INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
February 1949
~
~
Table X. Fraction Yield, wt. % Color Gardner Fatty(acids, 4 Rosin acids Saponificati'on No. Acid No. See Figure 12.
Tall Oil Fractionation I" Charge
d
49 175 162
Table XI. Fraction Yield, wt. % Color Gardner F a t t i acids, Rosin acids, lo Saponification No. Acid No. See Figure 13.
8
r
e v 70 ? COLOR BODIES j?oslr A = , ~ -
287
~~
I
I1
I11
5.0 Black
35.0 14 20
60.0 8
1E 146
172
40 55 145 110
60 33 177
Tall Oil Fractionation IIa Charge
I
I1
111
18% 45 49 176
5.0 Black 40 55 145 110
70.0 11 30 63 176 162
25.0 7 87 6 178 176
162
Acto FRacrioN
F A T w
Figure 13. Tall Oil (Table XI)
In a rosin acid fraction of 73%, while the fatty acid content dropped to 20%. The saponification number followed this change by dropping from 175 to 165. Figure 13 shows a similar tall oil fractionation where an attempt was made to isolate a fatty acid-rich fraction. In this case, a 25% cut was removed as an overhead product, after the removal of a 5 % color body fraction, and a 70% rosin acid-fatty acid fraction. Analytical results on these fractions are shown ln Table XI. The fatty acid value in fraction I11 increased to 87%, while the rosin acid content dropped t o 6%. Additional studies on tall oil are being carried out in attempts to improve the decolorization of the oil, as well as the fatty acid-rosin acid separation. Many of the results obtained and pictured in this paper were the initial runs made on oils, and more extensive studies have been and are being carried out on the various oils. It appears from
the work which has been conducted thus far that the application of the Solexol process in the glyceride oil field should bring about some striking changes in the refining of various fats and oils, and its commercial acceptance is already definitely established. Bibliography (1) Drew, D. A., and Hixson, A. N., Trans.Ant. Znst. Chem. Engra., 40, 675 (1944). (2) Hixson, A. W., and Bockelmann, J. B., Ibid., 38,891 (1942). (3) Hixson, A. W., and Hixson, A. N., Ibid., 37,927 (1941). (4) Hixson, A. W., and Miller, R., U. S. Patent 2,219,652 (1940). (5) Ibid., 2,226,129 (1940). (6) Ibid., 2,247,496 (1041). (7) Ibid., 2,344,089 (1944). (8) Ib$d., 2,388,412 (1945). (9) Larner, H. B., U. S. Patent 2,432,021 (1947). (10) Schaafsma, A., Ibid., 2,118,454 (1938). (11) Van Orden, L., Ibid., 2,394,968 (1946). RBCIIYED February 26, 1948.
Synthetic Drying Oils Don S. Bolley National Lead Company, Brooklyn I , N . Y. 'The drying oil chemist has become accustomed to consider synthetic drying oils as oils prepared through chemical treatment of fatty oils. A n extensive and critical literature review of drying oils of this nature was made. These included dehydrated castor, methods of increasing un*aturation, maleic oils, drying oil esters of polyhydric alcohols, nonfatty drying oils, and copolymerized drying ails. Experimental data are given on the comparative properties of linseed pentaerythritol ester with linseed ail and soybean pentaery thritol ester with soybean oil.
T
materials is given in Table I. Drying oil, as used in this discussion, means an oil-like material which dries by oxidation when exposed in a thin film to the air. This might be considered a restricted definition; the more general definition is: an oil-like material which dries when exposed in a thin film. The general term would include oxidizing resinous solutions dissolved in thinner which dry by solvent evaporation. A raw drying oil is one obtained from the seeds or nuts directly by hydraulic pressing, expelling, or solvent extraction. I t has had no additional treatment except possibly a storage period to allow suspended material to settle out. The soybean and edible
HE term, synthetic drying oils, as used by the paint and
varnish chemist, as well as the drying oil chemist, might be misleading t o those outside of the field. Synthetic drying oil usually means an oil which has been prepared through chemical treatment of fatty oils. Less frequently, i t may refer t o drying materials of an oily nature which have been made from nonfatty materials. Since the drying oil chemist uses a variety of special terms in reference to oils, a suggested classification of various drying oil
Table I. Drying Oil Materials Raw drying oils Refined drying oils Modified drying oils Synthetic fatty drying oils Synthetic nonfatty drying oils Copolymerized drying oils Drying varnishes Drying oil resins
INDUSTRIAL AND ENGINEERING CHEMISTRY
288
oil industry quite often refer to these so-called raw oils as crude oils. To explain the next classes, it would be best to consider the composition of an oil. Roughly, it is made up of minor components and triglycerides. The triglycerides consist of materials having poinB of unsaturation and ester groups. A refined oil then may be considered one in mhich the minor components have been partially removed or modified. This includes alkali treatment to remove free fatty acids, bleac3hing to remove coloring matter and other materials, refrigeration to remove waxes, and acid treatment to remove mucilaginous materials. A modified drying oil is one in which the double bonds of the triglyceride arc affected. This would include heat bodying, blowing, maleic addition, and isomerization. A synthetic fatt,y drying oil may be thought of as one in which t'he ester grouping has been altered. Thus, if a natural drying oil is hydrolyzed to fatty acids and glycerol, and the fatty acids re-esterified with another polyhydric alcohol such as pentaerythritol, t,he product is called a synthetic drying oil. The source of a synthetic, nonfatty drying oil is derived from substances other than fats, These may be synthetic unsaturated materials, modified petroleum products, etc. A copolymerized drying oil, as used in this discussion, is considered one in which polymerizable unsaturated materials are added to fatty materials and the whole intcrpolymerized, usually using heat. An example would he styrene heated with dehydratcd castor oil. A drying varnish might be considered a resin dissolved in oil with or without the presence of suitable solvents, such as an ester gum linseed varnish. A drying oil resin is a material mhich will oxidize on exposure to air, and is of a solid nature in the absence of solvents-for example, a drying alkyd. These classifications arc not proposed definitions; it is realized that many drying oil materials might be considered to fit several of the classes. Hoxwver, this scheme of classification has proven useful in the writer's laboratory. The following discussion will be limited to two types of modified drying oils (dehydrated castor and maleic), synthetic fatty and nonfatty drying oils, and copolymerized drying oils. Many of thc oils discussed are covered by patents. Dehydrated Castor Oil The modern type of dehydrated castor oil, under the above clawification, would be considered a modified oil. However, since it was originally a synthetic oil, and many people consider it a synthetic oil, this discussion is believed rightfully to come under the title of this paper. It was the first synthetic drying oil to attain general commercial usage and is still of the greatest interest to the paint and varnish chemist of all the so-called synthetic drying oils. Dehydrated castor oil was originally made by Seheiber (SQ)in about 1930 by dehydration of castor oil fatty acids. The following equations show the reactions involved. CH,(CHz),CHZCH=CH CH=CH(CH?)1COOH ,_ - - - - -
