C.
Ethyl linolenate. In a
1-l. Erlenmeyer flask 80 g. of the pure hexabromide is dissolved in
190 ml. of absolute ethanol, and
40 g. of granulated zinc (20 mesh) is added. The mixture is refluxed for 1 hour, at the end of which time the solution should be clear. About
10 g. of zinc dust is added, refluxing is continued for a short time, and then
10 ml. of 4 N ethanol-hydrochloric acid (p. 530) is added. Refluxing is continued for 6 hours, and during this time
5 ml. of the ethanolic hydrochloric acid is added every 30 minutes. At the end of 6 hours, the solution is removed from the unchanged
zinc by decantation into another flask, and the
zinc is washed with
15 ml. of absolute ethanol to complete the transfer of the solution. A
10-ml. portion of ethanolic hydrochloric acid is added, and the solution is refluxed for a period of 3 hours, with addition of
5-ml. portions of ethanolic hydrochloric acid at 30-minute intervals. The mixture is poured into
500 ml. of hot saturated brine solution in a
1-l. separatory funnel, and the crude ester is allowed to settle for 10–20 minutes. The
brine is removed, and the ester is washed (Note
9) at room temperature with
500 ml. of 0.5% sodium carbonate solution. The rather stable emulsion is broken by centrifuging the mixture for 5 minutes at 3300 r.p.m The ester and any remaining emulsion are washed with 150 ml. of warm water, and the emulsion is broken by centrifuging. Washing (Note
10) is continued until the wash water is neutral to
methyl orange. The neutral ester is distilled under reduced pressure. It boils at
174°/2.5 mm. and
198°/6.5 mm.