AUGUST 15, 1940
-4NALYTICAL EDITION
portions of water untll the washings were no longer alkaline to phenolphthalein paper. A 250-ml. beaker was heated on a steam bath in direct contact with the steam, Tviped with a cloth, allowed to cool in the open, then weighed. The beaker was heated directly with steam and the ether extract added in several portions, each portion being allowed to concentrate to a small volume before the next was added. By this rapid evaporation, creeping of the 011 up to the edge of the beaker with consequent losses was minimized.
465
Summary
Analysis and Yields of Recovered Xylidine
The dyestuff 2-naphthol-azoxylene (Oil Red XO or F. D. and C. Red No. 32) may be reduced smoothly in dioxane solution b y means of zinc and hydrochloric acid for the purpose of determining the proportion of combined m-xylidine in the dyestuff by means of the analysis of the recovered xylidine. With a 10-gram sample of dyestuff, yields of from 90 to 95 per cent of t'hetheoretically expected xylidine may be recovered.
The recovered xylidine was analyzed for total amine content by diazotization with excess 0.1 N sodium nitrite solution in a stoppered flask, followed by treatment with a measured excess of 0.1 N sodium sulfanilate solution and a back-titration with 0.1 N sodium nitrite solution. The recovered xylidine u-ill have a diazotization value close to 100 per cent (about 98 to 100 per cent) xylidine if the method has been carried out properly. Yields of xylidine (calculated as 100 per cent by diazotization) will be about 90 to 95 per cent of the theoretically calculated value.
(1) Brochet, Bull. SOC. i n d . Mulhouse, 88, 703 (1922). (2) Conant and P r a t t , J . rlm. Chem. Soc., 48,2468 (1926). Japan, 59,634 (1938). (3) Kotake a n d Mita, J . Chem. SOC. J . SOC.Dyers Cotourisfs, 52,205 (1936). (4) R o a e , F. &I., (5) Seaman, Norton, and Mason, IKD. ENQ.CHEM.,-4nal. Ed., 12,345 (1940).
Literature Cited
Wijs Iodine Method J. W. XIcCUTCHEON, Lightfoot Schultz Co., Hoboken, N. J.
A
LTHOUGH it has been shown repeatedly that the Wijs iodine value can be relied upon to give consistent results and values lying very close to those of the other available methods, the iodine value in general is lower than the theoretical unsaturation, as measured by the hydrogen value (3, 6). How much this value is lower in the case of the Wijs method has never been determined. as far as the author is aware, although in experiments on linoleic and linolenic acids, extending over some years, values never greater than 98.8 per cent of theory were obtained, whether the determination was made on the acid or the derived ester. Since linolenic acid, prepared through its hexabromide, is much more difficult to debrominate than linoleic, it was considered unlikely that the conbtant ratio of iodine value to unsaturation could be due to a coincidence or to the presence of residual traces of bromine which could not be identified by analysis. T o investigate this problem further, it was decided to prepare an unsaturated acid b y some means other than debromination. Elaidic acid J%-aschosen, since its high melting point allows a much better separation from linoleic acid than is possible with oleic. TABLE I.
COXSTANTS O F
1 159.5
ETHYL ELAID.4TE
2 171
7.5
4
185
200
12 212
16 221
51.3 1.4384
57.6 1,4359
Refractive Indices Temperature C. Refractive inhex
25.0 1,4486
29.2 1.4470
31.5 1,4461
40.0 1.4428
Specific Gravity 15.5'/4'
C.
Apparent True
25. 0°/40 C. 0.8704 0.8706
Apparent True
Various constants, together with boiling point data a t reduced pressures using equipment previously described (4), are given in Table I. Wijs iodine values, by the method of the American Oil Chemists' Society ( I ) , are given in Table 11, together with data on two highly purified unsaturated esters prepared by t'he debromination process (4). TABLE
11.
WIJS I O D I X E V A L U E S
Ethyl linoleate Methyl linolenate (from hexabromide of m. p. 181.9') Ethyl elaidate Elaidic acid
Boiling Point Data Pressure, mm.o Temperature, C. (corr.)
the elaidic was separated from the unchanged oleic acid by repeated crystallizations at -20" C. from a 20 per cent acetone solution. The elaidic acid (50.1 grams) was then converted into the lithium salt and recrystallized three times from 80 per cent alcohol, reconverted into the acid (20.0 grams of melting point 43.5" C.), esterified, and triple-distilled under a pressure of 0.5 mm. of mercury. The melting point on a small sample of the saponified ester was 43.6" C., which was not changed on crystallizing the derived lithium salt five times from 80 per cent alcohol solution. Solid acids by the method of Bertram ( 2 ) were less than 0.01 per cent.
0.8635 0.8636
Four hundred grams of pure olive oil were saponified in the usual manner, and the resulting 361.1 grams of fatty acids separated into liquid and solid acids by the Twitchell method, with the exception that the entire solid acid fraction from the first precipitation was discarded. The resulting 191.8 grams of liquid acids were fractionally chilled in a 50 per cent acetone solution, by volume, at -15' C. The filtrates from the first four crystallizations were combined and the fatty acids precipitated by di!uting with hot water. The yield was 147.8 grams, of iodine value 110.30. The acids Twre then elaidinized in the usual way with nitric acid and sodium nitrite, the mixture was washed thoroughly with hot water to remove traces of nitric acid, and
Found
Theoretical
A of Theory
162.49 162.29
164.7
98.6
257.33 80.85 88.82
260.57 81.81 89.93
98.8 98.8 98.8
The Wijs iodine value, as prescribed in the official methods of the American Oil Chemists' Society, gives results on the unsaturated acids and esters of the oleic series that lie very close to 98.8 per cent of the theoretical unsaturation. The reliability of the method is somewhat greater than is generally supposed, although corrections should be applied when the iodine value is to be used as a measure of the purity of a compound.
Literature Cited (1) Am. Oil Chem. SOC.."Official a n d Tentative Methods", p . 31,1939. (2) Bertram, S. H., Chem. m'eekblad, 24, 226 (1927). (3) Kok, IT. J. C. de, Waterman, €I. I., a n d Westen, H. A. Van, J . SOC.Chem. I n d . , 5 5 , 225-ST (1936). (4) McCutcheon, J. W., Can. J . Research, B16, 158-75 (1938). (5) Waterman, H. I., Bertram, S. H., a n d Westen, H. A. Van, J . SOC.Chem. Ind., 48, 50-1T (1929). CONTRIBUTION from the Department of Chemistry, University of Toronto, Toronto, Canada.
