Directed Interesterification in Glycerides

ture for several hours at 572” F. (300' C.), ethyl acetate and ... form for laboratory use is a suspension of the finely divided solid ... In the ce...
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INDUSTRIAL AND ENGINEERING CHEMISTRY

July 1948

nitrogen in present-day fertilizer use. The experiments also indicate t h a t the rate of availability of urea-form nitrogen can be eontrolled t o approximate the nutritional requirements of long season crops by proper choice of the conditions under which the product is prepared.

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Einhorn, A,, Ann., 343, 207 (1905); 361 (1908); Einhorn, A,, and Hamburger, A,, Ber., 41, 24 (1908). Hale, W. J., U. S. Patent 2,096,742 (1937). Hodgins, T. S., andHovey, A. G., IND.ENG.CHEM.,30, 1021-9 (1938); 31, 673-7 (1939).

Kadowaki, H., Bull. Chem. SOC.(Japan), 11,284-91 (1936). Keenen. F. G.. and-Sachs,W. H.. U. S. Patents 2,255,026, 2.255.027 (1941).

ACKNOWLEDGMENT

The authors desire t o acknowledge the valuable assistance rendered by V. L. Gaddy and 0. C. Davis in the preparation of many of the products, and by Irene 0. McAuliffe in their analysis. LITERATURE CITED

Armiger, W. H., Forbes, I., Jr., Wagner, R. E., and Lundstrom, F. O., J . Am. SOC.Agron., 4 0 ( 4 ) , 342-56 (1948). Davis, R. 0. E., School, W., and Miller, R. R., IND.ENQ.CHEM.,

Marvel, C. S., Elliott, J. R., Boettner, F. E., and Yuska, H., J. Am. Chem. SOC.,68, 1681-6 (1946). Rohner, L. V., and Wood, A. P., U. S. Patent 2,415,705 (1947). Rubins, E. J., and Bear, F. E., Soil Science, 5 4 , 4 1 1 - 2 3 (1942). Stuart, N. W., Division of Fertilirer Chemistry, 112th Meeting AM.CHEM.SOC., New York, N. Y., 1947. U. S. Dept. Agriculture, press release, (April 11, 1947). Walker, J. F., “Formaldehyde,” A. C. S. Monograph 98, p. 257, New York, Reinhold Pub. Corp., 1944. 32,377-95 (1936). (16) Walter, G., Trans. Faraday SOC., (17) Yee, J. Y., and Love, K. S., Proc. Soil Science SOC.Am., 11, 38992 (1946). RECEIVED October 1, 1947. Presented before the Division of Fertilizer Chemistry at the 112th Meeting of the AMERICAN CHBMICALSOCIETY, New York, N. Y.

27, 69-71 (1935).

Dixon, A. E., J. Chem. SOC.,1 1 3 , 2 3 8 - 4 8 (1918). Edgar, D. E., U. S. Patent 2,101,534 (1937).

Directed Interesterification in Glycerides J

E. W. ECKEYl The Procter & Gamble Company, Ivorydale, Ohio Interesterification can change the composition and properties of a fat, simply by changing the arrangement of the different fatty acid radicals in the triglyceride molecules. Of the many possible arrangements, the one corresponding with completely random distribution of the fatty acid radicals is always approached when.a given fat is interesterified, by the processes previously known, in completely molten condition. In contrast, the method of directed interesterification at temperatures low enough to cause fractional crystallization, as described in the present paper, provides a considerable degree of control over the positions taken by the fatty acid radicals, so that a fat may be made to assume a composition and properties much different from those corresponding with random distribution. The essentials of the method and typical results obtained with various fats are given.

T

HREE processes have been called interesterification-

namely, interchange of radicals between ester and alcohol, between ester and acid, and between ester and ester. The first mentioned has had the most study for the longest time (16, $3); the formation of ethyl stearate by reaction of glyceryl stearate with ethyl alcohol was reported nearly a hundred years ago (7). I n comparison, ester-ester interchange has required more drastic conditions and has been generally less convenient to use. The application of ester-ester interchange to triglycerides is attractive, nevertheless, because of the large changes in composition and properties that could be produced if i t were possible to shift the various fatty acid radicals of a given f a t t o any desired positions in the triglyceride molecules. The number of uses t o which a given natural fat could be applied, and the number of fats and oils that could be used as materials for making a given type of product, could be increased by such means. Considerable attention has been given t o interesterification of glycerides in recent years (3, 9, 11, 16, 18, $0,23)but the poten1 Present address, E. W. Eckey Researoh Laboratory, 338 Crescent Ave., Cincinnati 15. Ohio.

tialities of the process have been limited by the fact t h a t no method has been available for controlling or directing the course of the reaction. As carried out in the past, the reaction has taken place at high temperature with all the reactants molten, in a single liquid phase. Under these conditions, the reaction tends to produce the equilibrium composition corresponding with complete shuffling of the various fatty acid radicals at random among the various hydroxyl groups of the glycerol. The compositions and properties of the products t h a t can be produced by such undirected interesterification, with a given fat as starting material, therefore lie within the range between the starting material and the equilibrium composition. The present paper describes a method by khich the reaction can be directed along a different path, so t h a t products with radically different compositions and properties can be produced. The method depends upon the directing influence exerted by the crystallization of part of the triglyceride mixture while interesterification is continuing to take place; its development was made possible by the fact t h a t ester-ester interchange can take place i n triglyceride mixtures at temperatures much lower than those previously known t o be adequate, and sufficiently low t o allow ordinary triglycerides having moderately high melting points t o crystallize. The conditions that allow such low-temperature reaction to occur, and typical results obtainable by directed interesterification of several fats and oils i n comparison with those obtained in the high temperature or undirected reaction, are described. CONDITIONS FOR ESTER-ESTER INTERCHANGE

Without catalyst, the reaction will take place but requires a high temperature and a long time. Friedel and Crafts (10) heated a mixture of ethyl benzoate and amyl acetate’ for 60 hours at 392 O t o 464 O F. (200’ t o 240 O C.) and obtained from the resulting mixture some amyl benzoate, but in such small yield t h a t separation was difficult. When they heated the same mixture for several hours at 572” F. (300’ C.), ethyl acetate and amyl benzoate were isolated easily from the products. Later

