US2963437A - Lubricant compositions - Google Patents

Description

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LUBRICANT COMPOSITIONS Herman E. Ries, In, Chicago, Ill., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Filed Feb. 17, 1955, Ser. No. 488,982

Claims. (Cl. 25249.8)

This invention relates to lubricants of improved rust preventative properties obtained by incorporation of a very small amount of a mono-ester of'a long chain hydrocarbon phosphonic acid.

Anti-rust or rust preventative properties are important attributes of most lubricants including engine oils, greases, gear oils and particularly turbine oils. As a consequence, a wide variety and great number of additives have been proposed or used for the purpose of imparting anti-rust properties to lubricating oils. Although the use of certain alkyl phosphonic acids and their diesters has been proposed, insofar as I know, mono-esters of hydrocarbon phosphonic acids have not been proposed or tested for value in oils. I have now found that certain monoalkyl esters of long chain hydrocarbon phosphonic acids are surprisingly effective in imparting anti-rust properties to lubricating oils. For example, I have found that the monomethyl ester of octadecyl phosphonic acid is more effective than the corresponding free acid as an antirust in turbine oils. This is surprising because film balance studies have shown that the free acid is a stronger film former than the monomethyl ester. Thus, the collapse pressure, measured in dynes per centimeter by the Langmuir-Adam-Harkins film balance, of a film of the monomethyl ester of octadecyl phosphonic acid is 48 compared to 53 for the free acid. On this basis, the free acid would be expected to show superiority in rust protection. In terms of practical utility, however, the monomethyl ester when tested for anti-rust properties under the conditions of the ASTM D665 film-tenacity test was found to give perfect protection at a concentration as low as 0.001 percent Where the free acid showed incipient breakdown and rusting. The monoalkyl esters are considerably superior to the corresponding diesters as anti-rust agents apparently because the complete elimination of the free acid group reduces film forming properties to an undesirable extent although the diesters do appear to retain detergent properties.

In the practice of the invention, the monoesters of long chain hydrocarbon phosphonic acids are added to the lubricant base, which may comprise a typical hydrocarbon lubricating oil fraction in a concentration of about 0.0001 to about 1.0 percent by weight. The phosphonic mono-esters are characterized by the association of the strongly polar phosphonic group with its long chain hydrocarbon radical and the shorter ester group leaving one free acid radical in the molecule. The long chain hydrocarbon group must contain an essentially straight aliphatic chain of at least carbon atoms length in order to provide the close molecular packing necessary for good film forming properties. Octadecyl phosphonic acid is a suitable example although hydrocarbon chains of greater length may be used, often with advantage in improved oil solubility, up to very long chains such as in the case of hexatriacontanyl phosphonic acid. Mixtures such as tallow phosphonic acids are suitable. In terms of practical availability, however, materials such as dodecyl phos- 2,963,437 Patented Dec. 6, 1960 lQQ phonic acid and hexadecyl phosphonic acid have special value. In the longer chain products, some chain branching and ring substitution can be tolerated without interfering with close molecular packing for high film strength. The introduction of rings, particularly when close to the phosphonic group, also tends to have a beneficial effect on oil solubility. Alkyl benzene phosphonic acids however should be para-positioned to preserve the essentially straight chain character. The methyl branching in olefin chain polymers such as propylene tetramer, or in polybutene chains, also appears unobjectionable.

The new additives may be characterized structurally by the following formula:

It is important that there be at least one free acid group. The R may be an aliphatic radical containing less than 10 carbon atoms. The monomethyl ester is superior to the higher alkyl esters such as ethyl, propyl, and butyl because the small methyl group appears to interfere less with close molecular packing in film formation. As the alkyl groups lengthen however there is some evidence that their freedom to bend restores close packability.

