A.
Dimethyl 3-chloro-2-pentenedioate. A dry,
500-ml., three-necked, round-bottomed flask fitted with a
ground-glass stopper, a
condenser provided with a gas bubbler, a
gas-inlet adapter attached to a
nitrogen (or
argon) source, and a
magnetic stirring bar, is charged with
60.0 g. (0.297 mole) of diethyl acetone-1,3-dicarboxylate (Note
1). A steady, gentle flow of
nitrogen is started through the reaction vessel (Note
2), and
65.0 g. (0.313 mole) of phosphorus pentachloride (Note
3) is added in thirteen, approximately equal portions through the stoppered joint to the neat diester at 3-minute intervals with vigorous stirring (Note
4). After the addition is complete, the reaction mixture is warmed to 40° in a
water bath for 30 minutes. The red solution is cooled in an
ice bath and poured onto
ca. 100 ml. of ice in a
500-ml. Erlenmeyer flask immersed in an ice bath. A
1 : 1 mixture of water and dichloromethane is used to rinse traces of the product from the reaction vessel into the Erlenmeyer flask, and the resulting mixture is stirred for 15 minutes (Note
5). After separating the two layers, the aqueous phase is extracted with three
100-ml. portions of dichloromethane, and the combined organic extracts are dried over anhydrous
sodium sulfate. Filtration through glass wool and removal of solvents with a
rotary evaporator affords
ca. 60 g. of a red oil, which is placed in a 500-ml., round-bottomed flask containing
20 ml. of concentrated sulfuric acid in
300 ml. of anhydrous methanol (Note
6), and the solution is refluxed using a heating mantle for 18 hours. Excess
methanol (200 ml.) is distilled, and the residual yellow solution is cooled to room temperature and poured into 100 ml. of water.
Sodium chloride is added to saturation, and the solution is extracted with eight
100-ml. portions of diethyl ether. The combined extracts are washed successively with
150 ml. of aqueous saturated sodium hydrogen carbonate and
150 ml. of aqueous saturated sodium chloride, dried over anhydrous
sodium sulfate, and filtered. Concentration of the extract with a rotary evaporator affords a yellow oil which is distilled, yielding
33.5–34.4 g. (
59–60%) of
dimethyl 3-chloro-2-pentenedioate2 as a colorless liquid, b.p.
50–60° (0.02 mm.) (Note
7).