Preparation And Bromination Of The Esters Of Menhaden Oil

In order to compare the methyl, ethyl and butyl esters of menhaden oil and their behavior towards bromination, they were prepared by a modified form of Haller's method12 of alcoholysis.

2 Hofstaedter, Ann., 91, 177 (1854).

3 Fahrion, Chem.-Ztg., 17, 521 (1893).

4 Bull, ibid., 23, 996 (1899); Tidskrift Kemi, Farm. Tempi, 14, 1 (1917). 5 Tolman, J. Ind. Eng. Chem., 1, 341 (1909).

6 Twitchell, ibid., 6, 564 (1914); 9, 581 (1917).

7 Tsujimoto, J. Coll. Eng. Imp. Univ. Tokyo, 4, 1 (1906).

8 Majida and Okada, Science Repts., Tohoku Imp. Univ., 3, 1 (1914).

9 Tsujimoto, J. Chem. Ind. (Japan), 23, 1007 (1920).

10 Since the above was written, Professor Tsujimoto, writing of Japanese sardine oil, has again given the name clupanodonic acid to the compound C22H3402 [ Chem. Umschau Fette, Oele, Wachse Harz, 33, 261 (1922)]. Since the acid C18H28O2, to which the name was originally given, undoubtedly occurs in oils from the herring family, we can see no reason for the change in the use of the name. We feel that more confusion will be caused by a change now, since a number of authors, among others MacArthur and Burton [J.Am. Chem. Soc, 38, 1375 (1916)] have reported clupanodonic acid, C18H2802, as a constituent of animal tissues.

11 Dr. A. M. Patterson has kindly verified the nomenclature of these acids.

Menhaden oil was refluxed with 1.5 times its weight of absolute methyl alcohol or an equivalent amount of the other alcohols, containing about 2% of dry hydrogen chloride, for 24 hours. The mixture was cooled and washed with strong brine to remove the excess of alcohol, the liberated glycerol and hydrochloric acid, the esters then being distilled under reduced pressure. The esters were dissolved in 9 times their weight of dry ether and bromine slowly added in 10% excess, while the mixture was kept at a temperature of - 10° to - 5° by a bath of ice and salt. After standing for 6 hours the precipitated bromides were washed with ether by decantation until freed from bromine, then dried in air. These methods of esterification and bromination were used generally throughout this investigation. The percentage yield of bromides based upon the original weight of ester, or polybromide number, and the percentage of bromine in the bromides were determined. The mixed butyl esters of the acids of linseed oil were carried through a like process to determine whether evidences of substitution would appear.

Determination Of Bromine In The Polybromides

The bromine content of the ester polybromides was determined by the aid of the Parr peroxide bomb, using the authors' modification of the procedure outlined by Lemp and Broderson.13

A sample of about 0.3 g. was placed in the fusion cup together with 1 g. of accelerator, in this case sodium nitrate, 0.5 g. of granulated sugar and a measure of sodium peroxide. After ignition, either by a Bunsen burner or the improved electrical method, the fusion mixture was cooled and dissolved in 150 cc. of water. The solution was acidified with 22 cc. of conc, nitric acid, an excess of 0.1 N silver nitrate solution added and the solution heated to boiling; 10 cc. of a 4% solution of hydrazine sulfate was added to reduce any bromate ions present and boiling continued until the precipitate had coagulated thoroughly. After the mixture had boiled, 5 cc. of a saturated solution of ferric alum was added and the excess of silver nitrate titrated with 0.05 N ammonium thiocyanate solution. A blank determination was made with the reagents and sugar alone.

Table I. A Comparison Of The Behavior Of The Methyl, Ethyl And Butyl Esters Of Menhaden Oil, Towards Bromination

a Two lots of ethyl esters were made and distilled into 2 fractions as shown above. The higher-boiling fractions were combined.

b 59.38% is the theoretical bromine content of butyl hexabromo-stearate. This compound sintered at 157° and melted at 160°. It has not been previously described.

12 Haller, Compt. rend., 146, 250 (1908).

13 Lemp and Broderson, J. Am. Chem. Soc, 39, 2069 (1917).

It has been suggested that sodium bisulfite solution be used as a reducing agent instead of the hydrazine sulfate. This must be added and the excess oxidized with potassium permanganate solution before the addition of the silver nitrate solution. The results with this procedure were not always of the best. One of us (J. B. B.) has had an illuminating experience in the determination of iodine by this method. The peroxide reaction apparently gave only iodate since silver nitrate in the acid solution formed no precipitate. Immediately on adding the hydrazine sulfate solution silver iodide was precipitated and bubbles of nitrogen gas were evolved. There was no appearance of free iodine. When sodium bisulfite was used as the reducing agent iodine invariably appeared.

Was Pure Clupanodonic Acid Obtained?

The percentage of bromine in the polybromides obtained from the higher-boiling fraction of the ethyl esters and from the butyl esters is an indication of the presence of more highly unsaturated acids than clupanodonic. These acids are furthermore of higher molecular weight, since they are in the higher-boiling fraction. Qualitative tests indicate that the solubility of the polybromides of the esters increases with an increase in the molecular weight of the alcohol radical. The absence of more than traces of substitution in the method of bromination employed is indicated by the fact that butyl hexabromo-stearate as prepared had practically the calculated bromine content, and no evidence of formation of hydrobromic acid could be obtained. Debromination of the bromides of the fractions of the lower-boiling ethyl ester in absolute ethyl alcohol with zinc dust gave an ester with an iodine number of 333. The acid mixture as obtained by saponification had an iodine number of 342 and a molecular weight by titration of 305, which values are not in agreement with those for clupanodonic acid.

The Effect Of Heat On The Fatty Acids Of Menhaden Oil

The free acids of fish oils could be distilled only with difficulty, since a thick viscous liquid remained in the distilling flasks. To test the effect of heat a quantity of mixed fatty acids from menhaden oil was placed in a Claisen flask and heated to 240°. To prevent oxidation a gentle stream of carbon dioxide was passed over the acids. Samples were withdrawn from time to time and the molecular weight was determined by titration.

The maximum temperature to which the fractions are subjected under the conditions of fractional distillation under vacuum is 240°. A similar experiment conducted with the esters of these same acids showed practically no change in molecular weight. This apparent polymerization may explain why large quantities of tarry residue are found in the distilling flask on fractionating the free acids, while the esters may be distilled almost to dryness. All subsequent distillations, when possible, were of esters.