August
INDUSTRIAL AND ENGINEERING CHEMISTRY
19%
1591
CONCLUSION
LITERATURE ClTED
From the viewpoint of paint technology, the conclusion can be reached that the most desirable products are obtained by s t y r e nating castor oil that has been dehydrated to a minimum hydroxyl content and then has been bodied to a viscosity approaching 15 poises.
(1) Brice, B. A., and Swain, M. L., J. Optical SOC.A m . , 35, 532-44
ACKNOWLEDGMENT
The work described here is the result of a cooperative program undertaken by The Dow Chemical Company and The Baker Castor Oil Company. The oil samples were made by Baker and w e r ~ c o ~ o l ~ m e r iwith a e d styreneand subjected tocompleteevaluation in the Dow laboratories.
(1945). (2) Griew G. A., and Teot, A. S. (to Dow Chemical Co.), U. 9.
Patent 2,468,748(May 3, 1949). (3) Hewitt, D. H., and Armitage, F., J . Oil 61. Colour Chemists' As-
29,NO.312,109-28 (1946). Peter, in Mattiello, J. J., "Protective and Decorative Coatings," Vol. IV, New York, John Wiley & Sons, Inc., 362405 (1944).
SOC.,
(4) Kam, J.
R E C E I V E D October 18,1949. Presented before the Division of Paint, Var. nish, and Plastics Chemistry a t the 116th Meeting of the A x ~ CHEMI~ i CAL SOCIETY. Atlantic City, N. J.
Inositol-Linseed Fatty Acid Drying Oils d
U
-
J. P. GIBBONS
AND K. M. GORDON' Mellon Institute, Pittsburgh 13, Pa.
A new synthetic drying oil has been prepared from inositol, a hexahydroxycyclohexane, and linseed fatty acids. Esterification of inositol proceeds preferentially to the hexa ester regardless of the molar ratio of linseed fatty acids to inositol. Studies on the rate and extent of esterification with linseed fatty acids indicate that inositol is comparable to other polyols containing secondary hydroxyls. A t 293' and 310' C. the bodying characteristics of the inositol oil above 5 poises viscosity are suggestive of those of oiticica and tung oils. Varnishes prepared from the inositol drying oil and Bakelite resin BR-254 produce films with good drying properties and excellent alkali and water resistance. .4 temperature control apparatus is described for use with an electric heating mantle. With this apparatus the reaction medium could be maintained within *2' C. at 235" C. for periods of 24 hours with a minimum of attention.
I
N R E C E N T years increased attention has been directed
toward the preparation and properties of synthetic drying oils. Interesting and useful oils have resulted from the esterification of linseed fatty acids with polyhydric alcohols such as pentaerythritol, polypentaerythritols, mannitol, and sorbitol. meso-Inositol, a hexah~~droxycyclohexane, having the following stereochemical structure ( 5 , 6 ) ,represents a type alcohol different from those already investigated:
H
.c-HO/OH C, \H C.OH
H
c--. OH\H C
OH /Or3
$-
The aim in the research reported here was to ascertain the differences in reaction rates and properties that would be effected by the cyclized structure and the presence of only secondary alcohol groups. Although Burns (3) has patented the preparation of oil-modified alkyds with inositol and quebrachitol, there appears t o be no published reference to the employment of inositol in making synthetic drying oils except for that in a recent article by Bolley (1). 1
Present address, College of William and Mary, Williamsburg, Va.
