Transcription
[Music] foreign [Music] Science nerds, and welcome to my channel, Let's Chemistry! We are continuing our attempts to synthesize 1,3-benzodioxole, or otherwise 1,2-methylenedioxybenzene, from catechol.
In the last experiment, we proved the viability of this method. We have decided to give it a try on a larger scale. Again, we think we have improved our technique after the last successful run. The reagents presented on the table are the same; we have taken the same amounts as we did the first time. So we weighed out 36.66 grams of catechol. A 1-liter round bottom flask was charged with 33 milliliters of dichloromethane and 166 milliliters of DMSO, dimethyl sulfoxide. We discussed in our previous video where to get and how to purify the DMSO solvent. This time we are going to equip the flask with a large condenser, a thermometer, and a stir bar. We lower the flask to the oil bath and start heating and stirring. The flask must be heated to 120 degrees Celsius, and the temperature is going to be maintained for two hours.
We wait out 28.33 grams of sodium hydroxide. We are grinding it to a powder. During the last experiment, I noticed that powdered sodium hydroxide had been more hygroscopic, so we have covered the beaker with powder. According to the procedure, the catechol and sodium hydroxide should be added portion by portion while the solution of dichloromethane is heated. From the last trials, we have learned that the addition rate must be slow, but we have to finish the addition before the temperature in the flask reaches 75-80 degrees. At this point, the vigorous exothermic reaction starts; the temperature reaches 120 degrees within the flask, and I think most of the reaction is done during this time. So I prefer having all the reagents added at this point. As soon as we started the addition, the color of the reaction mixture has turned into blue. During the last two procedures, we had seen just an emerald greenish tint of the liquid, and it changed to black very fast. This time we have taken a transparent bowl for the oil bath, and all the interesting changes in the substance can be better observed. The color of the reaction mixture is darkening after each addition, but at some point it has become yellowish when we add too much catechol and less base. After adding another portion of the base, the liquid is taking a dark blue coloration again. Nearly at the end of the addition, a new surprise has emerged: the reaction substance has thickened; it is barely possible for the stir bar to function properly. I have not observed such behavior during the last two experiments. Fortunately, with the increase of the temperature, the liquid has been getting more and thinner, so it is easily steerable. An additional 8.3 milliliters of DCM are added to rinse down a glass funnel, and the exothermic reaction starts as expected. The condenser has hardly managed to contain the vapor. If we were doing the reaction on a larger scale, we would need a more efficient condenser. After the subside of the violent boiling, the oil bath temperature has been maintained at 110 degrees Celsius for two hours.
[Music] [Music] [Music] foreign [Music] [Music] foreign [Music]
After that, we are going to steam distill, like we did last time, using the steam generator. We are going to use our beloved broken flask as a water boiler again, as it managed to survive last time. We have changed the setup to simple distillation in a 1-liter flask. Milky condensate is starting to collect. The liquid forms two phases. In total, 500 milliliters of distillate are collected. We have poured the collected liquid into a 1-liter separatory funnel. Now we are separating the lower organic phase. The water phase has been extracted with 30 milliliters of DCM three times. The water layer in the funnel forms a nasty emulsion with the chlorinated solvent, and to ease the separation, we are adding more water. It helped a little; and phases are separating much faster. We have combined the organic phase and the DCM extracts. Now we are going to wash it with 100 milliliters of 5% sodium hydroxide solution. At this time, as we can see, there is no problem with the separation. Now we need to wash our DCM extracts with distilled water to remove sodium hydroxide. The liquid forms a much worse emulsion than last time. I think we can skip the second wash, as it is too time-consuming. Adding sodium chloride might help with the separation, but we haven't tried.
After having the separation done, we are going to dry the collected organic phase with molecular sieves and evaporate the solvent under reduced pressure. We have assembled the setup for vacuum distillation. Unfortunately, we have used up all the ice we had, so the water in the condenser is not ice-cold. The organic phase after drying is a little bit cloudy, and we are going to filter it through cotton directly to the distillation flask. After connecting the vacuum, we start to heat the flask. We forgot to add the stir bar or boiling stones; that is a mistake. We are watching the liquid in the flask and the temperature readings on the thermometer inserted into the apparatus. There is no sign of boiling in the flask, but the temperature has dropped to 12 degrees Celsius within the system. Nothing is being collected in the flask. The solvent is evaporating at a much lower temperature than our circulated water in the condenser. We have underestimated the power of our vacuum pump. To ease the evaporation process, we are going to add a small stir bar. We have temporarily switched the vacuum off after placing the stir bar and switching the vacuum on. A violent bumping occurred, and most of the solvent has gone. We continued the so-called distillation for a few more minutes. I have a strong feeling that we lost some part of the product as well. Let's buy our final yield. We have got 20.860 grams, which is the same as the previous result and represents 69-70 percent of the theoretical yield. Thanks for watching, guys!