Although four years ago, I successfully isolated bromine from BCDMH, the process was rather difficult since BCDMH only contains 33% bromine by mass. I finally was able to find sodium bromide, which contains 78% bromide, in the pool supply section of a local hardware store. Perhaps earlier, I was looking in the wrong places. It is sold for establishing a bromide level in new pools for use as a disinfectant. 56 g NaBr cost me $2.79.
Isolating bromine from a bromide salt is a very well-documented reaction, and there are several ways of oxidizing the bromide ion to elemental bromine. I chose to use chlorine as my oxidizing agent. I made my chlorine by reacting sodium bisulfate with calcium hypochlorite. Both of these chemicals are also sold for use in pools. Sodium bisulfate is used to decrease the pH of pools, and calcium hypochlorite is used as a chlorine disinfectant.
2NaBr + Cl2 --> 2NaCl + Br2
Once the bromine is isolated, it can be purified by distillation and dried by shaking it carefully with concentrated sulfuric acid.
Bromine is a useful reagent for the home chemist and is something that I would like to have access to in fairly large quantities. Firstly, bromine can react with carbon-carbon double bonds to give dibromides. These dibromides are useful intermediates in producing alkynes, since they can undergo double dehydrohalogenation to yield a carbon-carbon triple bond.
Bromine undergoes violent reactions with many metals including magnesium and aluminum to give the corresponding bromide salts. These reactions are not only spectacular to witness, but anhydrous aluminum bromide is a useful reagent in organic chemistry since it is a strong Lewis acid. It can be used as a substitute for the anhydrous aluminum chloride typically used in Friedel-Crafts alkylations and acylations.
I also want to produce bromine because it can be used to produce acetic anhydride, an extremely important chemical that can otherwise be difficult for the home chemist to acquire. The reaction of dry bromine with sulfur and anhydrous sodium acetate produces acetic anhydride. This is definitely a reaction I want to attempt due to its apparent simplicity.
4S + 2Br2 + 4NaOAc --> 2Ac2O + SO2 + 3S + 4NaBr
The whole reaction setup that I used is shown in the picture above. The chlorine gas generator is located on the right side. In the separatory funnel, I had a solution of 100 g sodium bisulfate in 160 mL water, which dropped into 55 g of solid calcium hypochlorite. During the experiment, I dropped in the bisulfate solution at a rate of about 2 drops per second to generate a nice and steady stream of chlorine gas, which fed into the bottom of a round bottomed flask. The flask contained 32.3 g sodium bromide dissolved in 50 mL water, and was immersed in a water bath which I held at a temperature of about 80C. This reaction flask was connected to a simple distillation apparatus to collect the formed bromine which has a boiling point of 59C. Bromine was collected in the receiving flask which was cooled in a salt-ice bath. I set up an exit tube at the end of the distillation apparatus so that the chlorine gas could be absorbed into a solution of sodium hydroxide and then a solution of sodium bicarbonate. You can see the two gas washing containers at the bottom right of the picture above.
The distillation apparatus used standard 19/22 glassware. For the gas tubing, I used plastic tubing and connectors sold for sprinkler drip systems. These held up throughout the course of the reaction although they did suffer some damage. You can also get away with constructing the distillation apparatus out of PVC pipe, which I did when I made bromine from BCDMH.
After about 1 hour of reaction time and adding all of the sodium bisulfate solution, I ended up with about 2 mL of bromine, which is about 25% of the theoretical yield. This was not a great yield, and I probably could have gotten more bromine if I ran the reaction longer. Nevertheless, I was quite satisfied with my product, and it sure was neat seeing a deep red liquid come out of what started out as a completely clear solution! I decided not to dry my bromine with sulfuric acid and proceeded to have some fun. I placed about 0.5 mL bromine in a test tube and introduced a large piece of aluminum foil. Nothing happened for a good thirty seconds or so, but then the reaction commenced. I was greeted with bright flashes of red light and thick white aluminum bromide smoke. Don’t breathe it!
I stored the rest of my bromine in a round bottomed flask with a glass stopper. I wrapped the stopper in Teflon and hoped for the best. Bromine is notoriously difficult to store due to its high vapor pressure and promiscuous reactivity. The only sure way to keep it around for a long time is to seal it in a glass ampoule. So far though, my bromine has lasted for more than a week with no noticeable evaporation. I don’t expect it to last for long though.
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