or
CH,(CHg),CHCHCH2CH=CH(CHz),COOH
,-
I
1 - 1- HOH
-
ii
- _ - - _ _ I
CHs(CH2)aCH=CHCHpCH=CH(CH2)&OOH When castor oil is hydrolyzed, the fatty acids arc found to be composed of about 85% ricinoleic acid. This acid contains a double bond in the 9,10 position and a hydroxyl group on the 12th
Vol. 41, No. 2
carbon atom. Scheiber found that by subjecting this acid to a distillation treatment, a more highly unsaturated acid is produced; this could be combined with glycerol to produce a drying oil which was known as Scheiber oil. The reaction may take place by the elimination of water from the hydroxyl group on the 12th carbon atom and a hydrogen on the l l t h , or by the hydroxyl group on the 12th carbon atom and a hydrogen on the 13th. In the former case, a conjugated acid is produced, while in the lattcr, a nonconjugated acid results. Scheiber claimed a preponderance of conjugated acids formed, but later expcrimcnts indicate that. this is not the case. Shortly after Scheiber's discovery, it was found that castor oil could be dehydrated by the use of catalysts without resorting t o hydrolysis. The type of catalyst (25) generally used for this purpose is of an acidic nature, such as sulfuric acid, potassium and sodium acid sulfates, phosphoric acid, phthalic anhydride, acid earth, etc. The oil and a small amount of catalyst are charged into a large stainless steel kettle which is heated to 450" to 475" F. with agitation in a vacuum to facilitate removal of water. When the reaction is complete, the catalyst is removcd by filtration. More modern mcthods involve the use of a continuous method of treatment and soluble catalyst. There has been considerable discussion on the percentagc of conjugated and nonconjugated bonds formed by the reaction. The diene determinat>ion using maleic anhydride indicates that commercial products contain 17 to 26% conjugated and 59 t D 64% nonconjugated acids. In other words, i t is usually coilsidered that there are three nonconjugated groups formed to every conjugated. Nore modern technique, using the ultraviolet absorption spectrophotometer, indicates a slightly higher percentage of conjugated acids, perhaps about 2.5 to 1. The dehydration process apparently is never quite complete as the present dehydrated castor oils have a hydroxyl value of 12 to 20. However, this is a great improvement on the original dchydratcd castor oil which had a high pcrcentage of hydroxyl groups which result,ed in sticky films because of the plasticizing action of free castor oil. The properties of dehydrated castor oil mighl be consitlered ar lying between those of linseed and tung. However, somc caution should be used in applying this generalization. Drying time, rate of heat polymerization, and resistance to water and alkali by varnish films are intermediate between linseed oil and t,ung oil. They produce films which are softer than those of linseed and much softer than tung, but of superior elasticity than either. Because of its lack of triply unsaturated acid, the resistance to, yellowing is outstanding. TRIENOL
In about 1930, a process for making a triply unsaturated con-jugated ester from castor oil by the Miinzel proceas was an-. nounced ( 4 ) . (The Munzel works are located in Switzerland.) Castor oil is dehydrated using a freshly precipitated tungstic acid anhydride. The Munzel process claims this produces nearly exclusively conjugated dehydrated castor oil. Workers in this country have found that while tungstic acid anhydride can be used efficiently to dehydrate castor, about the samc proportion of conjugated and nonconjugated oils are formed &s from othcr catalysts. Munzel's conjugated dehydrated castor, known as Dienol, then is treated with hypochlorous acid. This adds a hydroxyl group to the 9th carbon atom and a chloride group t o the 12th. By simult,aneous removal of hydrogen chloride and mater, a triply unsaturated conjugated est,er is formed. Thc double bonds during Eormation are said to shift over one carbon forming Trienol which has the points of unsaturation a t the same place as eleostearic ester or tung oil. There seems to be considerable doubt as to the actual production of this oil. Some Trienol was received in this country and found to bo equivalent, if not identical with, tung oil. All outside attempts to prepare Trienol have been unsuccessful.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
February 1949
INCREASED UNSATURATION There are a number of references, mostly patents, on increasing the unsaturation of fatty oils of low unsaturation through chlorination followed by removal of hydrogen chloride (26, 40). Theoretically, every double bond so chlorinated would yield two double bonds in the conjugated position. The difficulty with the procedure is that usually dark colored resinous materials of poor drying characteristics are formed rather than the improved oil one might hope for when working out the reactions on paper. The writer does not know of any commercial oils made in this manner. A similar reaction involving hydroxylation and dehydration seems t o offer greater promise. Light colored hydroxylated oils can be made in a variety of ways and the methods of catalytic dehydration used on castor oil may bo applied (13, 36). Again, as far as the writer is aware, this method for increasing unsaturation and producing conjugation has not been used commercially. However, it might be pointed out that blowing a n oil with air forms some hydroxyl groups and on subsequent heat treatment this hydroxylated oil will be dehydrated and show increased bodying rate. I t s absorption spectra shows the presence of some conjugation.