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workers have used cohditions within the range suggested by these results. Reid (22) obtained only a very small yield of ethyl acetate and benzyl benzoate from a mixture of ethyl benzoate and benzyl acetate that had been heated for 44 hours a t 410 to 421" F. (210" to 216" C.). With triglyceride mixtures similar results have been obt,ained; at temperatures below 482' F. (250 C.) the reaction is slow, and even a t temperatures near 572" F. (300" C.) a reaction time of several hours is required to complete the change in properties produced by the react'ion. Thus Normann ( 9 ) lieated a mixture of 10 parts of tristearin and 90 parts of soybean oil for 17 hours a t 482" F. (250" C.) and found that the melting point had dropped from 130.1" to 110.7" F.; a further period of 7 hours at 482 caused the melting point to drop to 93.7 '. Van Loon found that the melting point of a mixture of 20 parts of beef stearin and 80 parts of soybean oil dropped from 108.5" to 97.0" during 16 hours' heating a t 527" F. (275" C.), and stated (16) that the reaction still was not. a t an end. Other results in line with these have been obtained (8). The reaction temperature can be lowered by the use of ca,talysts. Numerous substances have been proposed. for this purpose, including acids, bases, sodium ethylate, compounds of alkali and alkaline earth metals, water, and metals such as tin, zinc, cadmium, and lead and their compounds. The cat,alysts most frequently mentioned are metallic tin and stannous hydroxide, which make possible the use of temperatures in the neighborhoodof450" F. or alittle lo\yer (5,9, 16,20). I n the present investigation, alkali metal alkoxides have been found t o be extremely effective catalysts when used under the proper conditions. Sodium ethylate has been used before (9, 16, 19) as catalyst for interchange in glycerides, but was used at temperatures from 275 to 400" F. which are much higher than is necessary when the catalyst is prepared and used under favorable cpnditions, and higher than is desirable in view of the reactions other than interesterification that are catalyzed by sodium alkoxides a t elevated temperatures. All the reaction conditions cited have involved temperatures much too high to allow triglycerides to crystallize, even those having the highest melting points; the reactions therefore have been single-phase reactions. Interesterification takes place rapidly a t temperatures below 120" IF. with sodium alkoxide catalyst in proportions as low as 0.1% or less, when the glyceride mixture before addition of catalyst is dry, acid-free, and peroxide-free and when the catalyst is dispersed rapidly throughout the mixture a t the moment of addition. This is accomplished by using the catalyst in appropriate form, and by stirring or shaking the mixture vigorously when the cat.alyst is added. To prevent loss of c?talyst during the reaction, air and moisture should be excluded from the reaction vessel. Sodium methoxide is effective when added as a concentrated methanol solution or as a fine powder. A convenient form for laboratory use is a suspension of the finely divided solid in xylene, or in other nonreacting solvent, made by a modification of the method of Bruhl ( 6 ) . With catalyst prepared and used in t,his way, interesterifieation will take place a t temperatures low enough t o allow part of the triglycerides in a reaction mix t o crystallize while the reaction is proceeding. EXPERIMENTAL UNDIRECTED INTERESTERlFICATPON

The temperature can be kept high enough to prevent crystallization', even though such active catalysts are being used. In that case, the result is not fundamentally different from that obtained with other catalysts except that equilibrium is attained more quickly. The. reaction of cottonseed oil under these conditions was used to test the activity of catalyst preparations and to study the effects of undirected interesterification.

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PREPARATION OF SODIUM SIETHOXIDE IN XYLENE SUSPENSION. In the center neck of a 1-liter three-necked Pyrex flask was fixed a stopper through which was passed a long bearing for an iron shaft driven by a 4000-r.p.m. electric motor. The lower end of the shaft carried a hollow T-shaped agitator which would draw liquid up from near the bottom of the flask and throw it out through the horizontal arms of the T. To one side neck of the flask was attached a reflux condenser, the top of which was connected to an oil seal to prevent diffusion of air into the system. The other side neck carried a Keston thermometer, inlet for nitrogen, and connection to a dropping funnel for admitting alcohol, With 500 ml. of dry xylene a t room temperature in the flask, 23 grams of freshly cut sodium were added through the center neck. The flask Kas then closed and a stream of purified nitrogen was passed through the flask while the xylene was being heated to 212 'F. After the sodium had melted, the stirrer was started and the temperature kept at 212" or alittle higher. After thesodium was finely emulsified, the addition of methanol from the dropping funnel, which contained 33.6 grams of anhydrous methanol diluted with 2 volumes of xylene, was started. The heat of reaction raised the temperature to about 230" F.; the temperature was held a t about this point during the addition of the methanol, which took about 1hour. Agitation was continued until the mixture lost all grayish color and became a white suspension. The mixture was then allowed to cool, still in the atmosphere of purifiedaitrogen, and then was transferred to a reagent bottle. Concentration of sodium methoxide in the suspension was determined by titration in alcohol of a sample pipetted from the freshly shaken suspension by means of a pipet with a wide opening to avoid clogging and permit rapid transfer. The reaction of sodium above its melting point with the alcohol much more rapid than the reaction of a cooled suspension of sodium; it is believed to be safer as well as more rapid to run the reaction as described. Other styles of agitator, such as a slower speed folding-blade stirrer with shaft passing through a stuffing box, have been used satisfactorily. Alkoxides have been made from various alcohols other than methanol by the same procedure, except that in some cases i t is necessary to use a larger proportion of xylene to keep the suspension thin enough to handle conveniently. UNDIRECTED INTERESTERIF'ICATION O F COTTONSEED OIL. When cottonseed oil is hydrolyzed and re-esterified, or when direct interchange of radicals is brought about, a change in the melting point and associated properties of the oil occurs. The cloud point ( 1 ) is a convenient means for observing the progress of the interchange reaction. 1s

