Acetyl chloride & Acetic anhydride FAQ From: (Nick Coffey) Date: 1996/01/25 newsgroups: alt.drugs.chemistry Hi kids, time for a new one. Here's how to make acetic anhydride and acetyl chloride. Why? Because its fun! And...you can make your own aspirin. Acetyl Chloride Connect a dry 250 ml three neck flask with a distillation adapter, condenser and addition funnel. Use a 250 ml rb falsk for the receiver connected to the condenser with a vacuum adapter. Use the vacuum adapter to make a gas trap with rubber tubing to an anhydrous CaCl2 drying tube exiting to an inverted funnel suspended over a beaker of water. This important stage is to protect the distillate from water while absorbing HCl evolved in the reaction. Place 54 g. (52 ml.) of glacial acetic acid in the three neck flask, close with a stopper and add slowly through the addition funnel 46 g. (29 ml.) of phosphorus trichloride. Cool the flask by immersion in a water bath. Mix the reactants thorougly and, after allowing the mixture to stand for ten minutes, heat the water bath to 40-50º and maintain it at this temperature for thirty minutes, with occasional swirling of the flask. During the heating the liquid usually separates into two layers. Acetyl chloride forms the upper layer. Distill the acetyl chloride by heating the water bath to boiling and maintaining it at that temperature as long as any liquid passes over. Cool the receiver in an ice bath during the distillation. The syrupy residue in the distilling flask is phosphorous acid, which is discarded. --> CAUTION: The reaction mixture must not be overheated since this will lead to formation of phosphine, which is spontaneously flammable in contact with air. To the distillate add two drops of glacial acetic acid, to destroy mixed phosphorous-acetic anhydrides that would cause turbidity to develop on standing. Redistill the acetyl chloride from a distillation apparatus arranged as before except without the addition funnel and with a thermometer. Collect separately in a dry receiver the portion boiling at 50-56º and transfer it to a dry weighed glass-stoppered bottle. Acetyl chloride attacks corks and rubber stoppers. The yield is 44-56 g. Acetic Anhydride The apparatus for this process is similar to that used for the preparation of acetyl chloride. The same precautions for exclusion of moisture must be observed but it is unnecessary to provide the inverted funnel arrangement, since hydrogen chloride is not evolved. In a 250ml. rb flask fitted as for making acetyl chloride, place 60 g. of finely pulverized anhydrous sodium acetate.* Arrange in place the condenser, dry receiving flask and drying tube; the receiver need not be cooled. Check to insure that all connections are tight. Cool the reaction flask in a bath of cold water and add dropwise, through the addition funnel, 40 g. (36 ml.) of acetyl chloride. Afer the addition has been completed, remove the water bath and shake the flask to obtain good mixing of the reactants. Recheck the connections for tightness. Dry the outside of the flask with a towel and heat it with a mantle or oil bath. Continue the heating until no more distillate comes over but do not overheat the solid residue. To the distillate add 4-6 g. of finely powdered anhydrous sodium acetate, to react with a small amount of acetyl chloride that may be present. Add a boiling chip and redistill the crude acetic anhydride. Collect the product distilling at 132-138º in a dry flask. The yield is 30-40 g. * NB: Commercial anhydrous sodium acetate usually contains some moisture. To remove moisture fuse 70-80 g. in a casserole and stir until no more water is evolved. Do not overheat! Cool and quickly pulverize. Store in a tightly sealed container before use.