March, 1935
I N D US T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
improvements resulted in all cases. The straight-run gasolines showed very marked improvement, returning to almost the original color upon removal of haze by filtration; this showed that the apparent color of the unfiltered gasoline was mainly due to suspended particles, Filtration of cracked gasolines resulted in clarification with but slight improveshowing that the produced 'POn exposure ment in was largely due to soluble colored compounds.
329
LITERATURE CITED (1) Bennett and Story, oil J., 25 (48), 162 (1927). (2) Brooks, cREM., 18, 1203 (1926). (3) Faragher, Morrell, and Monroe, Ibid., 19, 1281 (1927). (4) R u e and Espach, Bur. Mines, Bull. 333, 57 (1930). R E C E I V E D August 27, 1934. Presented before the Division of Petroleum Chemistry a t the 88th Meeting of the $merican Chemical Society, Cleveland, Ohio, September 10 to 14, 1934.
Antioxidant Properties of Vegetable Lecithin EVERETTE I. EVANS Department of Physiology, University of Chicago, Chicago, Ill.
W
HEN fats, especially 100" C., and their oxygen u p Vegetable lecithin is shown to possess antioxithose containing d Y C take has been determined. The dant properties in vegetable oils where the autoxierides of the unsatulonger the induction period, the dation is catalyzed by a n active metal. It is berated fatty acids, are left exposed efficient the that it may serve as a n eficient antioxidant For several years w o r k e r s t o the atmosphere, these fats in the protection of edible oils if used in the have been using the peroxide tidevelop, even under aseptic conditions, a i w h e s s of taste and tration technic as a measure of amounts of 0.05 to 0.1 per cent by weight. an acrid odor known as "ranthe o x i d a t i o n of an oil. Becidity," It is now well known cause the writer believes that that this phenomenon is, in the main, the result of atmos- certain substances which may be efficient as antioxidants a t pheric oxidation (4) and it has been shown repeatedly that room temperature may be destroyed by higher temperatures, this oxidation is autocatalytic in nature; that is, the rate he has used a catalyst to accelerate the autoxidation rather of oxidation per quantity of oxidizable substance increases than keep the oils a t 70" to 100" C. until the oxidizable substance is used up completely. A number of antioxidants have been proposed as inhibitors EXPERIMENTAL METHOD of oxidation for certain industrial products such as rubber, To study the use of vegetable lecithin as an antioxidant, c r a c k e d gasolines, and vegetable oils. cottonseed oil was selected as the base for oxidation. The Only a few of the vegetable lecithin was compared with several well-known m substances can be antioxidants to determine its relative efficiency. The oil used in a food prod- (which contained no peroxides) was weighed out in 100-gram u c t s u c h as a n lots in clean, dry Erlenmeyer flasks. A control to which no edible oil because of antioxidant was added was run in each experiment. the toxic nature of 3 the i n h i b i t o r , Of 3+ the nontoxic antia w o x i d a n t s recently PI introduced, the maleic acid of Greenbank (3) appears to 1% '' x, '"HdKS be one of the most FIGURE 1. COURSEOF AUTOXIDATION Promising* HydroOF SEVERAL OILS quinone, pyrocateREACTION chol, diphenylguanidine, and other substituted secondary amines are efficient inhibitors of oxidation but may be so toxic that they are not widely used in food products. The author has found that vegetable lecithin, as it is produced by the Bollmann extraction method from soy beans, is FIGURE 2. EFFECT OF STEROLS AND LECITHIN an efficient antioxidant. Because of this property and its ON COTTONSEED OIL nontoxicity, it is believed that vegetable lecithin can be used as an inhibitor of oxidation in vegetable oils. This communication deals with the antioxidant property of vegetable leciThe catalyst employed was a trace of cobaltic oleate comthin in vegetable oils. pound prepared by the reaction of 10 per cent hydrogen perSeveral methods (2, 7) have been proposed for the study of oxide on cobaltous oleate as described by Hyman and Wagthe antioxidant properties of certain chemicals in vegetable ner (6). The catalyst was so diluted that ten drops of the oils. Most of these methods have judged the efficiency of chloroform solution were added to each flask (except the the antioxidant by its ability to prolong the induction period blanks), thus allowing each sample of oil to contain about one of the oil being oxidized. The oils have been kept a t 70' to mg. of the active metal. Pure oxygen was admitted to the
ze Z6
330
INDUSTRIAL AND ENGINEERING CHEMISTRY
reaction chamber once or twice each day and each time after the flasks had been opened. The gas in the reaction chamber was under no positive pressure. After tightly corking the flasks, the contents were thoroughly shaken. The flasks were placed in a dark room and kept a t 25" to 28" C. Ab designated periods a sample of oil was taken for titration.
FIGURE3. ANTIOXIDANT PROPERTIES OF LECITHIN AND POTASSIUM CYANIDE
The vegetable lecithin used in these experiments was prepared from Manchu soy beans by extraction with 95 per cent benzene and 5 per cent alcohol, and was precipitated from this extract (after removal of 90 per cent of solvent by vacuum distillation) by steam which hydrates the lecithin and causes it to settle. This precipitate of hydrated lecithin was centrifugalized and dried in vacuum. The lecithin used analyzed 98.2 per cent saponifiable material; the unsaponifiable material was largely plant sterols. It contained the bases choline and cholamine; for this reason the term vegetable "lecithin" is used to designate a mixture of lecithin and cephalin. P~ROXIDE DETERMLVATION. In a Counce (120-cc.) oil sample bottle, a 1-gram sample of the sus ected oil was weighed out 3 cc. of glacial acetic acid were addecf and the mixture was shaken vigorously for 15 seconds. Twenty cubic centimeters of 5 per cent alcoholic potassium iodide solution were then added, and the bottle was tightly corked and shaken again for 10 seconds. The bottle was immediately placed in the dark where it was allowed to remain for exactly 5 minutes, the time bein taken from the moment the alcoholic potassium iodide was addefto the oil. At the end of 5 minutes 20 cc. of distilled water and 1 cc. of 1 per cent starch reagent were added. This mixture was shaken for 15 seconds (the color of the starch iodide does not a ear immediately). Titration was then carried out with 0.01 psodium thiosulfate until the starch iodide color had disappeared. The peroxide index was calculated as the cubic centimeters of 0.01 N thiosulfate per gram of oil. It should be stressed that the method does not account for all the oxygen consumed in the oxidation reaction; rather, it uses as an indicator a certain special type of peroxide which theoretically should increase with total oxidation.
Figure 1 illustrates the course of the autoxidation reaction of several vegetable oils, the reaction being followed by the peroxide titration technic. The sesame, cottonseed, corn, and oleo oils were all high-grade commercial products of good taste, color, and low free-fatty-acid content. In general it was found that with these oils the autoxidation proceeded until the curves reached a plateau, when no further increase in peroxide was found. Also, the decrease of the iodine number of the fat closely paralleled the increase in peroxide content as the autoxidation proceeded. In the case of the cottonseed oil used, when the iodine number had fallen to 65, no further oxidation occurred. If the oxidized oils were kept long enough, it was found that the peroxide values decreased. Also, oils kept in the light, or to which were added free organic acids, oxidized a t a faster rate. The presence of
Vol. 27, No. 3
water inhibited somewhat the oxidation of these oils when that oxidation was catalyzed by the cobalt catalyst. Corn oil is known to have a longer induction period and to resist oxidation somewhat. Crawford and Mattill (1) believe that this inhibition is due to the relatively high amounts of plant sterols present in corn oil. Figure 2 shows the effect of adding 100 mg. of cholesterol, stigmasterol, sitosterol, and lecithin to 100 grams of cottonseed oil. Of the sterols, only sitosterol appeared to have any antioxidant properties. This sterol was found also to have some protective action on certain unsaturated hydrocarbons. It is apparent that the antioxidant properties of palm oil must be due in part to the sitosterol present in this oil; Markley and Mattack (6) have recently reported that the phytosterols of palm oil are largely sitosterol. In Figure 3 the antioxidant properties of vegetable lecithin (100 mg.) are compared with the well-known inhibiting property of potassium cyanide (50 mg.). This result was obtained with four different samples of vegetable lecithin, all produced by the Bollman extraction process. Cottonseed and soybean oils to which had been added lecithin in 0.1 and 0.05 per cent amounts withstood oxidation for 4 months when kept a t room temperature. Smaller amounts of vegetable lecithin afforded less protection. The optimum percentage of lecithin to be used probably depends upon the amounts of active catslyfit presI I I I I I/ I ent in the refined oil. Figure 4 gives the results with hydroquinone (12 mg.), diphenylguanidine (25 mg.), and lecithin (25 mg.) in approximately e q u i molecular amounts. In this r e a c t i o n , catalyzed by cobaltic acetate, neither as so '5 H~URS hydroquinone n o r FIGURE4. ANTIOXIDANT PROPERTIES diph en y 1gu n i d in e OF LECITHIN (25 MG.),HYDROQTJINONE (12 MG.), AND DIPHENYLGUANIDINEwas an efficient anti(25 MQ.) oxidant. If larger amounts of hydroquinone were used, the inhibition of oxidation was more complete. The oxygen uptake of this system was determined by the well-known Warburg technic, The results are as follows, and here again vegetable lecithin demonstrated its antioxidant property :
p '-m
OXYQENUPTAHB Oil 4Oil
+
Hours 2 3.6 11
cc
.
12.6 10.3 8.3
+
il 0.1% lecithin CC.
Cc.
cc.
0.7
1.8
0
2.6
0
1.8
0.4
1.4 1.4
a Three timea the amount of catalynt used in columns 2 and 3; about 3 mg. active metal per 100 grams od.
To what group in the lecithin or cephalin molecule may be ascribed its antioxidant property is unknown, but it seems more than likely that the active group is probably free amino or hydroxyl, It is probable that lecithin inhibits the oxidation of oils by forming inactive complexes with the met.allic catalysts. The antioxidant property of vegetable lecithin is easily destroyed by heating above 65" C. Therefore,
March, 1935
I N D U S T R I A L A N D E N G I N E E R I IC' G C H E 11 I S T R Y
lecithin should not be used as an antioxidant until the oils have been cooled to at, least 50" C. ACKNOWLEDGMENT The author is indebted to R. Schonheimer for the plant sterols used, to Joseph Eichberg, of the American Lecithin Corporation, for the several samples of vegetable lecithin, and to R. W. Gerard for t,he determinations of oxygen uptake given in the table.
331
LITERATURE CITED (1) Crawford and Mattill, IXD. ESQ.CHEX.,22, 341 (1930). (2) Greenbank and Holm, I b i d . , 25, 167 (1933). (3) Ibid., 26, 243 (1934). (4) Holm, Greenbank, and Deysher, Ibid., 19, 156 (1927). (5) Hyman and Wagner, J. Am. Chem. Sot., 53, 3019 (1933). (6) Markley and Mattack, Science, 80, 206 (1934). (7) Powick, W. C., J. Agr. Research, 26, 323 (1923).
R ~ C E I V ESeptember D 8, 1934.
Oxygen Removal from Boiler Feed Water by Sodium Sulfite KENNETH A. KOBEAND WARDL. GOODING Department of Chemical Engineering, University of Washington, Seattle, Wash.
LTHOUGH scale formaMoberg (8) successfully used The factors governing the rate of oxygen referrous sulfate and sodium sulfite tion from boiler f e e d moval from water by sodium sulfite are shown to water has been scientifito prevent oxygen corrosion. be the p H of the water, temperature, catalysts, cally attacked from a chemical He found the ferrous sulfate sucand inhibitors present in the water. standpoint, the prevention of cessful in scaled boilers until all Sodium m b t e may be used to remove oxygen c o r r o s i o n resulting from disscale had dissolved; then violent solved oxygen has been chiefly foaming occurred. By changing f r o m boiler feed water with assurance that the treated mechanically (9). In to sodium sulfite, foaming ceased reaction is immediately completed at temperathe removal of oxygen and other and oxygen corrosion and pitting lures found in the boiler or hot process softener. dissolved gases from feed water were prevented. In one installaAt outdoor temperatures the reaction is less rapid by m e c h a n i c a l m e a n s , two tion corrosion above the water and time must be allowed for the reaction to be general methods are used: reducline was attributed to the addition of the air pressure above tional carbon dioxide liberated completed. The use of 0.1 p . p . m. copper sulthe water and preheating of the by the use of ferrous sulfate, fate (1 pound in 1,200,000 gallons) will catalyze water. Although differing in but by changing to sodium sulthe reaction to completeness in 2 minutes unless the details of operskion, both fite and feeding into the lower inhibitors are present. m e t h o d s are based upon the drum the corrosion was entirely same fundamental principle exprevented. pressed by Henry's law. This states that the solubility of a OXIDATION OF SODIUM SULFITE gas in a liquid is proportional to the pressure of the gas over the liquid; the pressure of the gas is the partial pressure calSodium sulfite appears to be an ideal chemical for oxygen culated by applying Dalton's law. In the first method the removal as it is cheap, oxidizes rapidly, and produces a comresult is accomplished by reducing the total pressure and thus pound beneficial in the boiler. It was the object of this work reducing the partial pressure of the oxygen over the water. to study the various factors affecting the rate and completeIn the second, the partial pressure of the oxygen is reduced by ness of the oxidation under conditions comparable to the addiraising the partial pressure of the water vapor by heating the tion of sodium sulfite to feed water. water. Various modifications of these two methods are emThe autoxidation of sulfite solutions has been studied from bodied in the equipment now in extensive use. Corrosion in the standpoint of chemical kinetics (4, 10, 14, 15). The rate this equipment itself represents a fault of the system. of solution of oxygen and oxidation of the sulfite solution was Chemical methods for the removal of oxygen have been determined by the decrease in pressure in the oxygen in the proposed and used to some extent. An apparatus, termed a reaction flask. The reaction has been shown to be a chain deactivator, contains iron turnings which are oxidized to rust reaction (6, 11), so that the rate will vary greatly with cataby the oxygen in the water (9, 13). The rate of removal is lysts or inhibitors present in the solution. influenced by the rate of flow of the water through the apparaEXPERIMENTAL METHOD tus and the amount of iron surface exposed. This method has proved to be too slow and cumbersome for commercial use. AnWater to be used was collected and allowed to stand in a other chemical method is the direct addition of chemical com- closed bottle for some time before use. The oxygen content was determined by the Winkler method (7). Two hundred millipounds to the feed water. Fager and Reynolds (6) state that of water were placed in a 250-ml. bottle and allowed t o alkaline tannates have been used with success. Ferrous liters come to e uilibrium in a thermostat. From an oxygen deterhydroxide, sodium sulfide, sodium thiosulfate, and sodium mination t%e amount of sodium sulfite necessary to remove all sulfite (12) have been considered. The objections to the use ox gen from the water Sam le could be calculated. A sodium of such chemicals have been stated by Solberg (12) to be the suhte solution was then mage up t o such a stren h that 10 ml. solution contained this calculated amount ot@sulfite. This increase in the soluble salt content of the boiler water, or for- of could not be done exactly because of air oxidation of the sulfite mation of a precipitate from ferrous hydroxide, failure to solution, but the solutions were very nearly equivalent. In remove carbon dioxide or other gases, and lack of assurance making a determination, 10 ml. of the sulfite solution were added that the required reaction will be completed between the time to the 200 ml. of water in the bottle, and at the end of a specified time 25 ml. of standard iodine solution were added to stop the the chemical is introduced and the water evaporated from the reaction and the excess iodine was titrated with standard sodium boiler. thiosulfate solution. Blanks were run t o determine the relative
.A
