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DOI:10.15227/orgsyn.070.0226

Organic Syntheses, Coll. Vol. 9, p.570 (1998); Vol. 70, p.226 (1992).

2-METHYL-1,3-CYCLOPENTANEDIONE[1,3-Cyclopentanedione, 2-methyl-]

Submitted by Philip G. Meister, Matthew R. Sivik, and Leo A. Paquette1.
Checked by David L. Coffen

1. Procedure
CAUTION! These operations result in the evolution of considerable amounts of hydrogen chlorideand should therefore be performed in a well-ventilated hood
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 (Note3). Stirring is begun and 1000 g (7.50 mol) of anhydrous aluminum chloride (Note 4) is added, followedby an additional 500 mL of dry nitromethane. After the reaction mixture cools to room temperature, thegas 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 ofhydrogen chloride gas which may cause the mixture to foam. Small quantities of the acid should beadded 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 dissolvedin 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 bysuction filtration and air-dried to give 157–171 g (56–61%) of 2-methyl-1,3-cyclopentanedione (Note9). The mother liquors are concentrated to approximately 1.5 L by rotary evaporation. The solution isboiled until crystals form, cooled in ice, and filtered to give an additional 20–23 g (7–8%) of product(63–69% overall yield).

2. Notes
1. Efficient stirring is mandatory.
2. The top of the condenser is equipped with a gas outlet leading via an oil bubbler into a large alkalibath or to a water aspirator. A steady stream of nitrogen should be maintained at all times.
3. Commercial nitromethane was dried over calcium chloride, filtered, and distilled. The forerun wasdiscarded. The checker used 96% spectrophotometric grade as received from Aldrich ChemicalCompany, Inc.
4. Aluminum chloride, which was obtained from Fluka Chemical Corporation, generates heat duringdissolution.
5. Succinic acid was obtained in powdered form from Fluka Chemical Corporation. If granular succinicacid is to be used, it should be pulverized to aid in dissolution.
6. Propionyl chloride was purchased from Fluka Chemical Corporation and Aldrich ChemicalCompany, Inc.

7. Two 17-cm Büchner funnels should be used simultaneously. However, if left to digest overnight, themixture can be conveniently filtered using a 3-L sintered glass funnel.
8. Use of a 17-cm Büchner funnel preheated with hot tap water has proven most convenient for thispurpose. The checker used an oven-heated, 3-L sintered glass funnel layered with Celite.
9. The crystals are off-white to tan, mp 211–212°C. It appears to exist in the enol form: 1H NMR (200MHz, CDCl3/d6-DMSO) δ: 1.05 (s, 3 H), 2.0 (s, 4 H), 10.7 (s, 1 H).

Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory";
National Academy Press; Washington, DC, 1995.

3. Discussion
A variety of methods have been published to achieve the preparation of 2-methyl-1,3cyclopentanedione.2,3,4,5,6 The present method, which was first reported by Schick, Lehmann, andHilgetag,4 provides for the acquisition of large amounts of the product in a single step from inexpensive
starting materials. The alternative multistep procedures are appreciably more laborious and costly.
The importance of the title compound as an intermediate in organic synthesis goes unquestioned,having been produced on an industrial scale. The syntheses and reactions of this class of compounds
have recently been summarized in an extensive review of the subject.7
The success of the present process appears to rest on the facility with which intermediate 1 is
produced and its capacity for ready intramolecular cyclization.4

References and Notes
1.
2.
3.
4.
5.
6.
7.

Department of Chemistry, The Ohio State University, Columbus, OH 43210.
Orchin, M.; Butz, L. W. J. Am. Chem. Soc. 1943, 65, 2296.
Grenda, V. J.; Lindberg, G. W.; Wendler, N. L.; Pines, S. H. J. Org. Chem. 1967, 32, 1236.
Schick, H.; Lehmann, G.; Hilgetag, G. Chem. Ber. 1969, 102, 3238.
John, J. P.; Swaminathan, S.; Venkataramani, P. S. Org. Synth., Coll. Vol. V 1973, 747.
Hengartner, U.; Chu, V. Org. Synth., Coll. Vol. VI 1988, 774.
Schick, H.; Eichhorn, I. Synthesis 1989, 477.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);(Registry Number)brine
calcium chloride (10043-52-4)

hydrogen chloride (7647-01-0)
nitrogen (7727-37-9)
Succinic acid (110-15-6)
carbon (7782-42-5)
aluminum chloride (3495-54-3)
toluene (108-88-3)
Nitromethane (75-52-5)
propionyl chloride (79-03-8)
1,3-Cyclopentanedione, 2-methyl-,2-Methyl-1,3-cyclopentanedione (765-69-5)
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