US3036970A - Grease compositions containing soaps of alkoxy and alkyl mercapto hydroxy fatty acids - Google Patents

Description

Unite States Patent Ofiice Patented May 29, 1962 3 036 970 GREASE COMPOSITIOlIS CONTAINING SOAPS OF ALKOXY AND ALKYL MERCAPTO HYDROXY 7 Claims. (Cl. 252-33.

This invention relates to lubricating compositions containing soaps of alkoxy hydroxy fatty acid and the corresponding alkyl mercapto hydroxy fatty acids. Particularly, the invention relates to lubricating greases having good structural stability and resistance to hardening or crust formation, which contain a metal soap of an alkoxy hydroxy fatty acid and/or an alkyl mercapto hydroxy fatty acid.

While the soaps of the alkoxy or alkyl mercapto hydroxy fatty acids of the invention can be used as the sole thickening agents for a grease, they are particularly useful in the preparation of soap-salt thickened greases. One commercial form of the soap-salt greases are those thickened with calcium salts of acetic acid in combination with calcium salts of high molecular weight fatty acids (i.e. C to C fatty acids). These greases are generally made by neutralizing a mixture of acetic and higher fatty acid with lime. By using a high molar proportion of acetic acid to higher fatty acid, the resulting soap-salt thickener forms greases having excellent anti-wear and load-carrying ability. However, one disadvantage of prior soapsalt greases of this type was that they had an excessive tendency to harden upon storage and to form an undesirable crust when made with a large molar proportion of acetic acid. It has now been found that by substituting alkoxy hydroxy fatty acids or the corresponding alkyl mercapto hydroxy fatty acids, either in place of all or a part of the higher fatty acid previously used, the excellent properties of the soap-salt lubricant are retained, while at the same time its tendency to harden excessively and form crust upon storing is eliminated.

The alkoxy and alkyl mercapto hydroxy fatty acids used in forming the soaps of the invention can be represented by the general formula:

wherein R is a C to C alkyl group, R is a C to C saturated aliphatic hydrocarbon group, R" is a saturated aliphatic hydrocarbon group containing 1 to 3 carbon atoms, While X is either oxygen or sulfur. The total number of carbon atoms in the molecule is 11 to 26. Preferably, R contains 6 to carbon atoms, R contains 10 to 4 carbon atoms, R" contains 1 carbon atom and the total number of carbon atoms is about 18 to 24. Specific examples of these acids will include 5-methoxy-6-hydroxy tetradecanoic acid, 9-methyl mercapto-IO-hydroxy tetradecanoic acid, 6-propyl mercapto-7-hydroxy octadecanoic acid, ll-methoxy-lZ-hydroxy octadecanoic acid,

11-ethoxy-12-hydroxy eicosanoic acid, 16-methyl mercapto-lS-hydroxy tetracosanoic acid, 15-ethoxy l6 hydroxy tetracosanoic acid, 15-propyl mercapto-l6-hydroxy tetracosanoic acid, and mixtures thereof.

Alkoxy hydroxy fatty acids and alkyl mercapto hydroxy fatty acids may be readily prepared by reacting an unsaturated fatty acid having a single olefinic double bond, such as oleic acid, with a peroxide at low temperatures to epoxidize the acid, the resulting epoxide being then reacted with an alcohol to form the alkoxy hydroxy acid or with a mercaptan to form the alkyl mercapto hydroxy fatty acid.

Also, the ester of an unsaturated fatty acid and a low molecular weight alcohol may be epoxidized, then reacted with an alcohol or mercaptan as above, and finally reacted With a metal base to form the metal salt thickener and split oif the low molecular weight alcohol which is readily driven off by heating. Epoxidations of the above type are known in the art. For example, a detailed illustration of the epoxidation of a fatty acid (oleic acid) and its ester (methyl oleate) is given in an article by Findley et al. in J.A.C.S. 67, 412 (1945). Another article of interest is the epoxidation of a butyl oleate as described in the article by Gail et al. in Ind. and Eng. Journal 47, 147 (1955).

