INDUSTRIAL AND ENGINEERING CHEMISTRY
90
tprtccos, for samples of nornicotine and anabasine, for suggestions, and for review of the manuscript. LITERATURE CITED
Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 6th ed., p. 64, 1940. (2) Barta and Marschek, Mszdagzdasa& Kutatdsok, 10, 29 (1937); cited by Markwood (9). A N A I , .ED., (3) Bowen, C.V., and Barthel, W. F., IND.ENQ.CHEM,. (1)
15,596 (1943).
(4) Ihid., p. 740.
Analysis
OF
Vol. 16, No. 2
(5) Bradford, J. A., Harlow, E. S.,Harlan, W. R., and Hanmer, H. R., IND.ENO.CHEM.,29, 45 (1937). (6) Haag, H. B., and Larson, P. S.,Science, 97, 187 (1943). (7) Larson, P.S.,and Haag, H . B., J . PharmacoZ., 7 6 , 240 (1943). 77* 343 (1943)‘ @) (9) Markwood, L. N., J . Aaaoc. O ~ c i a ZAgr. Chem., 23, 792 (1940). (lo) Ibid.? 283 (1943). (11) Markwood, L. N.,Science, 92, 204 (1940). (12) Waisman, H. A . . and Elvehjem, C. A., IND.
[email protected]., ANAL.ED.. 13, 221 (1941). (131 Wenusch. 4 . . and MMaiev. G., .lli/nch. Wochechr., 87, 1263 (1940) 26i
Bodied Drying and Semidrying
Oils
J. C. COWAN, L. B. FALKENBURG, AND H. M. TEETER, Northern Regional Research Laboratory, Peoria, 111. Operating details for determining the proportions and nature of those polymers in a heat-bodied vegetable oil resulting from self-addition of the fat acid portions of the oil are described. The method has been applied to the analysis of methyl esters bodied in the laboratory and of commercial oils.
RADLEY (3, 4,‘7) has emphasized the identity of drying phenomena with polymerization and the relationship between the functionality of oil molecules and their capacity to Iorm convertible films. In particular, he points out (S) that one factor of importance in more completely understanding the drying mechanism of oils consists in the ascertainment of “the Rhape and size of the molecular aggregations a t the sol-gel transition point”. In addition to considerable amounts of unpolymerized fat acid glycerides, a heat-bodied oil consists of polyesters of polymeric fat acids with glycerol. A convenient method of determining the relative proportions and molecular size of these acids would be valuable not only for characterization of polymerized oils, but also for use in the preparation of condensation polymers from the polymeric fat acids. The mode of origin and the chemical nature of the polymeric fat acids have been discussed by Bradley ( 6 , 6 , 7 ) ,Brod, France, and Evans (8), Kino (11, IS), and Ault ( 1 ) and will not be conBidered here. The monomeric fat acid is readily separated from the mixture of polymeric fat acids by distillation of the methyl esters, but Bradley and Johnston (6) reported that the polymeric methyl esters were nonvolatile at 300” C. and 1 mm. in Claisen flasks. Kino (11) partially separated dimeric and trimeric methyl esters by solvent extraction. Bradley and Johnston ( 6 ) were able to isolate relatively pure dimers and trimers from polymerized dehydrated castor methyl esters by molecular distillation in a cycIic still. Likewise, Morse (IS) fractionated a polymerized fish oil. While molecular distillation gives a good estimation of the proportions of monomeric, dimeric, and trimeric fat acids, experimental difficulties and time-consuming operations detract from the use of this method as a routine tool. As a part of the general program of the Oil and Protein Division of the Northern Regional Research Laboratory concerned with the polymerization phenomenon of oils, the separation of polymeric fat acids was studied. As a result, it was found possible to achieve fractionation of polymeric fat acids, in the form of their methyl esters, by distillation at a pressure of 1 mm. or less in a specially designed short-path alembic flask. By this method, data of sufficient accuracy to be employed in the equations of Flory (9, 10) are obtainable, and the maximum extent of reaction of polymeric fat acids with various difunctional molecules is readily estimated. Furthermore, the characterization of bodied oils in terms of their dimeric and trimeric Sat acid content can now be studied more conveniently.
