Fluorine containing esters of polycarboxylic acids are discussed. The use of these esters as extreme temperature lubricants and base fluids for greases is investigated

Breed, L. L.

Elliott, R. L.

English

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United States Patent Office 3,752,847Patented Aug. 14, 1973
3,752,847
FLUORINATED ESTERS OF POLYCARBOXYLIC
ACIDS
James C. Fletcher, Administrator of the National Aero-
nautic and Space Administration, with respect to an
• invention of Laurence W. Breed, Overland Park, Kans.,
and Richard L. Elliott, Kansas City, Mo.
No Drawing. Filed Sept. 23, 1971, Ser. No. 183,240
Int. CL C07c 69/42
U.S. CL 260—485 F 4 Claims
ABSTRACT OF THE DISCLOSURE
' Fluorine-containing esters of polycarboxylic acids hav-
ing the formula
r r iK LCOOCHsCF—0-CH2(CFjFs)I1Hjm
where R is a saturated hydrocarbon radical of 2 to 20 car-
bon atoms having only one carboxy group attached to any
one carbon atom, m is a whole number of 2 to 4 and n
is a whole number of 1 to 5. Esters embodying the in-
vention are useful for extreme-temperature lubricants and
base fluids for greases.
ORIGIN OF THE INVENTION
The invention described herein was made in the per-
formance of work under a NASA contract and is subject
to the provisions of Section 305 of the National Aeronau-
tics and Space Act of 1958, Public Law 85-568 (72 Stat.
435, 42 USC 2457).
BACKGROUND OF THE INVENTION
, This invention relates to fluorinated esters of polycar-
boxylic acids and to lubricating compositions based on
the same.
Improved lubricating fluids are needed for applications
involving service at extreme temperatures, and in 'par-
ticular for lubrication of equipment in cryogenic liquid or
gaseous oxygen systems. In addition to physical properties
amenable to extreme temperature service, namely, liquidi-
ty over a wide temperature range along with a minimum
pour point and a low evaporation rate, lubricant base
fluids for such applications should exhibit a high degree
of hydrolytic stability and a low reactivity with metals
under stress conditions. Further requirements include
•absence of impact sensitivity in the presence of liquid or
gaseous oxygen and effective lubricity.
Considerable progress toward meeting the above re-
quirements has been realized by means of structural modi-
fication of organic liquids to provide fluorine substitution
at selected sites in the molecule. Fluorine substitution in
general renders organic liquids more stable and less sus-
ceptible to oxidative reactions. Fully fluorinated com-
pounds, however, present disadvantages in their high pour
points, high volatility and high viscosity indexes. One
approach to obtaining improved lubricant properties has
involved the synthesis of partially fluorinated structures
which incorporate heteroatoms in the molecule. Various
partially fluorinated liquids have been disclosed by pre-
vious workers, including fluorine-containing esters of poly-
carboxylic acids as described in U.S. Pats. 3,081,342;
3,124,533; 3,223,726; and 3,096,363. While the previously
available fluorinated esters exhibit favorable properties in
many respects, further improvements are needed, and in
particular decreased pour points and lower evaporation
rates, consistent with hydrolytic stability, good wear prop-
erties and amenability to thickening.
SUMMARY OF THE INVENTION
The present invention is directed to fluorine-containing
esters of polycarboxylic acids having the formula5
 r r iR LCOOCHsCF-O-CHsfCFjFO.Hjn,
where R is a saturated hydrocarbon radical of 2 to 20
carbon atoms having only one carboxy group attached to
any one carbon atom, m is a whole number of 2 to 4 and
10 n is a whole number of 1 to 5. Esters of this formula,
exemplified by the bis(polyfluoroalkyloxy tetrafluoro-
propyl) 3-methylglutarates, show favorable overall prop-
erties for use as lubricants in cryogenic oxygen-containing
systems.
1"* It is therefore an object of this invention to provide im-
proved lubricants for extreme-temperature use.
Another object is to provide fluorine-containing esters
of polycarboxylic acids which have decreased pour points
and low evaporation rates.
20
 Still another object is to provide lubricant liquids hav-
ing a minimum reactivity with liquid or gaseous oxygen.
Yet another object is to provide fluorinated esters char-
