Lab 3-steam distillation carvone PDF

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Tanvi Kulkarni

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Lab 3: Steam distillation of (S)-(+)-Carvone from Caraway seeds and (R)-(-)-Carvone from Spearmint leaves Introduction: The goal of this experiment is to isolate carvone using the steam distillation of spearmint leaves and caraway seeds, which both contain enantiomers of carvone. To make sure that the carvone is isolated from the aqueous mixture we will use the Baeyer test and IR to confirm that functional groups are in carvone. Carvone is the molecule that is found in the oils of the spearmint leaves and caraway seeds, it has two enantiomers. The (R)- enantiomer corresponds to the oil extracted from the spearmint leaves and the (S)-enantiomer corresponds with the caraway seeds. Both enantiomers are exactly the same except for the way they reflect polarized light. They can both rotate the polarized light but they rotate in opposite directions because of the different orientations. The spearmint leaves with their R-(-)-Carvone will rotate the light clockwise while the caraway S(+)-Carvone will rotate it counterclockwise. The asymmetric reactions result in smells that our noses pick up. R-(-)-Carvone from spearmint leaves have a “minty” smell while S(+)-Carvone has a more “earthy” smell. This reflects the idea that the human nose is a chiral environment and can detect the stereochemical differences in compounds.

The major functional groups in the Carvone molecule that we will be isolating through steam distillation are ketone groups, alkene groups, and chiral groups. Steam distillation is used to separate volatile organic compounds that are incompatible with water. Carvone is nonpolar and immiscible with water so when mixed with steam distillation, it results in the partial pressure of each compound being independent of the mole fraction of each substance. This can be proved with Raoult’s law which states that partial pressure is equal to the mole fraction multiplied by the equilibrium vapor pressure. This means the total pressure is going to be higher than the vapor pressure of the component in the mixture and the boiling point of the nonpolar compound will reach a level below the boiling point component. This allows for the carvone to be collected in the steam distillation process. After the sample is isolated, Thin-layer chromatography and IR spectroscopy are used to confirm the presence of carvone in the caraway seed sample and spearmint sample. Using TLC, the isolated carvone sample will be compared to a sample of pure carvone. Their retention factors will be compared in

Tanvi Kulkarni

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order to figure out if the carvone was fully isolated. The IR spectroscopy will be used to confirm whether the functional groups in the isolated sample match the predicted functional groups. Procedure: Steam distillation 1. Each group will be given either caraway seeds or spearmint leaves. When you receive your sample, record which one it is before you begin the experiment. 2. Weigh the sample and record its mass, it should be around 5 grams. Transfer the 5 grams of sample immediately to a 500 ml round bottom flask. 3. Set up the steam distillation apparatus. 4. Add 150 mL of hot water to the sample that is in the flask. Fill the separatory funnel with hot water and do not add the stopper. 5. Heat the flask and place a graduated cylinder below the vacuum adapter which will collect the distillate. 6. Make sure the heating element is hot enough to produce distillate at a steady rate, if it is too hot it will cause splashing or foaming with the condenser. 7. When the constant drip rate is reached, open the stopcock of the separatory funnel and replace the water that has been lost so that the volume in the funnel will remain constant 8. Record the temperature of the distillate for every 10 mL obtained. By the end of the procedure you should have about 75 mL of distillate.

Source: http://ochemlabtechniques.blogspot.com/p/how-steam-distillation-works.html

Procedure: Extraction 1. Add 7 mL of methylene chloride using the separatory funnel and extract the distillate. Extract the distillate by inverting the funnel over itself about 10 times and repeat this twice more. Swirl the separatory funnel gently to see the bottom organic layer separated from the aqueous layer. 2. Combine the methylene chloride extracts into a 50 mL Erlenmeyer flask. 3. Add anhydrous sodium sulfate and swirl in the flask in order to remove the water present. 4. Use dry filtration to remove the sodium sulfate into a separate 50 mL Erlenmeyer flask. 5. Obtain a TLC plate and spot the dried methylene chloride.

Tanvi Kulkarni

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6. Evaporate a majority of the solvent using the heating elements in the hood. By the end of the heating process, you should be left with about 0.5 mL of product a. If you evaporate too much, you can add methylene chloride and reheat until the desire amount is reached 7. The final mixture will be a clear sample of essential oil that is dissolved in methylene chloride. Procedure: Characterization 1. Prep a TLC plate with your sample of isolated oil and a solvent system of hexanes and ethyl acetate and a small amount of an authentic sample of R-carvone. Put a co-spot of the two as well. The UV lamps will help in analyzing the TLC plate. 2. Calculate the retention factor value of the authentic sample and your own sample. 3. Using the TLC plate, place the Baeyer reagent on it and heat with a heat gun. Record colors that come out of it. 4. Hold the plate about a foot away from your face and waft the scent of the oil towards your face. Record your observations. Pre-lab questions 1. Carvone has a carbon chiral center and is a molecule with asymmetry so Carvone will have a higher boiling point than water. Water may have the characteristics of a high boiling point like polarity and hydrogen bonding, it is still a simple molecule in comparison to carvone. Because Carvone's boiling point is higher the vapor pressure is higher. It can be noticed by the distinct smells of both carvones enantiomers. Because the vapor pressure is higher, the smell is stronger and both enantiomers are volatile. 2. I do not expect carvone to be soluble in water because it is a chiral molecule and they dont mix well with polar solvents. Water and carvone have different boiling points so I think it will be difficult to bond the carvone with water if all the water has evaporated before the carvone reaches its boiling point. 3....