A solution of
270 g. (4.8 moles) of potassium hydroxide in 150 cc. of water is prepared in a
3-l. round-bottomed flask,
120 g. (0.5 mole) of crude 2,4-dimethyl-3,5-dicarbethoxypyrrole (p. 202) and a pinch of sand are added, and the whole is mixed thoroughly by shaking. The flask is fitted with a
reflux condenser, and the mixture is heated in an
oil bath at 130° for two to three hours with occasional shaking until the thick paste has become partially liquefied owing to the formation of
dimethylpyrrole.
The flask is next fitted for distillation with superheated steam and with a
separatory funnel for the introduction of water into the center of the flask. A 3-l. round-bottomed flask fitted with a vertical condenser is used as a
receiver (Org. Syn. Coll. Vol. I, 1941, 479). The temperature of the oil bath is raised to 160°, and superheated steam at 220–250° is introduced. The temperature of the oil bath is then gradually raised to 200°. If foaming becomes too great, a few drops of water are added from the separatory funnel, care being taken that the water does not strike the hot glass walls (Note
1). Steam distillation is continued until no more
dimethylpyrrole comes over. This takes from one to two hours, and the distillate amounts to 2.5–3 l. The distillate is extracted once with
200 cc. of ether and three times with 100-cc. portions, and the extract is dried for two hours over
20 g. of anhydrous potassium carbonate. The
ether is removed by distillation from a
100-cc. modified Claisen flask having a 15-cm. fractionating side arm, the solution being added gradually through a separatory funnel. After the
ether is removed the residue is distilled and the fraction boiling at
160–165° is collected. The yield is
27 to 30 g. (
57–63 per cent of the theoretical amount) (Note
2) and (Note
3).