The new additives may be made in a number of ways. If the corresponding free acid is available, the monoester can sometimes be prepared by partial esterification. More generally, the desired monoester can be prepared by partial hydrolysis of the corresponding diester, for example, with hydrogen chloride. To prepare the dialkyl ester, a dialkyl phosphite, e.g. diethyl phosphite, can be reacted with a long chain alkyl halide e.g. octadecylbromide, in the presence of metallic sodium. The resulting dialkyl ester then can be hydrolyzed or partially hydrolyzed with hydrochloric or hydrobromic acid to obtain the free acid or the mono-ester. Alternatively the long chain halide, e.g. octadecyl bromide, can be reacted with a trialkyl phosphite, e.g. triethyl or trimethyl phosphite. At about to C. the diester of the long chain phosphonic acid is formed and the volatile ethyl or methyl halide may be distilled off permitting the reaction to go to completion. In another method, a long chain olefin, e.g. octadecenc-l, is reacted with a dialkyl phosphite, e.g. diethyl phosphite in the presence of a peroxide catalyst or other free radical initiator such as a hypochlorite, or under the influence of ultraviolet light, at about 200 to 300 C. to obtain the diester.

The new lubricating oil additives can be used in a number of lubricating applications. They may be incorporated as anti-rust agents in crank case lubricating oil oils for internal combustion engines. In this application, they also appear to improve the properties of the lubricating oil with respect to cam-follower wear characteristics as well as functioning generally to improve the anti-corrosion properties of the oil. In addition, they appear to improve engine operation in respect of limitations such as octane requirement increase with use and preignition encountered with the use of highly leaded fuels. They also are useful in a variety of lubricants and viscous oil compositions as rust preventatives, for example, in turbine oil, cutting oil and grease formulations. The concentration level depends upon the intended use environment and to some extent on the solubility of the phosphonic rnono-esters in the hydrocarbon base oil. The concentration range may approximate 0.0001 to about 1.0 Weight percent but will be usually in the range of about 0.01 to 0.5 weight percent. Solubility may be improved by dissolving the additives in carrier solvents such as benzene, toluene, xylenes and higher aromatics in order to facilitate incorporation in the base oil. The base oil may be conventionally or solvent refined and may vary widely in viscosity range and other properties such as pour point, flash, etc. The finished oil blend ordinarily will contain other additives such as oxidation inhibitors, pour depressants, anti-foam agents and the like.

The following examples illustrate specific application of invention.

EXAMPLE I test perfectly, but the monomethyl ester showed unexpected superiority in the film tenacity test in view of the fact that the free acid forms a stronger film as shown by its higher collapse pressure when tested by the film balance procedure of Langmuir-Adam-Harkins. The high degree of effectiveness of the phosphonic type additives is shown by the comparison with stearic acid, a commercially accepted rust inhibitor. The test data also show that the tri-cresyl phosphate, which contains a different type of phosphorus containing group and non-polar substituent, was totally ineffective as a rust inhibitor. The rust data are tabulated below in Table I.

Table l ASTM Rust, Percent Concentration Film Tenacity, Percent Concentration stearic Acid Severe (Consider- Nonem. Severe.

able). S Tri- -cres lPh nhate evere n-oritadec ylphosphonic Acid None.-." None None Slight N N Monomethyl ester of n-octadecylphos- None None None N ne None phonic acid.

of methanol, grams (0.62 mole), in pyridine, 23.7 EXAMPLE III (0.30 mole), was added dropwise. The reaction flask was surrounded by water to control the temperature. A solid appeared and remained throughout the reaction. After all of the methanol-pyridine solution was added, stirring was continued for an additional 15 minutes. To the reaction mixture was added 50 ml. of water and the contents of the flask were stirred vigorously. This caused an emulsion to form. n-Octanol was found to extract the organic material out of the emulsion. The octanol layer was separated and washed with water. Ethyl acetate, 300 ml., was added to the octanol solution and white solid precipitated (I). Acetone was added to the filtrate and this solution allowed to stand in the cold room overnight. A second solid (II) precipitated which weighed 2.10 grams. II was recrystallized twice from acetone to give 1.47 grams of white solid, M.P. 65.5- 66.5 C. This material was found to be the monomethyl ester of n-octadecylphosphonic acid by elemental analysis and acid number.

