12.1: Preparation and Procedure
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ADVANCE PREPARATION (one week earlier)
Your lab instructor will assign one of the following spices to each group:
1. Weigh 2g of the spice and crack it into smaller pieces. There is no need to grind it into a powder or a paste, just smaller pieces.
2. Place the cracked spice into an erlenmeyer flask and add 15 mL water. Swirl a few times.
3. Seal the flask with parafilm or aluminum foil and allow it to stand in the drawer for a week.
1. Open the flask containing the spice mixture and boil the contents for about 5 min, being careful to control frothing and foaming.
2. Allow the spice bits to settle and pour 5mL of the supernatant a 10 mL round-bottom flask with a spin vane in it.
3. Assemble a distillation apparatus as shown in fig. 18.3, page 753 of your textbook. Use a sand bath instead of the aluminum block.
4. Begin the steam distillation by following the procedure described on page 505 of your textbook under the heading Steam Distillation (about mid page).
5. As the reservoir of the Hickman Head fills up with distillate, draw it out with a pasteur pipette and collect it into a graduated cylinder. At the same time, add more of the spice solution to the round-bottom flask to maintain a level of liquid of about half to two thirds of the flask volume. DO not fill the flask to the neck.
6. Continue the distillation process in this fashion until you have collected about 10mL of distillate.
7. Transfer the distillate to a centrifuge tube and extract the essential oil with methylene chloride as described on page 505 of your textbook under the heading Extraction of the Essential Oil.
8. Combine and dry the organic extracts using anhydrous sodium sulfate.
9. Transfer the organic extract to a small erlenmeyer flask or beaker (about 10mL in size), place it into a hot water bath (at about 80° celsius), place a wooden stick inside the solution, and proceed to evaporate the solvent until all the methylene chloride has been removed from the sample.
10. The boiling point of methylene chloride is about 40°. To make sure all the methylene chloride has evaporated, monitor the temperature inside the spice solution until it reaches about 80°. At the same time make sure you're not losing substantial amount of your product through evaporation (which you should not, because the boiling point of your product is likely above 200°).
11. It is important to evaporate all the methylene chloride because otherwise it will show a strong peak in the NMR spectrum that will interfere with the peaks from your product. The chemical shift of methylene chloride is about 5.3 ppm. Any peaks in this region whose integral is not a multiple of those of the other peaks in the spectrum might be due to residual methylene chloride. A similar reasoning applies to chloroform (a contaminant in deuterated chloroform), whose chemical shift is about 7.2ppm. For a list of NMR solvent chemical shifts see http://www.sdsnmr.com/cs_table.html
12. Record the percent recovery of your essential oil relative to the amount of spice originally weighed. Record an IR spectrum and submit a sample to your instructor for NMR analysis.
13. NMR ANALYSIS: Refer to the recitation notes for exp. 57A. Decide which of the structures shown on page 502 of your textbook best matches your NMR spectrum. Verify that the IR pattern agrees with your choice of structure, and report your conclusion along with your rationale.
NICE WEBSITE FOR ORDERING SPICES, TEAS, OILS, AND OTHER RELATED ITEMS
San Francisco Herb Co.: http://sfherb.com