Lubricating greases containing borate
US 3125526 A
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United States Patent LUBRICATIN G GREASES CONTAINING BORATE ESTER COMPOUNDS William R. Siegart, Wappingers Falls, and Clemence J. Henry, Newburgh, N.Y., assignors to Texaco Inc., New
York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 17, 1961, Ser. No. 83,186
, 7 Claims. (Cl. 252-403) This invention relates to lubricating greases and to a novel class of additives therefor. More particularly, it relates to lubricating greases containing intramolecular coordinated borate esters and amine complexes of such esters.
The intramolecular coordinated borate esters which are employed as grease additives in accordance with this invention are compounds containing 1-3 OR or SR groups attached to a boron atom, where R is an aryl group containing a nucleophilic group in a position ortho to the ester linkage. By nucleophilic group is meant a group containing an electron donating atom which is capable of undergoing chelation with a metal atom. Intramolecular coordination takes place in these compounds with the formation of a five or six membered ring including the boron atom, as shown below for an ester containing an ortho-nitrophenyl group:
Other such nucleophilic groups include, for example, ester, amide, keto, aldehyde and amino groups.
We have found, in accordance with the present invention, that increased dropping points and other advantages, including improved oxidation resistance, are obtained in hydroxy fatty acid soap thickened greases by employing therein minor amounts of compounds of the above class. In addition to these advantages, the amine adducts of the intramolecular coordinated borate esters also impart improved water absorption properties to hydroxy fatty acid soap thickened greases of the types which normally absorb large amounts of water and undergo objectionably high penetration changes as a result of water absorption, such as lithium hydroxy fatty acid soap thickened greases containing sulfurized fatty oils as extreme pressure agents.
It is not intended to imply that all of the compounds of this class improve the properties of hydroxy fatty acid soap thickened greases in exactly the same manner or to the same extent, since their properties in hydroxy fatty Patented Mar. 17, 1964 hydroxy fatty acid soap thickened greases were entirely unexpected on the basis of the experience with these compounds employed in conventional fatty acid soap thickened greases, wherein no advantages were obtained. While we do not intend to be limited by any particular theory, it appears on the basis of infrared analyses and other evidence that a stable coordinated compound is formed by electron sharing between the boron atom of the borate ester compound and the hydroxy group of the hydroxy fatty acid soap, which accounts for the diiference in the effect of the borate ester compounds in hydroxy fatty acid soap thickened greases and in conventional fatty acid soap thickened greases.
Suitable borate esters for the purpose of this invention are compounds represented by the following formulas:
where R is a hydrocarbon or substituted hydrocarbon group, R is hydrogen, a hydrocarbon group or substituted hydrocarbon group, at least one group represented by R being an aryl group containing an ortho positioned nucleophilic group as described above, X is oxygen or sulfur, n is a whole number from 0 to 2, inclusive, m is a whole number from 1 to 3, inclusive, the sum of n and m being 3, n is a whole number from 0 to 3, inclusive, m is a Whole number from 1 to 4, inclusive, and the sum of n and m is 4. Hydrocarbon groups represented by R and R include alkyl, aryl, alkaryl and aralkyl groups, and substituted derivatives thereof containing substituents such as hydroxy, alkoxy, phenoxy, amine, nitro groups, etc. and halogens. The preferred compounds are those wherein n and n equal zero, In being 3 and m being 4, and wherein all of the groups represented by R are hydrocarbon or substituted hydrocarbon groups, preferably containing at least 3 carbon atoms.
The intramolecular coordinated borate esters are obtained by the conventional methods of preparing borate esters, such as by esterifying boric acid with alcohols, at least one of which is a hydroxy aryl compound having an ortho positioned nucleophilic substituent group. The compounds are conveniently obtained by reacting a boric acid diester with a hydroxy aryl compound of this character.
Examples of suitable intramolecular coordinated borate esters include the following: di-isopropyl-monoomitrophenyl borate; di-stearyl-mono-o-nitrophenyl borate; dip-tert.-butylphenyl-monoo-carbomethoxy-phenyl borate; di-thiobutyl-monoo-nitro-thiophenyl borate; di-p-chloro phenyl-monoo-formylphenyl borate; di-(p-nonylphenyl)- mono-o-acetylphenyl borate; di- (2,4-dichlorophenyD- mono-o-carbomethoxyphenyl borate; di-p-cresyl-monooaminophenyl borate; di-sec.-butyl mono (2,4 dinitrophenyl) borate; tri-o-nitrophenyl borate; tri-o-nitro-thiophenyl borate; and mono-phenyl-di-o-carbomethoxyphenyl borate.