TABLE I. INTERESTERIFICATION OF COTTONSEED OIL AT 100" I?. AND HIGHERTEMPERATURES Cloud Point, ' F.,after Indioated Catalyst" Reaction Time 10 1.5 3.0 20 NaOCHs Form % of oil Original min. min. mln. hours Solution 0.1 26 43 49 57 Solution 0.02 26 34 36 37 120 Solution 0.04 26 39 44 47 120 Solution 0.06 26 50 56 59 120 Solution 0.1 26 54 59 59 120 Solution 0.1 26 54 56 57 140 Solution 0.1 26 . 57 57 58 26 180 Solution 0.1 57 58 220 Solution 0.1 26 57 58 120 Suspension 0 06 26 39 ,. 54 56 120 Suspension 0.1 26 49 58 58 Catalyst was a 20% solution of sodium methoxide in methanol, made by dissolving sodium in anhydrous methanol, or a suspension of sodium methoxide in xylene prepared as described in text. Reaction Temp., ' F. 100 120

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A few typical data are given in Table I. Rearrangement of the radicals causes the cloud point to rise rapidly a t first and then more slowly until a value of 56 O to 59 F. is reached, after which continued interchange produces no further net change in oomposition and properties. O

In these experiments, refined filtered cottonseed oil was dried by heating it under vacuum to 355" F. with agitation with steam, followed by cooling under vacuum. The oil was then transferred to a 3-necked round-bottomed flask, fitted with a drain cock at the bottom, from which samples could be withdrawn, a stainless steel 'motor-driven agitator, operating through a stuffing box,

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thermometer, inlet for purified nitrogen, outlet passing through a n oil seal, and inlet for admitting catalyst. With the dried oil in the flask, nitrogen was passed through to displace air, and the oil was heated to the desired temperature. Catalyst was then added during vigorous agitation of the oil. At the end of 10- and 30-minute agitation, samples were drawn off into bottles containing dilute aqueous hydrochloric acid and shaken t o destroy the catalyst. The oil was then washed thoroughly with water to remove mineral acid and given a light deodorization with steam under vacuum. After the 30-minute sample wm taken, the reaction flask was disconnected from the stirrer and other accessories stoppered, and placed in a constanttemperature oven overnight, after which another sample was taken and tested as before. With sodium methoxide catalyst i n proportion as low as O.OS%, equilibrium is reached in about 30 minutes a t 120' F. Other alkoxides were prepared in xylene suspension from various alcohols, including ethanol, isopropanol, tert-butanol, ethylene glycol, laurol, and others; on a molar basis they were approximately as active as sodium methoxide. EFFECT OF UNDIRECTED INTERESTERIFICATION ON GLYCERIDE COMPOSITIONS

Many of the natural fats, especially the fats contained in seeds, have glyceride compositions which differ considerably from the compositions they would have if their fatty acid radicals were combined indiscriminately with the glyceryl hydroxyl groups in a random or unoriented distribution ( l a ) . The compositipns 1. Triunsaturated glycerides produced i n nature are such that the seed fats, especially, contain 2. Trisaturated glycerides 8. Monosaturated diunsaturated glycerides a smaller proportion of fully saturated glycerides than the pro4. Disaturated monounsaturated glycerides portion calculated for random distribution. Thus, cottonseed oil has been estimated to contain only about 0.1% trisaturated on iodine numbers or other characteristics of the isoglyceride (14), although about one fourth of its fatty acids are lated fraction (17). In the present work, a single saturated acids. crystallizatioh from petroleum ether was used t o concentrate If interesterification shuffles the fatty acid radicals so that the high-melting fraction of the fat being examined. The method they are distributed a t random, i t should when applied to cottonwas used for comparative purposes, and was not intended to be seed oil cause a n increase in the proportion of saturated triglyca precise measure of the quantity of trisaturated glycerides; eride; because this type of glyceride has the highest melting it did, however, yield fractions with low iodine number, and in point, an increased proportion should produce a rise i n melting many cases serves as a fairly good measure of the saturated point and cloud point of the fat as a whole, as observed in Table I. triglycerides, The published information available on the subject indicates that interesterification does produce random distribution within Fifty grams of fat were dissolved in 500 ml. of petroleum ether the accuracy of the methods available for determining the comin a 1-liter flask and held 20 hours or longer in a constant-temperature box at 40' or 50 O F. The mixture was then filtered with position of glyceride mixtures (2, 30). Likewise, synthesis of suction on a 10-cm. (4-inch) Buchner funnel which had been held triglyceride by esterification of mixed fatty acids with a n equivaat the same temperature. The stearin on the filter was washed lent quantity of glycerol yields a product containing approxiwith 250 ml. of petroleum ether, also at the same temperature, matelv the calculated auantitv of saturated glyceride (4). then transferred to a tared Soxhlet flask, heated on the steam bath The calculation of the composition corresponding with random distribution is easily TABLE 11. UNDIRECTED INTERESTERIFICATION made ( 2 ) ; for the case of triCrystals from Petroleum Ether glyceride mixtures having two Capillary Temp. of Capillary kinds of fatty acid, the comThioCloud Melting arystalmelting Iodine cyanogen Point, Point, Unsapon- lization, Yield, Iodine point, positions are shown in FigFat No. No. a F. F. ifiable, % a F. % No. F. ure 1. Cottonseed oil 1 *.. ... .. . . . .. .. 109.3 U n f o r t u n a t e l y , practical if ... ... 40 None .... .* 108.4 40 0.8 .. Same, 16 hours a t 120° 58 ... ... ... 67.5 methods for determining the 0.2% sodium %thoxide catalyst proportions of the various 40 1.2 .. .. ... 50 ... ... Cottonseed oil 2 30 108.9 glycerides i n complicated mixmin. a t 120° F. k i t h 0.15% sodium methtures are not available, but oxide 79 105.2 ... 50 6.3 7.2 142 it is possible to determine apPalm oil 1 52.7 ... .. ... ... 50 11.2 3.4 136 Same, 72 hours a t 120° ... , .., proximately the proportion of F 0.15% sodium mAthoxide the fully saturated triglyceride ... 82 113.4 0.37 50 8.7 9.3 142 50.9 Palm oil 2 84 121.2 0.28, 50 13.1 4.4 139 fraction. With glycerides in Same 30 min. a t 120° ... F.,' 0.15% sodium which the saturated acids are methoxide ... 83 119.3 1.11 50 10.7 4.0 139 Same, van Loon pro... principally palmitic and acids cedure (16) 2 hours of higher molecular weight, a t .2000 d.,. 0.9% sodium ethoxide this can be done by isolat41.0 91 116.2 50 13.9 7.4 135 Tallow 45.8 89 112.3 50 13.7 7.0 132 Same, 30 min. at 120' ing the saturated fraction by F., 0 . 3 p sodium crystallization from solvent, methoxi e and applying corrections based

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SATURATED FATTY ACIDS,

Figure 2.

