A. α-Bromo-α-phenylacetone. A 1-l. three-necked flask is equipped with a sealed stirrer (Note 1), a dropping funnel, and a water-cooled reflux condenser provided with a short inverted U-tube on the open end; the equipment is assembled in the hood. In the flask are placed 200 ml. of dry, thiophene-free benzene (Note 2) and 37 g. (36.89 ml., 0.276 mole) of phenylacetone (Note 3). The stirrer is started, and 45 g. (14.42 ml., 0.28 mole) of reagent bromine is added dropwise during a period of 1 hour. The reaction mixture first becomes cloudy but changes to a clear orange-red solution by the time all the bromine is added. After the addition of bromine is complete, a rapid stream of dry nitrogen or carbon dioxide is passed through the solution by means of an inlet tube which now replaces the dropping funnel. The hydrogen bromide issuing from the inverted U-tube at the top of the condenser may be trapped in water in an Erlenmeyer flask or other container adjusted so that the water surface is about 1 cm. below the outlet of the tube. The reaction is complete when no more hydrogen bromide fumes can be detected in the gas issuing from the condenser. This operation requires 3–6 hours. During this period the reaction mixture becomes yellow to green. The benzene solution of α-bromo-α-phenylacetone is then transferred to a dry 500-ml. separatory funnel (Note 4).

B. α,α-Diphenylacetone (Note 5). The reaction flask used in A is again equipped as it was originally, and in it are placed 75 g. (0.56 mole) of anhydrous aluminum chloride (Note 6) and 150 ml. of dry benzene (Note 2). The stirrer is started, and the flask is heated by means of a steam bath so that the benzene boils gently. The benzene solution of α-bromo-α-phenylacetone (Part A) is added dropwise from the separatory funnel to the boiling mixture over a period of 1 hour. After the addition is complete, the almost black reaction mixture is heated to boiling for an additional hour, then cooled and poured with stirring onto 500 g. of crushed ice and 100 ml. of concentrated hydrochloric acid contained in a 2-l. beaker. The deeply colored benzene solution gradually becomes orange-yellow. When the ice has melted, the benzene layer is separated and the aqueous layer is extracted with three 50-ml. portions of ether. The combined ether and benzene solution is washed with 100 ml. of water and then with 100 ml. of saturated sodium bicarbonate solution. After the solution has been dried for at least 1 hour over 60 g. of anhydrous sodium sulfate, the solvents are evaporated on a steam bath until the solution no longer boils. The dark residue is transferred to a 250-ml. Claisen flask equipped for reduced-pressure distillation and having a receiver fused to the side arm (Note 7). The residual benzene is first distilled at 19–20 mm. while the flask is being heated on a steam bath. The steam bath is replaced by an oil or metal bath which is gradually heated to 190°. A small fore-run of yellow oil which darkens rapidly is collected. It is removed from the receiver by siponing and rinsing with acetone. The bath is allowed to cool to 100–120°, the system is evacuated with an oil pump (Note 8), and the diphenylacetone is distilled. The bulk of the material boils at 142–148°/2–3 mm. The distillate may solidify in the receiver (Note 9). The crude product is triturated with just sufficient petroleum ether (b.p. 35–60°) to moisten it, cooled in an ice-water bath, collected on a filter, and washed on the filter with small amounts of petroleum ether at 0–5° until nearly colorless. The amount of petroleum ether used up to this point should not exceed 50 ml. The product is then crystallized from petroleum ether using 8 ml. of solvent per gram of crude, dry solid. The hot solution is allowed to stand at room temperature until crystallization begins, and then at 0–5° for 16 hours (Note 10). The crystals are collected by filtration and dried in air at room temperature. The yield of nearly colorless product melting at 60–61° (Note 11) is 31–33 g. (53–57%).