Anomalous Behavior of M e t h y l I2-Hydroxy-9,IO-Octadecenoates in Rapid Iodine Number Determinations PHILIP S. %ELL1
AND
SOL B. RADLOVE2
Northern Regional Research Laboratory, Peoria,
in glacial acetic acid ( 5 ) was also tested. I t was found to react with equivalent speed. I n Table I, data are given which indicate the rate of reaction of methyl ricinoleate and methyl ricinelaidate with Wijs and bromine reagents. Aliquot portions from a standard solution of each of the esters in glacial acetic acid were used to obtain samples of equal weight. The molar concentration listed in the tables are the values calculated for the solut,ions obtained by mixing the reagents. To determine the effect of mercuric acetate on the course of the reaction, the halogenating agent was mixed with the esters and the mixture then treated with mercuric acetate solution. The time was recorded from the addition of the latter. Examination of the data from these experiments (see Table 11) demonstrates that the addition of mercuric acetate to solutions of dihalogenated ricinolcates or ricinelaidates in Wijs or bromine in acetic acid solutions results in a further utilizat,ion of the excess free halogen present. Since t,he ricinoleates and ricinelaidates differ from the normal unsaturated fatty acids only by the possession of the 12hydroxyl group, it is reasonable to conclude that the further utilization of halogens in the presence of mercuric acetate takes place at the hydroxyl group, probably involving an oxidation of the secondary alcohol group, or a substitution activated by the hydroxyl group. I n another series of experiments, three samplcs of methyl ricinoleate were alloxed to react with Wijs solution for 30 minutes. One of the samples was titrated, and the iodine value v a s determined to be 82.1. T o the other ttvo samples, mercuric acetate was added, and a t the end of 3 more minutes, the iodine value had risen to 88.8, and finally after 13 minutes, to 100.4.
The methyl esters of ricinoleic, ricinelaidic, and O-propionylricinoleic acids quantitatively add iodine chloride from Wijs reagent in less than 1 minute. However, if mercuric acetate i s present, methyl ricinoleate and ricinelaidate react with additional halogen, thus giving high iodine values, whereas the methyl O-propionylricinoleate behaves normally. This anomalous effect i s due to the presence of the free hydroxyl group.
T
HE use of mercuric acetate catalyst to speed the rate of
addition of Wijs reagent to nonconjugated, unsaturated double bonds constituted a decided improvement in the iodine number technique by allowing the attainment of quantitative addition in less than 3 minutes ( d ) , in contrast to the standard method for the determination of iodine value (1) which requires 30 to 60 minutes. Korris and Buswell (4) found that Hanus reagent with mercuric acetate was even more satisfactory than the Wijs reagent for the determinationof nonconjugated unsaturation.
Table I. Rate of Reaction with Time, Min.
Wijs and Bromine Reagents
(Without Mercuric itcetate) Halogen Equivalenta
Iodine Value
0 02568 M l I e t h j 1 Ricinoleate, 0 06861 . I I WIJS 1.0 '1.998 81,16 20.0 2.016 81.89 82.07 30.0 2.021
A.
B.
0,02411 -11 Methyl Ricinelaidate, 0.06861 .M Wija 2.006 81.50 2.005 81.45 2,009 81.60 81.50 2.006 2.004 81.40 2.009 81.60
1.0 3.0 11.0 30.0 30.0 60.0
Table II. Effect of 0.0147
C . 0.02568 .I4 Methyl Ricinoleate, 0.07449 '11 Bromine 1.0 1.0 10.0 20.0
2.030 2.035 2.021 2.024
Ill.
Time, N i n .
82.44 82.67 82.07 82.21
A.
Iodine Value
0 01968 .\I 1Iethyl Ricinoleate, 0.05257 .II Wijs
1 0
3 0 3 0 9 0 15.0 I5 0
Halogen equivalent is number of atoms of halogen absorbed per mole of compound. a
M Mercuric Acetate on Iodine Values
Halogen Equivalent 2.054 2.188 2.187 2.368 2.470 2.473
83.44 88.91 88.82 96.21 100.31 100.45
0 01847 41 Methyl Ricinelaidate, 0 05257 M Kv1j-i 1.0 2 051 83 30 3.0 2.116 85.97 10.0 2.193 89.08 I5 0 2 206 89.61
B.
