Organic Syntheses, CV 2, 276
[Sebacic acid, ethyl acid ester]
Submitted by Sherlock Swann, Jr, René Oehler, and R. J. Buswell.
Checked by Lee Irvin Smith and J. W. Clegg.
1. Procedure
In a
1-l. modified Claisen flask (Note
1), the side arm of which is corked, is placed a mixture of
202 g. (1 mole) of sebacic acid,
150 g. (0.58 mole) of diethyl sebacate (Note
2),
50 cc. of di-n-butyl ether (Note
3), and
30 g. (25 cc.) of concentrated hydrochloric acid (sp. gr. 1.19). A
reflux condenser is connected to the top of the distilling flask.
The flask is heated in a
Wood's metal bath at 160–170° until the mixture is completely homogeneous. The temperature of the bath is then lowered to 120–130°, and
60 cc. (1 mole) of 95 per cent ethyl alcohol is added to the solution through the condenser. The mixture is allowed to reflux for two hours. At the end of this period an additional
20-cc. portion of ethyl alcohol is poured into the solution and refluxing is continued for two hours longer.
The Wood's metal bath is allowed to cool to about 75° and the reaction mixture is subjected to distillation under reduced pressure, using a
water pump (Note
4). The temperature of the bath is increased slowly and distillation is continued, with a water pump, until the bath reaches a temperature of about 125°. The bath is again cooled to 75–80° and the distillation is continued at lower pressure, using an
oil pump.
The first fractions consist of a little alcohol, water, and
n-butyl ether (Note
5). The next fraction is
ethyl sebacate, b.p.
156–158° at 6 mm. (Note
6).
Ethyl hydrogen sebacate is collected at
183–187° at 6 mm. The product melts at
34–36° and weighs
114–124 g. (
50–54 per cent of the calculated amount, based on the
sebacic acid used). Refractionation of the fore-run (b.p.
175–183°/6 mm.) and after-run (b.p.
187–195°/6 mm.) gives an additional
24–26 g. of pure monoester. The total yield is
138–150 g. (
60–65 per cent of the theoretical amount) (Note
7) and (Note
8).
2. Notes
1. The
column of the flask should be at least 35 cm. in length and well insulated. Wrapping the column with 10-mm. asbestos rope is satisfactory.
2. The addition of diester at the beginning of the reaction decreases its formation from the reactants so that the monoester becomes the main product.
3.
n-Butyl ether is used in preference to other possible compounds because it permits the formation of a homogeneous reaction mixture.
4. At the beginning of the distillation the liquid in the flask foams excessively. It is advisable, therefore, to reduce the pressure gradually and not to use low pressures until the foaming subsides.
5. The
n-butyl ether may be recovered in pure condition by a simple distillation after the water has been separated from it.
6. After the
ethyl sebacate has distilled, it is well to drain the cooling water from the condenser in order to prevent the monoester from solidifying before reaching the
receiver. The recovered
ethyl sebacate weighs
150–175 g. and may be used directly in a subsequent preparation.
7. In subsequent runs the distillation residue is allowed to remain in the flask. In this way the yield is increased to
70–77 per cent for runs of one and two moles.
8. The submitters report that
ethyl hydrogen adipate, b.p.
155–157°/7 mm., has been prepared in
71–75 per cent yields on a one-mole scale by the same procedure.
3. Discussion
This preparation is referenced from:
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