The amine complexes of the above borate esters which are also employed in accordance with this invention are reaction products of the borate esters with aliphatic amines, including primary, secondary and tertiary monoamines containing at least six carbon atoms per molecule and diamines. Examples of suitable amines include dodecyl amine, tertiary tetradecyl amine, tertiary undecyl 3 amine, secondary dibutyl amine, hexadecylamine, ethylene diamine, hexane diamine, etc. The preferred compounds are monoamines containing from about 8 to about 26 aliphatic carbon atoms per molecule, particularly preferred compounds being primary amines wherein the alkyl group is a tertiary alkyl group.
Formation of the borate ester-amine complexes takes place readily over a wide range of conditions. The complex may be prepared by merely mixing together the borate ester and amine at room temperature or at moderately increased temperatures in the presence or absence of a solvent. It may also be carried out by reacting together boric acid and alcohols, including a hydroxy aryl compound containing an ortho positioned nucleophilic group, together with the amine in an organic solvent such as benzene, toluene, etc. The borate ester and amine are usually reacted in a 1:1 mol ratio. However, complexes containing reduced amounts of amine, such as borate ester-amine mol ratios of 2:1 to 1021 may be employed in some cases, particularly where there are severe copper anti-corrosiveness requirements.
The lubricating greases to which this invention relate are those containing metal soaps of high molecular weight hydroxy fatty acids in sufiicient proportions to provide at least a substantial thickening effect. The metal component may be any metal which is suitable for forming soaps employed as thickening agents in lubricating greases generally, including sodium, potassium, lithium, calcium, barium, strontium, aluminum, manganese, zinc, etc. The alkali metals and alkaline earth metals comprise a preferred class of metals for this purpose. The hydroxy fatty acid soap will usually be present in the composition in amounts from about 3 to about 15 percent by weight, although somewhat smaller or larger amounts are also suitable, such as amounts as low as about 2 percent by weight and as high as about 30 percent by weight of the composition.
The borate ester compounds are ordinarily employed in these lubricating greases in amounts in about the range 01-10 percent by weight, although somewhat larger or smaller amounts may be employed if desired. They are most suitably employed in amounts in about the range 0.55 percent by weight of the grease composition.
Suitable soap forming acid materials which may be employed in the production of these greases include hydroxy fatty acids containing from about 12 to about 24 carbon atoms per molecule and one or more hydroxy groups separated from the carboxylic group by at least one carbon atom, and the glycerides and other esters of such acids. The preferred acids are substantially saturated acids containing from about 16 to about 22 carbon atoms and one or two hydroxy groups per molecule. Such materials may be obtained from naturally occurring glycerides, by hydroxylation of fatty acids, by hydrogenation of ricinoleic acid or castor oil, or otherwise by processes such as the catalytic oxidation of hydrocarbon oils and waxes which have been extracted and fractionated to the desired molecular range. Mixtures of lrydroxy acids together with unsubstituted fatty acids may be very suitably employed, wherein the hydroxy fatty acid comprises at least about one third of the fatty acid mixture.
Lubricating oils employed in the greases include conventional mineral oils and synthetic coils, such as high molecular weight ethers, esters, silicones, etc. Suitable mineral oils include both parafiinic and naphthenic oils and blends thereof, having viseosities in the range from about 80 seconds Saybolt Universal at 100 F. to about 225 seconds Saybolt Universal at 210 F. A particularly suitable class of synthetic lubricating oils comprises synthetic dicarboxylic acid esters, such as di-2-ethylhexyl sebacate, (di-secondary amyl) sebacate, di-Z-ethylhcxyl azelate, etc. and polymers obtained by condensing dicarboxylic acids with glycols as disclosed in U.S. 2,628,974, as well as the sulfur analogs of such esters. Other synthetic oils which may be employed in accordance with this invention include the silicone polymers, including dia kyl silicone polymers such as dimethyl silicone polymer, diethyl silicone polymer, and mixed aryl-alkyl silicone polymers such as phenyl methyl silicone polymer, having viscosities in the lubricating oil viscosity range.
The grease preparation may be carried out in any suitable manner. The borate ester compound may be added either during the greater preparation or it may be incorporated into the preformed grease by heating a mixture of the grease and borate ester compound at about 150 F. with stirring, preferably followed by milling. It is conveniently added during the grease preparation when the mixture has cooled to about 200 F.
The lubricating greases of this invention may also contain other additives of various types such as are commonly employed in lubricating greases, such as extreme pressure agents, anti-corrosives, anti-oxidants, etc., as Well as other thickening agents, such as conventional fatty acid soaps and finely divided solids having grease forming properties.