PERCENT OF

TOTAL FATTY

ACIDS

Effect of Undirected Interesterification

,

1. Cottonseed oil 2. Cottonseed oil interesterified a t 120' F. 3. Palm oil 1 4. Palm oil 1 interesterified a t 120' F. 5 . Palm oil 2 6. Palm oil 2 interesterified a t 120' F. 7. Tallow 8. Tallow interesterified at 120' F. The saturated f a t t y acids in the mixed f a t t y acids of palm oil 1 were calculated from the weights, iodine numbers, and thiocyanogen numbers of the fractions obtained by precise ester-fractionation of the fat. For t h e other three fats, the saturated f a t t y acids were calculated from the iodine numbers and thiocyanogen numbers of the whole fats.

with a stream of gas to remove solvent, and weighed. The iodine number of the stearin was determined to indicate its degree of unsaturation; the presence of unsaturated material can be due either to mother liquor retained by the crystals or to the crystallization of partly unsaturated glycerides along with the saturated glyceride fraction. The results obtained by interesterification of a few samples of fat at 120' F. with sodium methoxide catalyst are given in Table 11. The yields of stearin obtained on crystallization from petroleum ether before and after the interesterification are shown in Figure 2, in relation to the estimated proportion of saturated fatty acid in the fats. Curve 2 from Figure 1 has been sketched in to show the relation of the results to the values calculated for random distribution. (The slight inconsistency due to the use of the weight basis for the data and molar basis for the curve is insignificant for the fatsincluded in Figure 2). Palm oil and cottonseed oil, which give points falling below the curve, were brought t o the curve by interesterification. Tallow, which before interesterification contains a quantity of saturated glycerides very near t o that calculated for random distribution ( l y ) ,was almost unchanged by the treatment. F a t mixtures whose compositions would fall above the curve may be made artificially, as, for example, the mixture of 10 parts of tristearin with 90 parts of soybean oil used in the experiment by Normann, cited above. Interesterification of such mixtures would cause a decrease in the content of saturated glycerides and a Iowering of the melting point as was observed by Normann. DIRECTED INTERESTERIFICATION O F GLYCERIDES

The surprising speed of the intere4terification reaction a t 120 O F. and lower temperature led to the hope that the reaction could be made to proceed in a glyceride mixture simultaneously with crystallization of the higher-melting portions of the mixture. This was tried first with palm oil, which contains enough saturated fatty acid to cause the glyceride mixture at random distribution to have a moderately high melting point.

Vol. 40, No. 7

The result was that crystallization of glyrerides did take place from palm oil while it was being interesterified a t 100' F.; when the reaction was allowed to continue under these conditions, it yielded a product radically different from that produced at higher temperatures. Presumably the reaction between the solid and liquid phases is so much slower than the reaction within the liquid phase that the crystallized portions of the mixture are withdrawn effectively from the reaction, so that. new equilibria corresponding with the changing compositions of the liquid phase are continually approached. This influence over the course of the reaction has remarkable power, in spite of the fact, that in most cases t,he crystallization takes place in such a way that the solid phase does not settle out during the reaction but remains finely distribut'ed t'hroughout the mixture. Furthermore the influence cont,inues, in a fatlike palm oil, even after the fat as a whole appears to have solidified and has become t,oo firm to be poured or stirred. PALMOIL AT 100' F. Typical results of interesterification of palm oil at 100" F. are given in Table I11 and Figure 3.

Refined palm oil was dried by heating it under vacuum With agitation at 392 F' (200" c.), then cooling in an atmosphere of nitrogen. The dried oil was placed in a round flask fitted with a motor-driven agitator with folding stainless steel blades. With an atmosphere of nitrogen in the flask, and with the oil a t 100" F., catalyst consisting of 0.5% of a 20% solution of sodium methoxide in methanol was mixed with the oil. I n the "unseeded" series, the oil had been cooled directly to 100" F. after the drying a t higher t'emperature, and thus was in a slightly supercooled condition when the catalyst was added. I n the seeded series, the dried oil was held in the reaction flask overnight a t 70 F., then warmed slowly to 100 F., so that when the catalyst was added the oil contained a small proportion of solid glycerides, finely dispersed throughout the mixture. Agitation was continued for 4 hours, within which time a noticeable thickening and an increase in opacity of the mixture were observed. At the end of the second hour a sample was taken and treated to destroy the catalyst. At the end of 4 hours another sample was taken, and the remainder of the mix was transferred t o bottles which were stoppered and placed in a constant-temperature cabinet at 100' F. These were successivelv treated to destroy catalyst a t the times indicated in the table. " To destroy the catalyst the fat was mixed with dilute phosphoric acid at the reaction temperature. After the acid had been mixed with the fat, the mixture was warmed and stirred until the fat was melted, after which i t was washed with water until free from mineral acid. If the fat were to be melted before destruction O

TABLE111. INTERESTERIFICATION OF P ~ L M OIL

AT 100" F. Stearine Crvstitlliaed capillary from Petrol&m Ether Reaction Cloud Melting __ a t 50° F. Time, Point, Point, Yield, Iodine Melting Hours F. pt., F. % No. ' F. 75.2 107.2 Original palm oil 6.2 6.8 141.4 2 83.1 117.3 Interesterifieda, 11.7 3.8 137.8 4 124.3 88.3 17.9 unseeded 3.0 140.7 6 126.8 91.2 21.8 . 2.5 141.8 129.9 94.1 14 25.8 2.3 142.3 129.5 24 26.8 94.3 1.8 142.9 130.4 94.5 48 27.7 1.6 142.7 Interesterifieda, 2 1Q.O 125.7 88.9 2.6 142.9 4 seeded 22.6 127.7 91 .Q 2.3 142.7 93.4 (see text) 25.2 128.4 ' 6 2.1 142.2 14 26.5 130 8 93.9 2.0 142.7 24 28.0 130.4 1.7 143.1 04.5 94.5 28.0 48 130.8 1.5 143.1 a Catalyst was 0.5% of a 20% Eolution of sodium methoxide in methanolLe., 0.1% sodium methoxide. I

