US2824838A

US2824838A - Lubricating grease compositions containing n-acyl-p-amino phenols

Info

Publication number: US2824838A
Application number: US481696A
Authority: US
Inventors: David W Young; Delmer L Cottle
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1954-06-04
Filing date: 1955-01-13
Publication date: 1958-02-25
Anticipated expiration: 1975-02-25

Description

United States Patent LUBRICATING GREASE COMPOSITIONS CON- TAINING N-ACYL-p-AMINO PHENOLS David W. Young, Westfield, and Delmer L. Cottle, Highland Park, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Original application June 4, 1954, Serial No. 434,676. Divided and this application January 13, 1955, Serial No. 481,696

7 Claims. (Cl. 25242.1)

The present invention relates to the stabilization of organic compositions normally subject to oxidative changes. More particularly, the present invention relates to the stabilization of organic compositions containing, besides carbon, at least the elements of hydrogen and oxygen, with N-acyl para aminophenols wherein the hydrocarbon residue of the acyl group has at least two carbon atoms. Still more specifically, the present invention relates to the stabilization of organic compositions comprising in particular organic acids, such as fatty acids, and their derivatives, including the mono, diand polyesters, soaps, glycerides, and the like.

The present application is a division of Serial No. 434,676, filed June 4, 1954; that application is a continuation-in-part of Serial No. 186,318, filed September 22, 1950, now abandoned, and also of Serial No. 334,725, filed February 2, 1953, now abandoned; the latter in turn is a continuation-in-part of Serial No. 237,476, filed July 18, 1951, now abandoned.

The compositions of the present invention find utility in the field of lubricants, i. e. as lubricating Oils and greases. These include simple and complex esters of long chain fatty acids with alcohols and glycols, mineral oil and ester oil compositions thickened into solids and semi-solids with thickening agents, such as soaps of long chain fatty acids, and the like.

The stabilized compositions of the present invention also find utility in the field of edible foods, such as animal fats and oils, vegetable fats and oils, long chain fatty acid soaps and the like, all of which tend normally to be subject to oxidation changes. Animal and vegetable fats and oils consist to a substantial extent of simple and mixed esters of poly alcohols, in particularly of glycerine. Thus triolein, tripalmitin, tristearin, trimyristin, and interand intramolecular mixtures of these esters, as well as other fatty acids, i. e. linoleic and linolenic, are components of such foods as lard, butter, cocoanut oil, soybean oil, hardened fats, such as bydrogenated cotton seed oil, olive oil and the like. In accordance with one; embodiment of the present invention, readily oxidizable oils, fats, fatty oils, fatty esters, fatty acids and salts of fatty acids are stabilized against rancidity and deterioration with minor amounts of 'N-acyl p-aminophenols wherein the hydrocarbon residue of the acyl group has at least two carbon atoms.

In one embodiment, the present invention relates .to lubricating grease compositions. Particularly this embodiment relates to lubricating grease compositions having outstanding oxidation resistant properties. More particularly, this embodiment of the invention relates to a lubricating grease composition comprising a lubricating grease containing combined therein a minor proportion of an acyl p-aminophenol as an oxidation inhibitor.

It is a common practice in the art of. manufacturing lugricating grease compositions to increase the resistance of the greases to oxidation by incorporation of substances known as oxidation inhibitors. There are various oxi dation inhibitors known to the art, examples being such materials as phenyl alpha naphthylamine, phenyl beta naphthylamine, phenolic type compounds, complex amine intermediates and the like. It has now been found that grease compositions containing minor amounts of acyl p-aminophenols have outstanding characteristics in regard to oxidation stability and also superior retention properties. a

'The acyl p-amino phenolic derivatives contemplated for use in the grease compositions of this invention have the following general structure:

H O HO lake wherein R is an alkyl group containing from 2 to 24 carbon atoms, preferably non-benzenoid in nature, and R and R are hydrogen atoms or alkyl groups.

