.
166 Table 1.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Effect of Extraneous Substances on Diphenylbenzidine End Point k l . of 0.025 M
Eubstance (Plus Blank) Blank (21.6 mg. of Z n + + in s p roximately 50 ml. of
Potassium Ferrocyanide 8.85
Effect on Indicator Color Change Yellow-green end point color change
* O h
10 mg. 10 mg. 10 mg. 10 mg. 10 mg.
of P b + + of A s + + + of S b + + + of 8 n + + of A1 + + +
20 mg. of F e + + + (as pyrophosphate complex) 40 mg. of F e + + + (as pyrophos hate complex) 60 mg. of F e + +$? (as pyrophosphate complex) 10 ma. of N i + + 10 mz. of T h +
10 mg. of Magnus cleaner b 10 mg. of gelatin 10 mg. of thioglycol 10 mg. of acid pickling inhibitore 1 2 3
‘
0
b e
8.85
No effect N o effect No effect No effect Slightly slower color change Blue-green end point
8.85
Blue-green end point
8.85
Blue-green end point
8.85 8.85 8.85 8.85 8.85
15.05 8.85 8.85 8.85 8.85 8.85 9.15 8.90 8.85 8.85 8.80 8.85
... ... ... ...
(Ni precipitated as the ferrocyanide) N o effect N o effect N n nffwt. . .. .. .
No effect Color change slow No change No change No change Color change less sharp Color change less sharp No effect No color or end point
No color or end point No color or end po/nt No color or end point
An alkaline cleaner with about 10% silicate and 0.501 phosphate.
Similar t o Durodex b u t containing a small amount otsoap. The three types of inhibitors used are thought to be: 1, a pi eridine derivative. 2,a suyfonated primary or secondary aromatic amine. 3, an aldehydearomatic amine reaction product.
Each titration sample was prepared by pipetting 10 ml. of standard zinc chloride solution into a 180-ml. electrolytic beaker, adding 4 grams of ammonium sulfate, 6 ml. of 1 to 1 sulfuric acid, and finally the extraneous material to be tested. The resulting solution was diluted to 50 ml., heated to 45’ C., and titrated with the ferrocyanide solution. A common source of indicator trouble arises from the presence of small amounts of surface-active organic matter in the solution. Reference to Table I shows that such material is capable of preventing completely the formation of the colored form of the indicator and must as a consequence be destroyed before proceeding to the zinc titration. Certain common inorganic ions in concentrations as high as 0.2 mg. per ml. of solution do not interfere significantly with the titration. The end point is unaffected and
Determination
Vol. 16, No. 3
the color change remains sharp, though slight changes in hue may result. A silicate-ion concentration above 0.5 mg. per ml. renders the color change slow and less distinct, In the absence of iron the end point color is yellow-green; in the presence of iron, bluegreen. A few trials with solutions of known zinc content will familiarize the analyst with the various stages of the color changes before and at the end point. However, a few hints will aid ( 3 ) . With the initial addition of 3 drops of ferricyanide, a viplet color should develop. Lack of color a t this point indicates serious divergence from the suggested procedure. A new sample is indicated. With the addition of 0.025 molar potassium ferrocyanide (containing 0.3 gram of potassium ferricyanide per liter), the initial violet changes to blue. As the titration proceeds, the blue color fades to a light shade of blue. At a few milliliters from the end point, this light blue will change through blue-green, then yellow-green, and finally attains a light violet color. The color transitions obtained following the light blue stage depend on the rate at which ferrocyanide is added, on the temperature, and on the rate of stirring. Some stages in the color change may not appear. The color at about 2 ml. from the end point should, however, be violet. Enough time must be allowed for the development of the violet complex, which a t 40’ to 45’ C. is a very aensitive and mobile indicator.
If sufficient time is allowed for its development after each increment of ferrocyanide, the end point can be approached with certainty and precision. The titration requires 5 to 10 minutes. Starting with clear bath solution, the determination of both copper and zinc requires an average of 1.5 hours. A distinct advantage of the suggested procedure is that no transfers are required, the analysis being started and finished in the same vessel. ACKNOWLEDGMENTS
The labor of sifting, by laboratory trials, the present method from among the many methods reported in the literature fell also upon other members of the Motor Products Development Laboratory staff. The authors wish to acknowledge the help of V. F. Felicetta, C. A. Ihrcke, R. E. Mosher, and J. H. Sinclair. They wish also to thank the United States Rubber Company for permission to publish this work. LITERATURE CITED
(1) Aruina, A. S., Zavodahya Lab., 8,565 (1939). (2) Cone, W. H., and Cady, L. C., J. Am. Chem. SOC., 49, 356-60 (1927). (3) Oesper, R. E., “Newer Methods of Volumetric Analysk”, pp. 176-8, New York, D.Van Nostrand Co., 1938. (4) Tyler, W. P., and BIown, W. E., IXD.ENG.CHEM.,ANAL. ED., 15, 520 (1943). (5) Weiner, R.,and Kaiser, F., Z. Electrochem., 41, 153-8 (1935).