PREPARATION OF INOSITOL ESTERS
The inositol used in this work was the meso form (Corn Products Refining Company). It is a white, crystalline, nonhygroscopic solid, melting a t 224.5' t o 225.5' C. (corrected). The linseed oil fatty acids were of two types, a distilled product (Woburn Chemical Company's Linseedine Supra fatty acids) and an undistilled grade (Spencer-Kellogg Company). The apparatus consisted of a standard tapered three-necked, 3-liter flask having a well for a thermoregulator. The center neck was fitted with a mechanical stirrer. In one side neck a small tube was inserted extending about I inch below the joint to permit the passage of nitrogen over the surface of the reaction mixture. The third neck of the flask was provided with a threeway distilling connecting tube which led to a standard tapered two-necked 500-ml. r e c e i v e r equipped with an upright waterITR cooled condenser. The opening inbthe top of the three-way c o n n e c t i n g tube permitted a thermometer to be immersed in the reaction mixture, The heating unit was a 1 LOAD hemispherical electric mantle with ti thermoregulator To Flask Heater for t e m p e r a t u r e control. The therFigure 1. Temperature Controller moregulator was VT = Variabletransformer; TR = thermoregulator (Femwal A-7802)s SW =. connected to a variswitch; VM voltmeter; SR 100-ohm able t r a n s f o r m e r resistor
@--
I
-
p
~
~
~
1592
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 8
~
TABLE I. PREPARATION AND PROPERTIES OF ESTERS OF LINSEED FAWY ACIDS AND INOSITOL AT 235 C. O
Molar Ratio, Linseed Fatty Acidsa t o Inositol 6:l 5:l 4:l 4:l
Equivalent Yield, G r a m d l 0 0 Acid ConGrams of Reactants Time of Equivalent Equivalent sumed per DisFree Acid Mole of Reaction, Free Acid PrepaProduct tillate in Product in Distillate Inositol Hours ration 92.4 5.8 26 0.29 0.047 5.5 1 93.7 6.2 0.052 4.7 22 0.21 2 94.2 5.6 23 0.25 0.048 3.7 3 94.2 5.5 11 0.31 0.041 3.7 94.9 4.8 2.1 R 0.39 0.036 2.7 * Undiatilled grade, color 9 , in all reactions 1 moles of linseed 011 fatty aclds were uscd. b Gardner bubble viscometer. c Hellige color comparator. d Wijs method.
2
OF POLYOLS TABLE 11. ESTERIFICATIOK
Preparation 6
Polyol Inoaitol
s
9
Jloles Linfieed Fatty Acida 4.00 4.18 4.18 4.18 4.18 4.18 4.18 4.18
10 11 12 13 ~. Composite of rune 6-13 14 Glycerol 15 Pentaerythritol b 16 Sorbitol 17 a Distilled grade of linseed fatty acids. b Esterification of pentaerythritol was Heyden Chemical Corporation). c Gardner bubble viscometer. Hellige color comparator.
Figure 2. 1
=
Moles, Polyol 0.73 0.70 0.70 0.70 0.70 0.70 0.70 0.70 1.33 1.06 0.93
4 :OO
4.22 4.19
WITH llolar Ratio, Linseed Fatty Acids to Polyol 5.5:l 6:1 6:1 6:1 6:l
6:1 6.1 6: 1
...
3:1 4: 1 4.5:l
Ratio 6:l
3 = 5:l 4 = 5:1 (catalyst)
Viscositvb Y23 23 23 22
Properties of Product SaponiAcid fication ColorC value value 13.2 188 9+ 9.5 192 9L 13 10.6 183 182 14 13.4 14415.8 184
LISSEEDFATTY A C I D S -4T 235 Time of Reaction, Hours 10 11 11 11 11 11 11 11
io
21'4 12
Viscosityc J+ J JXK
EK K -4 D
F
1 .
2"
Iodine valued 148 142 145 143 146
c.
Properties of Product _______ SaponiAcid fication Iodine Colord value value value ... 6+ 6 ... ... 11 -
12+ 79+ 77+ 8 10 lo+ 15
...
...
...
. .
...
...
... ...
187
135
185 185
ik
, . .
... ...
...
153
carried out a t 228O C.; pentaerythritol was technical grade and contained about 15% dipentaerythritol (Pentek,
Esterification of Linseed Acids w i t h Various Molar Ratios of Inositol a t 235' C.