Maleic Oils Rlaleic modified drying oils are an interesting and extremely versatile type of material. They may be considered under either oils or resins. A paper by K. A. Earhart given at this symposium presents some applications in the field of resin chemistry; this discussion, therefore, will be limited to the mechanics of the reaction and the preparation and properties of materials that would be considered drying oils. The reaction involves addition of maleic anhydride to the double bonds of a drying oil with subsequent modification of the maleic’s acidic groups. I n 1928, Diels and Alder (17) announced their famous reaction on the addition of maleic type materials to conjugated double bonds. This reaction is known as the Diels-Alder reaction or diene synthesis. Diels and Alder were originally concerned with quinones, although it soon became apparent their reaction could be generalized to many unsaturated materials. In 1930, Boeseken and Hoevers (5),in France, published an article concerning the action of ma’eic anhydride on dehydrated castor oil acids and esters. They used the diene synthesis to explain the reaction between the conjugated fatty acids of dehydrated castor and maleic anhydride in accordance with the following equations: CHa (CH2)rCH=CHCH=CH
+ HC=CH
(CHn)&OOR
289
both analysis before and after the reaction for hydroxyl value, aa well as the use of dehydrated castor containing few hydroxyl groups, seemed t o eliminate this postulate. Since maleic in this concentration does not gel other oils, the study of this phenomenon might shed some light on either the composition of dehydrated castor or the reaction mechanism. It was suggested a t this symposium (14) that the polymerization of maleic anhydride with dehydrated castor oil might be analogous to the reaction of maleic anhydride with cis- and trans-piperylene (16). The ciscis, 9,ll-octadecadienoic acid which probably occurs in dehydrated castor oil (SO) would be expected t o copolymerize with maleic anhydride, whereas the cis-trans, trans-cis, or trans-trans would be expected t o form a stable adduct, nonpolymeric in nature. Other oils tested with maleic anhydride apparently do not copolymerize readily, but form adducts. However, recent work indicates that some copolymerization occurs with even linoleic acid (45). Tung oil is composed mainly of glyceride ester,, containing three conjugated double bonds. Morrell (sd), in 1932, studied the reaction between maleic and tung oil acids and found that maleic reacted with one set of conjugated double bonds for CYeleostearic and another for p-eleostearic. Sometime later, Carleton Ellis obtained several U. S. patents (2f-%S) treating with the usefulness of the reaction product between maleic and tung oil. He found an aqueous soluble tung oil compound could be made by treating the anhydride groups of the combined maleic with alkali or ammonia. The possibility of preparing a rubbery-rosinous eompound by treating the adducts with polyhydric alcohols also was shown. However, little commcrcial use seems to have been made of the tung maleic adduct. Edwin T. Clocker, in this country, recognized that maleic anhydride and similar substances would react with nonconjugated oils as linseed, soybean, etc., and has obtained a series of U. S. patents (8-19)on this reaction and its application to the paint and varnish field. Bevin, in England, has obtained a somewhat similar set of British patents (2, 3 ) . Root (87) claims the reaction of maleic anhydride with an oil such as linseed can be facilitated by a peroxide. As a result of these studies, it is now recognized that maleic anhydride reacts with only conjugated type materials a t an appreciable rate up to near 200’ C. and with all types of double bonds that appear in fatty acids a t temperatures above 200’ C. There has been considerable speculation as to the possible mechanics of the reaction with nonconjugated systems. Clocker originally assumed that the reaction went in accordance with the following equation:
CHa(CHg)4CH=CHCHnCH=CH(CHa)&OOR
+
HC=CH
CH3(CH,)&HCH=CHCH(CH,)?COOR
HIL O=C
3 ’
AH I
c-0
By using this reaction, Boeseken and Hoevers concluded that dehydrated castor fatty acids were made up of 75% conjugated; this subsequently has been shown to be too high. When one attempts to make an adduct with 10 parts of maleic anhydride and 90 parts of dehydrated castor, a gel results (6). This can be prevented by carrying on the reaction in the presence of a nonconjugated oil such as linseed. The reason for the gel is not understood. It was originally thought that it might be due to the hydroxyl groups remaining in the dehydrated castor oil, but
While this explains the resulting properties of the oil, the reaction does not seem plausible because of the assumption of a butane ring which is difficult to form in this manner. I n addition, it has been shown that when the reaction is applied t o materials such as oleic esters, the oleic adduct still retains the unsaturation which would not be explainable by this reaction. To bring the reaction into line with the original Diels and Alder concept, i t has been postulated that nonconjugated bonds isomerized under the influence of heat to conjugated bonds which subsequently reacted as follows:
290
INDUSTRIAL AND ENGINEERING CHEMISTRY as resins.
