluble in KBr solution as it forms the KBr3 complex). Too much oxidant will result in some bromine getting oxidized into hypobromous acid or higher oxo-acids (HBrO, HBrO3). If this is taken strictly into account then you can suppose an almost quantitative formation of Br2 (I usually calculate for a 5 to 10% excess of Br2 in relation to the PEA×HCl being brominated, just to make sure there is enough of it even if the extraction is not quantitative).
Also there is no need whatsoever to make the freebase of the PEA substrate as it is described in PiHKAL and on the Rhodium’s pages. The bromination works just as good on hydrochlorides themselves, except that just slightly more solvent might be necessary to fully dissolve the salt. The difference is also in the work-up as you need to strip off the acetic acid solvent and do an acid-base extraction instead of filtering the less soluble hydrobromides from the acetic acid solution. The good thing is that the yields are good, and that you get a purer product at the end due to the acid-base extraction (I make the hydrochlorides at the end).

IndoleAmine · Dreamreader Deluxe

The bromine vapors come slowly in little puffs if you drip slowly (they're heavy), but this setup was just for the picture *cough*...

I bubble it into cold GAA usually - but the idea of generating it in the addition funnel is superior, I must admit! Cool

(a dewar flask chilled with acetone/dry ice could be capable of condensing the bromine into liquid form, but I have never tried that due to lack of a dewar and dry ice... Laughing

)

i_a

icecool · Insistent Chemist

Does this and how does this work for brominating 2C-H?

IndoleAmine · Dreamreader Deluxe

Yes - originally ála Shulgin, by condensing/dissolving the bromine in cold GAA, and adding it to 2C-H in GAA ( = 2C-H acetate in GAA) with cooling...

Or by adding the Br2 directly to the 2C-H acetate/hydrochloride in GAA, should work too and is maybe better considering bromine's very nature...
(see nicodem's post about adding the Br2 as in-situ generated haloalkane solution)

i_a

anime · Tue Apr 19, 2005 6:30 am

Nice post IA. It is easy to clean the glassware after the generation of the Br2?

Dissolving the Br2 is GAA definitely seems the way to go. Party stores generally sell dry ice. If you're looking to condense the bromine to a liquid I guess you can look there.

IndoleAmine · Dreamreader Deluxe

Glassware is cleaned from MnO2 very easily with dil. HCl and a squirt SnCl2 solution, oxalic is said to work well too (not tested)...

But honestly: Just because I included a pic of bromine vapors (cough), my post is not really special! Props go out to nicodem if you ask me, since his tweak of generating bromine as a saturated haloalkane solution in a dripping funnel is great - you don't have to mess around with any pure bromine at all, it is directly taken up by the solvent, and this DCM/Br2 solution is easily added to the amine/GAA just as would be done with liquid bromine.

No stink, no vapors (well almost...).

SWIAs favorite bromination method from now on!

i_a

stratosphere · Tue Apr 19, 2005 10:17 pm

whenever ive made bromine, ive used 1 equiv KBr (any aq soluable metal Br salt would do), 1 equiv 30% H202, while that should create bromine, i found the reaction wouldn't go without adding an acid, i usually used 1 equiv of HCl, and then distill off the Br2.

and yes it does stink and make your lungs raw if your not careful. good to keep the reciever in ice bath.

stratosphere · Tue Apr 19, 2005 10:17 pm

whenever ive made bromine, ive used 1 equiv KBr (any aq soluable metal Br salt would do), 1 equiv 30% H202, while that should create bromine, i found the reaction wouldn't go without adding an acid, i usually used 1 equiv of HCl, and then distill off the Br2.

and yes it does stink and make your lungs raw if your not careful. good to keep the reciever in ice bath.