A 2-l., three-necked flask is equipped with an efficient mechanical stirrer, a gas-inlet tube extending almost to the bottom of the flask, and an efficient reflux condenser fitted with a calcium chloride drying tube. After the apparatus has been dried in an oven, 800 ml. of dichloromethane (Note 1) and 157 g. (142 ml., 2.00 moles) of acetyl chloride (Note 2) are added to the flask. This solution is stirred while 320 g. (2.40 moles) of powdered, anhydrous aluminum chloride (Note 3) is added in portions over a 15-minute period. As soon as this addition is complete, a stream of propene gas (Note 4) is passed through the continuously stirred reaction solution at a rate sufficient to maintain a gentle reflux. The gas flow is continued until no more heat is evolved and refluxing ceases (10–30 hours, (Note 4), at which time the flask is nearly full and the contents separate into two layers after stirring is stopped. The contents of the flask are poured cautiously onto about 1.5 kg. of ice (Note 5), and the upper organic layer is separated. The aqueous phase is shaken with three 100-ml. portions of dichloromethane (Note 6), and the combined organic solutions are washed with 50 ml. of water and dried over anhydrous magnesium sulfate.

The resulting dark brown solution is placed in a 2-l., round-bottomed flask equipped with a thermometer, a magnetic stirring bar, a heating mantle, and an assembly consisting of a distilling head, a condenser, and a receiver which permits distillation under reduced pressure. The bulk of the dichloromethane and volatile hydrocarbons are distilled from the mixture at water-aspirator pressure while sufficient heat is supplied with the heating mantle, maintaining the temperature of the mixture at about 0° (Note 7). When the bulk of the solvent has been removed, a 1-l., round-bottomed flask, cooled in a 2-propanol–dry ice bath, is attached to the apparatus as a receiver, and the pressure is reduced to 1 mm. or less with a vacuum pump. With the heating mantle, the temperature of the viscous liquid in the distillation flask is raised slowly from about 0° to 45° over a period of 90 minutes, distilling the volatile products (dichloromethane, low molecular-weight hydrocarbons, 4-chloropentan-2-one, and 3-penten-2-one) (Note 7). The resulting distillate (400–500 g. of pale green liquid) is mixed with 256 g. (1.98 moles) of quinoline (Note 8) and heated to boiling. To remove the remaining dichloromethane and other low-boiling materials (Note 9), liquid is allowed to distil from the mixture until the temperature of the distilling liquid reaches 110–120°. The remaining solution is refluxed for 30 minutes, then cooled and diluted with the previously removed distillate and 200 ml. of pentane. The resulting solution is washed with successive 250-ml. portions of 10% hydrochloric acid until the aqueous washings are acidic. The aqueous washings are combined, acidified, and shaken with three 100-ml. portions of pentane. The combined organic solutions are washed with 50 ml. of saturated aqueous sodium hydrogen carbonate and dried over anhydrous magnesium sulfate. The resulting organic solution is fractionally distilled through a 30-cm. Vigreux column, and 42–63 g. (25–37%) of crude product is collected in the fraction boiling at 119–124°. This contains 3-penten-2-one of 86–92% purity (Note 10). If greater purity is desired, the crude product may be distilled through a 60-cm., spinning band column. Since this distillation may be accompanied by partial isomerization of the α,β-unsaturated ketone to the lower boiling β,γ-isomer (Note 10), the product from the fractional distillation should be subjected to an acid-catalyzed equilibration. In a typical purification 79.4 g. of a mixture of penten-2-one isomers, b.p. 117–119°, from a fractional distillation, is mixed with 400 mg. of p-toluenesulfonic acid and refluxed for 30 minutes. The resulting mixture is diluted with 100 ml. of diethyl ether and washed with 50 ml. of saturated aqueous sodium hydrogen carbonate and dried over anhydrous magnesium sulfate. The resulting ether solution is fractionally distilled through a 16-cm. Vigreux column, giving 60.4 g. of trans-3-penten-2-one of 97% purity, b.p. 121.5–124°, n²⁵D 1.4329 (Note 11).