2 = 6:l (catalyst)
~
--
Ratio 5 411 6 = 4:l (catalyst) 7 3:l 8 = 3:l (catalyst)
through the circuit shown in Figure 1. The power input TYas adjusted so that when the thermoregulator circuit was closed, a temperature 5" higher than t,hat desired for the reaction was obtained. IVhen t,he thermoregulat,or circuit was open, the power input was reduced by passing through resistance (SR) to give a temperature about 5" lower than that desired. The frequent adjustment of the variable transformer was eliminated by the thermoregulator circuit, and, without further attention, a temperature cont,rol of 1.2" a t 235" C. could be maintained throughout the duration of the reaction (usually 10 to 24 hours). The reactants were introduced into the apparatus a t room temperature, nitrogen sparging was begun ( a i the rate of approximately 200 ml. per minute), and full-line voltage was placed on the heating mantle for rapid heat-up. A sat,isfactory reaction temperature was found t o be 235" C., and, as this temperature was approached (usually 30 minutes), the thermostatic control was put in operation. Table I summarizes data on preparations representative of a large number of esterifications that were carried out. The molar ratio of reactants is a stronger factor in determining the character of the reaction than is time. Thus, as the molar ratio of reactants is decreased from the 6 : l ratio, there is an increased development of color, a higher viscosity, and a lower acid number, all attained in shorter periods of time. The equivalents of acid consumed per mole of inosit,ol v,-ere calculated from the number of equivalents of free acid in the product and the distillate. Only in the higher rat,io of reactants can these values be interpreted as representing the approximate number of hydroxyls esterified. At a molar ratio of 6:1, there is no sludge in the reaction product a t termination. As the molar rat,io is decreased, hobvever, there is a proportionate amount' of sludge, as shown by aiialysis to be unreacted inositol. .4t the 3 : 1 ratio, the amount of sludge is considerable. Suitable analogy can be drawn between t,his behavior and that exhibited in a simpler case-the acetylation of inositol; studies conducted in this laboratory have shown that the rate of disappearance of acetylating agent was identical lyith the rate of formation of inositol hexacetate. Furthermore, all attempts to acetylate inositol, partially by reduction of the molar reactant ratios, produced only hexacetate in direct theo-
August 1950
INDUSTRIAL A N D E N G I N E E R I N G CHEM
lS93
TABLE 111. PIUXPARATION AND PROPERTIES OF VARNISHES GwoUuing Schedule Tzm8.-, Heat;upa, Holding, Drying Time, Hours Oil min. min. Viscosityb Color6 Dust-free Tack-free Inmitd ester 17 100 D 14 2 6 C 15 2 8.25 'Sorbitol ester 20 120 11 2 8.25 Peeniaerythriitd e m 3 nm 30 ao C+ T u n g oil 232 75 75 C 8 0.5 1 Linseed oil 310 20 iao B 10 2.76 7.5 a Time r e q u i d $0 newoh tbemmgerabre. b Gardner bubble viscometer. Hellige color comparator.
retical proportiom 60 the amount of acetylating agent present. It is believed, therefom, that esterification of inositol with linseed acids proceeds preferentidy to the hexa ester regardless of the molar ratio caf~.ea*etmibs. The rate of esterification of inositol with linseed fatty acids was determined for the different reactant ratios a t 235' * 1' C. Results are illustyated in Figwe 2. Brandner, Hunter, Brewster, and Bonner ( 8 ) found that a catalyst comprising 0.5% of a mixture of 3 parts of d e i u m amtate and 1 part of barium acetate was especially effective in promoting the esterification of sorbitol. This catalyst was also observed to accelerate the esterification of inositol (Figure 2). The use of a catalyst, however, resulted in greater development of color and a tendency toward charring of the inositol. Reaction constantis for the 6:l ratio (no catalyst) were calculated here according to both the first and second order equations by determining the decrease in acid number a t definite intervals. No valid constants could be found for either of these equations. A comparison of the relative reactivities of various polyols in esterification with linseed acids is afforded by the data in Table 11. As was expected because of the presence of only primary hydroxyls, pentaerythritol was much more reactive than a n y of the other polyols. Thus a lower acid number was obtained in practically one fifth the time a t a reaction temperature IO' lower. Although glycerol possesses a slight advantage over sorbitol and inositol in respect to the ratio of primary to secondary hydroxyls, there are really no distinct differences in the rates of attainment of reduced acid numbers. The presence of secondary hydroxyls in the polyol, therefore, and not the ratio of primary to secondary hydroxyls apparently is the important factor influencing this rate. The inositol oils are all of considerably higher body. The oils described in Table I1 were later cooked into varnishes.