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of the catalyst, the reaction would go back toward random distribution and the effect of the reaction with crystallization would to a large extent be nullified. The washed fat was then deodorized with steam under vacuum t o remove the small proportion of methyl esters formed by the methoxy groups of the catalyst solution. The quantity of fully saturated glyceride formed in the reaction at 100" F. reached about 27%; the limit for the high temperature reaction for the same oil is about 1201, (cf. Figure 2). This change, of course, is associated with corresponding changes in the proportions of the other types of glyceride present. The speed of the reaction was influenced by the provision of seed crystals i n the fat before the start of the reaction, the time required for a given proportion of trisaturated glyceride to be formed being cut approximately in half by the seeding. INTERESTERIFICATION OF PALM OIL AT 80 F. Alkali-refined palm oil (No. 2 of Table 11) was bleached with fuller's earth and dried by blowing with steam under vacuum a t 410 F. O

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The dried oil, in an atmosphere of nitrogen in a flask equipped with an agitator, was cooled to 50" to 55: F. for 1 hour, then warmed t o 100" F. and stirred for 30 minutes. The oil at this stage contained crystals and was an opaque fluid. Catalyst was added in the form of a suspension in xylene, in quantity to give 0.15 part of sodium methoxide per 100 parts of fat, and stirred into the fat vigorously. The oil was held a t 100" F. with continued agitation for 3 hours, by the end of which time a substantial increase in the proportion of solid in the fat could be observed. The reaction flask was stored, without further agitation of the fat, in a cabinet at 80 " F. for 16 hours. The fat was then macerated with glacial acetic acid in slight excess over the quantity e uivalent to the catalyst used, after which it was melted, filterel and heated under reduced pressure t o remove the xylene introduced with the catalyst. The product had the following characteristics: cloud point, 100.4 F.; melting point, 133.2 F.; yield of stearin when crystallized from petroleum ether a t 50" F., 36.101,; iodine No. of stearin, 1.3; melting point of stearin, 143.1 O F . Thus, the proportion of the total saturated acids in the oil that 'was accumulated in the saturated triglyceride fraction was substantially greater than i t was when the final temperature was 100" F. O

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INTERESTERIFICATION OF COTTONSEED OIL WITH SIMULCRYSTALLIZATION. Since about one fourth of the total fatty acids of cottonseed oil are saturated acids, as compared with nearly one half for palm oil, the proportion of high-melting glycerides formed by undirectea interesterification is smaller with cottonseed oil than with palm oil. A lower temperature is therefore required for the start of crystallization simultaneous with interesterification. At 100 " F., no solid crystallizes from cottonseed oil during interesterification; at 90 " F. some directing effect can be obtained from crystallization simultaneous with interesterification; at 80" F. and lower temperatures the directing effect of crystallization becomes large. COTTONSEEDOIL INTERESTERIFIED AT 80' F. Refined, filtered, dried cottonseed oil was mixed for 15 minutes at room temperature (82 O F.) with 0.2'34 sodium methoxide in the form of a suspension i n xylene. TANEOUS

The mixture was transferred to several small glass jars which were closed with metal screw caps with rubber gaskets. ditrogen was blown into the tops of the jars just before closing, in a n attempt t o replace the air in the free space. The jars were then placed in an apparatus whish rotated them on their long axes at 9 r.p.m. The apparatus was placed in a constant-temperature room held at 80" F. Crystallization took place gradually, so t h a t the oil became a slurry of fat crystals in oil. At intervals, individual containers were removed and treated to destroy the catalyst and remove the xylene. Observations on the samples are given in Table IV.

TABLEIV. COTTONSEED OIL INTERESTERIFIED' AT 80" F., WITH CONTINUOUS ROTATION Yield of Crystals from Petroleum Cloud Point, Ether at 40° F. (50-G. Sample, 500 Time of Reaction, Hours F. M1. of Petroleum Ether), % Original oil (iodine No. 27 None 109.3) . 22 9.2 46 10.1 91 83 10.9 136 85 11.6 a Catalyst, 0.2% of sodium methoxide, in form of suspension in xylene.

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The proportion of fully saturated glycerides rose rapidly, so that within less than 24 hours i t was several times as great as the maximum attainable by undirected interesterification. When several days were allowed for the reaction, about half the total saturated acids in the fat were accumulated in t h e fully saturated glyceride fraction. COTTONSEED OIL INTERESTERIFIED AT 70", 60°, AND 50" F. At 70' F., a still larger fraction of the oil could be converted to fully saturated glyceride. Table V gives results obtained at 70" and lower temperatures. I n these experiments, the oil was

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TABLE V.

Reaction Temp., O F. 70

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COTTONSEED OIL INTERESTERIFIED AT 70 ",60 ", AND 50" F.a

Time I*"

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16 hours 82 10.4 3.0 i4'i 24 hours 84 10.8 2.5 40 hours 85 12.0 3.7 141 141 14.0 7 days 89 13.6 16 days 88 6.2 5 60 17 hours 74 60 40 hours 80 86 16: 6 3.'1 60 112 hours 60 9 days 88 60 26 days 92 14:2 4:1 50 16 hours 74 2.8 3.9 40 hours 75 ., 50 50 9 days 80 i.'4 4:5 50 25 days 89 10.2 4.0 50 25 daysb 585 a Oil No 2 of Table I1 treated with 0.2% NaOCHs catalyst 30 minutes at 120°'F then chilled tdform a aloud then stored without agitation. 1, This :ample after 25 days at 50° $., was held 24 hours at 120° F. before treatment to destroy catalyst. 70 70 70 70 70

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Cloud Point, O F.

Crystals from Petroleum Ether at 40° F. (50-G. Bample, 500 M1. of Solvent) Melting Yield, Iodine point, % No. O F. 1.2

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TIME, HOURS

Figure 3.

