October 1954
2205
INDUSTRIAL AND ENGINEERING CHEMISTRY
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velocity was reached with and without the plate, it might be inferred that the eddy behind the tube has little effect on this maximum b u t that it does help to increase the stable fuel range, Since the flame could not move behind the tube with the Plate in position, no cutback a t the rich limit was observed.
The characteristic flame stability diagrams obtained for lateral blowoff of Bunsen flames are quite similar to those for the flame holders place in a combustible stream. Small diameter rods produce rich blowoff limits exhibiting a curve reversal. I t would be of interest to determine the relationship between the two phenomena. A change in flow characteristics may be the cause of this cutback in both systems. ACCEPTEDJune 25, 1954. for review 26, 1954. This paper, adapted from a thesis by M. L. Thorpe, was in part conducted under t h e auspices of Project Squid, jointly sponsored by the Office of Kava1 Research and the Office of Air Research under Contract pu'6ori 105 Task Order 3, Dartmouth Sub-contract.
Synthetic Lubricants from J
Polyhydroxysteark Acids L. E. GAST, C. B. CROSTON, W. J. SCHNEIDER, AND H. 31. TEETER Northern Utilization Research Branch, Agricultural Research Seruice, U. S . Department of Agriculture, Peoria, I l l .
A
PREVIOUS paper (11)reported the preparation of 12diesters
of hydroxystearic acids and described some of their physical properties. The purpose of this work was to prepare certain new derivatives of domestically available, long-chain fatty acids, and to submit these derivatives to preliminary evaluation as synthetic, low-temperature lubricants. Whereas the derivatives reported would be satisfactory lubricating fluids in certain applications, they were not suitable as substitutes for such lowtemperature lubricants as bis-(2-ethylhexyl) sebacate because of their relatively high pour points. The authors have now prepared certain ether-diesters and triesters of dihydroxystearic acid and pentaesters of sativic acid (9,10,12,13-tetrahydroxy-
stearic acid), and have obtained compounds with lower pour points. However, the increase in number of functional groups altered other physical properties of these ether-diesters and polyesters adversely--e.g., the viscosity and ASTM slope are higher and the viscosity index is lower than those of the better diesters of hydroxystearic acid. EXPERIMENTAL
STARTINGMATERIALSAND INTERMEDIATES. 9,lO-Epoxystearic acid was prepared from commercial oleic acid (Emersol 233 LL Elaine) according to the method of Swern et al. (10) using peracetic acid as the epoxidizing agent. The crude product was
INDUSTRIAL AND ENGINEERING CHEMISTRY
2206
TABLE I.
Vol. 46, No. 10
. ~ L K Y L 9( ~O)-~~LKOXY-~~(~)-HYDROXYSTEARATES
CHa(CHzjrqH-CH(CHz)iCOOR'
OR b H (OH) (OR)
R
R'
Carbon Calcd. Found
Hydrogen Calcd. Found
69.66 1 1 . 7 0 11.73 CHs 69.75 11.90 11.81 70.90 1so-CaH1 70.92 11 98 12.04 71.48 71.40 n-CdHo 70.90 11 98 11.85 Iso-CIH~ 7 1 . 4 8 12 31 12.08 72.80 2-Ethyl- 7 3 . 2 5 hexyl CaHs CzHs 70 93 70.90 11.91 11.95 n-CeH; n-CaHI 72.00 71.90 12 07 12.10 Methoxydroxgb .. ... ... ... 0 See ( 7 ) . b Derivative of methyl esters of soybean f a t t y acids
CHa CH3 CHa CHa CH3
.
Saponification Equiv. Calcd. Found
Acid No. Crude Distilled
d;"
n3$
Molecular Refractivity Calcd.5 Found
344.5 372.6 386.6 386.6 442.7
338 371 380 389 441
1.68 0.11 2.04 0.39 1.27
0.05 0.05 1.37 1.03 0.73
0.9327 0.9181 0.9217 0,9176 0.9088
1.4501 1.4470 1.4503 1.4488 1.4831
372 400.6
363 390 341
5.3 0.17 1.53
3.7 0.40
0.9171 0.9092 0.9565
1.4479 1 0 8 . 6 5 108.73 1.4487 l l i 80 118.11 1.4579 ,. , ...