acterized by their hydrolytic stability, good wear proper-
ties and amenability to thickening.
A further object is to provide a method of preparing
such esters.
Other objects and advantages of the invention will be
apparent from the following detailed description.
30 DESCRIPTION OF THE PREFERRED
EMBODIMENT
Fluorine-containing esters of the formula given above
can be prepared by reaction of a saturated carboxylic
acid with' a 2-polyfluoroalkyloxytetrafluoropropanol hav-
35
 ing the formula
CFi
H(CFjCFj)nCH,-O-CF-CHi-OH
40 where n is a whole number from 1 to 5. Preferred
propanol compounds are those in which n is equal to 2
or 3. The propanol reactant can be prepared by condens-
ing hexafluoropropylene oxide with a polyfluoroalkyl al-
cohol in the presence of sodium hydroxide to form a 2-
45 polyfluoroalkyloxytetrafluoropropionic acid and reducing
the acid with sodium borohydride in tetrahydrofuran.
Polycarboxylic acids which can be used for preparation
of esters embodying the invention may be represented by
the formula R(COOH)m where R is a saturated hydro-
50 carbon radical of 2 to 20 carbon atoms having only one
carboxy group attached to any one carbon atom and m
is a whole number of 2 to 4. The saturated hydrocarbon
radical may be acyclic or alicyclic (containing a carbocyclic
ring) including alkyl substituted carbocyclic hydrocarbon.
55 Examples of saturated polycarboxylic acids which can be
used include 3-methylglutaric acid, 2-methylglutaric acid,
3,3 - dimethylglutaric acid, 2,2 - dimethylglutaric acid, d-
camphoric acid, and tricarballylic acid. 3-methylglutaric
acid is preferred.
60 ' Reaction of the polycarboxylic acid, or a functional
derivative thereof such as the anhydride, with the 2-poly-
fluoroalkyloxytetrafluoropropanol can be carried out by
conventional esterification techniques wherein a mixture
'of the reactants is heated in a solvent in the presence of a
6g strong acid catalyst. It is preferred to heat the mixture
under reflux conditions in toluene, using a sulfuric acid
catalyst, with water being removed as the solvent refluxes.
The product can be purified and recovered by dissolution
'in ether, washing with water and potassium carbonate and
70 drying, followed by fractional distillation. Other purifica-
tion methods such as solvent extraction or absorption of
impurities can also be used.
3,752,847
The invention is further illustrated by the following
examples
Example I
2-^'-heptyloxy-2,3,3,3-tetrafluoropropanol-1, formula
CF,
H(CF!),CH»-O—CF—CHsOH
was prepared by condensing hexafluoropropylene oxide
with ^'-heptyl alcohol to form 2-\J-'-heptyloxytetrafluoro-
propionic acid and reducing the acid with sodium boro-
hydride in tetrahydrofuran.
A mixture of 17.4 grams (0.034 mole) of the 2-^'-
heptyloxytetrafluoropropanol, 2.75 grams (0.019 mole) of
3-methyl glutaric acid, 0.07 gram of sulfuric acid and
16 milliliters of toluene was refluxed for 20 hours. 0.9
milliliter (calcd. 0.7 ml.) of water was collected in a
Dean-Stark trap. The residue was cooled, dissolved in 100
ml. of ether, washed sequentially with 100 ml. portions of
water, 10% potassium carbonate and water, and dried over
sodium sulfate. Fractional distillation gave 15.7 grams
(81%) of bis(2-i//-heptyloxytetrafluoropropyl) 3-methyl-
glutarate, B.P. 180-184° C. (0.5 mm.), n0w 1.3478. Analy-
sis calculated for C2eHi8F32O6 (percent): C, 30.19; H, 1.75;
F, 58.78. Found (percent): C, 30.09; «, 1.89; F, 59.04.
In a second preparation using the above procedure with
21 ml. of toluene, 3.65 grams (0.025 mole) of 3-methyl-
glutaric acid, 23.1 grams (0.050 mole) of 2-^'-heptyloxy-
tetrafluoropropanol and 0.07 gram of sulfuric acid, 21.6
grams (84%) of bis(2-^'-heptyloxytetrafluoropropyl) 3-
methylglutarate, boiling at 169-171° C. (0.2 mm.), /iD20
1.3488,
dg 1.668
was obtained.
Additional properties of the fluorine-containing ester
product were determined as follows: Pour point, —50° F.;
viscosity 47.95 cst. at 100° F., 5.08 cst. at 210° F.; lubrici-
ty of the ester containing 2 weight percent tricresyl phos-
phate (four-ball wear scar diameter, 50 kilogram load,
2 hours at 147° F. and 600 revolutions per minute) 0.4
millimeter; hydrolytic stability (milliliter 1 N NaOH/
mole) 3.81; evaporation rate (percent at 300° F., one
hour) 1.36; reactivity to aluminum under shear'(1,500
revolutions per minute, 1000 pounds per square inch, for