These authors noted, however, that, although castor oil yielded t'he expected iodine number of 84.0 with the usual Hanus reagent, the addition of mercuric acetate resulted in an iodine number of 90.7. They attributed this anomaly to ricinoleic glycerides, since a similar result was obtained with petroleum ether-extracted castor oil acids. I n connection with other work, the authors had prepared pure methyl esters of ricinoleic and ricinelaidic acids (the cis and trans isomers of 12-hydroxy-9,10-octadecenoicacid), and had independently observed an analogous effect while determining their iodine numbers by the Wijs mercuric acetate technique. They further observed that Wijs reagent alone adds quantitatively to methyl ricinoleate and methyl ricinelaidate. Despite the absence of mercuric acetate catalyst, the reaction occurred with surprising speed, being essentially complete in less than 1 minute. To determine whether Wijs reagent was unique in its ability to add rapidly t o these unsaturated compounds, a standard solution of bromine
C . 0 01968 M Methyl Ricinoleate, 0 05644 M Bromine 1.0 3 0 10 0 20.0 60.0
D.
2,032 2,071 2.123 2,172 2.318
82.53 84.13 86.22 88.23 94.10
0.0'2991 M LIethyl 0-Propionylricinoleate, 0.05246 A1 JVijs 1 0 1,989 68.52 3 0 1.983 68.29 15 0 1.993 68 0,j
To prove conclusively that the excessive utilization of the haloken reagents was due to the free hydroxy1 group, methyl 0propionylricinoleate was prepared and examined as above. The behavior of this ester was entirely normal as shown in Table 11, thus demonstrating that the anomalous behavior of the ricinoleate and ricinelaidate is due to its free hydroxyl group. From a practical point of view, the results of Wijs mercuric
1 Present address, Williom .ilbert Nores Chemical Laboratory, University of liiiiois. Urbana, ill, ? Present address, Maytag Co., Newton, Iowa.
67
68
INDUSTRIAL AND ENGINEERING CHEMISTRY
acetate iodine number determinations should be critically examined if the presence of free hydroxyl groups is suspected. EXPERIMENTAL
Vol. 18, No. 1
pure ester which had the following constants: b.p. 186" a t 1 mm., = 1.4510, saponification equivalent, 185.6 (theory, 184.3),acid value, 0.0, and iodine value, 68.5 (theory, 68.9). Automatic pipets were used to obtain aliquots of PROCEDURE. all standard solutions. An aliquot portion (10.96 ml.) of the compound and 24.98 ml. of the halogen reagent were mixed and allowed to react for the stated time interval, and the excess reagent was then titrated to obtain the results given in Table I. To determine the effect of mercuric acetate shown in Table 11, the ester and halogen reagent were mixed, and immediately treated with 10.0 ml. of 2.57, mercuric acetate in glacial acetic acid, and allowed to react for the intervals recorded, beginning with the addition of mercuric acetate. Blank experiments, without the presence of the unsaturated compound, were performed in all the series to e1:minate corrections necessitated by the presence of small amounts of oxidizable materials in the mercuric acetate solution.
PREPARATION O F hlETHYL RICINOLEATE (5). Castor oil was converted to castor oil methyl esters by saponification, isolation of the acids, and esterification with 2 to 47, sulfuric acid in absolute methanol. The esters (650 grams) were fractionally distilled through a 60-cm. (24-inch) Vigreux column, and methyl ricinoleate was collected a t 157' to 158' C. at 1-mm. pressure. The yield was 474 grams of material having the following constants: n3 = 1.4596, iodine value, 82.0 (theory, 81.2). PREPARATION OF METHYLRICINELAIDATE ( 3 ) . From 2000 grams of castor oil, 530 grams of crude ricinelaidic acid were obtained by elaidinization of the acids with oxides of nitrogen ( 3 ) . The acids were converted to the methyl esters by refluxing with 2 to 4% sulfuric acid in absolute methanol and separated from nonvolatile material by distillation from a Claisen flask a t 1-mm. pressure. There was obtained 465 grams of impure product. (1) This was then fractionally distilled as above, and the main fraction collected, b.p. 181O a t 2 mm., and recrystallized twice from a mixture of Skellysolve F and diethyl ether. The yield was 290 (2) grams of pure methyl ricinelaidate, m.p. 30" to 31" C., ny = (3) 1.4582, iodine value, 81.5 (theory, 81.2). PREPARATION O F METHYL 0-PROPIONYLRICINOLEATE (6). (4) Castor oil methyl esters, prepared as above, were heated rapidly and briefly to 180" C. with two-thirds their weight of propionic (5) anhydride. The mixture was fractionally distilled to obtain the (6)
LITERATURE CITED
Fat Analysis Committee of the American Oil Chemists Society and AMERICAN CHEMICAL SOCIETY, IND.ENG.CHEM.,18, 1346 (1926).