Calcd. for C H PO C, 65.48; H, 11.86. Found: C, 65.50; H, 11.78.

Acid No. (mg.KOH/gm.): Calcd., 163. Found, 171.

I after 2 reerystallizations from acetone gave 0.55 grams of a mixture melting 67-74 C.

EXAMPLE II The monomethyl ester of n-octadecyl phosphonic acid of Example I was tested for its ability to impart rust preventative properties to turbine oils under the conditions of the ASTM 111st test for steam turbine oils ('D 66554) and the film tenacity modification thereof. The performance of the monomethyl ester of the invention was checked by comparison with free n-octadecyl phosphonic acid, stearic acid and tri-p-cresyl phosphate.

In the ASTM test, a mixture of 300 ml. of the test oil with ml. of distilled water is stirred at a temperature of 140 F. for 24 hours with a cylindrical steel specimen completely immersed therein. The film tenacity test is performed by removing the specimen, replacing the oil with fresh distilled water and repeating under the same conditions of temperature and time. The repeat run atfords a basis for distinguishing between anti-rust agents which are effective enough to pass the ASTM test but which may not stand up in service.

The base oil in the test was a highly acid refined stock having a flash exceeding 380 F., a pour point lower than 10/0 and a viscosity of 155-460 SSU at 100 F.

Both the monomethyl ester of octadecyl phosphonic acid and the tree acid passed the conditions of the regular Using the'base oil of Example II with 0.01 percent of phenyl ct-naphthylamine, the effectiveness of the monomethyl ester of octadecyl phosphonic acid was further compared with the corresponding free acid at a concentration of 0.01 weight percent under the conditions of the ASTM Turbine Oil Oxidation Test (D4943). It will be noted from the test data which are tabulated below that the mono-ester provided satisfactory protection throughout the test period and clearly out-performed the free acid.

I claim:

1. A steam turbine lubricant composition, having the property of inhibiting rust in the presence of steam and moisture, which composition consists essentially of a hydrocarbon lubricating oil fraction and from about 0.001 percent to about 1.0 percent by weight of a monoalkyl ester of a phosphonic acid which contains a long chain hydrocarbon group comprising an essentially straight aliphatic chain of at least 10 carbon atoms attached to the phosphorus atom and in which the alkyl radical of the ester group contains less than 10 carbon atoms.

2. The lubricant composition of claim 1 in which the ester is a monoalkyl ester of octadecyl phosphonic acid.

3. The lubricant composition of claim 1 in which the ester is a monomethyl ester of dodecyl phosphonic acid.

4. The lubricant composition of claim 1 in which the esteir is the monomethyl ester of hexadecyl phosphonic aci 5. The lubricant composition of claim 1 in which the estelr is the monomethyl ester of octadecyl phosphonic aci Benning et a1. May 11, 1937 Sullivan Sept. 26, 1939

Claims (1)

1. A STEAM TURBINE LUBRICANT COMPOSITION, HAVING THE PROPERTY OF INHIBITING RUST IN THE PRESENCE OF STEAM AND MOISTURE, WHICH COMPOSITION CONSISTS ESSENTIALLY OF A HYDROCARBON LUBRICATING OIL FRACTION AND FROM ABOUT 0.001 PERCENT TO ABOUT 1.0 PERCENT BY WEIGHT OF A MONOALKYL ESTER OF A PHOSPHONIC ACID WHICH CONTAINS A LONG CHAIN HYDROCARBON GROUP COMPRISING AN ESSENTIALLY STRAIGHT ALIPHATIC CHAIN OF AT LEAST 10 CARBON ATOMS ATTACHED TO THE PHOSPHORUS ATOM AND IN WHICH THE ALKYL RADICAL OF THE ESTER GROUP CONTAINS LESS THAN 10 CARBON ATOMS.