As an example of the lubricating greases comprising a preferred embodiment of this invention, various intramolecular coordinated borate esters were added to a lithium hydroxy fatty acid soap thickened grease in amounts suflicient to give 1-10 precent by weight of the borate ester in the finished grease. The base grease consisted of a lubricating oil comprising 2-ethy1hexyl sebacats and a highly refined paratiinic distillate oil, having a Saybolt Universal viscosity of about seconds at 100 F, in a 3:1 ratio by weight, respectively, thickened to a grease consistency with 6.0 percent of lithium 12-hydroxystearate. It was prepared by saponifying I-Iydrofol acids .200 with a slight excess of lithium hydroxide in the presence of a major proportion of the mineral oil contained in the grease. The method comprised essentially heating the saponification mixture to 190 F. during about 35 minutes to allow for completion of the saponification, and thereafter heating the mixture to 400 F. while adding the major portion of the Z-ethylhexyl sebacate and circulating the mixture through a shear valve at 75 pounds pressure drop while the mixture was maintained at 400 F. The mixture was then cooled to 200 F. during about 2 /2 hours while additional amounts of mineral oil and Z-ethylhexyl sebacate were added. The grease was finally drawn and finished by milling in a Premier colloid mill. The borate ester compounds were incorporated into the base grease thus obtained by heating a mixture of the grease and borate ester compounds in suitable proportions at F. for 30 minutes with stirring.
The borate ester compounds employed in these compositions were prepared by the method comprising treating a boric acid diester with a phenol containing an ortho positioned nucleophilic group. Following is a detailed description of the preparation of di-(dinonylphenyl)- mono-o-carbomethoxyphenyl borate: 61.8 grams of boric acid (1.0 mol), 694.0 grams of dinonylphenol (2.0 mols) and 250 ml. of xylene were charged to a 2 liter 3 necked flask equipped with a stirrer, condenser and distilling recevier, and the solution refluxed for 2.9 hours until 43 ml. of Water had been collected. 152.0 grams of methyl salicylate (1.0 mol) were added and the reflux carried out for 7 hours until 18 ml. of water had been collected. The flask was then cooled to room temperature and the solid removed by filtration and dried. The compound analyzed 0.94 percent boron, as compared with 1.26 percent, theory.
Amine adducts or association complexes of these borate esters were prepared by adding an amine slowly to the ester in an inert solvent, employing equimolar proportions of the amine and borate ester. The amine employed for forming these complexes was a commercial material sold by Rohm & Haas under the trade name of Primene 81-R consisting of tertiary alkayl primary amines in the range from C H NH to C H NH Table I below shows representative results obtained by employing various intramolecular coordinated borate esters in a 3 percent concentration upon the dropping point and oxidation resistance of the lithium hydroxy fatty acid soap thickened grease.
In contrast to the above results, no improvement was obtained by adding the intramolecular coordinated borate ester compounds to conventional fatty acid soap thickened greases.
Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and only such limitations should be improsed as are indicated in the appended claims.
1. A lubricating grease consisting essentially of a lubrieating oil thickened to a grease consistency by a metal hydroxy fatty acid soap and containing about 0.1-10 percent by weight of a compound selected from the class consisting of intramolecular coordinated borate esters represented by the formulas:
Where R is selected from the class consisting of hydrocarbon groups and substituted hydrocarbon groups, R is selected from the class consisting of hydrogen, hydrocarbon groups and substituted hydrocarbon groups, at least one group represented by R being an aryl group containing an ortho positioned nucleophilic group, X is selected from the class consisting of oxygen and sulfur, n, is a whole number from 0 to 2, inclusive, m is a whole number from 1 to 3, inclusive, the sum of n and m being 3, n is a whole number from 0 to 3, inclusive, m is a whole number from 1 to 4, inclusive, and the sum of n and m is 4.
2. A lubricating grease according to claim 1 wherein the said nucleophilic group is chosen from the class consisting of nitro, amine, ketone, aldehyde and amide groups.
3. A lubricating greases according to claim 1 wherein the said borate ester is a compound represented by the said formulas wherein n and n equal 0 and the groups represented by R are chosen from the class consisting of hydrocarbon groups and substituted hydrocarbon groups.
4. A lubricating grease according to claim 1 wherein the metal component of the said metal hydroxy fatty acid soap is chosen from the group consisting of alkali metals and alkaline earth metals.
5. A lubricating grease according to claim 1 wherein the metal component of the said hydroxy fatty acid soap is lithium.
6. A lubricating grease according to claim 1 wherein the said lubricating oil is a mineral oil.
7. A lubricating grease according to claim 1 wherein the said lubricating oil is a dicarboxylic acid ester.
References (Iited in the file of this patent UNITED STATES PATENTS 2,154,098 Loane et a1. Apr. 11, 1939 2,160,917 Shoemaker et a1. June 6, 1939 2,846,394 Brunstrum et a1. Aug. 5, 1958 2,961,443 Ashby et a1 Nov. 22, 1960 3,007,873 Reynolds et a1 Nov. 7, 1961 3,014,061 Irish et al Dec. 19, 1961 3,020,307 Luvisi Feb. 6, 1962