Directed Interesterification of Palm Oil at 100" F. t

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INDUSTRIAL AND ENGINEERING CHEMISTRY

Vol. 40, No. 7

first carried to random distribution by being mixed with the catalyst for 30 minutes a t 120" F., then transferred t o small containers which were chilled until the oil became cloudy, then placed i n constant-temperature boxes a t the temperatures indicated in Table V.

For these reasons, a stepwise or gradual reduction in temperature during interesterification in many cases will cause the formation of a greater proportion of high-melting glycerides in a shorter time than is obtained by use of a single temperature throughout the reaction. By stepwise reduction of the temperature of cottonseed oil beginning a t 70 F. and ending at 40 F. as much as 19% of the oil has been converted to fully saturated glyceride. TABLEVI. COTTONSEED OIL INTERESTERIFIED AT 50" F.0 TALLOW.Tallow is an example of a fat which is not much Crystals from Petroleum changed by undirected interesterification, because the composiEther at 40' F. (50-G. tion of the natural fat is not far from that calculated for random Sample, 500 M1. of S n. l w-n ) -. -t., distribution (I?'). Cloud Melting Time a t Iodine Point, Yield, Iodine point, Table VI11 gives results obtained with edible tallow inter50° F. No. % No. F. F. esterified a t various temperatures. The fresh deodorized tallow Oil before treat0 106.3 26 was mixed with catalyst for 30 minutes at 120" F.; portions of ment 30 min. a t 120° F. 0 ,. 58 .. ~. .. the mix, in stoppered bottles, were held 30 minutes in a 50" F 18 hours . . 69 .. cabinet t o start crystallization, then stored in constant tempera13 days .. 88 79 days _. 89 14:8 2.4 137 ture cabinets at the temperatures shown in the table. 4months ~. 89 15.2 ~, *. 4 monthsb .. 59 .. .. ~. The interesterification without crystallization, a t 120 F., a Oil, treated with 0.2% NaOCHs, 30 minutes a t 120° F., sealed under produced a relatively small change in characteristics of the fat vacvum in Pyrex tubes and held in room a t 50° F. With progressive cryqtallization a t lower temperatures, the fat b Sample after 4 months a t SOo F. was held for a day a t 120° F. before treatment to destroy catalyst. became harder and higher melting, owing to a large increase in the proportion of saturated glycerides as shown by the proportion of glycerides insoluble in petroleum ether at 50 " F. As shown by the results in Table VII, this chilling to induce The reaction with stepwise reduction of the temperature to crystallization increases the rate of the reaction at. 70" F., when 70" F. produced a greater change in the fat than reaction a t 70" agitation is not used. throughout. MEKHADENOIL. h sample of menhaden oil, iodine No. 177.5, having saturated acids as estimated by Twitchell analysis TABLE VII. EFFECT OF CHILLING TO INDUCE CRYSTALLIZATION equal to 24.5% of total fatty acids, was blown with steam under Cloud Point of Treated Oil, F. vacuum for 30 minutes a t 350" F. O

I

I

I

.

Chilled in ice box until cloudy Time a t 70° F.@ Not chilled before placed a t 70° F. 22 hours 68 83 2 days 78 .. 5 days 85 88 5 Cottonseed oil treated with 0.2% NaOCHs 30 minutes a t 12OCF., then held without agitation at 70° F., with and withd.ut chilling.

.

At 60' F., the formation of high-melting glyceride vias slomer than at 70" F., but eventually the proportion equaled or exceeded that formed at 70" F.; at 50", still slower formation of highmelting glycerides was observed, but as shown by the data of Table VI, the proportion will exceed that formed a t higher temperature if sufficient time is allowed. The slowness of the formation of fully saturated glycerides at 50" F. in comparison with 70" F. is due not only to the slower rate of the intercsterification reaction a t the lower temperature, but to crystallization of the intermediate-melting disaturated monounsaturated glyceride fraction along with the trisaturated fraction. This is manifested in Table V in the difference in the relationship a t 50' and 70" F. between cloud point of the fat and the yield of glycerides insoluble in petroleum ether. By reference to Figure 1, it may be seen that a fat whose fatty acids are 25y0 saturated may be expected to have more than 40% of disaturated monounsaturated glycerides and about 1.5% of trisaturated glycerides when completely interesterified without directing influence. If such a fat is cooled rapidly to a low temperature, some of the disaturated fraction will solidify, together with most of the trisaturated fraction. Various observations on interesterified cottonseed oil indicate that a t 70" F. and higher temperatures, the solid that crystallizes during interesterification is mainly trisaturated glyceride, but that when the oil after being carried to random distribution is cooled rapidly to temperatures below 70" F., the solid that crystallizes contajns mixed saturated-unsaturated triglycerides. Since the reaction takes place much more slowly between solid and liquid phases than it does within the liquid phase, a very long time is required to reach the final equilibrium composition after crystallization of a solid fraction containing a large proportion of intermediate-melting glycerides has taken place.

The oil at 120" F. was mixed for 30 minutes with 0.2% sodium methoxide catalyst in the form of a suspension in xylene, then cooled quickly to 85' F. and mixed with 1% of a crystal slurry of cottonseed oil that had been interesterified at 70" F. After this seeding with crystals, the vessel containing the mix waa closed air-tight and placed in an apparatus which rotated it s l o ~ l y(about 9 r.p.m.) for 20 hours in a room held at 80" F., then for 26 hours at 70" F., and finally 96 hours a t 60" F. After removal of catalyst and xylene, a portion of the mix was dissolved in petroleum ether (50 grams of fat, 500 ml. of solvent) and held overnight at 20' F. The yield of crystals obtained after filtration

TABLE VIII.

Reaction Temp., O F. Original fat 120 100 100 100 100

100 90 80 70 60

---

1 nn

90 70 100 90 80 70 60 50

INTERESTERIFICATION OF TALLOW" AT VARIOUS TEMPERATURES

Timeb, Days 30 'min. 1 . 5 hours 3 . 0 houra 5.5hours 23hours 7 7 7 7 7 11

1. 5 3' 2 2 3' 2 2,

Properties of Whole F a t Cloud Melting point, point, F. F. 91 115.2 89 112.3 93 94 95 li8.6 97 99 IZi.8 100 100 99 122 99 120.2

..

..

