A 500-ml., three-necked flask equipped with a magnetic stirring bar, a pressure-equalizing dropping funnel, a thermometer, and a 25-cm. Vigreux column attached to a trap cooled in an acetone–dry ice mixture is charged with 100 ml. of diethyl phthalate (Note 1) and 43 g. (0.30 mole) of tetracyanoethylene oxide (Note 2). The dropping funnel is charged with 44 g. (0.30 mole) of distilled n-butyl sulfide, the pressure is reduced to 5–20 mm. with a water aspirator, and the reaction flask is warmed with a 50° water bath. The n-butyl sulfide is added dropwise with stirring over 20–25 minutes, and the internal temperature is maintained at 50 ± 2° by controlling the temperature of the water bath. The reaction is exothermic at the start, but it is necessary to supply heat toward the end of the addition. The internal temperature is increased to 80° over 10–15 minutes after the sulfide has been added. The vacuum on the system is released by the introduction of nitrogen. The solid carbonyl cyanide that has collected in the trap is allowed to warm to room temperature under nitrogen, and 2 g. of tetracyanoethylene oxide (Note 3) and a boiling stone are added. The mixture is then warmed to 50°, and the product is distilled under reduced pressure (5–20 mm.) into a second trap cooled in an acetone–dry ice mixture. Another portion of tetracyanoethylene oxide (1 g.) is added to the distillate, and the carbonyl cyanide is distilled, again under reduced pressure (5–20 mm.), into a distillation flask cooled in acetone–dry ice mixture. Fractionation of the distillate through a 20-cm. column packed with glass helices gives 20.8–21.8 g. (86–91%) (Note 4) of faintly yellow carbonyl cyanide, b.p. 65–66° (Note 5), (Note 6), and (Note 7).