0.1 Extraction of carvone  (Page 3/3)

4) Repeat step 3 with the spearmint leaves extract using a clean pre-wetted piece of filter paper. Transfer this filtrate into a cleaned 50 mL flask.

5) Obtain a TLC plate that contains an indicator (metal or glass backed only) and draw a pencil line about 1 cm from the bottom on the side coated with silica. Draw a parallel line 1 cm from the top. On the lower line, draw four small lines evenly spaced along this line to indicate where you will place your samples.

Label the lines "+" (for (+)-carvone), "-" (for (-)-carvone), "c" (for caraway extract), and "s" (for spearmint extract). See your TA, if you haven't already, about preparing a spotter in lieu of using a capillary tube.

6) Dip the tip of a spotter (or capillary tube) into your caraway extract and quickly dab this tip onto the line where it is labeled“c”. You may find it beneficial to do this under UV light to see how much sample you are placing and how large of a spot you are creating. You should see a very small amount of the caraway extract soak into the plate. For the two extracts, it is a good idea to spot multiple times (or to concentrate your sample) as the amount of carvone in the sample is small. Simply spot, let the solvent evaporate (leaving the sample on the plate), and then spot again at the same location. DO NOT SCRATCH THE TLC PLATE FOR MARKING.

7) Repeat this procedure for the spearmint extract.

8) Now do the same thing with the diluted (+) and (-) carvone standards. Since they are more highly concentrated than your extracts, make sure that you just barely touch the plate with the spotter/capillary tube. Also, you may want to dilute down the sample with more solvent to avoid large, blotchy spots.

9) When you have spotted all four of your samples, obtain about 5 mL of 10% ethyl acetate in hexanes in your 250 mL beaker. Place the beaker on your bench top.

10) Make sure that the solvent is initially below the line you used to spot the plate. Place your TLC plate gently into the beaker. You will see capillary action begin immediately as the solvent rises up the plate.

11) Cover the beaker to prevent evaporation (a watch glass or aluminum foil is sufficient). After a few minutes, the solvent will reach the upper line. Remove the plate and allow the solvent to evaporate.

12) Let the plate dry and then place it under UV light. The spot of carvone should be visible under UV light. Mark the spot by holding a UV light to it and circling all the spots you see in pencil. You should see a carvone spot in all four samples, though it may be larger in some than in others. Note any differences you see. Be sure to record a diagram of your TLC plate in your notebook to the correct scale.

13) You can also stain the plates with p-anisaldehyde stain. This stain turns carvone a reddish brown color while most other compounds turn blue. Therefore, it should be easy for you to identify the carvone spot. Using forceps, dip your plate into the anisaldehyde solution. Wipe off the glass back of the TLC plate with a paper towel, and then use a heat gun to heat the plate. You will see a pinkish color develop over the whole TLC plate and blue or brown spots where the material ran. Be sure not to overheat the plate or it may crack. Once done, check your TLC plate with your TA.

Again, draw a diagram of the stained plates in your notebook and determine the $R_f$ values. Can you find the red-brown carvone spot in all four samples? Can you tell by the spots which enantiomer is contained in spearmint and which is in caraway seeds?

14) Go see the IR demonstration and receive a copy of the IR for both pure carvone samples. Do the two enantiomers have distinctly different peaks? Could you tell the difference between enantiomers based on their IR spectra?

15) Smell the pure samples of + and - carvone and then smell some unused caraway and spearmint leaves. Can you tell by smell which of the enantiomers is from spearmint and which is from caraway?

Extraction of carvone(total 30 points)

On my honor, in preparing this report, I know that I am free to use references and consult with others. However, I cannot copy from other students’work or misrepresent my own data.

…………………………………………………………….. (signature)

Print Name: _________________________________________

1. Which methods that you used in this lab (IR, TLC, and smell) proved to be effective in distinguishing enantiomers? (2 points)

2. Separating enantiomers from a mixture is difficult but possible. Since these compounds have the same melting point, boiling point, and density, as well as other properties, there are few methods that allow a chemist to separate enantiomers. Think of or find a method that will allow a chemist to separate enantiomers. (3 points)

3. What functional groups do you observe in the IR spectrum? (2 points)

4. Circle and name the functional groups in the following molecules. (1 points each for a total of 10 points).

5. Answer the following true or false questions by placing a legible T (for true) or F (for false) in the line provided at left and explain. (2X3= 6 points)

a. ______ The $R_f$ value of the solvent front is always 1.

b. ______ If you are working-up a given reaction and have 100 ml of ether and 100 ml of water in your 500 mL separating funnel, water will be the top layer.

c. ______ The silica gel TLC for compound 3 (shown below) was run in 20% diethyl ether/hexanes. The $R_f$ value will increase if the solvent system is changed to 60% diethyl ether/hexanes.

6. Questions a-d refer to the following TLC diagram: (4 points)

a. In the above TLC, the most non-polar spot is _______.

b. The base line is _______.

c. The solvent front is _______.

d. The $R_f$ value of spot B is _______.

7. The following TLC (run in 40% ${\text{Et}}_{2}O/\text{hexanes}$ ) is of an organic reaction.

The starting material is on the right, the mixed spot is in the middle, and reaction is on the left. (3 points)

(A) What is the $R_f$ of the starting material?

a. 0.30b. 0.60c. 1.75d. 3.5e. none of these

(B) What is the $R_f$ of the product?

a. 0.30b. 0.60c. 1.75d. 3.5e. none of these

(C) Is the reaction complete? a. yesb. no