0.3 Friedel-crafts reaction  (Page 3/3)

Experimental procedure

1. Place 0.25 g. of ferrocene in a 10 mL round-bottom flask containing a magnetic stir bar. Prepare a hot water bath by heating the water to nearly the boiling point while preparing the following reaction mixture.

2. In a fume hood, add 1.0 mL of acetic anhydride and 0.15 mL of 85% phosphoric acid to the flask. The reaction mixture should heat up and darken in color. Swirl the flask, heating occasionally in a hot water bath if necessary, until all the ferrocene dissolves.

3. Attach a reflux condenser then heat the reaction mixture with stirring in the hot water bath prepared in step 1. Heat the mixture for 10 minutes during which time a purple color may develop.

Workup and purification:

4. Pour the reaction mixture onto 2 or 3 cubes of ice in a 400 mL beaker, then rinse the flask with two 5 mL portions of ice water. (A black residue may remain in the flask.) Stir the orange-brown mixture with a glass rod for a few minutes. Any insoluble black material present will be removed in the following steps.

5. Add 6.0 mL of 3 M aqueous NaOH solution, then carefully add solid sodium bicarbonate in small portions until the remaining acid has been neutralized (about 2-3 grams). Use great care to avoid excessive foaming during bicarbonate addition. This step can be done with magnetic stirring, but make sure to use a stirring plate that is not hot. Stir well and crush any lumps to afford a dark-brown suspension.

6. Allow the mixture to stand for 20 minutes, and then collect the crude product by vacuum filtration. Continue to pull air through the product for a few minutes to dry it. Finish the drying process by pressing the solid product between two sheets of filter paper or paper towels. Save some of this crude product for TLC analysis.

7. Transfer the solid and a stir bar to a 50 mL beaker and add 10 mL of hexanes. Boil for 5 minutes with stirring, and then decant the dark-orange solution into another Erlenmeyer flask leaving behind a black gummy substance. If you boil off all the liquid, try again with another 10 mL of hexane and lower heat.

8. To the hot solution, add a spatula-full of decolorizing carbon (If you use too much, you will reduce your yield of carbon). Heat with swirling, and then perform a hot filtration to remove the decolorizing carbon.

9. Set the flask aside to cool slowly. Red-brown needles of acetylferrocene should begin to form. Once the flask has reached room temperature, cool it in ice. Collect the crystalline product by vacuum filtration and washing with a small quantity of cold hexane, then dry by continuing to pull air through the product for a few minutes. If you add to much cold hexane here, you will lose your product.

Characterization:

10. Record the yield and melting point range for your recrystallized acetylferrocene.

11. Analyze your crude and recrystallized products by TLC. Separately dissolve very small amounts of pure ferrocene, the crude product, and the recrystallized acetylferrocene in a few drops of toluene. Spot the solutions on silica gel plates and develop with 30:1 toluene/absolute ethanol. Visualization is simple as each compound is brightly colored.

Safety

Wear safety goggles and gloves all the time.

Waste disposal

Organic compounds must be disposed in the proper container.

Approximate lab time 2 – 2 ½ hours

Report 4: friedel- crafts

(Total 30 points)

(Click here for the Report Form

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’ work or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

1. Draw the mechanism for the reaction of ferrocene, acetic anhydride, and phosphoric acid. (6 points)

2. Show your theoretical and percent yield calculations for the reaction. (3 points)

3. The melting point of your re-crystallized acetylferrocene is: ---- (2 points)

4. Draw the TLC plates and show your $R_f$ calculations (4 points)

5. Classify each of the following species as anti-aromatic, aromatic, or nonaromatic.

Support your answer. (4 points)

6. Ordinarily the barrier to rotation about a carbon-carbon double bond is quite high (40

kcal/mol), but the compound below was observed to have a rotational barrier of only about 20 kcal/mol. Explain this result. (3 points)

7. Propose a mechanism for the following reaction. (8 points)