A specific alkoxy hydroxy fatty acid used in several of the working examples of this invention was prepared using isooctyl epoxy stearate. A 4-neck flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 2385 g. methanol and 865 g. isooctyl epoxy stearate (Sap. No.=136.4 mg. KOH/g.). After cooling the mixture to -30 C., 7.5 g. of H SO was added over a period of 5 minutes with the temperature being maintained at 30 to 33 C. The resulting mixture was warmed to reflux temperature and then refluxed for 2 hours. After being allowed to cool to room temperature, the mixture was treated with 15 g. NaHCO filtered, then evaporated on the steam bath to remove methanol. The crude product of 953 g. was distilled in a short path still at a pressure of 0.3 mm. Hg and a fraction of 388 g. was obtained having a boiling range of 181 C. This fraction was dissolved in 1165 cc. of acetone and chilled to -25 C. to precipitate any di-hydroxy compound present. The mixture was filtered and the acetone solution obtained as a filtrate was evaporated leaving 331 g. of crude methoxy hydroxy stearic acid isooctyl ester.

The above 331 g. of product was saponified with KOH in ethyl alcohol after which it was diluted with water and extracted with petroleum ether. The methoxy hydroxy stearic acid was sprung by acidifying with HCl. After separating this acid and heating to drive off any petroleum ether or ethyl alcohol the product had a weight of 234 g. with the following analysis:

Neutralization No==156 mg. KOH/g. Saponification No.=l71.5 mg. KOH/ g. Hydroxyl No.=132.0 mg. KOH/ g.

While the above reaction is an indirect procedure, it was followed because of the ready availability of the isooctyl epoxy stearate as a starting material. The reactions carried out above can be illustrated by the following equations:

l CH3OH H2504 OCH; 011

l KOH O HsOlI OH OCH;

stearic acid) Theoretically the above methoxy hydroxy stearic acids should have the following analysis:

Neutralization No.=l70 mg.KOH/ g. Saponification No: 170 mg.KOI-I/ g.

Hydroxyl NO.:17O mg. KOH/ g.

The metal component of the alkoxy or alkyl mercapto hydroxy fatty acid soap can be any metal commonly used in the grease-making art, e.g., aluminum, zinc, etc. However, it is preferably an alkali metal such as sodium, lithium, potassium or an alkaline earth metal, such as calcium, barium, strontium and magnesium, as these metals are most commonly used in grease-making.

The soap is formed by neutralizing the alkoxy or alkyl mercapto hydroxy fatty acid with a metal base such as hydroxide, oxide or carbonate of the desired metal constituent, e.g., Ca(OH) The reaction mixture is then heated to dehydrate and to remove the water of reaction.

The preformed soaps of the alkoxy hydroxy fatty acid, or the alkyl mercapto hydroxy fatty acid, may be directly added to oil in forming the grease compositions. How ever, it is more advantageous to form the soap in situ in at least a portion of the lubricating oil to thereby obtain a finer dispersion of the soap in oil. Thus, the acid may be directly dissolved in the oil and then neutralized with metal base. If the acid is solid then it is added to the oil and then heated sufficiently to melt the acid so it can be stirred into solution. The metal base is added and the mixture is next heated to a temperature of about 212 to 600 F., e.g. 250 to 450 F. in order to complete the reaction and to dhhydrate the mixture. After dehydration, the oil-salt product may then be further blended with other oil or grease materials to form a finished grease. The finished grease can then be homogenized by passing it through a Charlotte mill, a Morehouse mill or a Gaulin homogenizer in order to obtain a smoother product.

Metal soaps of the alkoxy hydroxy fatty acid or the alkyl mercapto hydroxy fatty acid can be used in combination with metal salts of C to C fatty acids. In general, the alkoxy or alkyl mercapto hydroxy fatty acid soaps can be utilized with metal salts of low molecular weight C to C fatty acids, intermediate molecular weight C to C fatty acids, high molecular weight C to C fatty acids or any combination thereof.

Suitable low molecular weight acids include saturated and unsaturated, substituted and unsubstituted aliphatic monocarboxylic acids and their anhydrides having about 2 to 6 carbon atoms per molecule. These acids include fatty acids such as acetic, propionic, and similar acids including their hydroxy derivatives such as lactic acid, or their anhydrides, e.g., acetic anhydride. Acetic acid or acetic anhydride is preferred.

The intermediate molecular weight fatty acids operable for the salt formation include those aliphatic saturated or unsaturated, unsubstituted monocarboxylic acids containing 7 to 12 carbon atoms per molecule, e.g., capric, caprylic, nonanoic, lauric acids, etc.

