FIRST-SOLUTION

Preparation of Phenylacetone
(Part One)

Phenylacetone, also known as methyl benzyl ketone, or l-phenyl-2-propanone, is easy to make if one can get the chemicals. In this reaction, phenylacetic acid reacts with acetic anhydride with pyridine catalysts to produce phenylacetone plus carbon dioxide and water. In chemical writing:

Figure 1

Into a clean, dry in flask is placed 200 grams of phenylacetic acid, acetic anhydride and pyridine. This is done on a table covered with a sheet of newspaper, because phenylacetic acid, once it is exposed to the air, smells like cat urine, and the smell is next to impossible

to get rid of. Pyridine also smells awful. The pyridine and acetic anhydride are measured

out in a large glass measuring cup.

                                                                                                 Figure 2

The flask is then gently swirled until the phenylacetic acid is dissolved. The flask is then
assembled with the 50 cm condenser and the vacuum adapter, as shown in Figure 2. Before assembly, the joints are lightly greased with silicone based stop cock grease. This prevents the pieces from getting stuck together. All pieces should be clean and dry. The vacuum nipple of the vacuum adapter is plugged with a piece of tape. In the rounded section of the vacuum
adapter is a plug of cotton, then about two teaspoons of Drierite (anhydrous calcium sulfate),
then another plug of cotton. This makes a bed of Drierite, which is prevented from falling into the flask by a ball of cotton. The purpose of this is to keep moisture from the air away from the reaction.

                                                                                           Figure 3

The pan is filled cooking oil (Wesson works fine), This is so that the flask is heated evenly. The heat is turned about half way to maximum, and the flow of cold water through the condenser is begun. A length of plastic or rubber tubing runs from the cold-water faucet
to the lower water inlet of the condenser. The cold water runs through the condenser and out of the top water exit, through another length of tubing to the drain. In this way, the rising vapors from the boiling pyridine are condensed and returned to the flask.

Within a half hour, the flask is hot enough to begin boiling. then turned down to stabilize the flask After seven hours, the heat is turned off. Twenty minutes after the boiling stops, the
glassware is set up as shown in Figure 4. The cotton and Drierite are removed from the vacuum adapter. Then four pea-sized pieces are broken off a pumice foot stone. They are added to the flask with the reaction mixture in it. But they are not added until 20
minutes after the boiling stops; otherwise they could produce a geyser of hot chemicals .

                                                                                                Figure 4