pencil Hardness 2 2 2 3
2
24, 1, 24. 24, 1,
Hours satisfactory failed Satisfactory satisfactory failed
BODYING
The bodying characteristics of the inositol oil, as shown in Figures 3 and 4, were determined a t 293' and 310' C. The general procedure used by Von Mikusch ( 7 ) and later by Burrell (4) was employed. This method consisted of heating the oil in a n hmosphere of nitrogen, periodically withdrawing samples, cooling them quickly to 25" C., and determining the viscosity by the Gardner bubble viscometer. The oil was heated a s rapidly as possible to the desired temperature, and timing was then begun. The inositol ester used was No. 14, which had a viscosity of 2.75 poises. The data of Burrell (4)on the bodying rates of pleopentaerythritol, dipentaerythritol, and pentaerythritol are also graphed for comparison. I n Figure 4 the curve for the inositol ester relates to results a t 293' C., whereas the curves for the pentaerythritol esters represent data a t 288' C. The rapid increase in viscosity of the inositol ester beyond 5 poises is suggestive of the bodying characteristics of tung and oiticica oils. As the viscosities increase above 6 poises, the inositol ester becomes more insoluble in acetone, COOKING AND COMPARISON O F VARNISHES
The inositol, pentaerythritol, and sorbitol drying oils listed in Table 11 were cooked into varnishes of 50-gallon length using a p-phenylphenol oil-soluble resin (Bakelite BR-254). The inositol oil used was that of the composite run (preparation 14). Varnishes of tung and linseed oils were also made for comparison. Cooking was carried out in a 1-liter, three-necked flask, equipped with a stirrer and an inlet tube for nitrogen sparging. Heating was effected with a hemispherical heating mantle. After t h e
IO0 60 40 I
cn
W20
u,
-B t v)
IO
86 'p
> 4
2
'
20 40 60 80 100 120 140 160 180 200210 220 TIME (MINUTES)
TIME (MINUTES)
F i g u r e 3. Bodying of Esters of Linseed Acids and Various Polyols at 310' C. 1
-
Inositol; 2 = pleopentaerythritol; 3 = dipentaerythritol; 4 = pentaerythritol
Figure 4. 1 3
-
9
Bodying of E s t e r of Linseed Acids and Various Polyols Inositol at 293" C.; 2 yleopentaerythritol! at 288' C.5
-
dipentaerythritol at 288 C.; 288' C.
4 = pentaerythritol a t
1594
INDUSTRIAL AND ENGINEERING CHEMISTRY
varnish had been cooked to the appearance of a satisfactory “string,” it wm allowed to cool and was then diluted to 50% solids with a solvent mixture comprising 40% mineral spirits, 40% VM&P naphtha, and 20% xylene (by volume). A naphthenate drier, consisting of 0.5% lead, 0.05% cobalt, and 0.025% manganese on the basis of drying oil, was added 24 hours prior to testing. Films were cast on 3 X 5 inch glass plates a t 0.003-inch wet thickness with a Bird applicator, and drying times were determined under conditions of 70’ F. and 65% relative humidity. Films for alkali testing were prepared by dipping a 1 X 6 inch test tube into the varnish and permitting it to dry in an inverted position for 1 week a t 70” F. and 40% relative humidity. The results of these tests, presented in Table 111, show that a satisfactory varnish can be made from the inositol ester. According to these findings the inositol varnish possesses drying characteristics comparable to sorbitol, pentaerythritol, or linseed varnishes. I t s alkali resistance is equal to that of pentaerythritol and decidedly superior to that of linseed oil. However, the poor alkali resistance of the sorbitol ester is probably not normal behavior, since Brandner and cc-workers ( g ) obtained alkali resistance equal to that of the pentaerythritol esters. It is believed that this investigation demonstrates that inositol
Vol. 42, No. 8
esters of linseed fatty acids can be made that have unique and perhaps valuable properties for certain purposes, although at present the cost of inositol discourages its general use in the manufacture of drying oils. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Corn Products Refining Company, donor of the multiple fellowship a t Jlellon Institute on R hich this work was done. LITER’ATURE CITED
(1) Bollev. D. S.. IND.ENG.CHEM..41. 287 (19491. (2) Bran&er, J. D., Hunter, R. H., Brewstor, hi. D., and Botiner, R. E., Ibid., 37,809 (1945). (3) Burns, Brit. Patent 408,597 (-4pril 6, 1934). (4) Burrell, H., IND. EKG.C m x , 37, 86 (1945). (5) Dangschat, G., and Fischer. H. 0 . L., Saturwissenschu/’ten, 30,
146 (1942). (6) Posternak, T., Hela. C h i m . Acta, 25, 746 (1942). (7) T o n Mikusch. J. D., ISD. ENG.C H E x f . , 32, 1061 (1940). R E C E I V E D December 29. 1949. T h e experimental work presented in this paper was carried out in 1945-4F with the hope of preparing a drying oil with properties superior t o those of linseed for the purpose of partially replacing the then scarce t u n g oil.