o=b
b=o
4
Y
CH~(CII,),CH~CHCII=CHCHCH(CH~)~COOR \ / HC---CH
O=C
I
I
C=O
----.A
0
Other studies have shown that corijugation iesults irom heat treatment of oils. However, since the addition reaction proceeds a t an appreciable rate a t 200" C., it IS doubtful if such conjugation can completely explain the reaction mechanism, It would be totally inadequate to explain the reaction betwerri maleic and oleic which has only one double bond. To account for the retention of unsaturation, the folloaing tn o reactions are proposed:
CH,(CH2)4CH-CHCH2CH-CH(CH2)lc00R
4HC=CH
'
O=C
I c=o
Hh-CH, I
I
J'd CHI (CH*),CH=CHCHCH=CH(CH2),COOR
( 21
Hd_,H* I /
o=c c=o
'd
Of the tTTo, it is believed that the second, involving a hydrogen shift from the methylene group, more nclarly f i t q modcrn theory of chemical reactions. Thus, the writer believes the main reaction is probably this reaction with some conjugated reaction a i previously indicated More work is necessary to definitely establish these postulates. The interesting feature of maleic oils is that one has a simple process for adding on acidic groups in the middle of the oil molecule. These groups make the oil useful as a grinding medium as well as give the oil compatibility with ethyl and nitrocellulose. The acidic groups may be reacted with a variety of substances such ah alkalies, polyhydric alcohols, and basic dyes to make the oil useful in water paints, textile sizes, cotton printing, adhesives, or
Vol. 41, No. 2
At present, the three inost important uses of maleic oils are as water vehicles, improving the drying and heat bodying properties of nonconjugated fatty drying oils, and the preparation of resins. The first two v d l be considered here. Maleic adducts are simple to prepare. The process merely involves heating maleic anhydride with the oil in a closed vessel, properly vented, with stirring until completion of the reaction. Use of copper, iron, or mild steel should be avoided as the maleic is corrosive. Glass, stainless steel, and aluminum are satisfactory. For example, a 10% maleic linseed complex may be made by heat,ing 90 parts of a refined linseed oil with 10 parts of maleic anhydride with stirring to 200" C. in 1 hour, holding a t this ternperature for 1 hour, raising the temperature to 230' C. in 0.5 hour, and holding for 2 hours. Testing the cooled adduct' by washing out any free maleic anhydride will show the reaction to be over 99.7% complete. The time and temperature of heat'irig should be greater for soybean and other more saturated oils. Maleic oil adduct,s may be rendered water soluble by iieutralising the anhydride groups with inorganic alkalies, ammonia, or amines. Ammonia seems to be t,he preferred material. Adducts cont,aining a relat,ively high percentage of combined maleic anhydride, when neutralized with ammonia, are completely miscible with water. Water paints and other coating materials cont'aining water may be made from t,hese vehicles. However, present practices tend toward the use of lower percent,ages of maleic and a half methylated-half neut,ralized product. Such a vehicle, nhile not completely soluble, readily emulsifies with water and may be used in the production of the emulsion type of water paints. The base vehicle is made from the maleic oil adduct (usually containing about 10% maleic) by first adding equal maleic molar quantities of methyl alcohol. This transforms the anhydride group into a methyl ester plus an acid. The carboxylic acid group then is neutralized with ammonium hydroxide. These oile are sometimes referred to a9 solubilized oils. Water paints properly formulated with the solubilized oils dry readily to a good film. One might expect them not to have good wat'er resistant properties. However, on drying, the oils lose their hydrophilic properties and have been found to have good washing resistance. The nature of this inversion is not well understood. J. C. Coman (16)believes it could be explained by the fact that these oils dry to give polymeric materials and the presence of a few maleic anhydride groups on the polymer molecules mould not make t,hem water soluble, whercas one group on a single fatty acid or oil might make it water soluble. Borrowing a reaction from the alkyd resin chemist, the maleic oil adduct may be react,ed wit,h polyhydric alcohols such as glycerol or pentaerythritol to increase its complexity. When only a small amount of maleic anhydride is used, less than 5%' the oil is only somewhat hodied and may be used without thinner. However, if larger quantities of maleic are used and esterified, II viscous material results; this is claimed by the resin chemist. As an example, a useful maleic oil may be prepared as follows: A 10% maleic linseed oil complex is prepared as previously de-. scribed. This is diluted v,.ith an equal weight of refined linseed oil, which result,s in essentially a 5% complex. A stoichiometric quantity of pentaerythritol is a,dded to the oil a t about 190" C. during the course of 4.5 hours. At the end of this addition, the mixture is heated under mild vacuum for 2 hours. 4 slight turbidity usually rcsults, which may be removed by filtration. The oil is then heat-bodied a t 260" C. to a 22 viscosity in an atmosphere of carbon dioxide. The resulting oil is of light color with an acid value of about 10. I n general, the maleic oils may be used to advantage in paints and varnishes. They dry faster and heat-body considerably faster than t,he oil from which they are made. Although of increased ester content, their water resistance is good. In varnishes, they cook rapidly and easily with most resins with the exception of limed rosin. They impart improved drying and hardness t o the varnish films.
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1949
Swain (43) suggests a variation in the above described procedure for preparing maleic oils. A diglyceride is first made by ester interchange with 2 moles of glyceride oil plus 1 mole of glycerol. The diglyceride is then reacted with a maleic adduct to obtain a similar type of product. Schwarcman (41, 4%') suggests preparing oil with free hydroxyl groups by partial ester interchanging with glycerol, pentaerythritol, or mannitol with subsequent reaction with maleic anhydride. There are a number of other compounds such as fumaric, itaconic, and aconitic acid that react similarly, but at a slower rate than maleic. However, because of the ease with which maleic anhydride adds on to oil and the price oonsideration, little use seems to be made of them in the abnormal diene synthesis. Synthetic Fatty Drying Oils
Drying oil fatty acids may be esterified with various polyhydric alcohols. The esters so formed are usually referred to as synthetic drying oils. Various alcohols of interest are shown by the following formulae: CHIOH
CHzOH
Methyl Alcohol
AHOH
I I
CHOH CHaOH
CHzOH
dHaOH
Erythritol
Ethylene Glycol
CHzOH
CHiOH
CHOH
dHoH
CHOH
dHgOH
AHOH
Glycerol
AHOH
I I-
I
CHZOH CHzOH
Mannitol and Sorbitol
I
8
HOCHz-C-CH20H
-. x
&"OH
/Y CHOH
Pentaerythritol
CHpOH I
HOHC
CHzOH I
HOCH2-C-CH2-O-CHa-b-CHzOH
L20H
Inositol
I
CHzOH
Dipentaerythritol The folloa ing generalizations are frequently referred to in drying oil theory and have been confirmed on an experimental basis. As one might expect from the theory of functionality, the methyl esters of drying oil fatty acids, while oxidizing at about the same rate as oil, do not form a solid film. When ethylene glycol is esterified with fatty drying oil acids, a slow forming soft film may be obtained from those fatty acids, such as tung and perilla, that have a large amount of unsaturation. This film, however, would not be sufficiently tough to find use in the paint and varnish field. The glycerol ester of fatty acids, of course, is similar to the glycerides formed in nature. There is one Interesting difference: the synthetic glyceride oil has a short induction period, while the natural product, particularly raw
29 1
oils, has a pronounced induction period, probably due t o the natural antioxidants contained in the minor constituents. From the performance of these three esters, it would be expected that as complexity of alcohol increases, the rate of drying and heat polymerization, as well as the toughness of the film should increase also. This has indeed been found the case and is the basis for the value of the various synthetic oils made from higher polyalcohols. Erythritol is the next higher polyhydric alcohol with a structure similar to glycerol, Fatty esters of this material have been found by this laboratory to dry somewhat faster and harder than the glycerides. However, some difficulty attributable to secondary alcoholic groups has been encountered in this esterification and the erythritol is fairly expensive. Little work has been done on this material, and insofar as the writer is aware, no commercial application of it has been made in the field of synthetic oils. I t should not be confused with pentaerythritol, which will be discussed in detail later. Mannitol and sorbitol are hexahvdric alcohols further along in this series. The chemical structures of the two materials are similar except for spacial arrangements of the hydroxyl groups which are not incorporated in the formula given. Their properties are similar and synthetic oils resulting therefrom, while showing some slight differences, may be considered alike. A great deal of work has been done on the preparation of synthetic oils from these materials since they are of reasonably low cost and are readily available. It has not been found possible, without the use of special tricks, t o add six fatty groups to these alcohols. When mannitol and sorbitol are heated to the temperature necessary to esterify them direct with fatty acids, they have a tendency to split off a molecule of water and form an inner ether. This prevents the complete esterification of the hexahydric alcohols with the fatty acids. It has been found that about 4.5 moles of fatty acids may be added direct t o the mannitol and sorbitol, I n addition, since two thirds of the hydroxy groups are secondary alcohols, this adds to the difficulty of esterification. It has been found that a low temperature, long heating, and stepwise addition of the alcohol assist in the preparation of a good product. These synthetic oils dry more rapidly and with a harder film than the glycerides. Varnishes may be prepared although they are somewhat dai k and many of them are not too satisfactory. Our observations have shown that outdoor paints formulated with esters have stood up well on over 5 years' exposure. It is hoped that the research work now in progress will allow more complete esterification of these two alcohols; this should result in an improved product. Continuing with increasing complexity of alcohols of this type leads to polysaccharides and starches. Some work has been done along this line, although a great deal of difficulty is encountered when using unsaturated fatty acids for their esterification. As far as is known, there is no synthetic oil on the market made from the fatty drying acids and these high polyalcohols. Pentaerythritol has proved the most useful of all the polyhydric alcohols in the preparation of synthetic oils; the formula shows that it contains four hydroxy groups, all primary. It is easy to esterify, and because of its increased functionality, gives harder drying oils. A typical pentaerythritol oil has been made in this laboratory as follows: 1.05 moles of technical pentaerythritol are added t o 4 moles of linseed fatty acids. The mix is heated gradually to 200" C. with stirring and passing carbon dioxide over the mixture. Conducting under a mild vacuum is preferable. At 200' C. a homogeneous solution results and i t is held a t this temperature for 2 hours. The temperature is raised to 230" C. in about 0.5 hour and held for 3 hours. At this time the esterification is substantially complete. It is then held at 250' C. until the desired viscosity is reached. At a viscosity of G, the oil should have an acid value of less than 5. Table 11, compiled from data observed in these laboratories, compares the properties of a pentaerythritol ester of linseed, a
INDUSTRIAL AND ENGINEERING CHEMISTRY
292 Tahle 11.
Properties of Oils and Pentaerythritol Esters
Viscosity Color Appearance Acid value Saponification value Hydroxyl value Iodine value Unsaponifiable Refractive index Specific gravity
Drying (drier) Set to touch, hr. 24-hr. dryness Water resistance Cold hr. Hot 'min. Alkhi, min. Absorption, 3'% Film solubility Water, % Hexane, % Acetone, % Alcohol benzol, %
Linseed Pentaerythritol H 12 Clear 4.0 181 28 155.6 1.99 1.4850 0.9324
Linseed Oil G 6 Clear 2.1 189 5.4 165 1.43 1.4841 0.9430
Soybean Pentnerythritol
H
12 Clear 3.3 186 52 125 1.00 1,4796 0.9475
Soybean Oil F 54Clear 2.2 189.6 5.0 119.0 1.15 1.4768 0.9358
72 106 120 13
138 228 253 9-
120 183 195 14f
312 455
2.5 Slight tack
3.5 Moderate tack
3.75 Moderate tack
8
24+ 8 8 8.8
140 35 30 12.5
16
1; 30
10.4 17.7 33.9 37.1
9.5 21 3 44.7 48.6
10.2 23.8 56 2 60.8
3 3 12.8
....
