Checked by C. R. Noller
1. Procedure
In a
1-l. round-bottomed, three-necked flask fitted with an efficient
reflux condenser,
liquid-sealed stirrer, and
dropping funnel is placed
13 g. (0.53 gram atom) of magnesium turnings. A
few cubic centimeters of a solution of 60 g. (42 cc., 0.55 mole) of pure ethyl bromide in
50 cc. of absolute ether is added and the stirrer started (Note
1). When the bromide begins to react
200 cc. of absolute ether is added, and then the balance of the bromide solution is run in as fast as the refluxing permits (about one-half hour). After allowing fifteen minutes for the completion of the reaction, a solution of
40 g. (0.42 mole) of 2,4-dimethylpyrrole (p. 217) in
100 cc. of absolute ether is added in the course of twenty minutes (Note
2) and the mixture is refluxed for one-half hour on the
steam bath.
The reaction mixture is cooled to room temperature, and a solution of
58 g. (51 cc., 0.53 mole) of freshly distilled ethyl chloroformate (b.p.
92.5–93.5°) in
100 cc. of absolute ether is added dropwise in the course of one-half hour (Note
3). The mixture is heated on the steam bath for one and one-half hours and then allowed to stand overnight at room temperature.
The flask is placed in an ice-salt mixture, and the contents are decomposed by the gradual addition of
300 cc. of saturated ammonium chloride solution and 100 cc. of water (Note
4). The aqueous layer is removed by means of a
1.5-l. separatory funnel, and sufficient
ether is added to dissolve the yellow precipitate. The total volume of
ether solution is about 1 l. This is washed with two 200-cc. portions of water, and the three aqueous layers are extracted consecutively with a
100-cc. portion of ether. The combined
ether solution is dried over
30 g. of anhydrous sodium sulfate, concentrated on the steam bath to a volume of about 200 cc., and cooled to room temperature. The product which crystallizes is collected with suction and washed with two
25-cc. portions of ether. The yield is
35–38 g. of light yellow product, m.p.
122–123°. The
ether is completely removed from the combined filtrates by heating on the steam bath, and the black oil is allowed to stand overnight. The semi-solid mass is filtered with suction and washed with a minimum amount of cold
ether. In this way an additional
6–7 g. of yellow material is obtained which melts at
119–121°.
The combined crude material is crystallized from
75 cc. of 95 per cent alcohol and yields
37–39 g. of slightly colored material, m.p.
123–124°. A second crystallization from alcohol gives
34–36 g. of colorless product melting at the same temperature. By the systematic working of the alcoholic mother liquors, an additional
5–6 g. of pure material is obtained, making the total yield
40–41 g. (
57–58 per cent of the theoretical amount).
2. Notes
1. Stirring is continued without interruption throughout the preparation to the point where the mixture is allowed to stand overnight.
2. The reaction is not exothermic, but the large volume of
ethane evolved necessitates the regulated addition of the solution of
dimethylpyrrole.
3. Considerable heat is produced during the addition of about two-thirds of the solution, after which the addition may be more rapid.
4. The first third of the
ammonium chloride solution must be added quite slowly with frequent and thorough shaking.
3. Discussion
Appendix
Compounds Referenced (Chemical Abstracts Registry Number)
1-[2,4-dimethylpyrrole-5]-2,4-dimethylpyrrole-5-carboxylic acid
alcohol (64-17-5)
sulfuric acid (7664-93-9)
ether (60-29-7)
ammonium chloride (12125-02-9)
magnesium turnings (7439-95-4)
Ethyl bromide (74-96-4)
sodium sulfate (7757-82-6)
sodium ethoxide (141-52-6)
ethyl chloroformate (541-41-3)
2,4-Dimethyl-5-carbethoxypyrrole,
2-Pyrrolecarboxylic acid, 3, 5-dimethyl-, ethyl ester (2199-44-2)
2,4-Dimethylpyrrole (625-82-1)
ethane (74-84-0)
dimethylpyrrole
2,4-Dimethyl-3,5-dicarbethoxypyrrole (2436-79-5)
5-trichloroaceto-2,4-dimethylpyrrole
2,4-dimethylpyrrole-5-aldehyde
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved