Bewig, K. W., Zisman, W. A., J . Phys. Chem., 68, 1804 (1964). Brace, N. O., J . Org. Chem., 27,4491 (1962). Du Pont Information Bulletin 111759, 1939. Fox, H. W., Chrisman, Jr., C. H., J . Phys. Chem., 56, 284 (1952). Fox, H. W., Zisman, W. A., J . ColloidSci., 5 , 514 (1950). Hare. E. F.. Shafrin. E. G.. Zisman. iT. A,. J . Phus. Chem.., 58., 236 (1954). Harkins, W. D., Jordan, H. F., J . Amer. C h e m SOC., 52, 1751 (1930). Jovce, Jr.. R. M., U.S. Patent 2,359,628 (July 10. 1951). Schwarz, E. G., Reid, TVV. G., I d . Eng. Chem., 56, 26 (1964). Shafrin, E. G., Zisman, W. A., J . Phys. Chen., 6 6 , 740 (1962). Union Carbide Product Information Bulletin 70-1, 1964.
Zisman, W. A., Bernett, 31. K. 3,498,922 (llarch 3, 1970a). Zisman. W. A.. Bernett, 11. K. 3,498,923 (March 3, 1970b). Zisman, W. A. Bernett, h1. IC. 3.509.061 iA&l 28. 1 9 7 0 ~ ) . Zisman,' A:, Berr;ett, 11. K. 3,511,708 (1Iay 12, 1970d). Zisman, W. A., Bernett, 11. K. 3.316.938 (June 23, 1970e).
w.
(to U S . Govt.), U.S. Patent (to U.S. Govt.), U.S. Patent
(to U.S. Govt.), U.S. Patent (to U.S. Govt.), U.S. Patent (to U.S.Govt.), U.S. Patent
RECEIVED for review July 22, 1971 ACCEPTED October 18, 1971
Fluorinated Ester Lubricants Containing Ether Structures Laurence W. Breed' and Richard 1. Elliott Midwest Research Institute, Kansas City, Mo. 64110
Carlo
F. Key
Astronautics Laboratory, Jfurshull Space Flight Center, Ala. S5St2
Two series of highly fluorinated aliphatic esters containing ether groups were prepared and characterized. Methods were developed for the preparation of the necessary precursors. Properties of selected members of these lubricant series are reported.
A l t h o u g h synthetic lubricants based on organofluorine structures have attracted attention because of their oxidation stability a t high temperatures, needs exist for lubricants that are not only stable at high temperatures but also have satisfactory properties at low temperatures and are compatible with strong oxidants such as liquid oxygen (LOX). Many fluorine-substituted substances, however, have high pour points, high vapor pressures a t elevated temperatures, and poor viscosity-temperature relationships. Such is particularly true of perfluorinated organic substances, which usually exhibit a smaller liquid range than the corresponding hydrocarbyl compounds or t h e partially fluorinated derivatives. Chemical modification of the fluorine-containing lubricant structure provides a possible means for extending the liquid range of candidate lubricants while maintaining good stability against oxidation. A high degree of oxidative stability can be retained in liquid esters derived from fluorinated precursors even if a substantial proportion of the structure is present as methyl or methylene groups (Breed et al., 1970; Faurote et al., 1956; Ravner et a]., 1963), but the liquid ranges of these materials are also limited. Messina (1967) and Gumprecht (1966) have shown that the incorporation of ether-oxygen into a perfluorinated structure substantially improves the temperature-vapor pressure relationship. The purpose of this work is to select, synthesize, and screen candidate lubricants that are predominantly fluorinesubstituted b u t which contain a n ether-oxygen structure and some hydrogen substitution. Such structures should provide the greatest opportunity for obtaining improved liquid ranges while maintaining good oxidative stability. 1