B
APPARATUS
The apparatus used is shown in Figure 1. It may be ronstructed in various sizes. Capacities from 10 mi. to 5 liters have been used successfully a t this laboratory, although more accurate results are obtained with the 1- to 2-liter sizes. The dimensions are not critiral. Those shown in the figure are satisfactory for a flask of I-liter c’aparitg. Other sizes have proportional dimensions. The flask is equipped with two side arms, A and B , for introduction of a thermometer and of a capillary tube through which an inert gas, usually carbon dioxide, is passed in order to prevent humping and to provide an inert atmosphere. When flasks of 200-ml. or less capacity are used, bumping is controlled by packing the flask with glass wool; no side arm is then necessary for the capillary. A second thermometer, C,is placed in the neck of the alembic to obtain vapor temperatures. It is fitted with a splash baffle plate made by boring a hole in a Pyrex disk and attaching this to the thermometer with a small clip of Nichrome wire. The flask may be readily heated by use of an air bath or glass heating mantle. The large side arm, D,leads to a small McCleod vacuum gage and thence to the pumping system. A good rotary vacuum pump is satisfactory for flask sizes up to 500 ml.; for larger sizes ti mercury diffusion pump is necessary. The arm, E, carries the distillate to a fraction cutter. If approximate rwilts are &.sired, an ordinary “pig” carrying a t l~rtst
BULB FROM 1000ml.
Figure 1.
Apparatus
ANALYTICAL EDITION
February, 1944 148307I48lOt14790' 14770L 14750,147301-
-I
SOY BEAN METHYL ESTERS
-!
14710~ I46901
i
-,
14670 14650-14630;1,4610145901
I
9
-
1457014550-
-
I4530 -
or by splitting followed by re-esterification. Unpolymerized esters are removed by distillation a t 5 to 10 mm., in either ordinary apparatus or the alembic flask. If large amounts of monomer are present, i t is more convenient to remove it in ordinary apparatus than to use an alembic flask of a size disproportionate to the amount of residual polymeric material to be distilled. The pot temperature during removal of monomer should not exceed 210 C. in order to avoid any possibility of polymerization. The manner of conducting the remainder of the distillation depends upon the method of removing monomer. If an alembic flask is used, the pressure is slowly lowered to 1 mm. or less and distillation is continued; the material is not allowed to cool during this process. Small fractions of approximately equal weight are collected during the course of the distillation. When the pot temperature reacheR 300" C., the distillation is stopped. If removal of monomer is conducted separately, a sample of residual material is charged into an alembic flask of appropriate size, then degassed by warming while the pressure is slowly lowered to 1 mm. or less. When foaming subsides, distillation ia begun and conducted as described above. When a pip is iised as fraction cutter, fractions are collected in
14900I.4SSOC
14880 I 4860 -I4840 I 4820 I4800 -
I.4560L l4840y 1,4820r
1.48ooc ;2
LINSEED OIL METHYL ESTERS
-
,
t
1.4780b l.4760t 14740
14680146601.4640-14620-
I 4780
i
-
I4760 -
-J
;I
4720r
II 4 7 0 0 1
91
I
I 4740 L
I4720
-
% 14700-
.J
I4680 I 4660
I 4620 14600 I4580 I.4640
--
Figure 9
149OOLI4880
I 4 8 2 0 - TUNG OIL METHYL I4860 I 4840
four test tubeb or small flasks is adequate. For more accurate work or for large distillate volumes, a fraction cutter is necessary. Since the distillation must not be interrupted while changing receivers, ttn auxiliary pump is required.
