Experiment #2: Steam Distillation of Essential Oils
Chemistry 102
Background:
Distillation consists of heating a liquid until it vaporizes, and then condensing the vapor and collecting it in a separate container. Distillation is used to separate mixtures of liquids that either have different boiling points, or that have one component that does not distill. There are many types of distillation, each of which has a distinct purpose. Steam distillation is used to isolate volatile substances that have high boiling points. When two immiscible liquids are distilled together, the amounts of each component in the distillate are constant. Also, the boiling point of the mixture is lower than that of either of the individual components. This is because the components do not have compatible intermolecular forces, and so the component in lesser concentration will form “bubbles”, like oil droplets in water, weakening the overall intermolecular forces in the mixture, and thus lowering the boiling point. This process allows high-boiling compounds, which can decompose before they boil if heated alone, to be distilled at temperatures below 100C.
Steam distillation is one of the methods used for obtaining essential oils from various substances. Essential oils are used widely in foods, fragrances and medicines. These oils consist primarily of fragrant compounds that are most often aromatic compounds and/or aldehydes, phenols, esters and alkenes. Because one of the components in steam distillation is water, the boiling point of the mixture should be less than 100C. In this experiment you will isolate the essential oil from one of the following sources: cloves, cinnamon, lemon peel or orange peel. Typically, cloves contain 10-15% eugenol and cinnamon contains around 5% cinnamaldehyde (not sure how much limonene is typically in citrus peel). Cloves will be provided in the lab, but you must bring your own if you want to do one of the other three. Cinnamon sticks are best (not powder) if you choose that one. You will isolate your oil from the distillate using a method called extraction. Extraction consists of partitioning the components of a mixture between two immiscible liquids in order to separate the components. The structures of the primary components of each of these essential oils are shown below:
Materials:
5 g cloves (or cinnamon, lemon peel or orange peel from home), 100 mL round-bottom flask, water condenser, distillation head, thermometer adapter, vacuum adapter, thermometer, heating mantle, power supply, 50 mL graduated cylinder, 2 beakers, 2 erlenmeyer flasks, clamps for glassware, Keck clamps (blue plastic), mortar and pestle (or scissors), 125 mL separatory funnel and watch glass
Safety Precautions:
Dichloromethane is not flammable, nor is it considered carcinogenic, but it can cause liver damage if ingested, or with repeated inhalation or skin exposures. It should be used in the fume hoods (inhalation of vapors can cause nausea or drowsiness). Avoid spills; it can also pass through both latex and nitrile gloves.
Procedures:
1. Prepare the spice. Weigh out approximately 5 grams of your spice and record the mass. If you are using cinnamon sticks you should break them up into small pieces and grind them up a bit with a mortar and pestle. If you are using citrus peels you should cut them up with scissors. If you are using cloves you should grind them up a bit with a mortar and pestle.
2. Set the 100 mL round-bottom flask in the heating mantle and clamp it to a ringstand. Place two boiling chips in the flask; add your spice to the flask; add about 50 mL of distilled water.
3. Assemble the rest of the distillation apparatus (see figure on page 4, your set-up will be similar), connecting the pieces with the clips provided. Make sure the entire thermometer bulb is below the sidearm of the distillation head. Water should go in on the lower side of the condenser and exit on the upper side. You may want to clamp the loose hose end over the sink so it doesn’t spray the lab. Place the Erlenmeyer flask below the end of the condenser to receive the condensed liquid.
4. Heat the flask with the heating mantle so that the liquid boils gently. Record the temperature when the first drop comes over. Try to obtain a steady rate of distillation, around 1 drop per 2-3 seconds. If you approach the boiling point too quickly, or boil too hard, you may get frothing and or bumping, which can contaminate your distillate. Every so often transfer the distillate from the Erlenmeyer to a graduated cylinder. Continue distilling until you have collected about 30 mL of distillate. Record the temperature again at the end of collection.
5. Remove the flask from the heat and turn off the heating mantle. Let the apparatus cool before taking it apart. The small clamps go back in the box. The blue clamps for the glassware go back in their box on the cart. Dry off the thermometers and put them back. The glassware should be rinsed with water, and then placed in the dirty glassware bin.
6. Place all of the distillate into a separatory funnel. Add 10 mL of dichloromethane, shake, and allow the layers to separate. Collect the dichloromethane in a clean Erlenmeyer flask (the dichloromethane will form the bottom layer). Do not collect the middle emulsion layer. Repeat this 2 more times. On the third extraction, shake more gently and allow more time for the emulsion to clear. Rinse the sep funnel with water and place it in the dirty glassware bin.
7. Add a few small scoops of drying agent (sodium sulfate); add until the drying agent no longer clumps together when swirled (should look like a snow-globe). Allow to stand for 10-15 minutes, stirring occasionally.
8. Carefully decant the liquid into a clean, pre-weighed beaker, trying not to pour over any of the solid. If time permits, evaporate the dichloromethane with a gentle stream of nitrogen (or air, if nitrogen is not available) while heating to around 40C. Or, if time is up, place a cover loosely over the beaker and leave to dry in the hood until the next class period. When it is dry, weigh the beaker + oil and record the mass.
9. Calculate the mass of the oil and the percent by mass recovery (based on the mass of the spice used).
Waste Disposal:
Aqueous solutions may be diluted and flushed down the drain with plenty of water. Allow the dichloromethane to evaporate from the drying agent and then place it in the solid waste container. Put solid spice residues in the trash (do not wash down the sink as they may cause a clog). Place any extra dichloromethane into the organic waste container.
Pre-Lab:
Prepare your notebook as described in the lab notebook handout. Include: name, partner’s name, title of experiment, date, purpose, structure of compound to be isolated (based on which spice you choose), procedures (bulleted list), sketches of glassware set-ups, separation scheme (flow chart) and data (make spaces to record masses, volumes and temperatures). Leave spaces for observations.
Report:
1. In your notebook, write a brief discussion of the experiment. In this section you should summarize your results (mass of oil obtained and % recovery), note any interesting observations (odor and color of oil) and make any possible conclusions about the experiment (successful vs. unsuccessful and reasons why). Be sure to compare your results to the expected results (quantitatively, if possible).
2. Answer the post-lab questions.
3. Make a copy of your lab notebook pages (do not tear out the originals) and attach the questions (if on a separate page). Staple all pages and turn it in.
Post-Lab Questions:
1. Why does the distillate that you collect initially appear cloudy (hint, see Ch. 9)?
2. Why does the dichloromethane form the bottom layer during the extraction step (hint, see Ch. 1)?
3. What is a drying agent and how does it work (hint, see Ch. 9)?
4. Would you expect to get all of the essential oil out of your spice using the procedures in this lab? Why or why not?