Org. Synth. 1992, 70, 226
DOI: 10.15227/orgsyn.070.0226
2-METHYL-1,3-CYCLOPENTANEDIONE
[1,3-Cyclopentanedione, 2-methyl-]
Submitted by Philip G. Meister, Matthew R. Sivik, and Leo A. Paquette
1.
Checked by David L. Coffen
1. Procedure
CAUTION! These operations result in the evolution of considerable amounts of hydrogen chloride and 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 (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).
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 alkali bath 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 was discarded. The checker used 96% spectrophotometric grade as received from Aldrich Chemical Company, Inc.
4.
Aluminum chloride, which was obtained from Fluka Chemical Corporation, generates heat during dissolution.
5.
Succinic acid was obtained in powdered form from Fluka Chemical Corporation. If granular
succinic acid is to be used, it should be pulverized to aid in dissolution.
6.
Propionyl chloride was purchased from Fluka Chemical Corporation and Aldrich Chemical Company, Inc.7.
Two
17-cm Büchner funnels should be used simultaneously. However, if left to digest overnight, the mixture 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 this purpose. 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 (200 MHz, CDCl
3/d
6-DMSO) δ: 1.05 (s, 3 H), 2.0 (s, 4 H), 10.7 (s, 1 H).
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
A variety of methods have been published to achieve the preparation of
2-methyl-1,3-cyclopentanedione.
2,3,4,5,6 The present method, which was first reported by Schick, Lehmann, and Hilgetag,
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.
7The 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
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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