88
To whom correspondence should be addressed. Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 1 , 1972
Experimental
The yields and properties of the substances prepared are shown in Table I. The analytical verifications of their structures are summarized in Table 11. 4 '-Alkoxyacetic Acids. T h e following are typical of the two procedures employed for the preparation of $'-alkoxyacetic acids (+'-alkyl indicates -CH2(CF2).H) : Xethod A . h mixture of 38.4 grams (1.60 moles) of sodium hydride (70.5 grams of a 55% dispersion in mineral oil) and 800 ml of ether was treated with 232 grams (1.76 moles) of $'-propyl alcohol over a 2-hr period, and then 75.6 grams (0.80 mole) of chloroacetic acid was added over a 1.5-hr period. After the mixture was cooled to room temperature and stored overnight, 400 ml of 25y0hydrochloric acid was added, and the ether layer was separated and dried over sodium SUIfate. Evaporation of the ether and a first vacuum distillation gave the acid contaminated with mineral oil. After the mineral oil was extracted with petroleum ether, bp 35-6OoC, the ester was purified by fractional distillation under vacuum. Method B. When a solution of 378 grams (4.00 moles) of chloroacetic acid and 176 grams (4.40 moles) of sodium hydroxide in 1 liter of water was added to a mixture of 1020 grams (4.40 moles) of $'-pentyl alcohol and 176 grams (4.40 moles) of sodium hydroxide during 1.5 hr, a n exothermic reaction occurred. After the mixture was refluxed overnight, cooled, and neutralized with 20% aqueous hydrochloric acid, the lower layei was separated, Iyashed with two portions of 20y0 aqueous hydrochloric acid and two portions of water, and purified by fractional distillation under vacuum. 2-$'-Alkoxytetrafluoropropionic Acids. Xethod C. I n a typical experiment, a mixture of 320.2 grams (1.380 moles) of $'-pentan01 and 27.6 grams (0.69 mole) of sodium hydroxide
Table I. Preparation and Properties of Fluorine-Substituted Esters and Their Intermediates Compound no. la
2
3 4
Yield, Compound name
92-3/0.9 134-5/10 128-30/0.3 124-6/20 130-2,' 11 94-6/20 104-611 1 212-16/0.08
1.3471 1.3281 1.3252 1.3254 1.3239 1.4036
1.463
82
223-4/0. OSd
1 ,4048
1,450
52
154-6/0.10
1.3962
1.367
91
233-6/0.07
1.3815
1.606
86
230-40/0,10
1.3822
1.582
E
94
171-4/0.08'
1.3760
1.514
E
86
168-78/0.07/
1.3601.
...
E
94
179-85/0.06
1.3642
1.639
E
80
151-3/0.3
1,3550
1.603
E
81
180-4/0.5
1.3478
1.668
$'-l'roposyacetic acid +'-Pentoxyaretic acid
89 84 50 20 46b 67b 32 39
$'-Iieptosyacetic acid
c, 7 9 10
11 12 13 14 15 16 17
I , 11-Triinetliyloletlia~ie ~ tiis( I,! '-proposyacetate) 1,1,l-TriinetIiylol~~ro~~aiie tris($'-propoxyacet a t e) 2,2-I)imetliylol1,ro~~aiie his($'-proposyacetate) 1,1,~-'~rimethyloletl-iane tris($'-pentosyacetate) I , 1,I-Triinetliylolpropaiie tris($'-peiit'osyacetate) 2,2-I>i1netliylol~,fopane his($'-pentosyacetate) 2,2,3,3,4,4-€Iesafluoropro~,anediol bis ($'-pen t'osyaceta t e) 2,2-l)imethylolpropane his($'-heptosyacet'ate) Bis(2-$'-pentosytetrafluoropropyl) 3niet81iylglutarate His(2-$'-heptosyt~et~rafluoropropyl)3met.liylglut arate
dZe,,
nZ0D
1.3697 1.3565
0
8
BPt "C/mm hg
%
Method
... ...
... ... , . .
