Org. Synth. 1941, 21, 48
DOI: 10.15227/orgsyn.021.0048
ETHYL 1,16-HEXADECANEDICARBOXYLATE
[Octadecanedioic acid, diethyl ester]
Submitted by Sherlock Swann, Jr., René Oehler, and P. S. Pinkney.
Checked by Lee Irvin Smith, James W. Horner, Jr., and J. W. Clegg.
1. Procedure
To
86.5 g. (0.38 mole) of ethyl hydrogen sebacate [Org. Syntheses Coll. Vol. 2, 276 (1943)] is added slowly and with cooling
125–130 ml. of approximately 3 N potassium hydroxide. The solution is then diluted to approximately 250 ml., yielding a
1.5 N solution of potassium ethyl sebacate.
The solution of potassium ethyl sebacate (Note 1) is poured into a 500-ml. tall beaker provided with a cooling coil (Note 2), a thermometer, a stirrer, a platinum sheet anode 45–55 sq. cm. in area (Note 3), and two platinum wire cathodes (Note 4). To the solution 10 g. of monoethyl sebacate (Note 5) is added.
The electrodes are connected to a suitable source of direct current, 10 amperes of which is allowed to pass through the cell. To the solution there is now added 40 g. more of monoethyl sebacate in portions of 10 g. each over a period of 10 minutes (Note 6). The temperature of the cell is held below 50° by running cold water through the cooling coil (Note 7).
The run is finished in 60–70 minutes. The reaction will have reached completion when a few drops of the electrolyte removed with a pipet show an alkaline reaction to phenolphthalein. The alkalinity should be tested every 10 minutes after the first 45.
When the electrolyte has become alkaline, the oily product floating on the top is removed by means of a pipet (Note 8). The oil is washed with an equal volume of 10% potassium carbonate (Note 9), then with an equal volume of 3.5% hydrochloric acid, and finally twice with half its volume of water (a little ether effectively breaks up any emulsions which may form at this point). It is then crystallized from methanol, filtered by suction, and washed twice while in the funnel with ice-cold methanol (Note 10). The product, snow-white and waxy in appearance, is dried in a desiccator over sulfuric acid. The yield is 16–22 g. (40–55%) of material melting at 41–42°. These figures for the percentage yields, however, are based only upon the 50 g. of ethyl hydrogen sebacate used in the second part and no account is taken of the 86.5 g. used in preparing the electrolyte solutions. This preparation becomes practicable, therefore, only when several consecutive runs are made (Note 8).
2. Notes
1.
The reaction mixture may require slight warming on the
water bath to make a homogeneous solution.
2.
The checkers used a
copper cooling coil. This was slightly attacked during the electrolysis: the solution became blue, and
copper deposited on the cathodes.
3.
Convenient dimensions for the anode are 3.75 by 6.0 cm. (the area of the anode [both sides] used by the checkers was 52 sq. cm.). Care should be taken to submerge it in the solution to a depth such that the oil that gathers on the top of the solution during the electrolysis will not insulate it, thus increasing the current density. The wire tab of the platinum sheet may be sealed into a glass tube so that only the sheet is exposed to the solution.
4.
The cathodes should be equidistant from the anode to ensure uniform current density on both sides of the anode.
5.
As the
potassium salt of monoethyl sebacate is decomposed during the electrolysis, the free acid forms new salt. The alkalinity of the solution may, therefore, be used as the end point of the electrolysis.
6.
If the
50 g. of monoethyl sebacate is added all at once, excessive foaming will occur.
7.
Addition of more water (50 ml.) makes possible a much better control of the temperature.
8.
If it is desired to prepare larger amounts of product, more free acid may be added to the solution without turning off the current after the product has been drawn off by the pipet. Between ten and fifteen batches of
monoethyl sebacate may be converted in this way. The length of time for a run will gradually increase with the number of runs. After ten to fifteen runs, the time required to convert a 50-g. batch is 3.5–4 hours. The electrolyte should then be renewed.
9.
Unchanged mono ester may be recovered by acidification of the carbonate washings, followed by extraction with
ether.
10.
About the same amount of by-product as main product is in solution in the
methanol. The first material that crystallizes is pure main product.
3. Discussion
Diethyl 1,16-hexadecanedicarboxylate has been prepared by the electrolysis of
potassium ethyl sebacate1 and by the electrolysis of a mixture of
sodium and hydrogen sebacates.
2
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
sodium and hydrogen sebacates
potassium carbonate (584-08-7)
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
methanol (67-56-1)
ether (60-29-7)
platinum (7440-06-4)
copper (7440-50-8)
potassium hydroxide (1310-58-3)
phenolphthalein (77-09-8)
Ethyl hydrogen sebacate,
monoethyl sebacate (693-55-0)
ETHYL 1,16-HEXADECANEDICARBOXYLATE
Octadecanedioic acid, diethyl ester,
Diethyl 1,16-hexadecanedicarboxylate (1472-90-8)
potassium ethyl sebacate,
potassium salt of monoethyl sebacate
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