...
recrystallized once from n-hexane to > ield epoxystearic acid with a melting point of 55" C.: neutralization equivalent, 300 (calculated 298.5); and epoxy oxygen, 5.18% (calculated 5.36%). Structurally the derivatives subsequently prepared from this product may be regarded as related predominantly to high melting 9,lO-dihydroxvsteaiic acid. 9( 10),12( 13)-Dihydioxystearic acid was prepared from pure methyl linoleate by treatment with anhydrous formic acid and catalytic amounts of perchloric acid followed by saponification of the formylated material with alkali ( 4 ) . The product, obtained in 25% yield, had a melting point of 80-85' C.: neutralization equivalent. 321 (calculated 316); and hydroxyl, 10.2% (calculated 10.7y0). High melting 9,10-dih3.droxS.stearic acid was prepared from commercial oleic acid (Emersol 233 LL Elaine) bv oxidation with potassium permanganate ( 6 ) . The product had a melting point of 126-128" C.; neutralization equivalent, 319 (calculated 316); and hydroxyl 10.8% (calculated 10.7%). Diastereoisomeric low melting 9,lO-dihydroxystearic acid was prepared from commercial oleic acid, anhydrous formic acid, and hydrogen peroxide ( I O ) , and had a melting point of 84-88' C ; neutralization equivalent, 319 (calculated 316); hydroxyl 10.6% (calculated !0.7'%). Sativic acid was prepared in 50% yield from methyl linoleate bv oxidation v,-ith potassium permanganate (6). The product melted at 158-161' C.; its neutralization equivalent was 347 (calculated 348); hydroxyl. 2o.3yO (calculated 19.5%). The methyl ester of sativic acid was prepared in 94% yield with a melting point of 127-133" C. Treatment of sativic acid with 2-ethylhexanol, benzene, and sulfuric acid yielded an ester ( 9 i % yield) which was separated into a solid (39%), with a melting point of 140-146' C., and an oil (61%). P R E P l R A T I O S O F ALKYL 9( 10)-!lLKOXY-10(9)-HYDROXYSTEARATES. Methyl methouyhydroxystearate, ethyl ethoxj-hydroxystearate, and propyl propoxyhydroxystearate were prepared from 9,lO-epoxystearic acid, the appropriate alcohol (4 ml. per gram of acid), and sulfuric acid (0.1% total charge) by heating for 3 hours on a steam bath (8). The sulfuric acid was exactly neutralized with sodium hydroxide and the excess alcohol distilled at 30- to 40-mm. pressure. The product was washed with water to remove any inorganic salts and dried. This material was dissolved in acetone (3 ml. per gram) and the solution was cooled to -20" C. and filtered to remove any alkyl dihydroxystearate. The acetone was removed, and the product was purified bv distillation on a falling-film molecular still.
,
..
99 41 108.65 113.27 113 27 131.76
99.28 108.44 112.79 112.97 131.69
Distillation Data Pressure, Temp., microns C. 3 3 3 3 3
100 106 110 115 120
3 3
100 105
...
...
ATES. The alkyl alkoxyhydroxystearates were acylated according to the following typical example. A mixt'ure of 1 mole of alkyl allroxyhydroxystearate, 14.i moles of propionic or acetic anhydride, and 0.35 mole of the corresponding acid chloride was heated on a steam bath for 3 hours. Excess acylating agent was removed by distillation at reduced pressure. The residue was washed with water, 10% sodium bicarbonat'e, and finally with water. I n most cases the products were purified by distillation in a fallingfilm molecular still a t pressures and temperaturps shown in Table 11. Usually the product became cloudy when cooled to lo^ temperatures. It was observed that treatment of the distilled product with methanol saturated with urea produced a small amount of cryst,alline romplex. After removal of the complex, the product recovered from the filtrate did not cloud at its pour point. PREPARATION OF ALKYL DIPROPIOSOXYSTEARATES. One mole of alkyl dihydroxystearate, 7 moles of propionic anhydride, and 1.5 moles of propionyl chloride were aliowed to react as described above. Analytical data on the final products are shooi-n in Table 11. PRnPARATION O F ALKYL TETRA?.CYLOXYSTEbRATES. The methyl and 2-ethylhexyl esters of sativic acid were acylated Qith propionic anhydride containing a small amount of propionyl chloride to form the tetrapropionoxy esters. Methyl sativate was treated with acetic anhydride and acetyl chloride to produce the tetraacetosy ester.
