A 3-l., three-necked, round-bottomed flask fitted with a dropping funnel (Note 1), a mechanical stirrer, and a distillation head with a thermometer and efficient Liebig condenser is charged with 1.4 l. of xylene (Note 2). The xylene is stirred and heated to boiling with a heating mantle, while 179 g. of a solution containing 43 g. (0.80 mole) of sodium methoxide in methyl alcohol (Note 3) is added over 20 minutes. During this period 450 ml. of solvent is distilled.

After addition is complete, 300 ml. of xylene is added and the distillation continued until the vapor temperature rises again to 138°. During that time an additional 250 ml. of distillate is collected, leaving a white suspension to which 18 ml. of dimethylsulfoxide is added. A solution of 100 g. (0.633 mole) of ethyl 4-oxohexanoate (Note 4) in 200 ml. of xylene is then added (Note 1) to the vigorously stirred sodium methoxide suspension over 25 minutes, while 900 ml. of distillate is collected continuously, maintaining the vapor temperature at 134–137°. The orange-colored mixture is stirred and heated for an additional 5 minutes, then cooled to room temperature. Addition of 165 ml. of water with vigorous stirring over a 5-minute period (Note 5) gives two clear phases, which are cooled in an ice bath and acidified by adding 82 ml. (0.98 mole) of 12 N hydrochloric acid with vigorous stirring. After the mixture is stirred at 0° for another 1.5 hours, the crystalline product is collected by suction filtration and carefully washed successively with 100-ml. and 50-ml. portions of ice-cooled diethyl ether (Note 6).

The crude product is dissolved in 1 l. of boiling water, and the solution is filtered quickly through a preheated fritted-disk funnel (Note 7). The filtrate is concentrated on a hot plate at atmospheric pressure to a volume of 550–600 ml. and allowed to stand at 0° overnight. The crystals are collected by filtration and dried at 85°, yielding 50.0–50.6 g. (70–71%) of 2-methyl-1,3-cyclopentanedione, m.p.210–211° (Note 8).