OF
Sesamin
MARTIN JACOBSON, FRED ACREE, JR., AND H. L. HALLER U. S. Department of Agriculture, Bureau of Entomology and Plant Quarantine, Beltsville, Md.
A method for the quantitative determination of resamin in sesame oil is based upon measurement of the greenish-yellow color produced b y sesamin when it is allowed to react with a mixture of perchloric acid and hydrogen peroxide.
S
ESAME oil, a vegetable oil extensively used in Europe and Asia for culinary purposes, has commanded but little attention in this country, and the number of published American investigations (7) on it is small. I n a large measure this is probably because it is an imported oil and is not an important article of our commerce. In 1940 Eagleson (1, 3) showed that the toxicity to houseflies of a kerosene solution of pyrethrins was considerably increased by the addition of a small amount of sesame oil. The oil
alone in kerosene was without effect and was the only one of 42 animal and vegetable oils tested (g) that produced synergism. By fractional distillations of sesame oil Haller et al. ( 5 ) showed that the principle responsible for this synergistic effect is sesamin, one of the components of the nonsaponifiable fraction and a characteristic constituent of the oil. Sesamin is a substituted bicyclodihydrofuran and is not very reactive chemically. It can also be removed from the oil by extraction with 90% acetic acid, or by adsorption (6) on charcoal or clay, from which it can be removed by elution with suitable solvents. Besides sesamin, sesame oil contains sesamolin, which on treatment with mineral acid yields sesamol, a phenol. This compound is responsible for several of the color tests (8, 9) used to identify sesame oil. Its value as a synergist with pyrethrum is not known.
ANALYTICAL EDITION
March, 1944
20' 0
I
I
0.1
0.2
0.3
I
I
1
0.4
0.5
0.6
I 0.7
I
I
0.8
0.8
J 1.0
M I L L I G R A M S OF S E S A M I N PER MILLILITER I N DEOBASE SOLUTION
Figure 1.
Standard Reference Graph
With the curtailment of pyrethrum imports due to the war, the discovery that sesame oil containing sesamin could mve part of the pyrethrins in insectidical compositions has assumed considerable importance. The addition of 5% of sesame oil to a solution of pyrethrins in kerosene (2) or dichlorodifluoromethane (4) saves about 50% of pyrethrum. T o be effective as a synergist with pyrethrum, sesame oil must contain sesamin, but the minimum quantity needed has not yet been determined because the sesamin content is variable, and no quantitative method has been proposed for its detection and estimation. M'hether the variability is due to variation in the seed or to removal of more or less of the sesamin in the process of refining the oil also remains to be determined. This paper proposes a method for the determination of sesamin, based upon the observation that a mixture of perchloric acid and hydrogen peroxide gives a greenish-yellow color with any vegetable oil containing sesamin. The color persists for about 6 minutes and this allows ample time for measurement. A curve is established, from which the sesamin content of unknown solutions is read directly, by measuring the color produced by standard solutions of pure sesamin dissolved in sesaminfree sesame oil. The color is measured in this laboratory in an Aminco photoelectric photometer employing a No. 46 blue filter (optical centroid at about 460 millimicrons) and water as a blank to balance the photometer a t 1 0 0 ~ transmission. o (Formation of bubbles of oxygen, after 10 to 15 minutes, in reagent-refined kerosene mixture precludes its repeated use as the blank.) By carrying out the following procedure for preparing the standards and the reagent and for developing the color, it is believed that reasonably accurate result3 may be obtained. PROCEDURE
PREPARATION OF REAGENT.Caution must be exercised in handling the following reagents, since they are extremely corrosive. Add, with shaking, 2 ml. of 30% hydrogen peroxide to 4 ml. of 70 to 72YGperchloric acid maintained at 15" to 20" C. A mixture that is prepared below 10' C. gives erratic transmission values. This amount of reagent suffices for one reading only. The reagent must be made up fresh for each reading not more than 10 minutes before use. If allowed to stand longer, it oxidizes rapidly and also gives erratic values. PREPARATION OF STANDARD SOLUTIONS.The sesamin-free sesame oil used in the standard solutions is prepared by dissolving 100 grams of sesame oil in 100 ml. of petroleum ether (b.p. 30' to 60" C.) and extracting it in a separatory funnel about six times with 20-ml. portions of 90% acetic acid, or until a teet portion of the oil shows no color in the reagent described above. The petroleum ether solution of the oil is washed free of acid with water and then dried over sodium sulfate. The oil