Analytical data and viscosity-temperature characteristics for these compounds are shown in Table 111. DETERMISATION OF VISCOSITIES, VISCOSITY ISDICES, AND POUR POINTS. Xinemat,ic viscosities (based on a value for water of 1.007 cs. at 78" F.) were determined using Ostwald-CannonFenske pipets. Pour points were determined according to ASTM method D 97-47 ( 8 ) as modified by Russell, Smith, and Schniepp (6) t o prevent' condensation of moisture in the cup. With the exception of the three compounds indicated in Tables I1 and 111, none of the compounds studied was found to crystallize on storage a t -70' F. for 72 hours. Viscosity indices were calculated according to ASTM method D 567-41 ( 1 ) . Reproducibility was about 0.37, for viscosities and 2 t o 3 viscosity index units for viscosity indices. DISCUSSION
Analytical data and physical properties of 10 ether-diesters of Table I lists analytical data on the compounds prepared by this 9,lO-dihydroxystearic acid, 4 triesters of dihydroxystearic acid, method. Included in Table I are the data on the methyl, isoand 2 ether-ester derivatives of soybean fatty acids are listed in propyl, butyl, isobutyl, and 2-ethylhexyl eEters of methoxyhyTable 11. Similar data for 3 pentaesters of 9,10,12,13-tetrahydroxystearic acid prepared by saponifying methyl methoxyhydroxystearic acid are listed in Table 111. A comparison of data droxystearate and re-esterifying with the appropriate alcohol. on these compounds discloses the following information. VISCOSITY. The ether-diesters of 9,lO-dihydroxystearic acid PREPARATIOX O F METHOXYHYDROXY DERIVATIVES OF METHYL have lower viscosities (15 to 25 cs.) tshan t,he triesters of 9,lO- or FATTY ACIDS. Soybean fatty acids (neuESTERS OF SOYBEAX 9( 10),12(13)-dihydroxyst,earic acid (19 to 34 cs.). The viscosity tralization equivalent, 283: iodine value, 1-12) were epoxidized of the ether-diesters increases regularly as the R" chain (Table as above with peracetic acid t o yield oil with a neutralization equivalent of 339; iodine value, 20; and epoxy oxygen, 4.07,. 11)is lengthened. Branching of R' also increases the viscosityThis material was treated with absolute methanol and sulfuric e.g., the butyl ester is 17.6 cs. n-hile the isobutyl compound is acid (9) t o produce the methoxyhydroxy derivative; OCH,, 19.6 cs. A small difference in viscosity is noted between t'he 14.93%. 2-ethylhexyl diesters of high- and low-melting 9,lO-dihydroxystearic acid. PREPARATION OF ALKYL 9( ~~)-ALKOXY-~~(~)-ACYLOXYSTEAR-
October 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY 3
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The pentaesters listed in Table I11 are too viscous for use as low-temperature lubricants. The exceptionally high viscosity of methyl tetraacetoxystearate is surprising when one considers that the other pentaesters, methyl tetrapropionoxy and 2-ethylhexyl tetrapropionoxystearate, have 4 and 11 more carbon atoms, respectively. However, all compounds studied that contained the acetoxy group had higher viscosities a t 100 F., lower viscosity indexes, and higher ASTM slopes than did the corresponding compounds containing the propionoxy group. Data showing these relationships ale compiled in Table IV. A possible explanation of these differences between acetoxy and propionoxy derivatives is that the carbonyl oxygen atoms are more exposed in the acetoxy derivatives than in the propionoxy derivatives. Intermolecular association would then occur to a greater extent in the acetoxy