I 4500
L
I 4780
I-
I4760
-
PROCEDURE
ESTERS
4," I 4 7 4 0 --
DISTILLATION. The sample of bodied oil is converted to
I 4720
methyl esters either by transesterification in the usual manner
I4 7 0 0 ~
r
Table
I. Refractive Indices of M e t h y l Esters
Source of hletbyl Ebter Soybean oil Linseed oil Perilla oil Tung oil Linseed oil (commercial budied)
-Fraction 1. .Monomer 2. Intermediate 3. Dimer
4. Volatile higher pplymera 5. Reaidue
I 4680 14660 I4640,b I 4620 C
Before polymerization
nSDO
After polymerization
1,4538 1.4585 1.4621 1.4880
1.4628 1.4711 1.4791 1.4905 1.4682
....
Table
II. Analysis of Bodied M e t h y l Esters
Refractive Index Range (n%') Soybean oil
Linseed oil
Figure 3
Per Cent of Total
for Various Fractions
Perilla oil
Tung oil
Commercial bodied Soybean 011 1inseed
Opto1.4590 Upto1.4676 Upto1.4700 Upto1.4732 Upto1.4646 48.0 1 .45901.46761.47001.47321.46461,4730 1.4772 1.4764 1.4820 1.4816 6.5 1.47301.47721.47641.48201.48161.4812 1.4874 1.4880 1.4890 1.4890 27.5 1.48121.48741.481101.48901.4924 1.4880 ...... 1.4912 1.4901 1.0 1.4869 1.4948 1.4970 1.4992 1.4975 18.0
......
Linseed
Commercisl bodied linseed 00.5
Perilla oil
Tung oil
48.5
33.5
44.6
2.0
2.0
22.6
20.5
21.0
16.6
2.6 24.5
44.0
....
6.5 25.5
15.5
011
2.5
5.5
2.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
92
the ranges up to 225' C., between 225' and 240" C., and between 240' and 265' C. ANALYSISOF RESULTS.The refractive index of each fraction collected is lotted against the total per cent distilled up to the mid-point o f t h a t fraction, and a smooth curve is drawn. This curve will indicate the presence of two fractions. The lower plateau corresponds to monomer and the higher plateau to dimer. The transition between these is designated as the intermediate fraction. [The intermediate fraction appears to consist of thermally cracked products or materials formed by recombination of cracked fragments @).I The per cent of total represented by each fraction is readily determined from the graph, as shown in Figures 2,3, and 4. A fraction collected between definitely established refractive indices will not necessarily correspond to monomer, intermediate, or dimer, unless all experimental variables are held constant. If distillation is carried out slowly with small flasks and a pig and the pressure is 1 mm., the temperature ranges suggested above may be considered to correspond to monomer, intermediate, and dimer, respectively. This procedure is not recommended for analytical work unless circumstances permit no alternative. However, it is valuable for rapid preparation of intermediate and dimer fractions of suficient purity for many purposes.
1.4820 1.4800 1.4780 1.4760 1.4740 1.4720 L4700
I i
14680
1.4660 1.4640 1.4620
r
-I
I
I
0
x)
40
50
The composition of each bodied methyl ester is given in Table 11, together with the refractive indices assigned to each fraction by inspection of the graphs. A smaller amount of nonvolatile residue than would be expected was obtained in the case of tung oil, since 6ome polymerization occurred during the initial distillation of the unbodied esters. Molecular weights of the dimer fractions as determined cryoscopically in benzene are given in Table 111. Also included is the analysis of a sample of commercially bodied linseed oil of X viscosity (Gardner-Holt scale). This Table
111.
Table IV.
Molecular Weights of Dimer Fractions Molecular Weight 590 633 590 598 584 600 688
B. P. Range
C.'
