INDUSTRIAL AND ENGINEERING CHEMISTRY
68
to note that the corrosion was lowest when the surface velocity was practically aero. When Figure 5 is compared with Figure 3 it is seen that over a wide velocity range, the effect of increasing the water velocity is to cause an increase in the corrosion rate of rusted steel. In other words, when test conditions approximate service exposure of uncoated metal under water, the results are similar to those reported by Speller and Kendall. This would be expected, as stated earlier, from the increased ease of diffusion of dissolved oxygen which results from an increase in water velocity. Thus by altering one surface condition of the metal it was possible to obtain results similar to those of Friend, and by suitable control of this same factor to pass to the other extreme of reported results and obtain data similar to Speller's. In the two longer runs on previously rusted metal shown in Figure 5, there is a range of maximum corrosion. This is not narrov, however, ,as is the case with short tests on bright metal but extends up to a velocity of nearly 4 feet
Vol. 19, No. 1
per second. The iilm of rust obtained at the highest velocities is particularly dense, hard, and tough. What effect more extended test periods would have on the corrosion at very high velocities is not known. This subject is being investigated, however, and the results will be reported later. Conclusions
1-The corrosion of steel under water increases with increasing water velocity over the range commonly encountered in practice providing the metal is coated with rust. 2-By suitably altering the surface condition of a steel it is possible to reproduce the apparently conflicting data which previously have appeared in the literature concerning the effect of water velocity on the corrosion of submerged steel. Acknowledgment
The photomicrograph of the steel used was made by V. 0. Homerburg and the x-ray diagram by E. W. Brugmann.
The Chemistry of Chinese Wood Oil',' By F. H. Rhodes and C. J. Welz' CORNELL UNIVERSITY, ITEACA, N. Y.
HINESE wood oil con-
The effect of heat treatment upon the molecular as the solvent, and that the weight, iodine number, and oxygen-absorbing power variations of the apparent sists essentially of the glyceride of eleomarof Chinese wood oil was determined. Gelatinized wood molecular weight have been oil was extracted with petroleum ether, and the soluble due to experimental error. garic acid. The raw oil contains from 90 to 95 per cent and insoluble fractions thus obtained were examined. Both benzene and chloroform of this eleomargarin, the reThe heat of gelatinization of Chinese wood oil was are known to cause associamaining 5 to 10 per cent being measured. Upon the basis of the experimental retion of the dissolved oil, and olein, unsaponifiable matter, sults thus obtained, there is formulated a theory to Wolff considers that the apetc, Eleomargaric acid itself account for the observed changes which occur during parent variations in molecular has been shown to be an unthe bodying and the gelatinization of Chinese wood oil. weight have been caused saturated fatty acid of the by variations in the degree of formula :* association of the solute in the CHa(CH2)aCH:CH.CH: CH(CHZ)&OOH solvent. He does not, however, explain clearly why these The bodying of Chinese wood oil is accompanied by an experimental errors have been consistently in the direction increase in the viscosity, specific gravity, and apparent which indicate higher molecular weights for the heated oils. molecular weight of the oil, and by a decrease in the iodine Wolff himself made some cryoscopic measurements, using number and the amount of oxygen absorbed during drying. camphor as a solvent, and found that the apparent molecular There is little or no change in the acid-number or the saponi- weight of Chinese wood oil does not increase when the oil is fication number unless the heat treatment is effected a t un- bodied. In further support of his hypthesis, Wolff points out usually high temperatures. Most authorities agree that these that when Chinese wood oil is heated the increase in viscosity observed changes are due to the polymerization of the glyceryl and the decrease in iodine number do not take place concureleomargarate, although different