Reported bp 104-6" (1 mm), n * 6 ~1.3699 (Beecham Hesearch Laboratories, 1962). * Yield calculation based on t'he assumption of a 2,57 conversion of hesafluoropropene to hexafliioropropene oxide. c Portion of the product was lost through spillage. Mp 33-7°C. Bp 359"C, differential thermal analysis. f Bp 367°C differential thermal analysis, mp 66-70°C. 0 Supercooled.
e
was treated at 80°C with hexafluoropropylene oxide generated from 135 grams (0.90 mole) of hexafluoropropylene (Sianesi et a]., 1966). After 500 ml of water was added, the mixture was extracted with 150-ml, lOO-ml, and 50-ml portions of ether, and the ether phase was dried over sodium sulfate. Distillation gave 236.7 grams of unchanged $'-pentanol boiling a t 88-92OC (90 mm) and 55.3 grams of solid residue, which was dissolved in 100 in1 of ether, washed with 100 ml of 10% hydrochloric acid and 100 ml of water. After the ether phase was dried over sodium sulfate, the free acid was purified by fractional distillation under vacuum. 2-~'-Alkoxy-2,3,3,3-tetrafluoropropan-l-ols. JIethod D . Niederpruem and Voss' (1967) procedure for 2,2,3-trifluoroethanol was followed. To a mixture of 6.3 grams (0.083 mole) of sodium borohydride in 33 ml of tetrahydrofuran was added a solution of 39.6 grams (0.15 mole) of 2-$'-heptoxytetrafluoropropionic acid in 17 ml of tetrahydrofuran, and the mixture was heated a t 65°C overnight. After the mixture was cooled, it was treated with 50 ml of water, stirred 1 hr, treated with 100 ml of 10% hydrochloric acid, and stirred another hour. This method differs from the previous procedure in that a longer heating period and a shorter period of stirring after the addition of water were employed. T h e bottom layer was separated and combined with two 50-ml ether extracts of the aqueous layer, washed with two 100-ml portions of water, and dried over sodium sulfate. Distillation gave 39y0 of 2-$'-heptoxytetrafluoropropanol and 32% of unchanged 2-$'-lieptoxytetrafluoropropionic acid. Fluorine-Substituted Esters. J l e t h o d E . T h e followiiig is a typical preparation. -4solulion of 190 grams (0.66 mole)
~~~
Table II. Elemental Analysis for Fluorine-Substituted Esters and Their Intermediates Compound no.
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Analysis,
%
-__ F
H
C Calcd
Found
Calcd
Found
Calcd
Found
31.59 28.98 27.71 25.55 25,22 26,53 25.99 37.74 38,78 40.18 33.35 34.12 35.19 30.17 32.56 31.67 30.19
31.48 29.08 27.73 25.70 25.11 26.35 25.91 37.97 38,73 40.16 32.87 33.64 35.24 29.67 32.80 31.78 30.09
3.18 2.09 1.55 1.07 0.85 1.67 1.31 3.80 4.03 4.50 2.58 2.75 3.11 1.87 2.38 2.17 1.75
3.05 2.03 1.62 1.21 1.01 1.68 1.43 3.84 3.94 4.54 2.62 2.89 2.91 1.96 2.51 2.27 1.89
39,98 52.99 58.44 60.62 63.85 62.96 65.78 35.83 35.05 33.91 48,69 47.98 46.89 55.27 53.75 54.65 58.78
40.98 52.23 58.56 59.38 62.05 61.54 66.12 35.38 35.47 33.71 48.52 48.44 46.67 55.15 53.42 54.97 59.04
of +'-pentoxyacetic acid, 24.0 grams (0.20 mole) of trjmethylolethane, and 1.0 gram of sulfuric acid in 200 ml of toluene was heated until 11.5 grams (calcd 10.8 grams) of water was collected in a Dean-Stark trap. After the product was washed sequentially with water, aqueous potassium carbonate, and water, the toluene was distilled off and the ester was purified by fractional distillation under vacuum. Ind. Eng. Chem. Prod. Res. Develop., Vol. 11, No. 1, 1972
89
Table Ill. Sequence of Preparations Reaction
Compound no.
