High temperature lubricants containing cesium, robidium, and lithium salts

In one respect, this invention is a lubricating composition which comprises a polyaryl ether lubricating fluid and an additive which is (a) cesium carbonate, (b) cesium phosphate, or (c) a benzoate of cesium, rubidium, or lithium wherein the additive is present in the lubricating composition in an amount effective to produce an antioxidative effect in the lubricating composition. In another respect, this invention is a process for reducing the rate of oxidation in a polyaryl ether lubricating fluid which comprises adding an additive wherein the additive is (a) cesium carbonate, (b) cesium phosphate, or (c) a benzoate of cesium, rubidium, or lithium to the polyaryl ether lubricating fluid in an amount effective to produce an antioxidative effect in the lubricating composition.

BACKGROUND OF THE INVENTION 
This invention relates to polyaryl ether, high temperature lubricants which 
contain antioxidants. 
There are only a few classes of compounds that qualify as high temperature 
fluids, that is, fluids used at temperatures above 300.degree. C. A well 
known class of such fluids are the polyaryl ethers. While generally 
stable, these lubricants can undergo oxidation at very high temperatures 
which leads to increased viscosity and shortened useful working life of 
the fluid. Therefore, it is desirable to find new and effective additives 
that serve as antioxidants for high temperature lubricants. Ravner et al. 
have reported the addition of various inorganic salts in polyphenyl ethers 
as antioxidants in ASLE Transactions, volume 15, pages 45-53 (1972) and in 
ASLE Transactions, volume 18, pages 1-4 (1975). However, the inorganic 
salts disclosed therein do not perform as well as is desirable. 
SUMMARY OF THE INVENTION 
This invention, in one respect, is a lubricating composition which 
comprises a polyaryl ether lubricating fluid and an additive wherein the 
additive is (a) cesium carbonate, (b) cesium phosphate, or (c) a benzoate 
of cesium, rubidium, or lithium and wherein the additive is present in the 
lubricating composition in an amount effective to produce an antioxidative 
effect in the lubricating composition. 
In another respect, this invention is a process for reducing the rate of 
oxidation in a polyaryl ether lubricating fluid which comprises adding an 
additive wherein the additive is (a) cesium carbonate, (b) cesium 
phosphate, or (c) a benzoate of cesium, rubidium, or lithium to the 
polyaryl ether lubricating fluid in an amount effective to produce an 
antioxidative effect in the lubricating composition.

