A dry,
5-L, three-necked, round-bottomed flask equipped with a
nitrogen inlet,
mechanical stirrer (Note
1), and an
efficient reflux condenser (Note
2) is charged with
500 mL of dry nitromethane (Note
3). Stirring is begun and
1000 g (7.50 mol) of anhydrous aluminum chloride (Note
4) is added, followed by an additional
500 mL of dry nitromethane. After the reaction mixture cools to room temperature, the gas inlet is replaced with a
Gooch tube attached to a
500-mL filter flask containing
295 g (2.5 mol) of powdered succinic acid (Note
5). The
nitrogen line is now attached to the sidearm of this flask. The
succinic acid is introduced in portions during 1.5 hr
(CAUTION: This process evolves a large volume of hydrogen chloride gas which may cause the mixture to foam. Small quantities of the acid should be added at a time and the foaming should be allowed to subside prior to introduction of the next amount). The mixture is stirred for 2 hr and the Gooch tube is replaced by a
500-mL pressure-equalizing addition funnel equipped with a nitrogen inlet.
Propionyl chloride (650 mL, 694 g, 7.5 mol) (Note
6) is added dropwise during 30 min and the reaction mixture is brought to reflux for 2 hr, cooled, and poured onto 4 L of crushed ice. After the precipitated brown solid is cooled in an
ice bath, it is separated by filtration (Note
7) and washed with
250 mL of brine and
250 mL of cold (0°C) toluene. The material is dissolved in 7 L of boiling water containing
20 g of decolorizing carbon, then filtered while still hot (Note
8). The filtrate is concentrated to a volume of 5 L, then cooled in an ice bath. The crystals are collected by suction filtration and air-dried to give
157–171 g (
56–61%) of
2-methyl-1,3-cyclopentanedione (Note
9). The mother liquors are concentrated to approximately 1.5 L by rotary evaporation. The solution is boiled until crystals form, cooled in ice, and filtered to give an additional
20–23 g (
7–8%) of product (
63–69% overall yield).