US3172897A

US3172897A - Esters of decahydronaphthalene dimethanol

Info

Publication number: US3172897A
Application number: US133332A
Authority: US
Inventors: Rai Charanjit; John B Braunwarth
Original assignee: Pure Oil Co
Current assignee: Pure Oil Co
Priority date: 1961-08-23
Filing date: 1961-08-23
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

United States Patent 3,172,897 ESTERS 0F DECAHYDRONAPHTHALENE This invention relates to new and useful improvements in high-temperature synthetic lubricants, and more particularly to a novel class of diesters of cyclo-aliphatic glycols. This class of esters is especially useful as hightemperature lubricants and these esters are characterized by thermal and oxidative stability.

In recent years, the need has arisen for thermaland oxidation-stable lubricants capable of withstanding severe conditions encountered in jetand rocket-propelled aircraft, missiles, and automotive gas turbines. A considerable amount of research has been done on synthetic lubricants such as esters, silicones, polyalkylene glycols, perfluorocarbons, halogenated hydrocarbons, silicate esters, and phosphate esters. These recent developments are reviewed in Review of Synthetic Lubricants, D. H. Moreton, Lubrication Engineering, April 1954, pages 65- 73, and Synthetic Oils Start Moving, Chemical and Engineering News, September 3, 1956, pages 424M248. Among the numerous compounds tested for use as lubricants, the dibasic acid esters have been very promising due to their lubricity, low volatility, low flammability.

The dibasic acid esters have received some attention for high-temperature use because of their thermal stability. However, in the presence of any appreciable amount of air, dibasic acid esters, such as dioctyl sebacate, take up oxygen readily and are badly oxidized. The monobasic esters are generally considered unsatisfactory as synthetic lubricants. Monobasic acid esters in general show relatively high wear, are volatile at elevated temperatures, and have relatively high pour points. Those which do not exhibit these weaknesses are not outstanding in lowtemperature characteristics and seem to be receptive to oxidative breakdowns. Glycol diesters of monobasic acids have not been extensively investigated as synthetic lubricants, but tend to have rather poor lubricating properties, as well as being inferior in oxidative and thermal stability.

The properties which are sought in a high-temperature synthetic lubricant are:

(1) High viscosity index (VI),

(2) Low volatility,

(3) Low flammability,

(4) High thermal stability,

(5) High oxidation stability,

(6) High lubricity.

At present, none of the organic esters known to the prior art combine all of these desired properties.

A considerable amount of development work on organic esters and other synthetic lubricants for use under high-temperature conditions has been carried out at the Wright Air Development Center under the direction of the US. Air Force. The Department of Defense has developed a military specification for synthetic-base lubricants for use in aircraft turbine engines. This specification, MIL-L-7808D, sets forth the requirements for synthetic lubricants for high-temperature use, and describes the various tests which a synthetic lubricant must pass to meet military specifications.

It is therefore an object of this invention to provide a new and improved synthetic lubricant which combines the properties of high lubricity, high thermal stability, high oxidation stability, low flammability, low volatility,

and high viscosity index.

Another object of this invention is to provide a new and improved synthetic lubricant which meets the requirements of Military Specification MILL7808D.

Another object of this invention is to provide a new and improved organic ester synthetic lubricant which combines high thermal and oxidation stability and high viscosity index.

A feature of this invention is the provision of a novel class of organic esters which are useful as high-temperature synthetic lubricants, combining properties of high lubricity, high thermal stability, high oxidation stability, low flammability, low volatility, and high viscosity index.

Another feature of this invention is the provision of a new class of monobasic esters of cycle-aliphatic glycols which are especially useful as high-temperature lubricants.

Still another feature of this invention is the provision of cycle-aliphatic glycol diesters which are useful as synthetic lubricants and meet the requirements of Military Specification MIL-L-7808D.

Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.

This invention is based upon our discovery that certain diesters of cyclic glycols are especially stable against thermal breakdown and oxidation at elevated temperatures, and provide a combination of desirable lubricating properties including high viscosity index. In particular, this invention is based upon our discovery of a novel class of diesters of C C alkanoic (straight-chain or branchedchain) acids of C -C cycle-aliphatic glycols and C bicyclo-aliphatic glycols having side chains with 1 to 10 carbon atoms therein. The esters of this invention have the general formula,

0 II It R COR R R O R where R is a C -C alkyl radical, R and R are C -C alkylene radicals (saturated divalent aliphatic hydrocarbon radicals) and R is a saturated C -C cyclo-alkylene radical or C bicyclo-alkylene radical. These esters are prepared by esterification of cyclic glycols of the formula, HOR R R OH, Where R R and R are as defined above, with C C alkanoic acids. The esterification is carried out by conventional esterification methods, with or Without an esterification catalyst, as needed, and using a diluent or an azeotrope-former, if desired. Cyclic glycols of the general formula which may be reacted with C C (straight-chain or branched-chain) alkanoic acids to produce the novel esters of this invention include the following:

ff (llHr CH-CH OH HOCHz-CH H CH2 CHa CH(CH2)IOOH HO(CH2)10 H CH;

CH, /CH: l-rocrr tllrr (IJHCmOH GE -CH2 /CH\gH/CH2 HOCH2?H CHz I /$H CH2OH CH2 H CH2 Alkanoic acids which may be reacted with the cyclic glycols include any of the straight-chain or branched-chain amass? C C acids, e.g., hexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, decanoic acid, lauric acid, palmitic acid, stearic acid, behenic acid, tricosanoic acid, etc.

The following non-limiting examples are illustrative of the scope of this invention.