I l f
Tacky
28.7
15.9 31.1 97.7 95.2
similar bodied linseed oil, a peritaerythritol ester of soybean, and a similar bodied soybean oil. For comparison, oils of similar viscosity should be used. While the examples are not identical in viscosity, i t is believed they are sufficiently close to permit valid deductions. The color of the synthetic oils is somewhat darker t,han usual. Other products prepared are only slightly darker t h m refined linseed or soybean oils. The acid value indicates little reactivit,y wit'h basic pigments; this has been found t o be t>rue. Saponification values of the synthetics are always somewhat below the natural glycerides. The hydroxyl values of synthetics are always high, akhough the soybean- shown here is perhaps abnormal. The heat bodying test on these oils was conducted in a quart metal beaker and is instructive. The rate of bodying of the linseed pentaerythritol ester is about. twice that of linseed oil, while the linseed oil and soybean pentaerythritol esters are similar; soybean oil is slow. The results indicate the synthetic esters to be more tack-free after 24 hours than the natural glycerides. Water resistance of the various oil films is somewhat incousistent. These results show that, in general, the pentaerythritol synthetic oils are somewhat inferior t'o the nat,ural product. The reverse is often true when the oils are used in varnishes. Film solubility ( 7 ) is measured by exposing the oil on sand for 3 weeks under a sunlamp in the constant temperature room. The sand-oil mixt.ure then is extracted with the various liquids for 3 hours in a Soxhlet thimble. The last section in Table I1 shows the results obtained. This type of data has not been correlated with actual performance. However, in general, the lesser the amount extracted, the higher the complexity of the film; this shows up in hardness, mater resistance, etc. Acetone is perhaps the best solvent for this purpose although all tell about the same story. Acetone extracts about one third of the material from a linseed pentaerythritol film, about one half from both linseed and soybean pentaerythritol oil films and netirly all of the soybean oil film. These results would change on aging; the soybean oil film would become more insoluble, whereas the others would reach a minimum, and then increase. Varnishes have been made up with a variety of resins and their properties thoroughly tested. Paints made from these types of oils have been exposed for 6 years outdoors. The story on both varnishes and paints is about the same as would be expected from the results of the films. Varnishes made from pentaerythritol esters are, in general, superior t o t,hose of the natural oil. In the
Vol. 41, No. 2
case of paints, the linseed peiitaerythritol showed only slight improvement over the linseed oil whereas the soybean pentaerythritol ester was a distinct improvement over the soybean oil, particularly the initial phases, and might be considered similar to linseed oil in most of its properties. This latter fact is highly significant since attempts are being made to introduce more and more soybean oil into paints and varnishes in place of linseed. Although some caution should be exercised, it is believed the soybean pentaerythritol ester may be used in most cases interchangeably with linseed oil. Techiiical pentaerythritol usually contains about 15% dipentaerythritol. Fortunately, this mixture seems t o be bettcr adapted for the paint and varnish field than the pure and more expensive explosive grade of C.P. pentaerythritol. Pent,aerythritols conhining larger amounts of dipent,aerythritol and tripentaerythritol are commercially available. synthetic oils prepared using the polypentaerythritols heat-body considerably faster, while drying is soniewhat,faster. They may be considered a harder drying oil than the esters made from the technical pent,aerythritol product. Inositol is a cyclic hcxahydric alcohol. At present, it, is expensive, but since it occurs widely in nature combined with organic phosphorus a large commercial use should permit its product,ion on a more economic basis. When 6 moles of fatty drying acids are esterified with 1 mole of inositol, the resulting syntheric oil dries to a hard tack-free film. Inositol linseed synthetic oils have been prepared by this laboratory; they dry much faster than linseed, although occasionally an oil results which actually dries slower than linseed. This is believed to be due t,o various antioxidants eirher present, iri the inosit.ol or formed during esterification. Additional research worlc should iron out these difficulties, aiirl if the price of inositol could be reduced, a new interesting oil would be available. Synthetic oils similar to those described above may br prepared also by ester interchange and alcoholysie. For example, a nat,ural glyceride may react with methyl alcohol resulting in the methyl ester plus glycerol. The methyl ester then may be reacted with mannitol to form the synthetic mannitol oil with the regeneration of methyl alcohol. Since all these reactions are equilibrium reactions, removal of one of t,he constituents allows the reaction to go in the desired direction in accordance with t,he laws of mass a d o n . The polyhydric alcohol ester--for example, mannitol--can be made direct from the glyceride by treatnient with mannitol and removal by distillation of the glycerol. 1Iowever, this is apparently more difficult than the previous method described. These are all examples of alcoholysis. An example of ester interchange would be treat,ment of triacetin with the methyl esters of fatty oils and production of the glyceride during removal of methyl acetate. Further study is necessary to make t,his type of rcaction commercially practicable. Little mention has been made of the various catalysts which are used in esterificat,ion. These include inorganic alkalies, alcoholat,es,litharge, and other inorganic oxides, acids, and salts. hlthough many of these assist, in the rate of esterification, they are not nccessary for the regular rcaction between alcohol and a. fatty acid. I n fact, they oftcn give precipitates and gels and darken the product,. However, they are highly essential in ester interchange and alcoholysis reactions. A large number of other polyhydric alcohols exist; many have made interesting oils and many remain to be tried. I n addition, research work is continually in progress on the preparation of new polyhydric alcohols which would be of interest to both the oil and resin chemist. Tall oil is a by-product of the sulfate pulp industry when pine wood is pressure-cooked with caustic soda solution and other chemicals. Tall oil is not an oil, since it is made up of mixtures of resin acids, fatty acids, and various unsaponifiable materials. The refined product may be esterified with the various polyhydric alcohols previously mentioned. The most interesting
February 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
product, the pentaerythritol ester, will dry in a reasonable time to a hard tack-free film. This product may be considered similar to about a 12-gallon ester gum linseed varnish. It may be used for interior paints, but only small portions should be used for exterior paints because of its high rosin content. The product may be improved further by treating with maleic and esterifying, as discussed under Maleic Treated Oils. A reverse ester was prepared by reacting fatty alcohols with polycarboxylic acids. For example, linseed alcohols were made from linseed methyl esters by sodium reduetion. They also may be made from a variety of other fatty derivatives such as the acids, nitriles, and esters by high pressure hydrogenation. Tricarballylic acid is similar to glycerol except that it has three carboxyl groups in place of three hydroxyl groups. Tricarballylic acid then was reacted with the linseed alcohols in a manner similar to the normal esterification, and a linseed tricarballylate obtained. This ester, which has the same functionality as a glyceride, was found t>oform dry films and act similarly to the glyceride. However, it was noted that during this preparation using sodium, some conjugation took place; this gave the oil the various properties which would be obtained from a somewhat conjugated glyceride ester of linseed. An infinite number of possibilities for the preparation of various synthetic oils exists. Fatty materials can be reacted with other than polyalcohols such as various polyamines, amides, phosphorous compounds, and silica compounds. Future research should turn up many interesting compounds of this nature. Synthetic Nonfatty Drying Oils
For a number of years various synthetic nonfatty drying oils have been prepared from petroleum. During the cracking process for the production of gasoline, various unsaturated hydrocarbons are formed. These are removed, polymerized, and frequently oxidized. The result gives a material which dries when exposed t o air as a film. Other methods used are chlorination and dechlorination to increase the unsaturation. These substitute petroleum drying oils which have come to the writer's attention dry slowly with an initially.soft film and some yellowing. I n addition, on aging, they check badly. Undoubtedly, they could be used in small quantities to extend natural drying oils, but the ones examined fall far short of exhibiting the desired properties for a paint and varnish oil. The writer has been informed that new petroleum drying oils of greatly improved properties are about to be introduced. A large variety of film-forming materials can be prepared from synthetic unsaturated materials not derived direct from the petroleum unsaturates. These include polymerized acetylene, polymerized butadiene, and acrylates and other vinyls. During the last war, the Germans, because of the shortage of natural fats, expended a great deal of energy in attempting t o develop products as drying oil substitutes. These substitutes now are being evaluated by the industry, and i t is probable that some will prove meritorious. In addition, a large number of new and cheap unsaturated products are being introduced commercially. The polymerization products of these unsaturates have commercial possibilities in the paint and varnish field. Foremost among these products are those prepared from acetylene by the new socalled Reppe chemistry.
