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%).