Example I The di-Z-ethylhexanoate ester of 1,4-cyclohexanedimethanol was prepared and evaluated for use as a hightemperature synthetic lubricant. 1,4-cyclohexanemethanol was denuded of methanol by distillation and a 569.3-g. portion of the purified material was charged with 100 cc. of toluene (as solvent) to a 1-liter reaction flask, fitted with a reflux condenser and a water trap. Then 528.8 g. of 2-cthylhexanoic acid and 3 g. of p-toluene sulfonic acid (as esterification catalyst) were added, and the mixture was stirred and heated at reflux temperature until water evolution ceased. The reaction mixture was then cooled, washed with water until neutral to litmus, and dried over calcium sulfate.

Resulting ester was, purified by distillation at a pressure of 0.075 mm. Hg to an overhead temperature of 160 C., to remove the toluene and unreacted Z-ethylhexanoic acid. The physical properties of the ester were as follows:

Acid number: 0.25

Carbon residue: Less than 0.1% Color (NPA): +3

Molecular weight (theon): 396 Molecular Weight (determined): 350 Flash point (COG): 430 F. Pour point: 65 F. or lower Viscosity (SUS), F.: 6000 Viscosity (SUS) 100 F.: 117.2 Viscosity (SUS) 130 F.: 69.8 Viscosity (SUS) 210 F.: 39.9 Viscosity index: 63.

The 1,4 cyclohexane dimethyl-di(Z-ethylhexanoate) ester was evaluated for lubricant properties and found to meet the requirements of Military Specification MIL-L- 7808B in all respects. The ester has a viscosity of 4.99 centistokes at 210 F. and 24.3 centristokes at 100 F. Its flash point was 430 F. and it had a pour point of 65 F. or lower. A portion of the ester was heated to 500 P. (which is a more severe treatment than the 347 F. treatment required by MiL-L-780SD), and air was bubbled through it at a rate of about 5 liters per hour for 20 hours. During this test, small squares of copper, steel and aluminum were placed in the liquid being heated, and aerated. The liquid loss in weight resulting from this treatment was only 1.6% as compared to the loss of 2.8% for a similar treatment of di-Z-ethylhexyl sebacate. The liquid had an increase of 6% in viscosity at 130 F. and an increase of 21% in viscosity at 0 F. as a result of this treatment. When di-2-ethylhexy sebacate was treated in this manner, the viscosity at 130 F. increased 18% and the viscosity at 0 F. increased 35%. As a result of this treatment, the acid neutralization number of the liquid increased from substantially 0 to 18.9. This change in acid neutralization number is Within the specifications of MIL-L-7 808D. The loss in weight of the copper, steel, and aluminum squares in the liquid was within the values specified by MILL7808D. This liquid has excellent lubricating properties, high viscosity index, high thermal and oxidative stability, and is useful for the lubrication of moving parts, e.g., gas turbine engines, throughout the temperature range from 0 to 600 F.

Exan'iple II v A one-moi portion of 1,3 cyclopentanedimethanol is charged with 100 cc. of benzene to a 1-liter reaction flask fitted with a reflux condenser and a Water trap. Then 2.0

mols of Z-ethylhexanoic acid and 3.0 g. of p-toluene sulfonic acid (esterification catalyst) are added and the mixture stirred and heated at reflux temperature until evolution of water has ceased. Finally, the reaction mixture is cooled, washed with Water until neutral to litmus, and dried over calcium sulfate. The ester is purified by vacuum distillation to remove diluent benzene and unreacted materials. The ester which is obtained is a liquid having high viscosityindex, high oxidation and thermal stability, and good lubricating properties throughout the temperature range of 0 to 600 F.

When 1,4-cyclohexanedimethanol is reacted with lauric acid or stearic acid in the same manner as described for Examples 1 and 2, the dilaurate or distearate ester is obtained. These esters have good lubricating properties, high thermal and oxidative stability and high viscosity index. These esters are liquids over a wide temperature range and are useful in the lubrication of high-temperature engines over a temperature range from 0 to about 600 Example III A one-moi portion of decahydronaphthalene dimethanol,

H2 is charged with 200 cc. of benzene to a 1-liter reaction flask fitted with a reflux condenser and a water trap. Then, 2.0 mols of lauric acid and 3.0 g. of p-toluene sulfonic acid (catalyst) are added and the mixture stirred and heated at reflux temperature until evolution of water has ceased. Finally, the reaction mixture is cooled, washed with water until neutral to litmus, and dried over anhydrous calcium sulfate. The ester is purified by vacuum distillation to remove diluent benzene and unreacted materials. The dilaurate ester which is obtained is a liquid having high viscosity-index, high oxidation stability, high thermal stability and good lubricating properties through out the temperature range from 0 to 600 F.

While We have described our invention fully and completely with special emphasis on several preferred embodiments thereof, we wish it to be understood within the scope of the appended claims this invention may be prac ticed otherwise than as specifically described herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An ester of the formula OH: H CH;

References Cited in the file of this patent UNITED STATES PATENTS Soloway et al Mar. 13, 1956 Staib et al. Mar. 13, 1956 Roelen et al. Dec. 24, 1957 Brannock Nov. 10, 1959 Pethrick et al. Oct. 24, 1961 Craven Jan. 30, 1962 OTHER REFERENCES His-Kwei: Chemical Abstracts 52, 154815 (1958). Liao et al.: I. Am. Chem. Soc. 77, 990-991 (1955).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,172,897 March 9, 1965 Charanjit Rai et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 30, for "C -C read C C column 3,

line 42, for "centristokes" read centistokes line 56, for "di-Z-ethylhexy" read di-Z-ethylhexyl column 4, lines'2'4 to 29, for that portion ofthe formula reading:

N I H read Signed and sealed this 3rd day of August 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. AN ESTER OF THE FORMULA