derivatives. Construction of Fisher-Hirschfelder models of several of the compounds mentioned in Table IV revealed that in certain configurations of the molecule the terminal methyl group of the propionoxy substituent could indeed shield the carbonyl oxygen in the substituent. In the acetoxy derivatives shielding of the carbonyl oxygen did not appear to be possible. The shielding effect of the propionoxy group appeared to be more pronounced in the tetrapropionoxy derivative. Here the propionoxy groups on carbon atoms 9 and 10 could, in certain molecular configurations, completely cover the carbonyl oxygens of the propionoxy groups on carbon atoms 12 and 13. This may account in part for the comparatively large differences in viscometric properties between methyl tetraacetoxystearate and methyl tetrapropionoxystearate. Because it is important that the viscosities of these low-temperature lubricants should not exceed 1800 cs. a t -40" F., it was desirable to measure viscosities in this range. Methyl 9( 10)methoxy-l0(9)-propionoxystearate, having the lowest viscosity a t 100" F. of any compound prepared, had a viscosity of 3691 cs. a t -40" F. (1.2). The graph of viscosity us. temperature for this ester on the ASThl chart was linear from 100 O to - 65 O F. There was a slight downward curvature from 100" to 210" F. POURPOINT.The pour points of the alkyl 9( lO)-alkoxy-l0(9)-acyloxystearates l i s t e d i n Table I1 are, with two exceptions, in the -50" to -70" F. range. The behavior of methyl 9( lO)-methoxy-lO(9)-pelargonoxystearate was rather surprising, in that it crystallized a t 35 O F. It was thought that a long branch chain would prevent close packing of the molecules and thereby favor ci low pour point. It appears that the pelargonoxy chain folds and thus becomes aligned parallel with the main carbon chain. A similar effect on the pour point was observed with methyl 9( 1 0 ) - p e l a r g o n o x y stearate (11). I s o p r o p y 1 9( 10)-methoxy-10(9)-propionoxystearate also had a relatively high pour point, The same behavior was observed with bis(isopropyl) sebacate (freezing point, 28" to 32 O F.) (S), bis-(isopropyl) adipate (freezing
2208
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 10
TABLE 111. ALKYL 9,10,12,13-TETRAACYLOXYsTEARATES C H3 ( C €12) a-CH-C
I
0
1
H-CHz-C
0
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R'
Acid No.
CHB CHI 1.0 CHI CzHa 2 . 0 2-Ethylhexyl CzHa 0 . 9 a Freezing point.
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H ~ I OOR C
c0 do
A, A, R
H-C
AI d I
R'
~ Carbon Calcd.
Found
1
R' Molecular Refractivity Calcd. Found
Hydrogen Calcd. Found
1.4489 1.4487
1.0483 1.0226
106.1 117.0
108 120
61 2
63,s
61.1 63.7
8.75 9.26
8.74 9.30
135.19 183.67
135 80 153 81
1,4507
0.9874
137 0
143
60.6
(37.1
10.01
10.08
186.01
186.67
V.I.
ASTM Slope
Pour point, O F.
2 5 9 . 1 12.04 Neg. 71.98 7.74 73
0.862 0.777
19a -22
0.732
-26
Viscosity, Cs. a t F. 100 210
87.25
9.35
90
TABLE IV. COMPARISOX OR VISCOMETRIC PROPERTIES OF XCETOXYAND PROPIOXOXY DERIVATIVES
Nethyl acyloxystearate (11) Ethyl ethoxyacyloxystearate Propyl propoxyacyloxystearate Methyl methoxyacyloxy soybean fatty esters hIethyl diacyloxystearate Methyl tetraacyloxystearate
Properties for Acyloxy Group Stated Viscosity, Cs. a t 100' F. --~_____ Viscosity Index ASTM Slope Bcetoxy Propionoxy Acetoxy Propionoxy Acetoxy Propionoxy 11 21 10.50 83 3 115 8 0.805 0.733 17 52 20.34
13.83 18.09
89.5 102.0
110.8 124.8
0.788 0.768
0.756 0,742
28.25 31.64 259.1
24.90 19.6 71.98
81.6 25.6 Neg.