investigators advance rently, the change in iodine number being almost completed different hypotheses as to the exact mechanism of the polym- before the most marked change in viscosity takes place. eriaation reaction. Wolff, however, holds that the thickenExperimental Work ing of the oils when heated is due solely to a change in the In the investigation of the effect of the heat treatment upon physical state of the 0il-i. e., to gelatinization-and that polymeriaation plays no essential part in this change. He the properties of Chinese wood oil here reported it was consays that the data for the determination of the average sidered desirable to develop a satisfactory method for followmolecular weights of the oil before and after heating have been ing the change in the molecular weight of the Oil with the obtained by cryoscopic methods, using benzene or chloroform temperature and time of heating. Hoffman6 and Long and Smull' have determined the molecular weights of heat1 Received June 29, 1926. treated Oils by the cryoscopic using benzene as a 2 This article is respectfully dedicated by the authors to Prof. I ,. M. solvent. This however, is open to criticism beDennis. I t will be reprinted as Article No. 4 in the Louis Munroe Dennis Quarter Century Volume, to be published in 1928 in commemoration of the cause of the known fact that benzene tends to cause some completion by Professor Dennis of 25 years of service a s head of the Departassociation of the solute and may therefore give incorrect ment of Chemistry a t Cornell University. The article is based upon the results. The use of camphor as a solvent in cryoscopic dethesis presented to the faculty of the graduate school of Cornell University termination has been suggested by Rast19 and by C. J. Welz in partial fulfilment of the requirements for the degree of doctor
C
of philosophy. I Du Pont Fellow in Chemistry at Cornell University. 4 Fokin, J , Russ. Phys.-Chcm. Soc., 46, 283 (1913). 5 2. angcw. Chcm., 81, 729 (1924).
THISJOURNAL, 17, 175 (1925). I b i d . , 11, 138 (1925). 8 Comfit. rend., 164, 1692 (1912). Bcr., 66, 1051,3727 (1922). e
@
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1927
Wittka,lo but preliminary experiments in this laboratory showed that some error may be introduced by the rapid volatilization of the camphor from the solution. The use of stearic acid as a solvent for cryoscopic measurements has been suggested by Seaton and Sawyer." The method which we finally adopted and used in the succeeding portions of this investigation was essentially similar to that developed by them.
69
samples were preserved in sealed tubes and kept shielded from direct daylight. The results of the analyses of the samples of heat-treated oil are given in Table I. The changes in the molecular weight and iodine number are shown graphically in Figures 1and 2. It is evident that the acid numbers and the saponification numbers are not appreciably affected by the "bodying" of the oil. There appears to be a very slight increase in the acid number as the heating is continued, but the increase in acid number is much less pronounced than that commonly observed in the bodying of linseed oil. Our results on the change in acid number and saponification number agree satisfactorily with those of Schapringer.12 Table I
TEMPFRATURE TIMB
OF OF MOL. H ~ A T I NHEATINO G WT. C. Hours
I50
2 3 5 8 12
Figure 1
A series of measurements with known pure solutes give
16
SOLUTE
793 786
6.156
6.532 8.594
782
796 785
797
The tung oil used in the study of the effect of heat treatment upon the molecular weight and iodine number was taken from a lot of authentic raw Chinese wood oil on hand in this laboratory. It showed the following analytical characteristics: Specific gravity (15.5e/15.5e C.) Iodine number Saponification number Acid number Refractive index (25' C.) Heat test
lo
2.deut. 61- F e l t d n d . , 44, 375 (1924) THIS JOURNAL, 8, 490 (1916).
1 2 3 5 8
190
-1
220
-3
2
1/2
ACID SAPONIFICATION No. No.
168.1
... ...
4.28
... ...
193.8
166:s
4:28
194:2
i6i:i
4:24 4.33 4.33 4.28 4.18 4.24 4.27 4.34 4.34 4.28 4.21 4.30 4.45 4.28 5.04
19317 193.7 193.5 193.8 194.4 194.5 194.3 193.9 192.9 193.8 193.8 194.4 194.5 193.8 194.1
160.4 159.4 168.1 168.0 166.1 165.5 162.5 157.8 168.1 167.3 160.4 152.9 168.1 150.3
... ...