293
defined as any unsaturated organic compound capable of forming chain polymers through its double bonds. In recent years there has been an increasing interest in these relatively new fatty oil copolymers as is evidenced by the more frequent mention of them in the literature, particularly in patents. At the present time, however, the literature does not reveal much concerning the structure of the resulting copolymer. Bearing in mind the slow progress made so far in elucidating the mechanism of the drying and polymerization of fatty oils, it is doubtful whether much more than general principles will result from investigations into the structure of the fatty oil copolymers. Many different fatty oils have been used as starting materials. I n this respect, it is apparent that conjugated oils-tung, oiticica, and dehydrated castor (90,98)-react with active unsaturated compounds more readily than the nonconjugated type. I n general, i t has been found necessary t o give the latter type (linseed and soybean) some pretreatment such as partial polymerization (46) or oxidation (18) to obtain homogeneous copolymers. I n some instances, preformed varnishes (94),oil modified alkyd resins, or concentrated standoils ( 9 9 ) have served as the fatty oil portion of the copolymer. The list of unsaturated compounds which have been reported t o copolymerize with the fatty oil coniponent includes styrene (228,W), a-methylstyrene, acrylic and methacrylic acids and their esters, vinyl halides (Sf?), vinyl esters (SS), vinyl ethers (SI),cyclopentadiene ( d 7 ) , acrylonitrile (It?), butadiene ( I ) , diallyl maleate (19), allyl esters of dimeric fatty acids (&), acyclic terpenes (B),and furylethylene (54). References to styrene outnumber all other compounds listed above. Thus, it seems safe to say that it lends itself readily to being the second component of fatty oil copolymers. Several copolymers made with styrene have been marketedrecently. Cyclopentadiene and dicyclopentadiene also are particularly adaptable to copolymer formation. End products which have resulted from copolymerization of the two classes of compounds just mentioned range from oily liquids capable of air drying in the normal manner when exposed as a thin film through solid polymers. Between these extremes, there are products which require stoving for conversion to solid films. Claimed uses for the fatty oil copolymers include: all kinds of coating compositions such as paints, varnishes, and enamels; adhesives; plastic compositions such as linoleum; and resins suitable for use in paints and varnishes. Professed generalized advantages of the copolymers, depending on composition, are production of fast drying, tough, flexible, adherent films showing strong resistance to water and alkali. At the present time it is not possible to predict just how valuable the fatty oil copolymers will become. Either they will show to advantage only in certain specialty uses, or they will exhibit properties that will cause their adoption on a much larger scale. The latter seems probable when it is considered that development work has only recently been undertaken in earnest and that new unsaturated compounds are constantly being made available on a commercial scale. Literature Cited
Ambros, O., and Reindel, H., German Patent 523,033 (Feb. 5, 1929).
Copolymerized Drying Oils
Bevan, E. A., British Patents 500,349 and 500,350 (Feb. 6,1939). Bevan, E. A., and Tervet, J. R., British Patent 500,348 (Feb. 6, 1939) Blom, A. V., Paint Oil Chem. Rev., 101, No. 15,9 (1939). Boeseken, J., and Hoevers, R., Rec. trau. chim., 49, 1165-8
The term copolymerization has conie to be known as the reaction of two different polymerizable materials with each other to give a homogeneous polymer built up from both materials. The resulting copolymer often has more desirable properties than the polymer of either of the two materials alone. This discussion will deal with those copolymers which have as one component a drying or semidrying oil. The second component might be broadly
Bolley, D. S., U. 5. Patent 2,414,712 (Jan. 21, 1947). Bolley, D. S., and Gallagher, E. C., J. Am. Oil Chemists' SOC, 24, NO. 5 , 146-9 (1947). Clocker, E. T., U. 8. Patents 2,188,882-90 (Jan. 30, 1940). Ibid,, 2,262,923 (Nov. 18, 1941). Ibid.,2,275,843 (Mar. 10, 1942). Zbid., 2,285,646 (June 9, 1942). Ibid.,2,286,466 (June 16, 1942). Colbeth, I. M., Ihid., 2,388,122 (Oot. 30, 1945).
I
(1930).
INDUSTRIAL AND ENGINEERING CHEMISTRY
294
14) Cowan, J. C., IND.ENG.CHEM.,41, 294 (1949). 15) Cowan, J. C., perbonal communication to Don S. Bolley. 16) Craig, J.Am. Chem. Soc., 65, 1006 (1943). 17) Diels, O., andillder, K., Ann., 460, 98 (1928). 18) Dunlap, L. H., U. S. Patent 2,382,213 (Xug. 14, 1945). 19) du Pont de Nemours & Co., E. I., Brit,ish Patent 552,095 (Mar. 23, 1943).
