Checked by Homer Adkins and Robert H. Jones.
1. Procedure
In a
3-l. three-necked round-bottomed flask fitted with a Hershberg stirrer and a thermometer are placed
1500 ml. of acetic anhydride and
300 g. (306 ml., 3.80 moles) of dry pyridine (Note
1).
Three hundred grams (4.6 gram atoms) of zinc dust (Note 2), in amounts of 5–10 g., is added with stirring over a period of 3 hours. Heat is evolved almost immediately, and a
cooling bath of water may be necessary. The reaction mixture becomes green after about 20 minutes. The temperature of the contents of the flask should be maintained between 25° and 30°. After the addition of the first
300-g. portion of zinc,
300 ml. of acetic acid is added to the reaction mixture and a
reflux condenser is attached to the flask. Then
120 g. (1.83 gram atoms) of zinc dust is added in small portions. Heat is evolved during the addition, and the reaction may become rather violent. The mixture is refluxed with stirring for 30 minutes. A third portion of
180 g. (2.75 gram atoms) of zinc dust is added all at once, and refluxing is continued for an additional half hour. The solution is now orange-brown.
The flask is allowed to cool, and the contents are transferred to a
5-l. round-bottomed flask. The mixture is cautiously neutralized with
2 l. of a 40% aqueous solution of sodium hydroxide. The mixture is steam-distilled until 3 l. of distillate is collected, after which the residue is discarded. The distillate, which separates into two layers, is saturated with
1.5–1.8 kg. of solid potassium carbonate (Note
3). The organic layer is removed by decantation; the remaining water layer is divided into two portions, and each is extracted once with
150 ml. of chloroform. The
chloroform extracts are combined with the organic layer.
The mixture is distilled using an
efficient fractionating column (Note
4). There is a large fore-run of
chloroform,
pyridine, and water (Note
5), after which the temperature rises and
145–167 g. of material, b.p.
145–165°/760 mm., is collected. This is refractionated, and
135–155 g. (
33–38%) of
4-ethylpyridine, b.p.
163–165°/760 mm.,
n20D 1.5010, is obtained (Note
6).
2. Notes
2. The
zinc is activated before use by stirring
830 g. of zinc dust in 300 ml. of 10% hydrochloric acid for 2 minutes, filtering, and washing the
zinc with 600 ml. of water, then with
200 ml. of acetone.
4. A
Fenske-type column 30 cm. in length and 18 mm. in diameter packed with glass helices gave satisfactory separations.
3. Discussion
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