The iodine number decreases as the bodying progresses, the decrease being more pronounced at the higher temperatures. Schapringer observed a similar decrease in iodine number, but found that the decrease is more pronounced when the oil is heated for the longer times a t the lower temperatures.
0.9401 168.60 193.45 2.27 1.5162 9 minutes 53 seconds
In bodying the oil the following procedure was used: About 100 grams of Chinese wood oil were placed in a widemouth, 150-cc. round-bottom flask. The flask was fitted with a cork carrying a thermometer, a glass inlet tube 5 mm. in diameter and leading to within 10 mm. of the surface of the oil, a Bunsen valve, and an 8-mm. glass sampling tube closed with a small cork. Samples were withdrawn by inserting a suitable pipet through the sampling tube. A gentle stream of nitrogen was admitted through the glass inlet tube and escaped through the Bunsen valve. The stream of nitrogen was started just before the heating was begun and continued until the flask had cooled to room temperature after the heat treatment. The nitrogen served to sweep out the air originally present in the flask and to prevent oxidation during the heating. An oil bath was used as the heating medium. The time required to bring the sample up to the bodying temperature was approximately one-half hour. Portions of Chinese wood oil were bodied a t 150°, 170°, 190°, and 220" C. Samples for examination were withdrawn a t intervals, starting shortly after the bodying temperature was reached and continuing until the end of the run. These l1
170
APPARENT
MOLECULAR WEIGHT
2.893 2.902 4.995
20
an average value of 46 as the freezing point constant of the stearic acid used. Preliminary experiments showed that the apparent molecular weight of Chinese woad oil, as determined by the cryoscopic method with stearic acid as a solvent, is independent of the concentration. The results obtained in these experiments were as follows: Grams / 100 crams solvent
-1
IODINE No.
Figure 2
Nagel and Gruss13 state that when Chinese wood oil is heated just to the point of gelatinization the iodine number falls to 110-120. They give no experimental results to support this statement, nor do they specify the temperature and the time of heating required to effect the drop. W0lff14 found that the ether-soluble fraction from freshly gelatinized Chinese wood oil had an iodine value of about 150. From the graphs representing the increase in molecular weight on heating it appears that, with this particular lot of Chinese wood oil, gelatinization occurs when the average molecular weight attains a value of about 1700. The molecular weight a t the gelatinization point is practically independent of the temperature at which the gelatinization is effected. Dissertation. Karlsruhe, 1912. 2. ongcw. Chem., 89, 10 (1926). 14 Ibid., 87, 400,729 (1924);88, 489 (1925). 1:
INDUSTRIAL AND ENGINEERI-VG C H E X I S T R Y
70
S t u d y of F r a c t i o n s from Gelatinized Oil
I n none of the preceding experiments was the Cliincse wood oil heated to gelatinization. I n order to obtain sonic information as to the composition of the gelatinized wood oil and as to the nature of the reactions which occur when tung oil is gelatinized, a series of experiments was conducted in which gelatinized oil was extracted fractionally by solvents. The fractions thus obtained were examined. This method had been used by Wolff16and by Schumann.16 Our procedure was as follows: A sample (200 grams) of the raw Chinese wood oil was placed in a flask and immersed in an oil bath a t the desired temperature until gelatinization occurred. The gelatinized mass was ground with about six and one-half times its weight of clean sea sand, and the mass was thoroughly extracted, first with several portions of petroleum ether and then with several portions of absolute alcohol. The petroleum ether was redistilled and only the lighter fraction was used for the extraction. All extractions were carried out at the boiling point of the solvent used. The petroleum ether extracts were combined and most of the solvent was removed by distillation on a water bath in a current of dry nitrogen. The residue was freed from the last traces of solvent by heating it for 8 hours on the water bath under a pressure of 2 to 5 mm. The final oil was stored in a sealed tube until used. All operations were carried out with the least possible exposure to the air. The alcoholic extracts were similarly combined, freed from solvent, and stored. The final insoluble residue after the extraction with alcohol was covered with an excess of an alcoholic solution of caustic potash (40 grams per liter) and the mixture was heated on the steam bath, under a reflux condenser, for 6 hours. The residue (sand) was removed by filtration, and the filtrate was evaporated to remove most of the alcohol. The residue from this distillation was treated with a mixture of equal parts by volume of aqueous potassium hydroxide solution (sp. gr. 1.4) and alcohol, using 80 cc. of this mixture to 50 grams of the residue. The resulting mixture was heated for 1 hour on the steam bath to insure complete saponification. The solution was then diluted with 1 liter of hot water, boiled to remove most of the alcohol, acidified slightly with hydrochloric acid (l:l), and warmed until the separated fatty acids formed a clear layer. The fatty acid layer was separated, washed with successive portions of water until the wash water was neutral to methyl orange, and finally dried by heating for 8 hours on the water bath under a pressure of 2 to 5 mm. I n each experiment a portion of the oil which was recovered from the solution in petroleum ether was also saponified (by heating with equal parts of an aqueous solution of potassium hydroxide and water), and the fatty acids were liberated from this soap and washed and dried as described. Three such series of experiments were conducted. In series 1 the original oil was gelatinized by heating for 1 hour a t 220" C. in an atmosphere of nitrogen; in series 2 the gelatinization was effected by heating for ll/zhours a t 220" C. in a sealed tube; and in series 3 the raw oil was heated for 15 minutes a t 360" C. in an atmosphere of nitrogen. The raw oil used in these experiments was from a new lot of material supplied by S. P. Gillespie and Sons. The analytical constants of this material were as follows: Specific gravity (15.5' CJ15.5' C.) Iodine number (Wijs) Saponification value Acid number Refractive index (25' C.) Heat test (Browne)
u Fdrber-Zlg.. 18, 1171 (1913). 16
THIS JOURNAL, 8,
5 (1916,.
0.9406 167.9 194.3 4.27 1,5168 S minutes 21 seconds
Vol. 19, KO. 1
The results of the experiments on fractional extraction are preseiited in Table 11. They indicate that there was little diffcience between the material gelatinized by heating for 1 liour a t 320" C. in an atmosphere of nitrogen and thc product obtniircd by heating the raw oil a t 220" C. for 1.5 hours in a sealed tube. The material obtained by heating a t 360" C. for 15 minutes, however, was quite different from either of the products formed at the lower temperature. Table I1 PER CENT
SUBSTANCE
BY
ypmhloL. WT.
ORl,~INAL
IODINE ACID
KO.
SAPoNxar-
No.
NO.
OIL
Series 1 Raw oil Petroleum ether fraction Alcohol fraction Acids: From raw oil From petroleum ether fraction From insoluble residue Raw oil Petroleum ether fraction Alcohol fraction Acids: From raw oil From petroleum ether fraction From insoluble residue Raw oil Petroleum ether fraction Alcohol fraction Acids: From raw oil From petroleum ether h a c tion From insoluble residue
100 51.7 5.5
40.5
4.27 5.32
823 1609
167.9 147.3
291
175.2
195.0
403 513
145.3 129.7
198.5 195.7
Too little to be analyzed
Series 2 823 100
4.27 5.51
59.3 4.4
1652
167.9 143.3
291
175.2
195.0
35.2
401 506
144.9 131.0
197.8 198.2
Too little to be analyzed
194.3 194.2
194.3 194.2
Series 3 4 . 2 7 194.3 823 167.9 100 95.5 35.8 185.6 05.7 835 1.5 Too little to be analyzed
37.4
291
175.2
195.0
364 457
98.9 108.7
181.5 192.0
The soluble fraction of the oil gelatinized a t 220' C. had, in each case, an average molecular weight almost exactly twice that of the original raw oil. This fraction is, therefore, either a dipolymer of the original oil or a mixture of higher polymers with unpolymerized material. The fact that in two experiments made under somewhat different conditions the soluble fraction had a molecular weight so nearly twice that of the original oil is strong presumptive evidence that this fraction is really a dipolymer. Polymerization of the simple glyceryl eleomargarate molecules may conceivably occur in several ways-for example: (I) By the union of two simple molecules through a tetramethylene linkage formed from a single pair of ethenoid bonds. /R /R
/RICH :CHR" C3Hr-R \R (2) By the coupling of two simple molecules through three such tetramethylene linkages, one linkage being formed between each pair of eleomargaric acid residues of the original oil molecules. (3) By the complicated series of reactions postulated by Salway1' involving (a)the splitting off of a molecule of free acid, followed by (b) the condensation of the free acid with a n acid residue of the glyceride, and ( c ) coupling of two of the resulting complex compounds.