one minute), no reactions in 6 trials; and impact sensi-
tivity with liquid oxygen (MSFC-SPEC-106B, "Testing
Compatibility of Materials from Liquid Oxygen Systems,"
Marshall Space Flight Center, impact energy 10 kg.-
meters), no reactions in 20 trials.
Example II
2-^'-pentyloxy-2,3,3,3-tetranuoropropanol-l, formula
CF,
Hf.CFiltCHt-O— CF— CHjOH
was prepared by condensing hexafluoropropylene oxide
with ^'-amyl alcohol in the presence of sodium hydroxide
to form 2-^'-pentyloxytetrafluoropropionic acid and re-
ducing the acid with sodium borohydride in tetrahy-
drofuran.
A mixture of 13.5 grams (0.037 mole) of the 2- '^-
pentyloxytetrafluoropropanol, 2.72 grams (0.019 mole)
of 3-methylglutaric acid, 0.07 gram sulfuric acid and 15
milliliters of toluene was refluxed for 18 hours. 0.8 millili-
ter (calcd. 0.7 ml.) of water was collected in a Dean-
Stark trap. The residue was cooled, dissolved in 100 ml.
of ether, washed sequentially with 100 ml. portions of
water, 10 percent potassium carbonate and water, and
dried over sodium sulfate. Fractional distillation gave 12.4
grams (80%) of bis(2-^'-pentyloxytetrafluoropropyl) 3-
methylghitarate, B.P. 151-153° C. (0.3 mm.), nD20 1.3550.
Analysis calculated for C22Hi8F24Oa (percent): C, 31.67;
H, 2.17; F, 65.65. Found (percent): C, 31.78; H, 2.27;
F, 54.97.
10
15
20
25
30
35
40
In a second preparation using the above procedure with
5.3 grams (0.036 mole) of 3-methylglutaric acid, 26.5
grams (0.074 mole) of 2-^'-pentyloxytetrafluoropropanol,
0.14 gram of sulfuric acid and 30 ml. of toluene, 25.9
grams (85%) of the fluorinated ester boiling at 144-
146° C. (0.1 mm.), nD2° 1.3548,
d% 1.603
was obtained.
Additional properties of the product ester were deter-
mined as follows: pour point, —65° F.; viscosity, 33.83
cst. at 100° F., 4.02 cst. at 210° F.; hydrolytic stability
(milliliter 1 N NaOH/mole) 1.65; evaporation rate (per-
cent at 300° F., 1 hour) 4.78; reactivity to aluminum
under shear (1500 revolutions per minute, 1000 pounds
per square inch, for one minute), no reactions in six trials;
and impact sensitivity with liquid oxygen (MSFC-SPEC-
106B) one reaction hi 20 trials.
It may be seen from the above that fluorinated esters
embodying the invention exhibit excellent overall prop-
erties for use as lubricants, in particular, their wide range
of liquidity, hydrolytic stability, low evaporation rate and
minimum reactivity with oxygen, as well as effective
lubricity. The esters can be used as lubricant oils with-
out additive modification. However, best results are ob-
tained by incorporating a small amount, Vi to 5 weight
percent, and preferably 2 weight percent, of an antiwear
additive such as tricresyl phosphate in the ester. Grease-
like compositions can be obtained by addition of thick-
eners such as a fluorocarbon telomer dispersion (avail-
able under the trade name Vydax 1000) preferably at
proportion of 15 to 20 weight percent. In addition to their
use as lubricants, esters embodying the invention are use-
ful for other applications requiring high stability and low
volatility, for example, as fluids for transmission of heat
and power.
It is understood that the preceding examples are mere-
ly illustrative and are not to be construed as limiting
the scope of the invention. Various changes and modi-
fications in the procedures given above can be employed
by one skilled in the art without departing from the in-
vention.
What is claimed is:
1. A fluorine-containing ester having the formula
45
50
55
60
»Hj,—C-C-C-LCOOCHjCF-O-CEWCFjCFj);
R' R' R'
where n is a whole number of 1 to 5 and R' is a hydrogen
atom or a methyl radical, at least one and no more than
two of said R' symbols representing methyl radicals, and,
for esters having two methyl radicals represented thereby,
both of said methyl radicals being linked to the same
carbon atom.
2. A fluorine-containing ester having the formula
CHsCH :
CFj
CHjCOOCHjCF—i ,Hj,
65
where n is a whole number of 1 to 5.
3. The ester of claim 2 wherein n is 2.
4. The ester of claim 2 wherein n is 3.
- - - -. References Cited
UNITED STATES PATENTS
3,096,363 7/1963 Ballard et al 260—485
70
 LORRAINE A. WEINBERGER, Primary Examiner
E. J. SKELLY, Assistant Examiner
U.S. Cl. X.R.
75 252—49.9, 54.6; 260—468 K.


Fluorinated esters of polycarboxylic acids

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