107.2 81.4 73
0.770 0,818 0.862
0,750 0 781 0.777
point, 30" F.) (a), and isopropyl 6-12-propionouystearste (freezingpoint, 7 " F.) (12). There is no significant difference in the pour points of the 2ethylhexyl 9,lO-dipropionoxystcaratesprepared from high- and low-melting 9,lO-dihydroxystearic acids. A slightly higher pour point is noted when the propionoxy groups are located on the 9( 10),12(13) carbon atoms. ASTLI SLOPEA N D VISCOSITYIXDCX. For alkyl 9( 10)-alkoxylO(g)-acyloxystearates having allrovyl and acgloxy groups that are less than four carbon atoms in length, the ASThI dope decreases and the viscosity index increases as the alkyl group becomes longer. -4long side chain, such as that in methyl 9( lO)-methoxy-10(9)pelargonoxystearated, favored a low slope and a high viscosity indeu. I n general, the viscosity indices of the alkyl 9( 10)-alkoxyl0(9)-acyloxystearates and alkyl dipropionoxj-stearates range from 82 to 133, the higher values being associated with the longer R" group (Table 11). CORCLUSIONS
A number of the compounds prepared have low pour points and other desirable properties as lubricants. However, it has not proved possible to obtain compounds having viscosities of 9000 cs. or less a t - G5 ' F. This difficulty may be attributed to a fundamental structural obstacle-namely, the fixed linear chain of 18 carbon atoms present in the original fatty acids. Thus, it was found that addition to this chain of necessary groups to secure low pour points resulted in undesired increases in viscosity. On the other hand, in cases where a low pour point could be obtained by introduction of small substituents, the viscosity index was excessively low. Although the compounds described in this and the previous re-
port ( 1 1 ) do not appear suitable for use in exacting military applications, they represent considerable improvement over earlier materials based on higher fatty acids. Because they may be obtained from readily available domestic raw materials, further study to determine suitable fields of application appears desirable. ACKUOWLEDGMENT
The authors express their appreciation to W. A. Zisman of the Naval Research Laboratory for determination of the viscosities a t low temperatures of methyl methoxy propionoxystearate and to J. C. C o n m of the Oil and Protein Section for hie helpful advice and encouragement during this investigation. They are also grateful to C. H. Van Etten, AI. B. Wicle, and C. E. McGrew for the microanalyses. LITERATURE CITED
Am. Sac. Testing Slateriais, "Standards," Part 5. p. 237, 1949. I b i d . , p. 736.
Breed, E. RI., Kidder, H. F., Murphy, C. hI., and Zisman, W.A., IND.EKG. CHEM., 39,484 (1947). Knight, H. B., Koos, R. E., and Swern, D., Division of Organic Chemistry, 122nd Meeting, AMERICAN CHEMICAL SoCIETT, Atlantic City, F.3. Robinson, G . RI., and Robinson, R. R., J . Chem. Soc., 1925, 175. Russell, C. R., Smith, H. E., and Schniepp, L. E., private communication. Shriner, R. L., and Fuson, R. C., "Identification of Organic Compounds," 3rd ed., p. 45, Sew York, John Wiley & Sons, 1948. Swern, D., Billen, G. N.,Findley, T. W., and Scanlan, J. T., J . Am. Chem. Soc., 67,1786 (1945). Swern, D., Billen, G. N., and Scanlan, J. T., I b i d . , 70, 1226 (1948). Swern, D., Findley, T. and Scanlan, .J. T.. I b i d . , 67, 412 (1945). Teeter, H. M.,Gast, L. E., Bell, E. W., and Cowan, J. C., IND. ENG.CHEM,, 45, 1777 (1953). Zisman, W. A, private communication. RECEIVED for review September 21, 1953. ACCEPTED June 23, 1954. Presented before the Division of Organic Chemistry a t the 124th Meeting of the AMERICAN CHEYICAL SOCIETY, Chicago, Ill. The mention in this article of commercial products under names of their manufacturers does not constitute endorsement by the U. 9. Department of Agriculture of w c h firms or products.