Frosting and Gas-Checking of Conjugated Drying Oils HANS DANNENBERG, J. IC. KAGERS, AND T. F. BRADLEIShell Development Company, Emerycille, Calif. T h e tendency of drying oils and resins containing fatty acid radicals of conjugated unsaturated structure to undergo “frosting” or “checking” during their drying and film formation has been subjected to new experimental investigations in an attempt to reach better understanding of this phenomenon, its cause, and means of correction. This effect has been found to be greatly influenced by atmospheric dust contamination. Fine dust particles, such as fibers or soot which may occur in the atmosphere and settle on the drying films, are significant factors tending to induce frosting and “gas-checking.” The soot generated by the kerosene lamp of the commonly employed gas-checking tester appears to have a similar effect. Small amounts of certain surface-active agents, such as calcium octoate and the calcium salts of phenolic resins, have been found to control frosting and checking. Nevertheless, it is recommended that the industry devote particular attention to the removal or minimization of dust contamination in the atmosphere in which coating compositions are applied and dried.
HE tendency of drying oils, such as tung, oiticica, dehydrated castor oil, isomerized (partially conjugated) linseed or soybean oils, and varnishes or alkyd resins made from these oils, to dry with frosted, finely wrinkled or finely checked surfaces is a well known and troublesome phenomenon which constitutes one of the major objections to the use of such products for many applications. Although it has been recognized that this tendency is largely confined to compounds which contain conjugated carbon-to-carbon double bonds and that it may be modified or eliminated b y the use of sufficiently high varnish-cooking temper-
atures or by the addition of large percentages of certain phenolformaldehyde resins, relatively little has been learned concerning the cause of this phenomenon and its true nature. Previous studies of the subject have followed devious paths and have led to a number of explanations. The cause has variously been held to involve the transformation of or-eleostearin or its equivalents to their p-isomers ( 7 ) , the presence of moisture ( l 7 ) , the influence of light radiation ( 2 , 7 ) ,unequal oxygen absorption ( 7 ) , and the influence of nitrogen dioxide (3, 12). The most commonly accepted view is that the phenomenon (often termed gas-checking because it can be induced in gas-heated ovens) is caused by improper ventilation or circulation of fresh air, by gas fumes which reduce the oxygen content of the air, or by a cold draught blowing on the film before it is dry and hard ( 1 6 ) . Federal varnish specifications often call for, and most laboratories apply, a so-called gas-check test to varnishes made from conjugated drying oils in which varnished panels are exposed to the atmosphere within a bell jar in which a kerosene lamp is burned until extinguished by its consumption of the oxygen of the contained air. Under these conditions frosting or checking 1s often induced in coatings which would not frost in normal air. Uncooked tung oil, however, will frost or check even under the latter conditions, and, according to Chatfield, it crystallizes a t the slightest provocation (j)., One of the authors, together with former associates, had p r c viously observed and reported a significant difference in the apparent mode of oxidation of conjugated as compared t o unconjugated drying oils ( d ) , an observation which appears to have been further strengthened by the work of Farmer and his associates ( 8 , 9). Although the mode of oxidation may eonstitute the basic cause for the confinement of gas-checking to the conjugated