167
is recovered in 97% yield by removing the solvent completely under reduced pressure. The ure sesamin used in the standard solutions may be obtained gy washing the combined acetic acid extracts once with 25 ml. of petroleum ether and then removing almost all the acetic acid under reduced pressure, at 15 to 20 mm., 60 O to 80' C. The residue crystallizes when 5 to 10 ml. of hot 95% ethanol are added. The sesamin is filtered from the cold solution and purified by several recrystallizations from ethanol. The sesamin used in these determinations melted a t 121-122" C. (corrected). All samples of refined sesame oil tested in this laborato were found by acetic acid extraction to contain approximatxy 1% of sesamin by weight. One hundred milligrams of pure sesamin, ground in a mortar to a fine powder, are made up to 10 grams with the sesaminfree sesame oil and dissolved with slight warming. Aliquots of 1000, 750, 500, 250, and 100 mg. of this solution are made up to 10 ml. with refined kerosene in separate volumetric flasks. (In these experiments the kerosene used was Deobase.) These standard sesame oil solutions therefore contain 1.00, 0.75, 0.50, 0.25, and 0.10 mg. of sesamin per ml., respectively. DEVELOPMENT AND MEASUREMENT O F COLOR. One milliliter of the standard solution is pipetted into a small, dry centrifuge tube. The 6 ml. of freshly prepared reagent are added, and the tube is closed quickly with a clean, tight-fitting rubber stopper. After being shaken vigorously for 30 seconds, the tube is centrifuged for 2 minutes to clear the resulting emulsion, and then the contents are carefully poured into a clean, dry photometer test tube. The aqueous layer, at the bottom of the tube, shows a color ranging from faint yellow to dark greenish yellow, depending upon the amount of sesamin present. The color is measured in the photometer exactly 5 minutes after the reagent is added. The procedure is re eated on each of the other standard solutions. As shown in gigure 1,the results are plotted on semilogarithmic paper as per cent transmission against concentration of sesamin, providing a standard graph for reference of all analyses made on the same instrument with the same reagents. To determine the sesamin content of a sample of unknown oil, usually 500 mg. of oil are diluted to 10 ml. with refbed kerosene. The 500-mg. sample is ideal for any oil containing from 0.25 t o 1.75y0 of sesamin. It is probably best to keep the transmission readings between 80 and 28% by adjustment, if necessary, of the size of sam le taken. A 1-ml. aliquot of this solution is pi etted into a f r y centrifuge tube and the procedure outlined aiove for developing the color in the standard solutions is followed exactly. The percentage of light transmission is measured in the photometer and is referred to the standard graph. The concentration of sesamin contained in the aliquot of the kerosene solution is read from the standard graph, and the percentage of sesamin in the unknown oil is calculated as follows: Per cent of sesamin =
concentration of sesamin X IO milligrams of unknown oil
PRECISION
x
100
OF M E T H O D
The curve shown in Figure 1 is drawn through 6 points, each of which is the average of 10 measurements. The standard deviations of the transmission readings tended to increase with the readings themselves, the largest deviation, *2.5%, occurring a t 65% transmission. Allowance for this trend and for the curvature of the standard line indicates that the standard error of the final result is practically constant, and that i t amounts to about &0.05% of sesamin when the result of a single determination on an unknown is read from a curve established from 10 replicates. LITERATURE CITED
Eagleson, C., Soap, 16 (7), 96-9, 117 (1940). Ibid., 18 (12), 125 (1942). Eagleson, C., U. S. Patent 2,202,145 (May 28, 1940). Goodhue, L. D., IND. ENG.CHEM.,34, 1456-9 (1942). Haller, H. L., MoGovran, E. R., Goodhue, L. D., and Sullivan, W. N., J . Org. Chem., 7, 163-4 (1942). Honig, P., C h m . Weekblad, 22, 509-12 (1925). Jamieson, G. S., "Vegetable Fats and Oils", A.C.S. Monograph, pp. 210-14, New York, Reinhold Publishing Corp., 1932. Kreis, H., Chem.-Ztg., 27, 1030 (1903). Malagnini, G., and Armanni, G., Ibid., 31, 884 (1907); Rend. SOC. chim. R o w , 5,133 (1907).