A study of the change of iodine number of the oil and of the change of the molecular weight, iodine number, and neutralization equivalent of the free fatty acid obtained by the saponification of the oils should make it possible to determine in which of these ways the polymerization actually proceeds. Table I11lists the theoretical and actual ratios of the constants of the doubly polymerized material to those of the original oil. 17
J . SOC.Chem. Ind.. S9, 3241' (1920).
January, 1927
INDUSTRIAL A N D EiVGINEERING CHEXISTR Y Table 111
material formed during the period of heating before gelatinior it may be due to the rapid formation and practically simultaneous coagulation of a product more highly polymerized than the liquid oil. If the gelatinization is due solely to the coagulation of material already present in the heated oil, the heat change during the formation of the jelly should be small. If it is due to the rapid formation of a new product which immediately separates as a jelly, the heat change may be relatively large. The following experiments were undertaken for the purpose of determining the approximate magnitude of the heat change which occurs during the gelatinization of Chinese wood oil, with the idea that such thermal data might throw some light upon the nature of the reactions involved. The calorimetric method used was, we believe, novel. A weighed sample of the raw oil (about 30 grams) was sealed in a thin-walled glass bulb (Figure 3), which was then inserted in a slightly larger tube. The space between the inner bulb and the outer tube was almost filled with melted naphthalene. A U-shaped outlet of capillary tubing was sealed to the top of the apparatus. Attached to this outlet by a ground glass joint was an extension of capillary tubing, terminating in an S-bend. A small globule of mercury in this bend acted as a valve and prevented ingress of gases or vapors into the space above the naphthalene but allowed the escape of vapors from this space. The extension tube was held firmly in place against the ground-glass joint by means of a pair of small spiral springs (not shown). The entire apparatus was suspended in a large widemouth Erlenmeyer flask, fitted with a cork stopper and an aircooled reflux condenser. About 250 grams of naphthalene were placed in the bottom of theflask and heat was applied until the naphthalene boiled and the entire flask was filled with naphthalene vapor. The naphthalene and the wood oil in the apparatus suspended in the upper part of the flask were thus heated to the boiling point of naphthalene (218' C.) and maintained just at this temperature. During the first part of the period of heating the air above the naphthalene expanded and escaped through the extension outlet tube, carrying with it a little naphthalene vapor. Even after the air was expelled there was a continuous but very slow evolution of vapor from within the tube. When the wood oil in the inner bulb began to gelatinize the heat evolved was transmitted to the surrounding liquid naphthalene, which was already at its boiling point. Consequently this heat was utilized in vaporizing naphthalene, the resulting vapor escaping through the outlet tube into the surrounding flask. When the gelatinization began the liberation of heat and the consequent evolution of naphthalene vapor (as evidenced by the movement of the globule of mercury in the outlet tube) were rather rapid. Even after the oil had set t,o a jelly the escape of naphthalene vapor continued, at first rapidly and then more and more slowly. Finally the rate of evolution dropped to about the small value that obtained during the period of preliminary heating before gelatinization. In making a determination of the heat, evolved during gela,tinization the tube containing the oil and the naphthalene was weighed, heated for 11/4 hours (at the end of which time gelatinization had not occurred), removed quickly, cooled, weighed, heated again for a3/, hours (during which time gelatinization did occur and naphthalene vapor was evolved), again cooled and weighed, and finally heated a third time and cooled and weighed. In each case the apparatus was removed from the flask containing the boiling naphthalene as soon as the heating was discontinued, so as to prevent naphthalene vapor from sucking back into the tube. In every instance the tube was cooled and the extension outlet tube was removed before weighing.