(1) n
=
2; (2) n
=
4; (3) n
=
6
[ CFz(CFzCHz0H)z (8) V, = 2; (11) n = 4 CH3C [CHZO,CCH~OCH~(CF~),H 13 CH3CHzC [CHZOZCCHZOCH,(CF,),H]~ (CH3)2C[CH2ozCCHzOCIIz(CF,).H 1 2 CFz [CF~CHZOZCCH?OCH~(CF,),H 12 r-7 NaOH 3. H(CFz)nCHzOH CF3CFCFzO H(CFZ),CH~O-CF(CF~)CO~H (4) n = 4; (5) n = 6 NaBH4 (6) n = 4; (7) n = 6 4. 1-I(CFz)nCHzOCF(CFs) CO2H H (CF,),,CH,OCF(CF,) CHzOH HzSO4 5. H(CF2) .CHzOCF(CFs) CHzOH CHsCH (CH*COZH)2 CH~CH[CHZC~ZCHZCF(CF~)OCH~(CF~).H]~ (16) n = 4; (17) n = 6
+
+
*
Discussion
The intermediate fluorine-substituted acids required for the synthesis of the two series of ester fluids are previously unreported substances. It was, therefore, necessary to develop suitable methods for their preparation. These methods and the properties of the two new series of fluorine-substituted acids are reported in full with the recognition that such compounds may find other uses. Two series of fluids were prepared by the reaction sequences described in Table 111, a first series prepared by Reactions 1 and 2, and a second series by Reactions 3, 4, and 5. Good conversions can be obtained in each of the steps although the reduction in Reaction 4 proceeded sluggishly, and substantial portions of the unchanged acid could be recovered. I n Reaction 3 the anticipated product would be a n ester, but in the course of the work-up procedure, ester hydrolysis occurred and the free acid was isolated. Usual esterification procedures (Reactions 2 and 5) with polyhydric alcohols were employed to convert the acids to esters suitable for examinatioti as candidate lubricants. From Table IV the fluids in the two series provide a choice of properties with a range of pour points, viscosities, and evaporation rates. For each fluid there is a n approximate correlation of increase in pour point and decrease in volatility
Table IV. Properties of Fluorine-Substituted Esters
with an increase in viscosity. Indeed, if these data are compared with similar data for the +'-alkyl 3-methylglutarat~es, the $'-alkyl tricarballylates, or the perfluorinated alkylerie ethers, the same kind of correlation can be found bet'ween each of these aeries as well as wit'hin this series. For example, tris($'-amyl) tricarballylate with a viscosit,y of 6.78 cSt a t 210'F has a pour point of -45'F and a n evaporation rate of 4,8y0 after 6 hr a t 300'F (Breed et a]., 1970); 2,2-dimethylolpropane his($'-heptyloxyacetate) with a viscosity of 7.02 cSt a t 210'F has a pour point of -35'F and a n evaporation rate of 5.9% after 6 hr a t 300°F; and a commercial perfluoroalkylene ether fluid with a viscosity of 5.4 cSt a t 210'F has a pour point of -50'F and mi evaporation rate of 6.1y0 after 6 hr at 300'F. The values for each of the three fluids fall within the same range even though individually they represent different chemical classes. It must, therefore, be assumed t'hat t'he dominant effect in det'erniining the properties of these materials is t'he presence of the polyfluoroalkylene segments and that other structural changes can be masked by their presence. A high degree of oxidative stability on the LOX impact test was evidept in representative samples of these fluids (Table V), However, the data indicate that the threshold of instability is being approached in structures in which the extent of fluorination has been reduced. l,l,l-Trimethylolethane tris($'-pentoxyacetate), which contains 2.58% hydrogen and 48.69y0 fluorine, did not react with oxygen in 20 trials. This result clearly demonstrates that specific require-
Evaporation.
Wt %,a Cornpound no.
+
300 2'F, 6 hr
Pour point,b O F
- Viscosity, cStC
210'F
looor
ASTM viscosity indexd
3.0 -5 14.41 339.4 - 18 1.4 -5 , . . ... ... 10 13.7 - 40 4.92 50.89 - 31 11 0.7 16,32 - 10 374,3 5 12 1.4 16.12 - 10 349.6 13 13 5.4 - 45 6.03 74.17 -49 15 5.9 - 35 7.02 91.03 - 12 16 14.46 - 65 4.02 33.83 - 105 17 4.5. 5.07 - 50 47.96 - 27 a Evaporation rates determined by loss of weight of fluid in a small aluminum dish on a hot plate in a well-ventilated hood. * Method D97-66 (ASTM, 1968). c Method D445-65 (ASTM, 1968). Method D2270-64 (A4STM,1968). e Estimated. 8 9
90
Ind. Eng. Chem. Prod. Res. Develop., Vol. 11, No. 1, 1972
Table V. LOX Compatibility of Experimental Oils.
