A. Fatty acids. In a 1-l. Erlenmeyer flask are placed 250 ml. of dynamite-grade glycerin (Note 1) and 40 g. (0.71 mole) of potassium hydroxide. The mixture is heated to 120–140° and is shaken by hand until the alkali is dissolved. To the hot solution there is added, in one portion (Note 2), 110 ml. (100 g., 0.11 mole) of sunflower-seed oil (Note 3) and (Note 4) which has been preheated to 110–115°. The hot solution is swirled vigorously until saponification is complete (Note 5). This is indicated by the formation of a permanent lather. After the mixture has cooled somewhat, 150 ml. of sulfuric acid (25% by volume) is added cautiously (Note 6) while the flask is swirled. Then 200 ml. of hot water is added, and, if necessary, the mixture is heated until the layer of fatty acid is clear. The water layer is removed, the acid layer is washed with two 500-ml. portions of hot water, and then it is filtered with the aid of suction through a large Hirsch funnel which is heated by a steam or hot-water jacket. The acids (90–95 g.) (Note 7) are dried thoroughly by heating them rapidly to 130°, with stirring.

B. Tetrabromostearic acid. In a 4-l. beaker equipped with a mechanical stirrer the above fatty acids are dissolved in 2 l. of petroleum ether (Note 8), and the solution is chilled to 0–10°. After 20–25 minutes, the solution deposits about 10 g. of solid saturated fatty acids, which are removed by rapid filtration with gentle suction. The filtrate is transferred to the 4-l. beaker and cooled to 0–10°. Then, with stirring, 30.7 ml. (90 g., 0.56 mole) of bromine (Note 9) is slowly introduced from a dropping funnel (Note 10). The bromine is added at such a rate that the temperature remains between 10° and 15°; about 20 minutes is usually required. Tetrabromostearic acid begins to separate toward the end of the addition. The solution, which should contain a slight excess of bromine (reddish color), is allowed to remain in the ice bath for 15–20 minutes (Note 11). The precipitate settles rapidly, and a large portion of the liquid is removed by decantation, after which the precipitate is finally collected with suction on a 12.5-cm. Büchner funnel and is washed with 200 ml. of petroleum ether. The solid is then thoroughly stirred with 300 ml. of petroleum ether (Note 12) in a 600-ml. beaker and is filtered as before. The gray-white tetrabromide, after being dried at 50°, is transferred to a 2-l. beaker and dissolved in 90–100 ml. of hot ethylene dichloride (Note 13). The solution is filtered through filter paper and allowed to crystallize at room temperature. The solid is removed by filtration and is washed on the funnel with 200 ml. of fresh petroleum ether. The tetrabromide is transferred to a glass plate and is worked to a powder (Note 14) with a spatula. The needle-shaped crystals are snow-white, with a silvery sheen, and have a melting point of 114.7–115.2°. The yield (Note 15) is 35–40 g. (32–36%) (Note 16). The product should be stored in brown screw-top bottles and kept away from sunlight.

C. Ethyl linoleate. In a 300-ml. Erlenmeyer flask are placed 26–30 g. of recrystallized tetrabromostearic acid, 85 ml. of absolute ethanol, and 30 g. of granulated zinc (20 mesh). This mixture is warmed gently until the debromination reaction begins. Since the reaction is exothermic, it is usually necessary to moderate it from time to time by dipping the flask into a basin of cold water. The vigorous reaction subsides in about 5 minutes, after which the flask is fitted with a reflux condenser and the mixture is refluxed for 30 minutes. In order to esterify the linoleic acid, 10 ml. of a 4 N solution of hydrochloric acid in ethanol (Note 17) is poured into the refluxing mixture through the top of the condenser, and successive 5-ml. portions are then added every 30 minutes for 2 hours. At the end of this time the solution is removed from the unchanged zinc by decantation into another flask. The zinc is washed with 15 ml. of absolute ethanol to complete the transfer of the solution. A 10-ml. portion of 4 N ethanolic hydrochloric acid is added and the solution is refluxed for an hour, with addition of a second 10-ml. portion of ethanolic acid after 30 minutes. The mixture is poured into 300 ml. of hot, saturated brine solution in a 500-ml. separatory funnel, and the crude ester is allowed to settle for 10–20 minutes. The brine layer is removed, and the ester is washed (Note 18) at room temperature with 300 ml. of 0.5% sodium carbonate solution. The rather stable emulsion is broken by centrifuging the solution, in 100-ml. tubes, for 5 minutes at 3300 r.p.m. The ester and any remaining emulsion are washed with 80 ml. of warm water, and the emulsion is again broken by centrifuging. Washing is continued (Note 19) until the wash water is neutral to methyl orange. The neutral ester is then transferred to a 50-ml. distilling flask and is distilled under reduced pressure; boiling point, 175°/2.5 mm., 193°/6 mm. The product is water-white (Note 20), gives a negative Beilstein test, has an iodine value (Wijs, 30-minute exposure) of 162.3–162.5, an n_D48 of 1.4489, and a true specific gravity of 0.8846 at 15.5/4°. The yield (Note 15) is 12–15 g.

D. Linoleic acid. The ester is dissolved in 200 ml. of a 5% ethanolic (Note 21) solution of sodium hydroxide in a 400-ml. beaker and is allowed to saponify overnight at room temperature. The resulting jelly is dissolved in 200 ml. of warm water, and a slow stream of carbon dioxide is introduced, beneath the surface of the liquid, while it is acidified with 50 ml. of dilute sulfuric acid (1:1 by volume). The stream of carbon dioxide is maintained throughout the subsequent operations. The linoleic acid rises to the surface as a clear layer. The water layer is siphoned off; the acid is washed once with hot water and then dried over anhydrous sodium sulfate and preserved under carbon dioxide. The yield is 10–12 g. of material having a melting point of −8° to −9° (Note 22).