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Organic syntheses vol 22 - Smith L.I.

Smith L.I., Adkins H. Organic syntheses vol 22 - John Willey, 1942. - 60 p.
Download (direct link): organicsynthesesvol221942.pdf
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15. These figures are based on the use of sunflower-seed oil containing 5 7 per cent linoleic acid. With other oils, the yield will be proportionally larger or smaller, depending on the analysis of the oil. Approximate values for three oils may be calculated from the values given in Note 3 above. The yield from cotton-seed oil is 26-30 g. The checkers have brominated about nine times the amounts stated in these directions and have obtained proportionate yields.
16. Two isomers, a solid and a liquid, are formed during the bromination.
17. The 4 N alcoholic-hydrochloric acid is prepared by passing dry hydrogen chloride gas into slightly warmed absolute ethyl alcohol until the calculated increase in weight is obtained.
18. The ester contains about 0.5 per cent of free fatty acid, and for some purposes this is not objectionable, particularly if the acid itself is desired. It is recommended, therefore, that this step be omitted where possible since the yields, particularly from the small batches, may be as low as 80 per cent of the crude ester used. In the absence of an alkaline wash, centrifuging is not necessary, as water alone causes no emulsions to form.
19. Usually three washings are sufficient.
20. A small amount of decolorizing carbon may be added before distillation, but it is usually unnecessary and is to be avoided if possible, for it is likely to cause priming in the still.
21. Ordinary 95 per cent denatured alcohol is satisfactory here.
LINOLEIC ACID
81
22. The ester is much more stable toward oxidation than the acid; it is recommended that the material be stored as the ester, and that the acid be prepared only for immediate use. The acid oxidizes to some extent under the best of conditions and, unlike the ester, cannot be distilled without some decomposition. It is for this reason that the constants are determined on the ester rather than on the acid.
3. Methods of Preparation
Ethyl linoleate is prepared by debromination of the tetra-bromide by action of zinc, or nascent hydrogen from zinc and glacial acetic acid;3 by zinc and alcoholic-hydrochloric acid;2, 4 and by zinc and alcoholic-sulfuric acid.5 The pure acid can be obtained by saponification of the ester, and directly by action of zinc and pyridine (quinoline, aniline, piperidine) on tetrabromo-stearic acid.6
3 Erdmann and Bedford, Ber. 42, 1324 (1909); Erdmann, Bedford, and Raspe, Ber. 42, 1334 (1909).
4 Rollett, Z. physiol. Chem. 63, 410-421 (1909).
6 Kimura, Fettchem. Umschau 4, 78 (1935).
6 Kaufmann and Mestern, Ber. 69, 2684 (1936).
82
ORGANIC SYNTHESES
LINOLENIC ACID
CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7C02H + 3Br2 -> 222(2)702
222(2)702
C2H50H
3Zn---->

2=2==2=(2)70225
+ 3ZnBr2
32=2=2=(2)70225
H2so4 + NaOH U
2=2=2==(2)702
+ NaHS04 + C2H5OH
Submitted by J. W. McCutcheon.
Checked by R. L. Shrinee and S. P. Rowland.
1. Procedure
{A) Fatty Acids.The procedure outlined for linoleic acid (p. 75) is followed, omitting Notes 3 and 4. Linseed oil is used as the raw material.
(.) Hexabromostearic Acid.In a 4-1. beaker equipped with a mechanical stirrer (Note 1), 90 to 95 g. of the fatty acids is dissolved in 2.5 1. of ethyl ether, and the solution is chilled to 0-10. Then, with stirring, 35 cc. of bromine (Notes 2 and 3) is introduced slowly, from a dropping funnel (Note 4), at such a rate that the temperature does not exceed 20; about fifty minutes is usually required. The solution, which must contain an excess of bromine (deep red color), is allowed to stand in an ice bath at 0-10 overnight. The excess bromine is removed by addition of a small amount of amylene, and then the white precipitate is collected with suction on a 12.5-cm. Buchner funnel and is washed with 200 cc. of ethyl ether. The hexabromide is
LINOLENIC ACID
83
thoroughly stirred with 300 cc. of ethyl ether in a 600-cc. beaker and is filtered as before. The yield is 20-22 g. of gray-white hexa-bromostearic acid (Note 5). It is recommended that 100 g. of the crude hexabromide (Note 6) be accumulated before proceeding to the next step.
In a 1-1. beaker 100 g. of crude hexabromostearic acid is heated to 70-80 with 600 cc. of dioxane (Note 7). The mixture is filtered, and the filtrate is set aside at 15-20 for several hours or preferably overnight. The precipitate is collected on a Buchner funnel with gentle suction and is washed thoroughly on the funnel with several 300-cc. portions of ethyl ether. The hexabromide is then transferred to a glass plate and spread out with a glass spatula to dry in the air. The fine snow-white crystals weigh 80 g. and melt at 181.5-181.9 (Note 8).
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