(20) Zbid., 556,113 (Sept. 21, 1943). (21) Ellis, C., U. S. Patent 2,033,131 (Mar. 10, 1936). (22) Ibid., 2,033,132 (Mar. 10, 1936). (23) I b i d . , 2,146,671 (Feb. 7 , 1939). (24) Flint, R. B., and Rothrock, H. S.,Ibid., 2,276,176 (Mar. 10, 1942). (25)
Forbes, W. C., and Neville, H. A , , ISD.ENG.CHEM.,32, 555-8
(26) (27) (28)
Gardner, H. A , , U. 8. Patent 1,452,553 (1923). Gerhart, H. L., Zhid., 2,361,018 (Oct. 24, 1914). Ilemitt, D. H., and Armitage, F., J . Oil & Colour Chemists'
(29)
Jordan, O., and Kollek, L., U. S. Patent 2,054,019 (Sept. 8,
(30)
Kass, J. P., presented before the Division of Paint, Varnish, and Plastics Chemistry at the Memphis Section Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn., 1942.
(1940).
Assoc., 29, 109 (1946). 1936)
I
Vol. 41, No. 2
Lawler, W. D., Hable, G . J., and Steinle, J. V., U. S. Patent 2,353,910 (July 1944). (32) Lawson, W. E., and Sandborn, L. J., Ibid., 1,975,959 (Oct. 9, (31)
1934). (33) Mighton, C. J.,Ibid., 2,346,858 (Agiil 18, 1944). (34) Ibid., 2,401,769 (June 11, 1946). (35) Milas, N. A., Ibid., 2,267,248 (Dee. 23, 1941). (36) Morrell, R. S., and Samuels, II., J . Chem. Soc., 1932, p. 2251. (37) Root, F. B., U.S. Patent 2,374,381 (April 24, 1945). (38) Rummelsburg, A. L., I b i d . , 2,370,689 (Mar. 6 , 1945). (39) Scheiber, J., Ibid., 1,979,495 (Nov. 6, 1934). (40) Scheiber, J., British Patent 316,872 (Nov. 24, 1930). (41) Schwarcman, A., U. S. Patent 2,412,176 (Der. 3, 1946). (42) Zbid., 2,412,177 (Dee. 3 , 1946). (43) Swain, R. A., Ibid., 2,304,288 (Dec. 8 , 1942). (44) Teeter, H. M.,and Cowan, J. C., Oil h Soap, 22, 177-80 (1945). (45) Teeter, H. >I., Geerts, M. J., and Cowan, J. C., J . Am. Oil Chemists' Soc., 25, 158 (1948). (46) Wakeford, L. E., andHewitt, D. H., U. S. Patent 2,392,710 (Jan. 8, 1946). RFCFXYBD February 28, 1948
Isomeri
ctions ils J. C. Cowan
Northern Regional Research Laboratory, Peoria, I l l . T h e fundamental and practical aspects of the isonierization reactions of the unsaturated acids are discussed. Of particular interest to the drying oil chemist are a review of the methods of effecting conjugation and evaluating the conjugated oils, and discussions on the drying of oil films, the relation of isomerization to drying and copolymerization, and the factors responsible for after-tack. Particular attention is given to the problem of making a tung oil replacement, to the mechanisms of isomerization, to alkali isomerization, to nickel and iodide catalysts for isomerization, and to styrene copolymerization.
S
IKCE early in this century when the process for gasproofing tung oil was developed, the importance of the isomerization of conjugated and nonconjugated oils in protective coatings has steadily increased, Tung oil is easily isomerized and its isomerization has definite commercial importance. When tung oil is exposed to sunlight or treated with sulfur, selenium, or iodine a change from a liquid oil to a solid fat is effected. This chznge of the liquid oil to a solid is the result of the isomerization of t i e a-eleostearic acid to the @-eleostearicacid. ljeedless t o say, the producer who is now fortunate enough to have a supply of tung oil does not desire to have the physical state of his raw mat,erial changed since he would be unable to handle it in equipment normally available in his American plant (23). American tung oil when prepwed by extraction is readily isomerized and a heat treatment is necessary to stabilize it,. Expressed oil benefits from a similar treatment (66). When the supply of tung oi. became limited during the Japanese occupation of China, attempts to prepare replacements for t,ung oil were made by a large number of investigators. One of the direct methods of approach which might lead t o a tung oil replacement is the shifting of the unsaturated bonds in nonconjugated oils such as linseed or perilla oils to give conjugated unsatu-
ration. Although some efforts of coinmercial importance have been made to obtain extracted oils of higher polyunsaturated fatty acid content, more efforts have been toward isomerizing the oil t o produce conjugated systems since it was known that the conjugation was primarily reqponsible for the reactivity of tung oil. In addition to this interest in preparation of conjugated oils for industrial uce, studies on isomerization reactions havc resulted in a new method for analys's of oils and have extended the scope of research on the problem of the utilization of vegetable oils by the preparation of new derivatives. KOattempt has been made in this paper t o covcr all thc literature on isomerization and conjugation. The many known isomers of the fatty acids which have been reported in the literature are not included specifically. This paper deals primarily with the isomerization and conjugation as it is related to the drying oils and their reactions. Theoretical Aspects of Isomerization of Fat Acids
The term isomers is generally applied t o those compounds which have the same molecular formula but which differ in a t least one of their physical and chemical properties ($6). The term isomerization is applied t o reactions which effect changes among isomers. With the mono-unsaturated fatty acids, the isomeric forms are limited to the cis-trans isomers of the different positional isomers with the omega-unsaturated fatty acid existing in only one form. The different forms of mono-unsaturated fatty acids can be rcpresented as follows:
R
R
,/"=\ \
/"l
I
'
t.=C H
I1
/" 'El
