Org. Synth. 1941, 21, 13
Submitted by Jonathan W. Williams and John A. Krynitsky.
Checked by Nathan L. Drake and Joseph Lann.
One hundred and sixteen grams (126 ml., 1 mole) of n-caproic acid is placed in a 250-ml. gas-washing bottle. The bottle is supported in an ice bath, and 0.50 to 0.55 mole of ketene is passed into the acid at a rate of approximately 0.45 mole per hour (Note 1) and (Note 2).
The resulting mixture is transferred to an apparatus for fractional distillation, and carefully fractionated, an oil bath being used for heating (Note 3). A low-boiling fraction, consisting of acetone containing some ketene, acetic acid, and a small quantity of acetic anhydride, is removed at atmospheric pressure. As the distillation progresses the temperature of the oil bath is raised to 220° over a period of about 1 hour and held there until 3 hours has elapsed from the time distillation started (Note 4).
The distillation at atmospheric pressure is then discontinued, the liquid is allowed to cool somewhat, and distillation is continued at a pressure of 3–10 mm. After a fore-run of less than 20 g., n-caproic anhydride is collected (b.p. 109–112°/3 mm., 118–121°/6 mm.). The yield is 86–95 g. (80–87%) (Note 5).
may be generated conveniently, at the proper rate, in the apparatus described by Williams and Hurd.1
Addition of 1 mole of ketene
per mole of acid does not increase the yield. Under these conditions more acetic anhydride
is found in the low-boiling fraction.
Submitters and checkers used a column of the Whitmore-Lux type
12 mm. in diameter, 50 cm. long, packed with glass helices, and provided with the usual jackets for heating. A less efficient column will serve in the preparation of caproic anhydride
but not in the preparation of propionic anhydride
or butyric anhydride
by the same method.
It is imperative to continue the distillation at atmospheric pressure until conversion of any mixed anhydride to caproic anhydride
is complete. The acetic acid
formed by this conversion comes off very slowly, and approximately 3 hours is necessary to complete the distillation at atmospheric pressure.
According to the submitters, equally good yields can be obtained in the preparation of propionic anhydride
and n-butyric anhydride
has been prepared by heating caproic acid
with acetic anhydride
by heating sodium caproate
and acetic anhydride
in a sealed tube
by the action of phosphorus oxychloride
on barium caproate
by the action of acetyl chloride
on caproic acid
and by treating a mixture of sodium caproate
The method used in the present synthesis was first described by Hurd and Dull.8
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
acetic acid (64-19-7)
acetic anhydride (108-24-7)
acetyl chloride (75-36-5)
Phosphorus Oxychloride (21295-50-1)
n-caproic acid (142-62-1)
n-butyric anhydride (106-31-0)
propionic anhydride (123-62-6)
n-CAPROIC ANHYDRIDE (2051-49-2)
sodium caproate (10051-44-2)
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