TYPEOI?POLYMERIZATION zation, Theovetical r a t i o Molecular weight of oils Iodine no. of oils Molecular weight of free acids Iodine no. of free acids Neutralization equivalent of free acids Actual r a t i o Molecular weight of oils Iodine no. of oils Molecular weight of acids Iodine no. of acids Neutralization eauivalent of acids
3
1
-
2
2:1 5:6 6:s 5:6 1:l
2:l 3:G 6:3 3:6 1:l
2:1 5:6
2.03:l
2.01:l 5,12:6 6:4.35 .
... ... ... ... ...
5.2li:G 6 : 4 34 4.98:6 1.02:l
4.9536
1.02:l
6:4 5:6
2:3
The results in Table I11 indicate definitely that the polymerization is not of type 2, that is, that the dipolymer does not consist of two eleomargarin molecules joined by three tetramethylene linkages. The ratio of the neutralization equivalents of the free acids from the polymer to the neutralization equivalent of the free acids from the raw oil indicate that the polymerization does not take place in the manner postulated by Salway. Of course it is possible that the complex acid radicals assumed by Salway may be broken up again into the simple acids during the saponification of the polymerized material, but in this case the acids] obtained should have very nearly the same molecular weight as those from the raw oil. I n general, the results indicate that the soluble fraction from gelatinized Chinese wood oil is a dipolymer in which the two component glyceride radicals are joined by a single tetramethylene linkage formed by the union of a single pair of ethenoid groupings. The molecular w e i g h t s of the acids from that portion of the gelatinized oil which was not soluble in petroleum ether indicate that these acids are more highly polymerized than are the acids from the soluble fraction. The available data do not suffice to show the exact manner in which polymerization has occurred. The fact that the neutralization equivalent of the polymerized acid is the same as that of the raw oil, however, shows that there has been n o elimination of carboxyl groups, while the comparatively high iodine number indicates that the polymerization has not taken place solely b y t h e f o r m a t i o n of tetram e t h y l e n e linkages between ethenoid groups. When Chinese wood oil is gelatinized a t 360' C. the product formed is quite different from that obtained a t 220" C. At the higher t e m p e r a t u r e Figure 3 some decomposition occurs, as indicated by the fact that an acrid vapor, smelling somewhat of acrolein, was evolved. The analysis of the jelly formed at 360" C. is probably not particularly significant, as this fraction was contaminated with various decomposition products. The insoluble fraction gave acids of lower molecular weight and much lower iodine number than those from the corresponding fraction from the jelly formed a t 220' C. Heat of Gelatinization of Chinese Wood Oil The gelatinization of Chinese wood oil on heating may be
due to the coagulation of comparatively highly polymerized
il
INDUSTRIAL A N D ENGINEERIXG CHEMISTRY
72
In calculating the heat of gelatinization from the data thus obtained, the loss in weight during the gelatinization period is corrected for the regular and small loss in weight which took place during the preliminary and final periods. This corrected value multiplied by the heat of vaporization of naphthalene (75.4 calories per gram) gives the net heat of gelatinization. Two experiments gave values of 3.06 calories per gram and 2.72 calories per gram for the net heat of gelat-
780
RAW OIL
8
I mu8 875 " lC.75 8 " 1451 OXYGEN ASSORB VOLATILE MATTLR
c 6 D 0 Y
0
-
50
100
150
200
300
3.50
430
300
350
100
Figure 5
100
zoo
zsa YOURS
Figure 6
