Checked by William S. Johnson and Duane Zinkel.
1. Procedure
In a
1-l. round-bottomed flask, fitted with a
thermometer extending nearly to the bottom, are placed
60 g. (1 mole) of urea and
69 g. (0.5 mole) of 95% n-heptanoic acid (Note
1). A
condenser (Note
2) is attached to the flask, and the mixture is heated by means of an electric mantle. When the temperature reaches 140°, the
urea is in solution, and a rather vigorous evolution of gas occurs which continues for several minutes. The temperature is maintained at 170–180° for 4 hours (Note
3), and then the mixture is allowed to cool.
As soon as the temperature drops to 110–120°,
400 ml. of 5% sodium carbonate solution is added carefully through the condenser, and the mixture is shaken vigorously (Note
4). The mixture is cooled in an
ice bath, and the product is collected on a
Büchner funnel. The solid, when dry, is slightly colored, and weighs
57–64 g., m.p.
85–91°.
The crude material is boiled for a few minutes with
200 ml. of 95% ethanol and a small amount of
decolorizing carbon (Note
5). The mixture is filtered by gravity, and 800 ml. of water is added to the filtrate. The resulting slurry is cooled in an
ice-salt bath and the solid is collected by filtration on a Büchner funnel. The product, which is almost colorless is air-dried. It weighs
44–48 g. (
68–74%) and melts at
91–94° (Note
6). Evaporation of the filtrate under reduced pressure and reprecipitation of the residue from
20 ml. of 95% ethanol and 80 ml. of water affords an additional
3–4 g. (
5–6%) of material which melts at
90–93°.
2. Notes
2. A condenser should be chosen which has an inside diameter of at least 1.5 cm.; otherwise frequent loosening of the sublimate is required to prevent clogging. A 3-ft., air-cooled tube with an internal diameter of about 2.5 cm. serves as a satisfactory condenser.
3. Temperatures below 170° lead to slightly lower yields, and temperatures above 180° cause excessive sublimation of
urea. Although the reaction is nearly complete after 2 hours, the yield appears to be improved by additional heating.
4. Failure to make the mixture basic leads to the formation of a greasy, colored product.
5. A small amount of solid does not dissolve in the alcohol.
6. Recrystallization from dilute
ethanol affords colorless material, m.p.
94–95°.
3. Discussion
The procedure described is based on the method of E. Cherbuliez and F. Landolt,
9 by which formic and acetic acids were converted into the corresponding amides.
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