Draft Version 5/7/99

Friedel-Crafts acylation: For this week's reaction, your TA will assign you one of the aryl substrates shown in the below reaction scheme. The procedure given for this experiment will work for all of these substrates.

Safety Precautions: This reaction is to be carried out in a hood. Measurements of anhydrous aluminum chloride and acetyl chloride need to be done in the hood. Precautions should be taken to prevent inhalation of the aluminum dust or acetyl chloride vapors. Both aluminum chloride and acetyl chloride are noxious, corrosive and reacts violently with water. Place your reaction set-up in the back half of the hood since HCl (g) is liberated.

Friedel-Crafts acylation experimental procedure:

1. In a hood, assemble the following reaction apparatus shown in figure 1. Use a 25 mL round bottom flask, Claisen head, drying tube, syringe with needle, 14/20 septum and spin vane. Charge a vial with 1.0 mL of the assigned aromatic compound. Weigh this vial and then cap and set aside for later use. 2. During the reaction, HCl gas is given off which needs to be diluted in water. Thus, attach a tube to the end of the drying tube (not shown in figure 1) with the end of the tube exiting into the sink. Allow a slow steady stream of water to flow through the sink. 3. To the apparatus, add 4 mL methylene chloride, 1.6 g anhydrous aluminum chloride. Stir the mixture. [DO NOT weigh the aluminum chloride. The store room will tape a vial loaded with 1.6 g of aluminum chloride. Use this vial to approximate the amount needed. Do this in the hood!] 4. Charge your syringe with 1.0 mL of acetyl chloride and inset into the 14/20 septum of the apparatus (as shown in figure 1). Slowly add the acetyl chloride over a 2-3 minute period. 5. Using the same syringe, add 1.0 mL of the aromatic compound over a 6-8 minute period. The reaction liberates heat so add slowly. Use 1 mL of methylene chloride to rinse the vial and then add this rinse to the reaction mixture. Stir the reaction for an additional 5 minutes.

Figure 1.

The Work-Up:

1. Transfer the reaction mixture to a 50 mL Erlenmyer flask. To the reaction mixture, slowly add 8 mL of ice cold water over a 5 minute period. Then add 8 mL of concentrated HCl. Using a glass rod, stir vigorously until all the aluminum salts dissolve.

2. Next, allow the layers to separate and isolate the lower organic layer in a centrifuge tube. A second transfer to another centrifuge tube may be necessary if any of the aqueous phase is present. [If no organic layer is observed then add more methylene chloride. Up to 4 mL of methylene chloride my be needed.]

This step may be tricky and require some patients since the methylene chloride and water form an emulsion. If an emulsion forms and cannot be broken up then transfer to a plastic centrifuge tube and centrifuge between 2-3 minutes (make sure to use a counter weight).

3. Rinse the organic layer with 2 mL of 5% sodium bicarbonate. Repeat this process until no more carbon dioxide is given off.

4. Dry the organic layer using anhydrous sodium sulfate. The organic layer should be clear.

5. Add several boiling stones and evaporate off the methylene chloride using a hot water bath. Methylene chloride boils at 35 °C. Your product boils at a considerably higher temperature. Thus, when the boiling ceases (and the volume is constant) then most of the methyl chloride will be gone (there will be some methylene chloride left over due to solvation).

Vacuum Distillation:

1. First, place some steel wool in the lower neck of the Hickman head as shown in figure 2. It is critical that none of the steel wool fibers stick out of the lower joint or above the lip of the Hickman head. Use scissor to trim off the fibers. This plug will prevent the liquid from bumping over during the distillation.

Figure 2.

2. With the steel wool plug present, pre-weigh the Hickman head.

3. In a hood, assemble the following vacuum distillation apparatus shown in figure 3 (notice that there is no compression cap connecting the Hickman to the conical vial). After lightly greasing all the joints, place the set-up under vacuum checking for leaks. 4. To the set-up add the crude product and several boiling stones. Slowly place the set-up under vacuum. Foaming is an indication that methylene chloride is being driven off. 5. Once under full vacuum and there is no more observed foaming then heat to 200-225 °C. 6. Supplemental heat will be needed to drive over the liquid. Using a heat gun to direct a stream of hot air on the neck of the lower Hickman head. This is need to drive the liquid out of the steel wool. [The steel wool has a lot of surface area and will act like a sponge adsorbing the liquid during the distillation process. Thus, the heat gum will help drive the liquid out of the steel wool]. 7. When there is no more liquid left in the conical vial remove the heat. 8. Determine the weight and calculate your % yield. Obtain an IR spectrum.

Figure 3.