During bromination, in addition to 2BK4, hydrobromic acid (HBr) and other substances were released, contaminating 2BK4. To remove all impurities from the solution, you need to perform several washes with a solution of baking soda and one wash with clean water. Baking soda neutralizes acid, and water rinses away dirt. 2BK4 is insoluble in water, so it remains in DCM (dichloromethane).
Prepare the solution: 100 g of baking soda per 1000 ml of distilled water. Take an empty 2-liter bottle, pour 1000 ml of water into it, and add 100 g of baking soda. Shake vigorously for 2-3 minutes, then let the remaining soda settle for another 2-3 minutes. The solution is ready; do not disturb the settled soda while draining.
Remove everything from the flask: transition, fridge, dropping funnel, and core.
Smoothly (slowly, in small portions), pour approximately 300 ml of the soda solution into our reaction mixture, close the lid, and turn the mixer on for a maximum of 2 minutes. The mixture should become lighter. It will bubble, hiss, and foam – this is the soda neutralizing the acid and bromine. The reaction is active, so add slowly.
Remove the anchor with the anchor extractor. Then vigorously shake with your hands for another 2 minutes (no stirrer can mix as well as you can with your hands in this case, it is important).
Next, set up a separating funnel on a stand and pour out everything in the flask.
Observe how the layers separate (it takes about 30 seconds). The top layer will be aqueous, and the bottom layer will be the 2BK4 solution in DCM.
Once the layers have separated, take an indicator paper and place a small drop of the bottom layer on it, just enough to moisten the paper. The desired color is neutral (yellow, where the paper gets wet but doesn't change color). If it was slightly alkaline, add a drop of soda solution. If it is acidic, repeat the phase by washing with baking soda, letting the bottom layer flow into the flask, and discarding the top layer. This is a crucial step – we need to neutralize all the acid with a soda solution. If you send an underwashed solution to the synthesis, you will likely ruin the batch.
So now there are two layers in the separating funnel. Let the bottom layer (most likely, after 2-3-4 washes with soda, you'll finally see a neutral color) flow into a bottle, and discard the top layer. At this stage, you can collect a small amount of the water layer without losing the 2BK4 layer.
To make it easier to transfer the bottom layer from the funnel directly into the flask, place a stand with the separating funnel on the edge of the table and move the supports aside (CAUTION, THE FUNNEL CAN HANG, FALL, AND BREAK – IT WILL BE VERY DIFFICULT TO CLEAN!). Alternatively, simply hold the funnel in your hands.
Once we finish washing with soda, wash again with clean distilled water: add 100-150 ml of distilled water to the flask, shake vigorously for 2-3 minutes, and pour into a separating funnel. Once again, let the bottom layer flow into the flask and discard the top layer.
Therefore, we have washed with alkali (1-4 times) and pure water (1 time) to remove unreacted bromine, acid, and other by-products, resulting in a pure solution of 2BK4 in DCM.
Cheers
After all, you can't put it in the bag wet and not know the exact weight. And it takes a very long time to dry and exudes tear fumes.