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Chamras Glendale Community College Chemistry 106 Laboratory

Experiment: Steam Distillation (Extraction of Essential Oil of Mint)

Introduction: a) Essential oils: An essential oil is a mixture of volatile as well as non-volatile organic compounds present in plants. An oil is "essential" in the sense that it contains the "essence of" the plant's fragrance, the characteristic fragrance of the plant from which it is derived. Essential oils are generally extracted by steam distillation. They are used in perfumes, cosmetics, soaps, food, and other products. Essential oils have been used medicinally in history. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer and often are based solely on historic accounts on use of essential oils for these purposes. Claims for the efficacy of medical treatments, and treatment of cancers in particular, are now subject to regulation in most countries. As the use of essential oils has declined in evidence-based medicine, interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that claims that essential oils and other aromatic compounds have curative effects.

b) Steam Distillation: Steam distillation is ancient technique, still in use as the primary means for extraction of essential oils. Although newer, more efficient techniques have been developed, due to ease of operation and the low cost associated, steam distillation remains as the most common technique. The chemistry (and physics) behind steam distillation could be explained, in the following way: Since water and the organic compounds of essential oils are not miscible, at the boiling point of water, the vapors of volatile organic compounds are simply carried by the water vapor. The vapor pressure of these volatile compounds is not affected by the presence of water vapor. Please review/study Raoult’s and Dalton’s laws. The essential oils do not obey Raoult’s law, because they are not miscible with water. You may find the following educational link useful: http://www.askiitians.com/iit-jee-solutions/raoults-law/ You may also want to read further on Raoult’s and Dalton’s laws. Procedure:

a) Set up for the distillation apparatus: Obtain a bunch of mint. Separate the mint leaves, cut them into half and fourth using a pair of scissors. Measure the mass of the cut mint leaves, and transfer them quantitatively into a triple-neck round-bottom flask. Add enough deionized water to approximately one-half capacity of the flask. Set up the apparatus according to the picture 1 below: As seen in picture 1, the set-up resembles simple distillation, with the difference that there is a separatory funnel connected to the round-bottom flask. The funnel is used as water replenishment container. When the water level goes down in the distillation flask, it could be replenished through the funnel. A 50mL round-bottom flask is used as distillation receiver.

*NOTE: All the junctions that will be exposed directly to the steam should be greased (vacuum grease) to prevent the steam from escaping into the room. Over-greasing however could be detrimental since it could result in contamination of the distillate by grease. Your instructor will demonstrate how to grease glassware junctions.

*NOTE: the heating mantle should always obtain power through a variable autotransformer (Variac). Never connect it directly to a regular power outlet.

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Picture 1: Macro-scale apparatus for steam distillation.

b) Steam distillation: Once the apparatus is correctly assembled, turn on the heat and start the steam distillation. Similar to any other form of distillation, a moderate dropping rate of the distillate is desired. A rapid rate of distillation will not result in a good recovery of the essential oil of mint. Record the temperature at the point of distillation. Collect approximately 30mL of distillate. *NOTE: Although not shown in the picture1 above, it is recommended to place the receiving flask in an ice bath, to minimize the loss of the distillate due to evaporation.

c) Disassembling the apparatus: Upon completion of distillation, turn off the heating mantle and separate it from the apparatus by lowering the big jack. Allow the water to run in the condenser and the apparatus to cool to touch for 5-10 minutes.

d) Isolation and purification: Quantitatively transfer the contents of the receiving flask into a separatory funnel. Rinse the flask with 5mL of dichloromethane and add to the contents of the funnel. Extract the oil using three 10mL portions of dichloromethane. Combine the organic layers and discard the aqueous layer. Wash the organic layer with two 10mL portions of brine solution. Dry the organic layer with anhydrous sodium sulfate. Filter the dried organic layer into a tared 100mL Kjeldahl flask. Rinse the filtered sodium sulfate with a fresh 2mL portion of dichloromethane and add it to the dry organic layer. Evaporate the solvent using rotatory evaporation (Rotovap), and measure the mass of recovered oil.

Product Analysis:

The following analyses need to be performed on the final product: 1. Measurement of mass; calculation of percent recovery. 2. IR spectroscopy.

To be included in laboratory report:

1. Results and discussion from Product Analysis section above. 2. Calculation for mass of oil per gram of mint leaves.