inization. As the gelatinized oil still contains from 50 per cent to 60 per cent of material soluble in petroleum ether, the heatlchange is about 6 calories per gram of insoluble material formed. The heat of coagulation of colloidal ferric oxide is about 2 calories per gram18 and that of colloidal silica is 11.3 to 12.2 calories per gram.lg Thus it appears that the magnitude of the heat of gelatinization of Chinese wood oil is not incompatible with the assumption that the gelatinization is due to the coagulation of substances already present in the bodied oil rather than to the sudden and rapid formation of a new insoluble compound. In view of all of the experimental evidence, the following hypothesis may be advanced to explain the changes that normally take place during the bodying and gelatinization of Chinese wood oil. '8
When the oil is first heated polymerization occurs. The principal product of this reaction is a dipolymer of eleomargarin in which the two simple glyceride molecules are connected by a single tetramethylene linkage. Simultaneously with this principal reaction a second and probably more highly polymerized product is formed. When the reactions have proceeded so far that the average molecular weight of the oil reaches a value of about 1700, the higher polymerization product precipitates or coagulates as a jelly, enclosing the liquid dipolymer very much as water is enclosed in a gelatin jelly. There is no evidence to show that the jellying is due to any sudden chemical reaction; the gelatinization appears to be due essentially to the change in the physical condition of the higher polymer. It is possible that long-continued heating of the original jelly may cause further conversion of the soluble dipolymer to the insoluble material, but this further change will be gradual, not sudden. Effect of Heat Treatment upon Oxygen Absorption
Figure 4
A
VOl. 19, No. 1
Kruyt and van der Speck, Kolloid-Z., 24, 145 (1919). Widemann and Ltideking, Wied. Ann., 26, 145 (1885).
In studying the heat treatment of Chinese wood oil it is of interest to determine not only the nature of the changes which take plaqe on heating but also the effect of the heating upon the rate of oxidation of the oil. Accordingly, samples of the oil which had been bodied by heating to various teinperatures for various lengths of time were examined to determine their oxygen apsorption, using the method of Rhodes and van SVirt.*O The Chinese wood oil used in these experiments 450 560 was from the same lot of material as that used in the study of the effect of heat treatment upon the molecular weight and the analytical characteristics of tung oil. In preparing the samples of bodied oil the procedure followed was identical with that already described. Portions of the oil were bodied at 150', 170', 190", and 220' C. The heating was done in an atmosphere of nitrogen, Samples of the bodied oil were withdrawn a t definite intervals and were preserved in sealed tubes until used. The results of these experiments are shown in Figures 4 to 7. Figure 8 shows the results of the study of the oxidation of the soluble fraction obtained by ex450 5J0 tracting gelatinized oil with petroleum ether. The raw oil from which these fractions were preDared was not from the same lot as that used in the other oxfdation experiments, but was from the lot used in the study of the extraction of gelatinized oil with solvents. The soluble fraction (dipolymer) from the oil gelatinized at 220' C. absorbs very nearly two-thirds as much oxygen in 500 hours as does the raw oil, although the iodine number of the dipolymer is five-sixths that of the original material. This lends color to the hypothesis that only three of the six double bonds in eleomargarin are directly concerned in the oxidation and that one of these three active ethenoid linkages is eliminated when the dipolymer is formed. This hypothesis agrees very well with the theory of polymerization here proposed and with the fact that only oils which show marked drying properties are those which contain glycerides of acids with two or more double bonds. Some of the heavily bodied oils absorbed less than onehalf as much oxygen as did the raw oil from which they were obtained, although the molecular weights of these bodied m Trru, JOURNAL, 16, 1135 (1923).
