Question

Extraction of solids: Experiment outlined below

Draw a “roadmap” of the experiment, containing chemical structures and “layers” (organic and aqueous). This should contain the individual reactions occurring in each step, and show which layer the various components are present. Make sure you think about whether the acetaminophen, caffeine and aspirin are neutral, protonated or deprotonated.

Preliminary separation obtain a sample (1.0g) of the mixture. weigh the sample and record it. this sample should consist of a 2:1:1 mixture (by mass) of aspirin, acitaminophen, and caffeine, respectively. Assemble the apparatus for a vacuum filtration (Zubrick p98), making sure the receiving flask is clean; you will be keeping both the filtrate and the insoluble material. Transfer the sample to your smallest Erlenmeyer flask, add 10 mL of dichloromethane, and warm the mixture for ten minutes on a hot plate at 35-40 °C. Note that a portion of the sample will not dissolve. Wet the filter paper in the Büchner funnel with dichloromethane, and filter the mixture. The filtration must be performed while the mixture is still warm - the success of your separation depends on this. Ensure that you have good suction in your filtration apparatus, and pour the solution quickly and smoothly to avoid crystallization in the filter. Rinse the Erlenmeyer flask out with an additional 2 mL of warm dichloromethane to transfer as much solid material to the Büchner funnel. Add an additional 5 mL of dichloromethane to the filtrate to redissolve any crystals that might have formed during the filtration. Label the filtrate Solution A. Allow the insoluble material to dry until you have completed steps 2 and 3. 2. Separation of Aspirin Solution A should contain the aspirin (an organic acid) and caffeine (an organic base). Aspirin may be separated from caffeine by extraction with 10% NaOH solution. Transfer Solution A to a 125 mL separatory funnel and add 10 mL of 10% NaOH solution. Shake the mixture 3 or 4 times and remember to vent the separatory funnel intermittently to relieve pressure (make sure you point the funnel away from both yourself and your labmates!). Remove the bottom layer into a clean 25 mL Erlenmeyer flask, and transfer the top layer to a separate clean 50 mL Erlenmeyer flask. Label the flask containing the top layer Solution B. Pour the bottom layer back into the separatory funnel (remember to close the stopcock), add 5 mL of distilled water, and shake again. Remove the bottom (organic) layer into a clean, dry 25 mL Erlenmeyer flask, and add anhydrous sodium sulfate until the drying agent no longer clumps together. Label this mixture Solution C. The remaining aqueous layer (the top layer still in the separatory funnel) should be added to Solution B. 3. Recrystallization of Aspirin Solution B contains the aspirin in the form of a water-soluble sodium salt. Slowly add 4M hydrochloric acid solution to Solution B until it becomes strongly acidic and an obvious persistent precipitate forms. Test the acidity using pH paper. The aspirin should rapidly precipitate ("crash") from solution. On a hot plate, heat the solution until all the aspirin has re-dissolved, then allow the solution to slowly cool to room temperature and place it in an ice bath. Isolate the formed crystals by vacuum filtration. 4. Isolation of Caffeine Solution C contains neutral caffeine. Decant the solution from the drying agent using a transfer pipette, and transfer the material to a clean, pre-weighed, 50 mL round-bottomed flask. Remove the dichloromethane using the rotovap to yield the caffeine. Weigh each of the isolated materials (aspirin, acetaminophen and caffeine), and record their masses in your laboratory notebook. Determine the melting point range of your caffeine sample, using a Mel-Temp apparatus.

Answer 1

OH OH Caffeine aspirin Paracetamol or acetaminophen acidic nature Base Acid Caffeine, Aspirin, Paracetamol dichloromethane Filtrate Precipitate Paracetamol Caffeine, Aspirin NaOH Organic layer aqueous layer Caffeine Aspirin sodium salt HCI Aspirin Paracetamol is not dissolved in dichloromethane, it is filtered and collected. Filtrate has Caffeine and Aspirin, Aspirin is acid reacts with base NaOH forms salt goes to aqueous layer. After neutrlization with base from the salt in aqueous layer Aspirin can be separated. Organic layer contains Caffeine, can be isolated by removing dichloromethane.