Crystals from Petroleum Ether a t 50° F. (50-G. Sample, 500 MI. of Solvent) Melting Yield, Iodine point a F. % No. 13.9 7.4 134.8 13.7 7.0 132.3 16.1 5.9 133.2 19.0 5.4 135.5 19.6 5.6 138.0 21.8 4.5 135.5 24.0 4.6 134.3 28.4 4.7 135.9 30.0 4.6 135.0 30.7 6.1 135.5 25.5 5.7 135.5

..

36.2

3.7

136.2

..

39.9

3.7

135.9

'

July 1948

INDUSTRIAL AND ENGINEERING CHEMISTRY

and removal of solvent was 21.9%; iodine No. of the crystals, 4.6. The original menhaden oil subjected t o the same crystallization from solvent yielded 1.1% of crystals. ,

Thus, by the process of simultaneous crystallization and interesterification, with seeding, continued agitation, and stepwise reduction of the temperature, it was possible to accumulate nearly all of the saturated acids of the oil in the trisaturated glyceride fraction. COCOABUTTER. The natural arrangement of the fatty acids in cocoa butter, in contrast with the arrangement in tallow, is such that although about 60% of the fatty acids in cocoa butter is saturated acid, the trisaturated glyceride content is only about

2% (IS). A sample of cocoa butter, iodine No. 38.7, capillary melting point, 91" F., was refined with alkali, filtered, and blown with steam under vacuum a t 410' F. When mixed with petroleum ether (50grams of sample, 500 ml. of solvent) and held 20 hours a t 50 " F., the fat yielded only a trace of crystals, indicating that

the proportion of trisaturated glycerides was small. A portion of the refined, deodorized fat was mixed with 0.45% of sodiu-m tert-butoxide in the form of a suspension in xylene; The mix was stirred, with exclusion of air, for 45 minutes at 120 to 130' F., then held without stirring for 24 hours a t 100O F., 24 hours at 90" F., and 24 hours a t 80" F. The solid fat thus obtained was macerated with glacial acetic acid in quantity e ual to 1.75 times the quantity equivalent to the catalyst used. %he fat was then melted and washed with dilute phosphoric acid and with water. After re-refining and deodorization it was found t o have a melting point of 135.9' F., and when crystallized from petroleum ether a t 50' F. it yielded 46.6% of crystals having an iodine No. of 2.9.

MAXIMUMCONVERSION AT VARIOUS TEMPERATURES. The data given for the different fats show that the quantity of saturated triglyceride that can be formed depends principally upon the kind of fat or fat mixture being handled, the temperature a t which crystallization occurs, and the time allowed. Figure 4 summarizes a large number of observations in terms of the practical maximum proportion of saturated triglyceride that has been formed a t various final temperatures when favorable conditions such as gradual reduction in temperature and liberal reaction s time were used. Individual batches of the fats named may deviate somewhat from the values shown, owing to the natural variation in the proportion of saturated fatty acids occurring in different batches of fat from the same source. Further development of the method may make it possible to raise the curves somewhat in the range of temperatures that allow crystallization to take place. DIRECTED INTERESTERIFICATION IN SOLVENT

The interesterification with simultaneous crystallization can be carried out with mixtures of glycerides and nonreacting solvents such as pentane, hexane, benzene, and toluene. In general, lower temperatures are required when solvent is present; the high-melting glycerides appear to be more soluble in the volatile solvents than in the liquid glycerides. Solvents such as alcohol would cause alcoholysis of the glycerides. ALTERNATIVE CATALYSTS

Sodium or potassium alkoxides made from a variety of alcohols have been found active enough to catalyze interesterification a t the low temperatures required for simultaneous crystallization. Sodium methoxide is attractive because of its low cost and its relative stability. In the form of a suspension in xylene or as a solution in methanol it is about equally effective, indicating that the presence of free alcohol is not an essential factor in the reaction. The suspension containing no free alcohol has the advantage that i t forms less methyl ester as a by-product than is formed when additional methanol is present. Practically all the methoxy groups added as catalyst or as free methanol appear as fatty methyl esters in the product. For some applications of

,1189

7

4

ED OIL

)YBEANOlLl )

,

40

FINAL TEMPERATURE OF INTERESTERIFICATION -'E Figure 4. Practical M a x i m u m Proportions of Tris a t u r a t e d Glycerides Formed by Interesterification at Different Final T e m p e r a t u r e s

the fats, such as in edible shortening, these by-product ester* must be removed by deodorization. In this respect, alkoxides made from tertiary alcohol-e.g., sodium lertbutoxide-have the advantage that a smaller proportion of nonglyceride ester is formed. It seems likely that the actual catalyst is formed by reactiori between the added alkoxide and the glycerides, so that any material capable of forming the alkali metal compound with the glyceride can form the catalyst. Sodium triphenylmethyl was found to be active; no doubt any of the organo-alkali compounds would be effective. Compounds of sodium with material much more acidic than alcohol, on the other hand, have not been found useful. For example, sodium phenoxide and sodium soap failed to catalyze the interesterification a t the low temperatures required for simultaneous crystallization. STABILITY OF CATALYST IN PRESENCE O F GLYCERIDES

The catalyst in mixture with fat is remarkably stable, provided that moisture and oxygen are excluded. Any moisture present, of course, allows the alkali metal compound to saponify an equivalent quantity of the fat to form soap, The data at the bottom of Tables V and VI show that the catalyst is active in a mixture that has been held for months in a sealed container; the fat aftgr having been interesterified a t low temperature t o form a large proportion of saturated glycerides was brought back t o the condition of random distribution simply by holding i t for a time a t a temperature above its melting point. In another case, the catalyst in a mixture that had been held for two years was found to be active. PRACTICAL APPLICATIONS O F DIRECTED INTERESTERIFICATlON

To give a detailed description of applications of the method is beyond the scope of this paper, but some of the possibilities may be mentioned. * Oil like cottonseed oil can be converted to the semisolid type

.