The high molecular weight fatty acids or aliphatic monocarboxylic acids which may be used along with the alkoxy or alkyl mercapto hydroxy fatty acids of the invention include naturally-occurring or synthetic, substituted and unsubstituted, saturated and unsaturated, fatty acids having about 12 to 30, e.g., 16 to 22, carbon atoms per molecule. Examples of such acids include palmitic, stearic, 12-hydroxy stearic, behenic, montanic, linolinic, linoleic, arachidic, ricinoleic, oleic, hydrogenated fish oil, tallow acids, etc.

The metal component of salts of the above fatty acids can be any of those previously described as operable in forming the salt of the alkoxy or alkyl mercapto hydroxy fatty acid. Generally, alkali and alkaline earth metals will be used. Again, such carboxylates may be preformed and then dispersed in the oil composition, or they too can be formed in situ in the oil by neutralizing the carboxy acid with a metal base.

The lubricating oil used in the compositions of the invention may be a mineral lubricating oil, a synthetic lubricating oil, or mixtures thereof. Synthetic lubricating oils which may be used include esters of dibasic acids (e.g., di(2-ethylhexyl) sebacate); esters of glycols (e.g., C Oxo acid diester of tetraethylene glycol); complex esters (e.g., the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethyl-hexanoic acid); formals, silicones, carbonates, polyglycols and other synthetic lubricating oils known in the art.

Various other additives may also be added to the lubricating composition in amounts of about 0.1 to 10.0 weight percent, based on the total weight of the composition. Examples of such additives include: corrosion inhibitors such as sorbitan monooleate and sodium nitrite; antioxidants such as phenyl a-naphthylamine; tackincss agents such as polyisobutylene; dyes, and the like.

The lubricant compositions of the invention will therefore comprise a major proportion of lubricating oil and about 0.5 to 30.0 weight percent of the metal soap of the alkoxy or alkyl mercapto hydroxy fatty acid. If the soap of the alkoxy or alkyl mercapto hydroxy fatty acid is to be used as the sole grease thickener, then generally about 8 to 30 weight percent of the total composition will be said soap.- If used in the form of a mixed-salt composition, then the composition will generally contain salts of: 0.5 to 15 wt. percent alkoxy or alkyl mercapto hydroxy fatty acid and 3 to 15 wt. percent of C to C carboxylic acid. Preferred mixed-salt compositions will contain salts of 3 to 6 wt. percent of alkoxy or alkyl mercapto hydroxy fatty acid and 6 to 15 wt. percent of carboxylic acid, all of said weight percents being used upon the finished grease. As mentioned above, said carboxylic acid may consist entirely of low molecular weight fatty acid e.g. acetic acid, or intermediate molecular weight fatty acid or high molecular weight fatty acid, or blends or these three types of fatty acids in any proportion. A particularly effective soap-salt lubricant is that containing about 4 to 20 molar proportions of salt of acetic acid per one molar proportion of higher fatty acids.

The invention will be further understood by the following examples wherein the methoxy hydroxy stearic acid was prepared as previously described and all parts are by weight.

EXAMPLE I 6 parts of methoxy hydroxy stearic acid and 4 parts Hydrofol Acids 51 (hydrogenated fish oil acids corresponding to stearic acid in degree of unsaturation and average chain length) were added to 87.6 parts by weight of a mineral lubricating oil having a viscosity of 55 SUS at 210 F. This mixture was then warmed to 150 F., at which point 1.4 parts of lithium monohydrate dissolved in 5.6 parts of water was added to the mixture. Heating was continued until a temperature of 250 F. was reached and all the water of reaction plus the water added in the form of the aqueous solution had been evaporated. Agitation was then shut off and 1.0 part of phenyl ornaphthylarnine, an oxidation inhibitor, was stirred into the composition. The composition was then allowed to cool below the transition point of the soap which is about 200 F. Then the mixture was again stirred to obtain a uniform composition, was then passed through a Morehouse mill have a 0.003" clearance and finally cooled to room temperature.

