Isopropyl Bromide
Isopropyl bromide is one of the alkyl bromides used in chemistry. It's a great isopropylating agent, and is relatively simple to make. It's made by the action of sulfuric acid on sodium bromide, which produces hydrobromic acid in situ, which then acts upon the alcohol to esterfy it to isopropyl bromide.
H2SO4 + NaBr ----> HBr + NaHSO4
C3H7OH + HBr ----> C3H7Br + H2O
C3H7OH + H2SO4 + NaBr ----> C3H7Br + NaHSO4 + H2O
Materials |
Equipment |
| 99% Isopropyl Alcohol | Refluxing equipment |
| Sodium Bromide | Distillation equipment |
| 94% Sulfuric acid | Oil and water baths |
| Calcium chloride | Separatory funnel |
| Sodium Bicarbonate |
To begin the synthesis, add 65ml of 99% isopropyl alcohol to a 1000ml flask. Add to this, 95g of sodium bromide and swirl it well. Measure out 100ml of concentrated sulfuric acid, and add 100ml of distilled water to it. This is very exothermic, so employ cooling during. Once the dilute sulfuric is sufficiently mixed, begin cooling it in the fridge or on an ice bath. It would also be wise to cool the flask of alcohol and sodium bromide. Once both are below room temperature, slowly add the dilute sulfuric into the 1000ml flask. You must go very slow, or else you will oxidize the bromine right out of the sodium bromide, which will cause a reduction in yield. It should take you anywhere from 10-30 minutes, the slower the better. A light tint of red or yellow is okay. Swirl it around constantly during the addition (or equip it with a magnetic stirrer). Once it has all been added, place it in an oil bath, and attach a reflux condenser to the flask. Begin heating the oil bath, and start running water through the condenserReflux this for 1 hour. After this time, remove it from the oil bath (carefully) with the water still running. Let the air cool it down until it is no longer boiling.
If you have a separate flask for distillation, transfer it once it has stopped boiling. Do not let it cool to room temperature if you are transferring flasks. Make sure it has stopped boiling, as the isopropyl bromide vapors are nasty for you. If you don't have to transfer flasks, then simply set it up for simple distillation Heat it with an oil bath up, keeping the bath at about 150C. The receiving flask should be kept in ice water, to minimize loss due to evaporation. Eventually, there will be an obvious clear layer above a milky white layer. Once it is mostly water coming over, stop the distillation. Add this to a separatory funnel, and shake it with distilled water - venting on occasion. Hang it upright and prepare a sodium bicarbonate solution. Remember, the bottom layer in the separator funnel is the one you want. Drain the bottom layer off into your receiving flask, then dispose of the top water layer. Add the isopropyl bromide to the separatory funnel and add the sodium bicarbonate solution to it. Shake it well, venting often. Drain and then repeat with distilled water once more.
Clean up your distillation set-up at this time. Use soap and water to get it all out, then rinse it with 99% isopropyl alcohol. The isopropyl alcohol will take the water out of the system. Once most of the alcohol has drained out, set it up for simple distillation one last time. Add a small amount of calcium chloride to the distillation flask, and drain the lower isopropyl bromide layer into the flask. Swirl it around, then begin heating it on a water bath. Keep the water bath below 80C and distill it dry. Yes, dry. There will be residual isopropyl alcohol left in there, to keep it from actually becoming dry, since that boils at 82C. Keep the flask on the heat until nothing more drips from the condenser This is now your isopropyl bromide. Store it in a fridge, or freezer. It evaporates very quickly. Theoretical yield is 100g, I obtained roughly 50ml, which is equivalent to 65g, so only a 65% yield Keep in mind, I added the sulfuric acid way too fast, and it oxidized a lot of the sodium bromide.
-Pictures-
First distillation - This is a picture of the receiving flask after the first distillation. You can see the milky isopropyl bromide layer, with a clear water layer above it
Final product - This is a picture of the 50ml of isopropyl bromide after the final distillation.