DETAILED DESCRIPTION OF THE INVENTION 
The antioxidant additives of this invention are cesium, rubidium, and 
lithium salts which are composed of the metal cation and an anion. 
Suitable cesium salts include those wherein the anion is carbonate, 
phosphate, or benzoate, preferably, the anion is carbonate or benzoate; 
more preferably, the anion is benzoate. Suitable rubidium salts include 
those wherein the anion is benzoate. Suitable lithium salts include those 
wherein the anion is benzoate. 
The carbonate and phosphate salts useful in this invention are well known 
materials and are readily available commercially. 
Suitable benzoates useful as anions in this invention include benzoate and 
substituted benzoates. When the benzoate is substituted, suitable 
substitutes include phenoxy, phenyl, trifluoromethyl, 
trifluoromethylphenoxy, trifluoromethoxy, trifluormethoxyphenoxy, and 
trifluoromethoxyphenyl. Substituted benzoate for purposes of this 
invention includes naphthoates. When the lubricating fluid contains 
fluorine, it is preferred to employ a phenoxy which also contains 
fluorine. Preferred substituted benzoates include 2-phenoxybenzoate, 
3-phenoxybenzoate, 4-phenoxybenzoate, 2-phenylbenzoate, 3-phenylbenzoate, 
4-phenylbenzoate, 1-naphthoate, 2-naphthoate, 2-(trifluoromethyl 
)benzoate, 3-(trifluoromethyl)-benzoate, 4-(trifluoromethyl)benzoate, 
2-(3-trifluoro-methyl)phenoxybenzoate, 
3-(3-trifluoromethyl)-phenoxybenzoate, 
4-(3-trifluoromethyl)phenoxybenzoate, 2-(trifluoromethyl )benzoate, 
3-(trifluoromethyl)-benzoate, 4-(trifluoromethyl)benzoate, 
2-(trifluormethoxy)benzoate, 3-(trifluoromethoxy)benzoate, 
4-(trifluoromethoxy)benzoate, 2-(3-trifluoromethoxy)-phenoxybenzoate, 
3-(3-trifluoromethoxy)phenoxybenzoate, and 
4-(3-trifluoromethoxy)phenoxybenzoate. 
The cesium, rubidium, and lithium benzoates are generally prepared by 
reacting the metal hydroxide with a corresponding benzoic acid to form a 
resulting organometallic salt. This reaction can be readily performed in 
neutral to basic aqueous media in the temperature range from about 
0.degree. C. to about 100.degree. C. The reaction can be stirred. The 
salts are recovered and purified, if purification is necessary, by 
conventional methods. The various benzoic acids can be prepared by well 
know methods. 
The cesium, rubidium, and lithium salts of this invention are used as 
antioxidant additives for lubricating fluids in a lubricant composition. 
Suitable lubricating fluids include polyaryl ether fluids, preferably 
polyphenyl ethers. Representative examples of polyaryl ethers include para 
and meta forms of bis(phenoxy-phenoxy) benzene (known as "5P4E"), para and 
meta forms of bis(phenoxyphenyl) ether (known as "4P3E"), and para and 
meta forms of phenoxyphenoxy benzene (known as "3P2E"). 
The cesium, rubidium, and lithium salts are employed in the lubricant 
composition in any amount sufficient to produce an antioxidant effect in 
the lubricating fluid. Preferably, the cesium, rubidium, and lithium salts 
are employed in a concentration, based on the weight of the lubricating 
fluid in the composition, of greater than or equal to about 0.1 percent, 
more preferably greater than or equal to about 0.5 percent, and most 
preferably greater than or equal to about 1 percent; and preferably less 
than or equal to about 20 percent, more preferably less than or equal to 
about 10 percent, and most preferably less than or equal to about 5 
percent. The additive can be added to the lubricating fluid at any time 
prior to use or during use. 
The lubricating composition of this invention can contain additional 
components such as corrosion inhibitors, additional antioxidants, and 
anti-wear additives. 
The following examples are given to illustrate the invention and should not 
be interpreted as limiting the invention in any way. Unless stated 
otherwise, all parts and percentages are given by weight. 
EXAMPLE 
Evaluation of Several Additives 
Formulations of commercial polyphenyl ether (5P4E) and cesium salts were 
prepared by adding 0.1 percent of the cesium salt to 5P4E, followed by 
mixing and heating at 150.degree. C. for about 2 hours. The admixed 
formulations were subjected to bulk oxidation stability evaluation at 
330.degree. C. using the Micro-Corrosion and Oxidation Stability 
(Micro-COS) test method for 24 hours in the presence of six metal coupons 
of Ti, INCO, M50 steel, Cr-M50 steel, Ag, and Al. During the test, air was 
bubbled through the formulation with a flow rate of 1 liter per hour. The 
percent change in viscosity was then determined. The results are reported 
below in Table I. In the Table, ".DELTA.Viscosity 40.degree. C." and 
".DELTA.Viscosity 100.degree. C." denote the differences in viscosity of 
the formulations after the evaluation at temperatures of 40.degree. C. and 
100.degree. C. respectively. In the Table, ".DELTA.TAN" indicates the 
change in total acid number of the formulation after the evaluation. Also 
in the Table, "Cs(Benz)" cesium benzoate. 
TABLE I 
______________________________________ 
Additive 
.DELTA. Viscosity 40.degree. C. 
.DELTA. Viscosity 100.degree. C. 
.DELTA. TAN 
______________________________________ 
None1 133.9 46.7 0.22 
Cs.sub.3 PO.sub.4 
14.8 5.9 0.04 
Cs.sub.2 CO.sub.3 
8.7 2.5 0.00 
Cs(Benz) 
8.4 0.7 0.05 
______________________________________ 
1Not an embodiment of the invention. 
The data in Table I shows that the viscosity of the formulation shows less 
change in viscosity as compared to a formulation containing no additive. 
Since the formulations were subjected to oxidative conditions during the 
evaluation, the data shows that the cesium salts tested function as 
antioxidants since the formulations containing cesium salts display less 
breakdown of the 5P4E fluid relative to untreated 5P4E. Breakdown of fluid 
leads to an increase in viscosity. Similarly, the formulations containing 
additive show less of an increase in acids as indicated by the change in 
total acid number relative to the formulation containing no additive. 
COMATIVE EXPERIMENT 
(Not an embodiment of the invention) 
The procedure of the Example was repeated using barium phosphate (Ba.sub.3 
(PO.sub.4).sub.2)and barium carbonate (BaCO.sub.3) as the additive. The 
results are shown in Table II. 
TABLE II 
______________________________________ 
Additive .DELTA. Viscosity 40.degree. C. 
.DELTA. Viscosity 100.degree. C. 
.DELTA. TAN 
______________________________________ 
Ba.sub.3 (PO.sub.4).sub.2 
309.6 97.0 0.37 
BaCO.sub.3 
61.4 21.4 0.00 
______________________________________ 
As seen in Table II, barium phosphate and barium carbonate are far less 
effective as antioxidants as opposed to the phosphate and carbonate of 
cesium tested in the Example. Whereas cesium phosphate and cesium 
carbonate both significantly reduce the amount of viscosity increase in 
the polyphenyl ether fluid relative to a fluid containing no additive, 
barium phosphate increases viscosity relative to fluid containing no 
additive and the effect of barium carbonate is relatively small as 
compared to the effect of cesium carbonate in Example 1. It is seen, 
therefore, that cesium phosphate and cesium carbonate are far superior 
antioxidants over barium phosphate and barium carbonate.