EXAMPLE II A lubricating grease composition was prepared by charging 7.5 parts of hydrated lime and parts of methoxy hydroxy stearic acid into 72.7 parts of mineral lubricating oil having a viscosity of 55 SUS at 210 F. The composition was mixed intimately and then 10 parts of glacial acetic acid was slowly added while stirring the mixture. After all the acetic acid was added, heating was initiated and the mixture was heated to 430 F. over a period of about 2 hours. The heat was shut off and the composition was cooled to 200 F. where 0.8 part by weight of phenyl a-naphthylamine was added. The composition was then cooled to 110 F. at which point 4 parts of a sodium nitrite-oil dispersion was added. This dispersion consisted of 50 weight percent sodium nitrite dispersed. in 50 weight percent of mineral lubricating oil of 55 SUS at 210 F. The grease composition was then passed through a Morehouse mill at 0.003" clearance.

EXAMPLE III 73.41 parts of mineral lubricating oil of 55 SUS at 210 F., 8.3 parts of hydrated lime and 1.83 parts of methoxy hydroxy stearic acid was added to a steam heated kettle and thoroughly mixed. Next, a blend consisting of 11 parts glacial acetic acid and 3.76 parts of Wecoline AAC acid (mixture consisting of about 28 wt. percent caprylic, 56 wt. percent capric and 16 wt. percent lauric acids) was slowly added to the kettle. The composition was then heated to a temperature of 325 F. and cooked at this temperature until a heavy grease structure formed. 0.5 part of additional lime was then added to completely neutralize the acids and give a slight excess free alkalinity. The grease was cooled while stirring and 1 part of phenyl a-naphthylamine was added at 200 F. The grease was then passed through a Morehouse mill having a 0.003 clearance.

The compositions of Examples 1 to III and their physical properties are summarized in Table I which follows:

Table 1 Example Ingredients (Parts by Wt.)

I II III Methoxy Hydroxy stearic Acid 6.0 5. 0 1.83 H drofol Acids 51 4. 0 ecoline AAC Acid 3. 76 Glacial Acetic Acid 10. 0 11. 00 Llthiurn Monohydrate 1. 4 Hydrated Lime 7. 5 9.00 Phenyl a-Naplithylamine 1. 0 0.8 1. 00 Sodium Nitrite Dispersed in M eral 011 /50 4. 0 Mineral Lubricating Oil having viscosity of SUS at 210 F 87. 6 72. 7 73. 41 Properties:

Appearance Excellent, smooth grease Dropping Point, F 340 500+ 500 Penetration, 77 F., mm

Unworked 322 322 322 Worked strokes 328 325 324 Worked 100,000 strokes 339 340 335 Norma Hofi'man OxidationHours to 5 p.s.i. Drop 350 300 300 Oil Separation after 22 hours storage at 210 F 0.5% 0.3% 1. 0% Lubrication Life 11 ms 1 (250 F.10,000 r.p.m.) 2, 000+ 2, 000+ 2, 000+ Crust formation after 120 days None None None Timken Load 45 Lbs Pass Pass Almen Test, Shock Load-Max. wts.

carried 15 wt. -Ball Wear Test (1,800 r.p.m.l0 kg. load-1 hour-75 C.) Scar diameter in mm 0. 60 0.25 0. 29 Wheel Bearing Tesl 220 F.

Tilted 451 hour Pass Pass Pass Slumps None None None Leakage in grams 4. 0 None None 1 ABEC-NLGI spindle test.

As seen by Table I, greases prepared from the methoxy hydroxy stearic acid in combination with high molecular weight fatty acids (Example I), or low molecular weight fatty acid (Example 11), or low and intermediate molecular weight fatty acids (Example LII), all formed excellent greases. All three greases were very stable to mechanical working as illustrated by the very small penetration changes upon working, as well as having other desirable properties including non-crusting tendencies.

EXAMPLE IV A grease was prepared by charging 7.5 parts ofhydrated lime and 5.0 parts by weight of methoxy hydroxy stearic acid into 74.5 parts of mineral lubricating oil having a viscosity of 55 SUS at 210 F. The composition was mixed intimately and then 10.0 parts of glacial acetic acid was slowly added while stirring the mixture. After all the acetic acid was added, heating was initiated and the mixture was heated to 430 F. over a period of Table II Example Comparative Formulation (Percent Weight) IV 01 In- Examples vention Glacial Acetic Acid 10. 0 10. 0 10. 0 10. 0 Methoxy Hydroxy Stearlc Acid 5. 0 Hydrofol Acids 51 Stearic Acid 5. 0 Oleic Acid..- 5. 0 Hydrated Lime 7. 6 7. 5 7. 5 7. 5 Phenyl a-Naphthylamine 1.0 1. 0 1.0 1.0 Mineral Lubricating Oil having a viscosity of 55 SUS. at 210 F 74. 5 74.5 74. 5 74.5 Properties:

Tendency to Crust and Harden Excessively Over Periods of Two Months Storage None Excessi'e Penetrations-ASTM at 77 F.

