Org. Synth. 1936, 16, 60
DOI: 10.15227/orgsyn.016.0060
PELARGONIC ACID
Submitted by E. Emmet Reid and John R. Ruhoff.
Checked by W. W. Hartman and G. W. Sawdey.
1. Procedure
A
5-l. three-necked flask is fitted with a
liquid-sealed mechanical stirrer,
reflux condenser,
dropping funnel, and
thermometer. In the flask is placed
2.5 l. of anhydrous butyl alcohol (Note 1), and
115 g. (5 gram atoms) of clean, bright sodium cut in small pieces is added at one time. Solution of the
sodium may be facilitated by stirring, but heating is unnecessary. After the
sodium has dissolved completely, the solution is allowed to cool to 70–80°, and then
800 g. (5 moles) of redistilled ethyl malonate (b.p.
135–136°/100 mm.) is added rapidly with stirring. After heating the reaction solution to 80–90°,
913 g. (5.1 moles) of pure heptyl bromide (
p. 247, b.p.
179–180°) is added. The bromide should be added rather slowly at first, until precipitation of
sodium bromide begins; it may then be added at such a rate that the
butyl alcohol refluxes gently. Usually about one hour is required for the introduction of the
heptyl bromide. The mixture is refluxed gently until it is neutral to litmus (about one hour).
The entire mixture, including the precipitated
sodium bromide, is transferred to a
12-l. flask together with a small amount of water used to rinse the reaction flask. A solution of
775 g. (12.5 moles) of 90 per cent potassium hydroxide in an equal weight of water is added slowly with shaking. The mixture is heated cautiously, with occasional shaking, until refluxing starts
(Note 2), and refluxing is continued until saponification is complete (about four or five hours). The flask is fitted at once for steam distillation
(Org. Syn. Coll. Vol. I, 1941, 479), and the mixture is distilled until no more
butyl alcohol passes over
(Note 3). To the residue
1350 cc. (15.5 moles) of concentrated hydrochloric acid (sp. gr. 1.18) is added carefully, with shaking, and the mixture is refluxed for about one hour
(Note 4). After cooling, the water layer is siphoned off and discarded
(Note 5).
The oil obtained in the preceding step is transferred to a 3-l. round-bottomed flask and heated under an air-cooled reflux condenser in an oil bath at about 180°. When the evolution of carbon dioxide has ceased (about two hours), the oil is decanted from a small amount of solid material. The solid residue on treatment with 200–300 cc. of concentrated hydrochloric acid gives an additional small quantity of oil which is added to the main portion.
The crude pelargonic acid is distilled in a modified Claisen flask having a fractionating side arm, and the material boiling at 140–142°/12 mm. (188–190°/100 mm.) is collected. The yield is 525–590 g. (66–75 per cent of the theoretical amount). The melting point of the pure acid is 12–12.5° (Note 6).
2. Notes
1.
Commercial
butyl alcohol was dried over solid
potassium carbonate and distilled through a
90-cm. indented column. The portion boiling at
117–118° was used.
2.
Two layers are formed at first, but the solution becomes homogeneous as saponification occurs. Boiling chips should be placed in the flask, and heating should be done carefully at first, with occasional shaking, or the reaction may get beyond control.
3.
The flask should not be allowed to cool between saponification and distillation. It is advisable to heat the flask to prevent the volume of distillate from becoming too large. Usually about 7 l. of distillate is collected, from which the
butyl alcohol can be recovered.
4.
When the oily layer ceases to increase, decomposition of the
potassium heptylmalonate is complete. A layer of salt sometimes accumulates at the bottom of the flask. Care must be taken in heating to prevent cracking the flask.
5.
It is unnecessary to extract the aqueous layer with an organic solvent.
6.
n-Caproic acid may be prepared by this method from
n-butyl bromide in similar yields (see also
p. 417). In this preparation a partial decomposition of the substituted
malonic acid is brought about by refluxing the aqueous solution in the 12-l. flask after the addition of the
hydrochloric acid.
Butylmalonic acid is appreciably soluble in water, and separation of the oily layer does not occur until the
malonic acid has been largely decomposed to
caproic acid. The time required is about eight to ten hours. It is advisable to heat the acid layer under air reflux as in the preparation of
pelargonic acid.
3. Discussion
Pelargonic acid has been prepared by the oxidation of
oleic acid1 and by hydrolysis of
octyl cyanide2 or
heptylacetoacetic ester.
3
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
heptylacetoacetic ester
potassium carbonate (584-08-7)
hydrochloric acid (7647-01-0)
n-butyl bromide (109-65-9)
sodium bromide (7647-15-6)
carbon dioxide (124-38-9)
butyl alcohol (71-36-3)
potassium hydroxide (1310-58-3)
sodium (13966-32-0)
Caproic acid,
n-caproic acid (142-62-1)
ethyl malonate (1071-46-1)
Malonic acid (141-82-2)
oleic acid (112-80-1)
Heptyl bromide (629-04-9)
Pelargonic acid (112-05-0)
potassium heptylmalonate
Butylmalonic acid (534-59-8)
octyl cyanide (2243-27-8)
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