I
I! 80
I
SO100
ny
oil was transesterified with methyl alcohol using sodium methylate as a catalyst and then distilled in an alembic flask without previous removal of monomer. The distillation data are shown graphically in Figure 4. I n order to determine the closeness of fractionation and to serve as a check upon the accuracy of estimation of fraction size, a sample of distilled methyl esters of polymeric soybean fat acids, collected in the refractive index range 1.4750 to 1.4800, was redistilled. It was found that only 6.4% of material of refractive index outside this range was present. Illustrative of the results obtainable in small flasks with pigtype fraction cutters are the data obtained by distillation of samples of methyl esters of polymeric corn fat acids and of methyl esters of commercial alkali-conjugated soybean fat acids. A 59-gram sample of polymeric corn methyl esters, from which most of the monomer had previously been removed, waB distilled in a 100-ml. alembic flask a t a pressure of 0.5 to 1 mm. of mercury, secured with an ordinary rotary vacuum pump. The flask was packed with Pyrex glass wool to prevent bumping, and was provided with vapor and pot thermometers. The distillation data, given in Table IV, indicate the presence of 14% monomer, 17.3% intermediate, 44% dimer, and 24.7% residue consisting of trimer and higher polymers. A sample of commercial alkali-conjugated soybean oil was saponified and re-esterified with methyl alcohol. Unpolymerized monomer was not removed prior to distillation in the alembic flask. Distillation data are shown in Table IV. The presence of 45% monomer, 36.3% intermediate, 10.7% dimer, and 8.0 trimer and higher ploymers is indicated.
Ault, W. c.,Cowan, J. C., Kass, J. P., and Jackson, J. E., 1x0. ENQ.CHEM., 34, 1120-3 (1942). Bradley, T. F., Ibid., 29,440-5 (1937).
Oils
Fraction
70
LITERATURE CITED
Distillation Data for Approximate Analysis of Bodied
Oil
I I I I
60
AV.% DISTILLED
Figure 4
EXPERIMENTAL
Distilled samples of soybean, linseed, perilla, and tung oil methyl esters were bodied without catalyst for 40 hours a t 295' C., except in the case of tung oil which was bodied for 20 hours. (To illustrate the distillation technique, it is immaterial whether the oil or its methyl esters is bodied.) Comparative refractive indices of unbodied and bodied esters are given in Table I. Monomer was removed from the bodied esters, and the residues, amounting to approximately 1 kg. in each case, were submitted to distillation in alembic flasks of 2-liter capacity. A mercury vapor diffusion pump was necessary to secure the required pressure, which was about 0.005 mm. a t the start of the distillation and increased slowly to about 0.01 to 0.03 mm. at the end. Pot temperatures ranged from 220' to 300' C. during the course of each distillation and vapor temperatures from 170' to 265' C. Small fractions, representing from 1 to 574 of the total, were collected and their refractive indices measured. These data were then graphed, taking account of the amount of monomer recovered in the initial distillation. The results are shown in Figures 2 and 3.
Source of Methyl Esters Soybean oil Linseed oil Perilla oil Tung oil Corn oil Commercial bodied linseed oil (Theoretical)
Vol. 16, No. 2
Weight, Grams
%
Zbdd., 29, 679-84 (1937). Zbid., 30, 689-96 (1938). Bradley, T. F., and Johnston, W. B., Ibid., 32,802-9 (1940). Zbid., 33, 66-9 (1941). Bradley, T.F.,and Pfann, H . F., Ibid., 32, 694-7 (1940). Brod, J. S.,France, W. G . , and Evans, W. L.,Ibid., 31, 114-18 (1939).
Flory, P. J., J. A m . Chem. Soe., 63, 3083-100 (1941). Flory, P. J., J. Phys. Chem., 46, 132-40 (1942). Kino, K.,Sei. Paper8 Znst. P h g s . Chem. Research (Tokyo), 16. Commercial alkaliconjugated soybean oil esters
Before distillation Residue
1 2 3
123-32 (1931).
.....
....
73.3
132-139 155-240 240-260
1.4565 1.4611 1.4795
28.2 28.4 7.5 5.6
.....
. ...
45.0 36.3 10.7
8.0
Ibid., 26, 91-7 (1935). Morse, R. S.,IND.ENQ.CHEM..33, 103943 (1941). PR~BBNTED before the Division of Paint, Varniah, and Plsstica Chemistry at the 106th Meeting of the A n r ~ ~ r c A CHEMICAL x SOCIETY, Pittsburgh, PS.