Experimental oil
LOX-impactb sensitivity of oil, no. reactions/ no. trials
Bis [(2-$'-heptoxy) tetrafluoropropyl] 3-methylglutarate (Compound 17) 0/20 Bis [ (2-$'-pentoxy) tetrafluoropropyl ] 3-methylglutarate (Compound 16) 1/20 2,2-Dimethylolpropane bis($ '-pentoxyacetate) (Compound 13) 2/20 l,l,l-Trimethylolethane tris($'-pentoxyacetate) (Compound 11) 0/20 a Determined in accordance with MSFC-SPEC-106B. Impact energy - 10 kg meters.
Table VI. Experimental Four-Ball Wear Test Data.
Additive
Experimental oil
Wear scar diam, mm, a t 50 kg
2,2-Dimet hylolpropane his($'-pent ouyacetate) (('ompound 13)
0.75
None 2 Wt yo tricresyl phosIhate
0.56 l,l,l-Trimethylolethane tris($'-pentoxyacetate) (Compound 11)
Conclusions
Two new classes of synthetic lubricants based on partly fluorinated structnres with ether and ester groups shobv a high degree of oxidative stability under the conditions of impact in the presence of liquid oxygen even though substantial proportions of the structures are not fluorinated. Little difference way observed in the liquid range properties of these materials and other partly or wholly fluorinat>ed lubricants. literature Cited
0.69 0.38
Kone 2 Wt yo tricresyl phosphate
of tricresyl phosphate was incorporated as an antiwenr additive (Table VI). These results are consistent with tests with similar classes of fluids, which respond to additive modification to provide improved wear performance.
ASTM Standards, 1969 Book of, Part 17, Petroleum Products, American Society for Testing and Materials, Philadelphia, P a . . lQ6X.
Bis[(2-heptoxy)tetrafluoropropyl] 3niethylglutarate (Compoiind 17)
2 W t % tricresyl phosphate
Beerham -Research Laboratories, Ltd., British Patent 873,244, Appl. (April 1, 1960); CA, 56, 780 (1962). Breed, I,. W., Wiley, Jr., J. C., Key, C. F., Ind. Eng. Chem. Prod. Res. Develop., 9, 53 (1970).
0.40
Two h r at 147"F, 600 rpm, 52-100 steel halls
Faitrote. P. I).. Henderson. C. M., 3IiirDhv. C. hl., O'Rear, J. G., Ravner. €5..Ind. Eno. C h m . . 4g. 445 ?1$56). Gumprecht, W. II., ASLE Traks.,b, 24-30 (1966). lfessina, J., Lubrication Eng., 23,459 (1967). Siederpriiem, H., Voss, P., German Patent 1,300,B36 (August 7, 1967j; CA, 71,90793(1969).
merits for stability can be met without the necessity of wholly fluorinated structures. The larger proportion of nonfluorinated percursors necessary for the preparation of these fluids should provide a cost benefit. The performance of these materials as lubricants on the four-ball wear test was satisfactory, particularly when 2 wt 70
Ravner. 11.. Russ. E. R.. Timmons. C. 0.. J . Chem. Ena. Data, 8, 59i (1963). ' Sianesi, I)., Pasetti, A., Tarli, F., ,J. Org. Chem., 31, 2312 (1966). 1t~cr~::rvm for review July 23, 1971 AccaPTeDl)ecember 6, 1971
The research was supported by the National Aeronautics and Space Administration under Contrart No. NAS 8-25510 and monitored by the ?.laterials Ilivision, Astronautics Laboratory, George C. 11arshall Space Flight Center.
Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 1, 1972
91