Hoffman, H. D., and Green, C. E., Oil and Soap, 16, 236 (1939). Kass, J. P..and Radlove, S. B., J. Am. Chem. Soc.,' 64, 2255 (1942).
Norris, F. A,, and Buswell, R. J., IND. ENG.CHEM.,ANAL.ED.. 15, 258 (1943). Uhrisr. K., and Levin, H., Ibid., 13. 90 (1941). Walden, P., Ber., 36,781-90 (1903).
Improved Device for Decomposition of Grease PFC. R I C H A R D W. T A R A R A ' Rock Island Arsenal Laboratories, Rock Island, 111.
IN
T H E laboratories of the Rock Island Arsenal, where the number of grease samples to be analyzed and the time available are determining factors, the standard method of the American Society for Testing Materials (1) for decomposing the soap in the grease was too time-consuming when a 30-gram sample was used, the time varying from 20 minutes with a light grease to 2 hours with some of the heavier greases. This method of soap decomposition consists essentially of shaking 8 to 30 grams of the sample, depending on the consistency of the grease, in a separatory funnel at room temperature with petroleum ether and 10% hydrochloric acid. Since the "boiling method" is used in many grease testing laboratories, its suitability for the Arsenal needs was looked into. Briefly, this method consists in placing about 30 grams of grease in a 400-ml. beaker, adding about 200 ml. of 10% hydrochloric acid solution, and then heating the mixture to the boiling point
* Present
addresa, c/o Dr. P. L. Tararrt, Mayo Clinic, Rochester, Minn
of the hydrochloric acid solution to accelerate the decomposition. It was found that the time required to break down the grease could be reduced to from 5 to 10 mihutes for the average grade to 20 minutes for the heavier grades. This method does not require the undivided attention of the analyst; however, unless the mixture is constantly stirred, steam has a tendency to build up pressure beneath the floating grease layer. I n the case of the heavier grades of greases especially, this steam pressure may cause violent bumping with subsequent loss of material due to splattering. To overcome this, several procedures were tried but only two proved effective. The first, which was very effective but cumbersome, consists in placing a slow-speed motor on a rack over the hot plate and stirring the mixture as it boils. The second procedure is the percolator method. When the grease percolator, as shown in Figure 1, is placed in the beaker with the grease sample and the hydrochloric acid solution, the steam is provided with an outlet, thereby preventing excessive bumping due to the pressure buildup. The percolator serves a twofold purpose. Primarily, it serves to prevent violent bumping with its subsequent loss of sample and, secondly, it is used t o agitate the grease, thus accelerating the decomposition by exposing more surface to the acid solution. This secondary effect is accomplished by means of the twist in the steam tube (see diagram). When the mixture reaches the boiling point of the hydrochloric acid solution, steam and hydrochloric acid solution "boil up" through the percolator out of the tube and are forced back into the surface of the grease layer by their own pressure. By placing the exit tube a t an angle, the steam and hydrochloric acid solution which spurt out with some force tend to agitate the grease layer, causing it to revolve on the surface of the hydrochloric acid solution. The percolator can be readily made in the laboratory from an ordinary 2.5-inch diameter 60-degree angle soft-glass funnel. Two or more venting grooves are bent in the lip of the funnel. The stem is then bent in the manner shown by the diagram. LITERATURE CITED
(1) Am. SOC. Testing Materials, Analysis of Grease, A.S.T.M. Serial
Designation D128-40, -4.S.T.M. Standards 1944, Part 111, p.
Figure 1
182.
