Organic Syntheses, CV 2, 371
Submitted by C. S. Marvel and J. C. Eck.
Checked by Louis F. Fieser and C. H. Fisher.
1. Procedure
The rearrangement of
120 g. (1.06 moles) of pure cyclohexanone oxime (Note
1) is carried out in twelve 10-g. portions according to the procedure given in the first eight lines of
(B), p. 77.
The acid solutions of
ε-caprolactam from the twelve runs are combined in a
3-l. round-bottomed flask which is fitted with a mechanical stirrer and a separatory funnel and packed in an ice-salt mixture. The solution is cooled to 0° and carefully made faintly alkaline to litmus by the addition of
24 per cent potassium hydroxide solution, added very slowly (five to six hours) with good cooling (Note
2). Usually about 1550 cc. of the alkaline solution is needed. The temperature must be kept below 10° to avoid hydrolysis during this stage of the preparation.
The
potassium sulfate which has separated is then removed by filtration and washed with two
100-cc. portions of chloroform. The faintly alkaline aqueous solution is extracted with about five
200-cc. portions (Note 3) of chloroform, and the combined
chloroform solutions are washed once with 50 cc. of water to remove any alkali. The
chloroform is then distilled and the product fractionated under reduced pressure. The yield of
2-ketohexamethylenimine, boiling at
127–133°/7 mm. and melting at
65–68°, amounts to
71–78 g. (
59–65 per cent of the theoretical amount) (Note
4).
2. Notes
3. The extraction is continued until no appreciable amount of product is obtained in the
chloroform layer.
4. The boiling point is reported in the literature as
139–140°/12 mm.; the melting point is reported at various temperatures from
65° to 70°.
3. Discussion
This preparation is referenced from:
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