I-VDUXTRIAL AND ENGINEERING CHEMISTRY
January, 1927
oils were lower than the molecular weight of the soluble fraction from the jelly. Furthermore, the rate of decrease of oxygen absorbing power does not parallel the rate of increase of molecular weight. During the early stages of the bodying a marked increase in molecular weight is attended by only a comparatively slight decrease in oxygen absorbing capacity; during the later stages of the heat treatment a slight increase in molecular weight involves a marked diminution of the
Figure- 7
ability to absorb oxygen. This is well illustrttted by the following data from the series of experiments in which the oil was bodied at 190" C. MOLECULAR WBIGHT 790 903
1120 1462
increase in the molecular weight and a marked decrease in the iodine number. Gelatinization occurs when the average molecular weight of the bodied oil is about 1700. Gelatinized Chinese wood oil contains a t least two components, one of which is soluble and the other insoluble in petroleum ether. The molecular weight and iodine number of the soluble fraction and the molecular weight, iodine number, and neutralization equivalent of the free fatty acid from this fraction indicate that this portion of the gelatinized oil is a dipolymer in which the two component glyceride molecules are joined by a single tetramethylene linkage formed for the union of a single pair of ethenoid groupings, one from each of the two component glycerides. The insoluble fraction of the jelly is a more completely condensed product of unknown composition. The heat of gelatinization of Chinese wood oil is of the general order of magnitude of 3 calories per gram of raw oil or 6 calories per gram of insoluble component of the jelly. The magnitude of this heat change is not incompatible with the hypothesis that the gelatinization of Chinese wood oil is due primarily to the coagulation of polymerized material already present in the bodied oil.
OXYGEN ABSORBED IN 450 HOWRS Per cent 37 34 33
18
All of these observations bear out the assumption that during the bodying of the oil a t least two types of polymerization products are formed, the dipolymer, which constitutes the soluble portion of gelatinized oil, and another and apparently higher polymer, which has lower oxygen absorbing power than the dipolymer. This higher polymer is formed after the formation of the dipolymer and is probably derived from i t by further condensation. This higher polymer is, presumably, the material that coagulates to cause the gelatinization of the oil. In a supplementary experiment the rate of oxidation of the free acid from raw Chinese wood oil was determined. The results are shown in Figure 9. It appears that the free acid oxidizes much more rapidly than the oil itself, although the total amount of oxygen ultimately absorbed is about the same in both cases. The form of the curve
O
73
mum
Fieure 9
When Chinese wood oil is gelatinized at temperatures as high as 360" C. decomposition occurs and the product is contaminated by decomposition products of low molecular weight. The dipolymer which constitutes the soluble fraction of gelatinized Chinese wood oil absorbs only two-thirds as much oxygen as does raw oil, although the iodine value of this polymer is five-sixths that of the original oil. This observation is in agreement with the theory that only one of the two double bonds in the eleomargaric acid residue is directly involved in the drying reaction, and with the hypothesis that the diDolvmer is formed bv the coupling of a single pacr of the ethenoid groupings from &e two component glycerides. The oxygen absorbing power of Chinese wood oil decreases as the oil is bodied. The decrease is comparatively slow at first, but becomes marked during the later stages of the treatment. Just before gelatinization the oxygen absorbing power of the bodied oil is considerably less than that of the dipolymer which constitutes the soluble fraction of the jelly. The foregoing observations justify the following
50
Figure 8
indicates that the oxidation of the free acid, like that of the oil, is-autocatalytic. Summary
The molecular weight of raw or bodied Chinese wood oil may be determined very satisfactorily by the cryoscopic method, using stearic acid as a solvent. The bodying of Chinese wood oil is attended by a marked
When Chinese wood oil is heated there is formed a dipolymer in which the two component glyceride molecules are joined by a single tetramethylene linkage formed by the condensation of one pair of ethenoid groupings. On continued heating, further condensation takes place and a polymer of as yet undetermined composition is formed. When the concentration of this higher polymer reaches a certain critical value, coagulation occurs and the oil sets to a jelly in which the dipolymer is enmeshed in the precipitated higher polymer, very much as water is enmeshed in a gelatin jelly.
