Transcription
Bromine is extremely dangerous, and its synthesis should not be attempted. This video is for entertainment purposes only, and you should not recreate anything you see. Like chlorine, bromine is extremely dangerous and can easily kill you. On top of this, bromine is a liquid and it is much more concentrated and therefore more dangerous than chlorine.
Bromine is a very interesting element and it appears as a fuming liquid at room temperature. The properties of bromine are extremely similar to chlorine, except for the fact that it's a liquid at room temperature whereas chlorine is a gas. In organic chemistry, the main use of bromine is for brominating various compounds. Outside of organic chemistry, in the real world, bromine is mainly used as a substitute for chlorine in pools or spas. And this is very convenient because we're going to use pool supplies to make the bromine.
Make the bromine; these are the three chemicals you will need: muriatic acid, TCCA, and sodium bromide. The sodium bromide here is pre-dissolved in a solution, but you can also use powdered sodium bromide. In Canada, only the sodium bromide solution is sold, and it's very hard to get the powdered form. The TCCA and hydrochloric acid will be used to produce chlorine gas, and the sodium bromide salt is our source of bromine. In short, the chlorine will displace the bromide ion to produce sodium chloride and bromine.
What's interesting is the amount of muriatic acid or hydrochloric acid that I use is three times less than what you would need if you did it stoichiometrically. I found it was possible to use less HCl, which means that the possibility of contaminating the final bromine with HCl is decreased. On the other hand, a stoichiometric amount of TCCA and sodium bromide is used.
The setup is a relatively basic, simple distillation. You can see on the left that I have an addition funnel attached to the round bottom, but this is optional. In order to limit losses, a long condensing column was used, and it was cooled using ice water. It's not shown here yet, but every single joint was sealed using concentrated sulfuric acid instead of grease, because the concentrated sulfuric acid is more resistant to bromine. The receiving flask is in an ice bath to prevent condensed bromine from escaping. The vacuum adapter leads to an inverted funnel bubbler trap, to neutralize any bromine that escapes. As a precautionary measure against spills, I place the second half of the distillation apparatus in a container.
To the round bottom flask is added 72 grams of crushed TCCA. To the addition funnel was added 60 milliliters of sixteen percent hydrochloric acid. Then to the round bottom is added 400 milliliters of the thirty-five percent sodium bromide solution. Immediately upon addition, some chlorine comes off of the TCCA and liberates bromine from the sodium bromide salt. So you can see here that a reaction occurs between the sodium bromide and the TCCA, which might explain why we actually don't need a stoichiometric amount of hydrochloric acid. But, strong stirring; the hydrochloric acid is then added dropwise. I was able to add it in a closed system because I have an addition funnel, but if you don't, you can also simply pour in the hydrochloric acid and then quickly stopper it. The addition of the HCl is not exothermic to any real degree, so adding it quickly is not a hazard. I added the HCl slowly to keep the concentration of the HCl low to prevent the formation of any HCl vapors that could contaminate my bromine product. However, even if you add it quickly, it probably won't contaminate your bromine product to any significant degree.
When the HCl is added, it reacts with the TCCA to release chlorine. The chlorine then reacts with the sodium bromide to form sodium chloride and bromine. As more and more HCl is added, more bromine is produced, and the dark red color of bromine becomes much more evident. After all of the HCl is added, the solution would be a very dark red with some fumes above it.
In order to separate the bromine, we're going to have to carry out a distillation. You can see here that even before the distillation, there is evident bromine fumes, but there's not enough to condense into liquid bromine. As the mixture is heated up and more bromine is liberated, the vapors will become darker and darker. It will reach a point where the bromine will start to condense into liquid and travel down the condenser. And here we can see the first few drops of bromine reaching the end of the condenser column. Soon it will pick up, and a lot of dense vapors will travel towards the condenser column. At this point, there's a relatively steady drip rate of bromine. In the condenser column, there is a gradient where the majority of the bromine is condensed to a liquid at the top. Unfortunately, with bromine, it's extremely volatile, and it's very hard to condense everything.
Soon the rate of distillation will decrease, the temperature will rise, and more and more water will start to come over with the bromine. I found that it's important to not end the distillation here because there is still a lot of bromine present. The reaction mixture was boiled at a hundred degrees Celsius until it completely cleared up. It should reach a point where you don't see any bromine vapors in the distillation flask. Once this point is reached, the dissolution is done, and the flask can be removed from heat. You can see at this point that only water is coming over and not a mixture of water and bromine.
This is the final yield of bromine. We have bromine on the bottom and a water layer above it. The bromine is on the bottom because it's three times as dense as water. The bromine was then transferred to a separatory funnel to isolate it from the water. During these steps, a lot of bromine vapor is released, so it's important to do this in a well-ventilated area with a respirator. Once the layers have settled, I drained the lower bromine layer directly into another separatory funnel. I did this because the next step is to dry the bromine using concentrated sulfuric acid.
To the bromine was added 20 milliliters of concentrated sulfuric acid. This step must be done very carefully because if water is present, it can be very exothermic and cause the bromine to boil. The next part is the most dangerous part, which is the capping and the shaking to mix the sulfuric acid and the bromine. It is important that the stopper is well greased with sulfuric acid to make sure that no bromine leaks out. I'm not sure why, but when the separatory funnel is capped and shaken, no pressure was created, and no bromine was released when I vented the stopcock. However, this is highly unusual and should be expected for bromine vapors to shoot out when the stopcock is opened.
The lower bromine layer is then drained into a round bottom flask. The final yield of dry bromine was a hundred and nine grams. This represents a yield of about seventy-five percent. The yield might be increased by increasing the amount of hydrochloric acid used, but for me, seventy-five percent yield is good enough.
The storage of bromine is extremely difficult, and it will leak out of almost any container. The best option for bromine storage is an ampule. Using a Pasteur pipet, the bromine was carefully transferred to homemade ampules. These ampules were made from test tubes, and I've shown how to do this in a previous video. After the bromine had been transferred to the ampule, it was sealed using a torch. This is the final yield of my bromine, all sealed in several different ampules. I sealed several different small ampules so I could use a small amount many different times, but it was a lot more work. These ampules are stored in a mixture of sand and sodium thiosulfate in a container outside. If any of these samples were to pop or break indoors, it would be a very big problem.