How to be a Successful Organic Chemist

16 How to perform an extraction. For simplicity’s sake,we will assume that the product is a neutral compound. 1. Make sure the stopcock is closed. Add a small amount of water or the aqueous solution you are using. Some- times the stopcock is improperly sealed, and you will find that it leaks. You would rather know that now, rather than after the organic material has been added. 2. Add the reaction mixture, as well as water if necessary, and the required organic solvent. Make sure that the solutions added do not touch the inside of the top of the funnel, as solids can crystallize here and prevent the stopper to seal properly, leading to leaks. 3. The funnel is closed with a stopper, turned on its head, and shaken very carefully. The stopper is always supported by your hand.The pressure is released after each round of shake by opening the stopcock (point it upwards into the hood, but never towards yourself or someone else), and then closed again.Now the two layers are shaken vigorously. It is imperative that the two phases are mixed, because no compounds will exchange without a good mixing. 4. The funnel is rested in a ring stand, and the stopper removed. The two phases are allowed to separate. The phases are removed by draining them out, one at a time. 5. The aqueous phase can be extracted again, up to three times. The combined organic fractions are typically dried with a drying agent, 9 then filtered, and the solvent evaporated. 9  A classic problem is that a student either has very little product after extraction (because of improper mixing of phases) or that the student requires a vast amount of drying agent (not allowing the two phases to separate properly). (A) The separatory funnel containing the two phases are shaken vigorously together. The stopper of the funnel is supported by one hand, and the stop-cock supported by the other hand. (B) The two phases are separated. The aqueous (or lower phase) is drained into a clean container. (C) The entire bottom phase is drained, and the stop-cock is carefully closed when all the phase has been removed, leav- ing the top-phase in the separatory funnel. (D) The top phase is then drained into a clean container. If necessary, either phase can be extracted again, to finish the extraction routine. Figure 2.6. Key steps in a liquid-liquid extraction