1190

INDUSTRIAL AND ENGINEERING CHEMISTRY

of shortening without hydrogenation, simply by the exchange of radicals in the glycerides. Such a shortening may have a n advantage, nutritionally, over a shortening containing a smaller quantity of unsaturated fatty acid. Palm oil as a n ingredient in shortening has the disadvantage that i t contains a high proportion of glycerides which have melting points within the range of ordinary room temperatures. For this reason, a shortening containing a large proportion of palm oil does nothave a good plastic range-that is, its consistency changes to a n undesirable degree with change in temperature. By the directed interesterification method palm oil may be improved in this respect, because its proportion of high- and lowmelting glycerides can be increased very greatly with correTponding decrease i n the proportion of intermediate-melting glycerides. The oil rearranged in this way may be mixed with oil such as cottonseed oil or bean oil, or with partially hydrogenated oils of soft consistency to make shortening with good plastic range, or the rearranged palm oil may be separated into fractions by graining and pressing or crystallization from solvent an! the fractions utilized in appropriate ways to produce superior products. Tallow, likewise, can be made more satisfactory as a material for shortening. Coconut, oil and other oils of its class can be made harder and higher melting, so that they are suitable for use directly as confectioners’ butters without graining and pressing to separate them into stearin and olein; by combinations of directed interesterification with graining and pressing and/or hydrogenation, confectioners’ butters of superior quality can be made in high yield. Fish oils suffer in many applications from the high proportion of saturated acids contained in them in the form of mived glyc erides, only a portion of which can be removed by ordinary winterizing ( 5 ) . By directed interesterification followed by graining and pressing, or by separation with selective solvents, most of the saturated constituents can be removed as saturated triglyceride, with a high yield of oil having a very small proportion of saturated constituents. Numerous possibilities exist for the improvement of fats for specialized uses, including hydrogenated fats. The directed interesterification method is covered by patent applications non- pending, and by two issued patents (21).

Vol. 40, No. 7

ACKNOWLEDGMENT

Grateful acknowledgment is made to F. H. hlaxfield, R. G. Folzenlogen, W. Lange, IGI. W. Formo, and other members of the Procter & Gamble Oil Research Laboratory, who performed most of the experimental \1-ork, and to A. S. Richardson for his helpful supervision and support throughout the investigation. LITERATURE CITED

(1) Am. Oil Chem. Soc., “Methods for Sampling and Analysis of CommercjftlFats and Oils,” revised, p. 35,1943.

(2) Bailey, A. E., Industrial Oil and Fat Products,” p. 683, New York, Interscience Publishers, 1945. (3) Ibid., DW. 684-5. i4) Bhattacharya and Hilditch, Proc. Roy, Soc. ( L o n d o n ) , A129, 472 fI93O’r ( 5 ) BrocklLsby, H. N., Fisheries Research Board of Canada, Bull 59, 333 (1941). (6) Bruhl, J. W., Be?.. 37, 2067 (1904); cf. ”Organic Reactions.” Vol. I. D. 279, New York. John Wilev & Sons. 1942. (7) Duffy,Patrick, J . Chem. Soc. ( L o n d o n j , 5, 303-16 (1852). (8) Eokey, E. W., U. S. Patent 2,378,006 (1945). (9) Firma Oelwerke Germania G.m.b.h. and Wilhelm Normann. German Patent 417,215 (1925), (IO) Friedel and Crafts,Ann., 133,207-11 (1865). (11) Gooding, C. M., U. S. Patent, 2,309,949 (Feb. 2, 1943). (12) Hilditch, T. P., “Chemical Constitution of Natural Fats,” Chaps. VI and 1‘11, New York, John Wiley & Sons, 1940. (13) Ibid., pp. 156, 202, 210. (14) Hilditch and Maddison, J . SOC.Chem. Ind.,59,163-7T (1940). (15) Houben, “Die Methoden der organischen Chemie,” 3rd ed., Vol. 2, pp. 704-15, Ann Arbor, Mioh., Edwards Bros., 1943. (16) Loon, C. van, U. S.Patent 1,873,513(Aug. 23, 1932). (17) Luddy, F. E., and Riemenschneider, R. W., Oil and Soup, 23, 386-9 (1946). (18) Markley, K. S., “Fatty Acids,” Chap. X, New York, Interscience Publishers, 1947. (19) Naudet, M., and Desnuelle, P., Bull. SOC. chim., 1946, 595-8. (20) Norris, F. A., and Mattil, K. F., Oil and Soup, 23, 289 (1946). (21) Procter and Gamble Co., Britihh Patent 574,807 (Jan. 22, 1946); 590,737 (July 28, 1947). (22) Reid, E. E., Am. Chem. J.,45,479 (1911). (23) Reid, E. E., in Groggins, “Unit Processes in Organic Synthesis,” pp. 508-11, New York, McGraw-Hill Book Co., 1935. ~

RECEIVED August 30, 1947. Presented before the Division of Agricultural and Food Chemistry a t the 112th Meeting of the AWERICANCHEMICAL SOCIETY, New York, N. Y.

Propeller Influence in Hi h Speed Stirring AVERY A. MORTON AND LESLIE M. REDMAN Massachusetts Institute of Technology, Cambridge, iMass.

T

HREE previous papers from this laboratory discuss operation at high speeds. The fist (6) described a flaskwith creases-an obvious improvement, as in the absence of a crease or baffle, the particles of higher density must swirl t o the area of maximum circumference, as if i n a centrifuge, and the process thereby becomes a cross between a separator and a mixer, rather than exclusively a mixer. The second (8)described a method for measuring efficiency, based on the proportion of chemical work obtained per accompanying mechanical energy expended and showed t h a t the best flask was one from which all opportunity for swirling, pocketing, or obstructing the flow of liquid mixture was eliminated. The propeller with the fewer number of segments was better. The third paper (7) recorded a second and

common method (although a far less critical one) of comparisonnamely, the yield in a chemical reaction-and emphasized that the primary, if not sole, role of the flask was to offer a surface for rapid transit of liquid from a position below the propeller t o one above it. The real mixing appeared t o occur on the surface of the propeller. The present paper describes a test specifically related t o propeller action and shows that increased effectiveness is attained by: (a) a high speed of rotation; ( b ) a large diameter propeller; (c) a n appropriate blade angle that may preferably be 45”; and (d) a downward bend of the lower edge of the propeller blade. A discussion of a few special effects of stirring i n chemical reactions is included.