Organic Syntheses, CV 5, 689
DL-KETOPINIC ACID
[1-Apocamphanecarboxylic acid, 2-oxo-]
Submitted by Paul D. Bartlett and L. H. Knox
1.
Checked by John D. Roberts
1. Procedure
A
4-l. beaker containing a solution of
100 g. (0.95 mole) of anhydrous sodium carbonate in 900 ml. of water is placed on a
steam bath, provision being made for efficient mechanical stirring. The stirrer is started and, when the solution is hot, one-third of a solution of
100 g. (0.63 mole) of potassium permanganate in 600 ml. of hot water is added all at once, followed by a
34-g. portion of DL-10-camphorsulfonyl chloride (Note
1). After an interval of 5–10 minutes, half the remaining permanganate is poured in, followed by
33 g. of the chloride. After a similar interval, the remaining permanganate solution and a final
33-g. portion of the chloride are added and heating is continued for an hour.
The excess permanganate is destroyed by adding a few milliliters of an acidified solution of
sodium sulfite. The reaction mixture is cooled and made strongly acidic by cautious addition (foaming may occur) of
20% sulfuric acid. The mixture is heated, and the precipitated
manganese dioxide is dissolved by stirring in powdered
sodium sulfite (usually 70–80 g. is required). The resulting solution is cooled and extracted with one
200-ml., two 150-ml., and one 100-ml. portions of ether. The combined
ether extracts are dried over anhydrous
sodium sulfate and the bulk of the ether removed by distillation from a steam bath. The residue is evaporated in a
crystallizing dish (Note
2). The crude acid (
38–45 g.) is recrystallized from hot water. Considerable oiling may occur and 250–400 ml. of water is usually required to give complete solution. The yield of recrystallized acid is
28–32 g. (
38–43%), m.p.
233–234° (Note
3).
2. Notes
1. The
camphorsulfonyl chloride is the crude product obtained as described on
p. 196. If it is not carefully dried, it should be oxidized reasonably promptly after its preparation. The oxidation is conveniently carried out in 100-g. portions. Several reactions can easily be carried out in parallel.
2. The checker found it convenient to use a
rotary evaporator at this point.
3. An additional small crop of crystals may be obtained by concentration of the mother liquor. The checker observed m.p.
240–242°.
3. Discussion
4. Merits of the Preparation
Ketopinic acid is of interest as a β-keto acid which fails to decarboxylate readily.
8 It may be converted to
apocamphane-1-carboxylic acid.
7
This preparation is referenced from:
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