Unworked 322 322 320 325 After Two Months Storage 315 260 255 240 As illustrated by Table II above, soap-salt thickeners prepared from acetic acid and the more common fatty acids (see the comparative examples) form crust and harden excessively upon storage as indicated by a considerable decrease in their ASTM penetration. By using the alkoxy hydroxy fatty acids of the invention these disadvantages are eliminated as illustrated by Example IV above.

While the preceding examples illustrate the use of a methoxy hydroxy stearic acid, the alkyl mercapto hydroxy fatty acids can be used in the same manner. To illustrate, Examples I to IV can be exactly repeated but using 9-methyl mercapto-lO-hydroxy tetradecenoic acid in place of the methoxy hydroxy stearic acid. To further illustrate the invention, Examples I to IV may be exactly repeated, but using -ethoxy-6-hydroxy tetradecenoic acid in place of the methoxy hydroxy stearic acid. Also, the hydroxy acids of the invention can be used as the sole grease thickener. Thus, Example I can be repeated, but using 10.0 parts by weight of the methoxy hydroxy stearic acid and no Hydrofol Acids 51.

What is claimed is:

1. A lubricating grease composition comprising a major amount of a lubricating oil, about 3 to wt. of a metal salt of a C to C fatty acid and about 0.5 to 15 wt. based on the weight of the total composition, of a metal soap of a hydroxy acid having the general formula:

RI! it on I A I R-C- R COOH ii I! wherein R is a C to C alkyl group, R is a C to C saturated aliphatic hydrocarbon group, R is an alkyl group containing 1 to 3 carbon atoms, X is a member selected from the group consisting of sulfur and oxygen, the total number of carbon atoms in the molecule is 11 to 26, and wherein said metal is selected from the group consisting of alkali metals and alkaline earth metals.

2. The lubricating grease composition according to claim 1, wherein X is sulfur.

3. The lubricating grease composition according to claim 1, wherein X is oxygen.

4. A lubricating grease composition comprising a major amount of mineral lubricating oil, and about 8 to 30 wt. percent of a metal soap of a methoxy hydroxy fatty acid having the general formula:

wherein R is a C to C alkyl group, R is a C to C saturated aliphatic hydrocarbon group, R is a methyl group and the total number of carbon atoms in the molecule is 11 to 26 and wherein said metal is selected from the group consisting of alkali metals and alkaline earth metals.

5. A lubricating grease composition comprising a major amount of mineral lubricating oil, about .5 to 15.0 Wt. percent of calcium soap of an alkoxy hydroxy fatty acid, and about 3 to 15 wt. percent of calcium salt of acetic acid, wherein said alkoxy hydroxy fatty acid has the general formula:

R! I E R('JC-R'OO0H wherein R is a C to C alkyl group, R is a C to C saturated aliphatic hydrocarbon group, R is an alkyl group containing 1 to 3 carbon atoms, X is a member selected from the group consisting of sulfur and oxygen, and the total number of carbon atoms in the molecule is 11 to 26, heating to a temperature of about 212 to 600 F. and removing the water of reaction, and then cooling to form said grease, wherein the amount of said fatty .acid is sufficient to form about 3 to 15 wt. percent of metal salt and the amount of said hydroxy acid is sufficient to form about 0.5 to 15 wt. percent metal soap, and wherein said metal base is selected from the group consisting of alkali metal bases and alkaline earth metal bases.

7. The method according to claim 6, wherein said fatty acid is acetic acid and said metal base is calcium.

Claims (1)

1. A LUBRICATING GREASE COMPOSITION COMPRISING A MAJOR AMOUNT OF A LUBRICATING OIL, ABOUT 3 TO 15 WT. % OF A METAL SALT OF A C2 TO C30 FATTY ACID AND ABOUT 0.5 TO 15 WT. %, BASED ON THE WEIGHT OF THE TOTAL COMPOSITION, OF A METAL SOAP OF A HYDROXY ACID HAVING THE GENERAL FORMULA: