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).