Five hundred grams (2.5 moles) of dry, powdered benzanilide (p. 82), 1025 g. (8.5 moles) of technical dimethylaniline, and 525 g. (307 cc., 3.4 moles) of phosphorus oxychloride are mixed (Note 1) in a 3-l. round-bottomed Pyrex flask (Note 2). The flask is fitted with a two-holed cork stopper which carries a reflux condenser and a thermometer. The top of the condenser is provided with a calcium chloride tube; the bulb of the thermometer reaches beneath the surface of the liquid.

The flask is warmed in a water bath until the appearance of a sudden exothermic reaction (Note 3), at which point the flask must be cooled at once by rotating it underneath the surface of cold water. The cooling is continued until the thermometer indicates a temperature of 125° or less. The flask is then immersed in a bath of boiling water for about three hours, after which the mixture is cooled to about 50°, and poured slowly into 2.5 l. of warm (Note 4) dilute hydrochloric acid, made from 325 cc. (about 4 moles) of concentrated acid, contained in a large crock of about 15 l. (4 gal.) capacity. The mixture is left for about three hours until hydrolysis is complete (Note 5).

About 8 l. of water is added to precipitate the p-dimethylaminobenzophenone. The solution, milky at first, soon deposits sandy crystals of light green color, which are collected on a 20-cm. Büchner funnel. They are transferred to a beaker and washed with 1.5 l. of water, after which they are again collected on the filter, washed, pressed as dry as possible, and air dried. With no further purification the melting point is 88–90°. The yield is 350–390 g. An additional 85–100 g. of inferior product, m.p. 70–80°, is obtained by treating the combined filtrates with a solution of 250 g. (6.2 moles) of sodium hydroxide. This product, air-dried as before, is dissolved in 300–400 cc. of hot alcohol from which, by partial evaporation and cooling, more than half separates in good crystalline form, m.p. 88–90.5°. This material may be combined with the first product of similar melting point. The total yield is 410–440 g. (72–77 per cent of the theoretical amount) (Note 6).

The crude product melts fairly sharply, but it is colored light green. The color may be almost completely removed by recrystallization from hot alcohol. The best result is obtained by dissolving 100 g. of the crude product in 600 cc. of boiling alcohol, heating with 5 g. of decolorizing carbon (Norite), filtering, and cooling the solution in an ice-salt bath. The crystals are then separated from the mother liquor by centrifuging (Note 7). The yield of almost colorless crystals melting at 89.5–90.5° is 80 g.