The method used in the preparation of these polybromides was essentially the same as that which had previously been employed.

A sample of commercial menhaden oil, dark reddish-amber in color, was available. Two portions of 3 kg. each were converted into their methyl esters. The first lot was re-fluxed with the acid-alcohol mixture for 12 hours and the second for 24 hours. The yields of esters on distillation, between the usual range of 190-250° under 15 mm. pressure were 2000 g. of ester for the first trial and 2700 g. for the second. The methyl esters were brominated in kilogram quantities in ether solution at a temperature which was kept below 0°, as has been previously described. In all, 1772 g. of polybromides was obtained. Three portions of the esters were brominated in ether containing 10% of glacial acetic acid, but no appreciable difference could be observed in either the yield or the percentage of bromine taken up.

Previous experiments have been rewarded with low yields when the polybromides were reduced.2 This was thought to be due possibly to the insolubility of the reacting substances. Accordingly normal butyl alcohol and benzyl alcohol were tried as solvents, since the polybromides appeared to be much more soluble in these liquids. Boiling benzyl alcohol dissolves the polybromides to the extent of 100 g. per liter, giving a dark colored solution from which the white polybromides deposit on cooling.

Reduction In Benzyl Alcohol

One hundred g. of the polybromides and an excess of zinc dust were placed in a Pyrex flask with about 200 cc. of benzyl alcohol. The mixture was carefully heated, but as soon as the reaction had begun it progressed violently, and the heat developed was sufficient to break the flask. A second lOOg. portion was mixed in the dry condition with 100 g. of zinc dust and added in small portions to 250 cc. of benzyl alcohol boiling in a 500 cc. flask under an air condenser. No heat was applied after the addition of the first portions of the mixture, the heat of the reaction being sufficient to keep the mixture refluxing vigorously. After cooling, the mixture was a very thick viscous liquid from which nothing could be separated. It was thought that the benzyl alcohol had possibly entered into the reaction.

Reduction In Butyl Alcohol

A mixture of the polybromides with zinc dust was re-fluxed for 10 hours in the presence of normal butyl alcohol, the alcohol filtered off and the residue washed twice with fresh portions of butyl alcohol. After the alcohol was removed an attempt was made to distil the residue, but nothing passed over even under 15 mm. pressure. After the distillation flask had been removed from the heat for 5 minutes a strongly exothermic reaction set in which resulted in the formation of a mass of tar in the flask.

Reduction In Methyl Alcohol

Equal parts of the polybromides and zinc dust were refluxed in methyl alcohol for 48 hours, the alcoholic layer was filtered off and the solid residue washed thrice with alcohol, the alcoholic filtrates being combined and the alcohol distilled under atmospheric pressure. The ester-alcohol mixture remaining was agitated with warm dil. hydrochloric acid to remove the remaining alcohol and to decompose any zinc soaps present. The ester layer was then separated and refluxed for 12 hours with twice its weight of absolute methyl alcohol and hydrochloric acid, under the usual conditions for methanolysis, this operation being made necessary by the formation of some free acid during the debromination. The esters which were finally recovered were distilled under 15 mm. pressure. The first two runs of 500 g. each gave a total of 137 g. of reduced ester; yield, 45%. A third run of 1050 g. of bromides gave 163 g. of esters; yield, 50.9%; iodine number of esters, 368.5; mean molecular weight of acids, 307.9; n20, 1.4910.

The esters distilled between 215° and 250° under 15 mm. pressure. There was practically no residue in the distilling flask after these esters were distilled, a fact accounted for by the absence of free acid carried into the alcoholic solution as zinc salt.