The preferred embodiment of the invention contemplates the use of compounds according to the formula above where R is an alkyl group containing from 10-18 carbon atoms and R and R are hydrogen, i. e., the acyl p-amino phenols. However, the alkylat-ed acyl p-amino phenols, exemplified by the formula above, R and R being alkyl groups containing from 1 to 20, preferably 4 to 15 carbon atoms, are also very satisfactory as oxidation inhibitors. Compounds such as N-n-valeryl- 4-amino-3 pentadecyl phenol, (N-n-pentanoyl-4-amino-3 pentadecyl phenol), N-n-propanoyl-4-amino-3 pentadecyl phenol, 'N-n-pentanoyl-4-amino-2,6, di-tertiary butyl phenol, N-n-hexoyl-4-amino-2 hexyl phenol are examples of the alkylated acyl-p-amino phenols operable.

The preparation of these acyl p-amino phenols may be achieved by admixing the desired acid or acid chloride with p-amino phenoland heating the mixture under proper conditions. The reaction progresses smoothly, splitting olf water (or hydrogen chloride) and giving the desired acylated aminophenols which may be purified by any of the various methods known to the art such as distillation, crystallization, extraction, etc.

As the acidic constituent of the reaction mixture, any organic acid containing from 3 to 24 carbon atoms may be combined with the p-amino phenol. The compounds especially preferred as oxidation inhibitors, however, are

those long chain fatty acids or fatty acid chlorides containing from 11 to 19 carbon atoms per molecule.

It may be found convenient in some instances to prepare the greases of invention in such manner that the desired acyl p-amino phenol is formed in situ. This preparation may be accomplished in one of two manners:

(1) To a heated oil solution containing the preformed soap there may be added the calculated amount of a p-aminophenol. The desired acid or acid chloride may then be added, the formation of the acyl p-aminophenol taking place upon the addition of the acidic constituent. The acylating group and the soap forming acid may or may not be the same; or

(2) There may be added to a heated oil solution a calculated amount of a long chain saturated acid or a mixture of these acids. To this mixture is added an amount of the desired metallic hydroxide suflicient to form the proper percentage of soap and to leave some unreacted acid present. p-Aminophenol is then added and reacts with the free acid to give the acyl p-aminophenol, the amount of the aminophenol added being suflicient to form the desired quantity of the antioxidant. In this procedure the acylating group and the soapforming acid are necessarily the same acid.

In both instances of the preparation of the antioxidant in situ, after the reaction is completed the mixture is stripped with heat, and water is removed to form the stabilized grease.

Thegrease compositions of this invention may be prepared by dispersing any of the common grease making soaps in a lubricating oil, using sufficient quantities of the desired soaps to form grease compositionsof varying consistencies. Any of the various alkaline earth or alkali metals such as calcium, strontium, barium, potassium, sodium, or lithium may be used to form the soaps of any of the Well known grease making acidic materials, exemplified by hydrogenated fish oil acids, stearic acid, hydroxy stearicacid, oleic acid, palmitic acid, lauric acid, tallow, cocoanut oil, the saturated or unsaturated glycerides of the various fatty acids or mixtures-of these in any'proportion.

The oil base in which the above mentioned soaps may be dispersed may be selected from either the natural occurring mineral oil distillates treated by any of the modern refinery technique or a synthetic lubricating oil such as the long chain esters .of aliphatic acids, esters of dibasic acids such as sebacates, adipates and the like, polymerized cracked wax, acylated aromatics, polyglycol esters, polyglycol ethers, polyglycol ether esters, and the like.

The grease composition'of this invention may be prepared by any of the procedures with which the art of grease manufacture is well familiar. For instance, a preformed soap may be admixed with a small proportion of the desired lubricating oil base, heated to the melting point of the soap with stirring and the remainder of the mineral oil then added and allowed to cool. Or, if it is desired, the soap may be prepared in situ by ad- -mixing with a minor proportion of the oil the desired amount'of the acidic material, forming the soap by adding the calculated equivalent of the desired metallic hydroxide, raising the temperature of the mixture to drive off the water formed, adding the remainder of the mineral oil and allowing it to cool to handling temperature. These methods are well known in the art and do not form a part of this invention.

The desired amount of the oxidation inhibitor maybe added to the grease composition at any stage of its manufacture. It is usually preferred to add from 0.25% to 2% of the acyl p-aminophenol with 0.5 to 1% being especially preferred in most formulations. If the oxidation inhibitor is being added to a preformed grease it is advantageous to first dissolve the acyl p-aminophenol in a naphthenic oil and then incorporate the solution into the grease composition that is slightly warm. When it isdesired to add the acyl p-aminophenol during the preparation of the grease composition this pre-solubilization is unnecessary and the compound may be added preferably after the soap has been formed.

In the preferred embodiment of this invention the following procedure is used:

A portion of the lubricating oil is admixed with the fatty material in a grease kettle equipped for heating by a steam jacket or by a direct flame. ,A solution of the desired metal, usually in the form of a metallic hydrox ide, is then added to the mixture with stirring. 'The temperature of the mixture is then raised to about 400 to 420 F. At that point the balance of the lubricating oil and the additive materials are added. Heat. is then stopped. The resulting composition is then pan cooled or cooled in a continuous grease cooler according to standard procedures.

EXAMPLE I A lubricating grease composition, according to the concept of this invention, was prepared by the procedure detailed above from the following formulation:

29.00% rapeseed oil 5.92% sodium hydroxide 1.00% petroleum sulfonate 1.00% N-lauroyl p-aminophenol 63.08% Coastal distillate having a viscosity at 210 F. of

55 S. U. S. and a V. I. of 50.

EXAMPLE II A second experimental grease was prepared by the procedure and formulation used in Example 1 except that N-myristoyl p-aminophenol was the oxidation inhibitor added.

EXAMPLE III In the third experimental grease prepared as Examples I and II above, N-stearoyl p-aminophenol was used.

EXAMPLE IV In the fourth experiment a grease was prepared as in Examples I to III above, using N-n-valeryl-4-amino-3- pentadecyl phenol as the anti-oxidant.

EXAMPLE V According to the following formulation a preformed synthetic ester base grease was prepared using known procedures.

76.75% di-Z-ethyl hexyl sebacate 22.75% lithium stearate .50% zinc naphthenate stant temperature, usually 100 C. under an oxygen pres sure of 110 p. s. i. The loss in oxygen pressure is a -function of the. oxidation. resistance of the. grease, that is to say, a grease. that is highly resistant to oxidation will show a small pressure. drop after an extended period of test time. The results of the. tests on these experimental greases. are. shown in Table I below. Included in the data on Table I are comparative test data obtained by subjecting identical grease formulations containing, instead of the acyl p-amino phenols, two acceptable commercially available oxidation inhibitors.

Table I.-N0rma-Hoflman bomb tests Hours To Pfrcssure Drop 0 Grease Sample Grease (no anti-oxidant) 24 52 74 Example I (N-lauroyl'p-amino phenol) 168 336 380 408 Example II (N-myristoyl p-amino phenol) 82 146 155 169 Example III (N-stearoyl p-amino phenol) 48 76 83 94 Example IV (N-n-valeryl-4-amino-3 pentadecyl phenol) 125 192 215 336 Example V (N-lauroyl p-arnino phenol in ester based grease) 744 1, 480. Example V (no anti-oxldant-control) 220 Mineral oil base 1 grease with commercial Inhibitor A 3 V 96 168 264 3650 Mineral oil base 1 grease with commercial Inhibitor B 3 112 186 262 302 1 Same type base grease as given in'Ex-ainple I. 2 A mine complex intermediate. 3 Phenyl alpha-naphthyla-minc.

An examination of the data reported in Table I above will show that the greases of this invention compare very favorably with the commercial preparations with the grease of Example I showing outstanding resistance to oxidation.

A recent U. S. Army specification,Specification 2134, requires that a grease sample containing a polished copper strip imbedded therein be subjected to pounds oxidation pressure in the Norma-Hoffman bomb for 20 hours without any drop in pressure and without showing any staining or discoloration on the copper strip itself or in the grease surrounding the imbedded copper strip.

The experimental greases and those containing the two Table II .-Army Specification 2-134, Norma-Hofiman bomb test (copper catalyzed) Hours to Pressure Drop oi- Discolora- Grease Sample tion Example I (no antioxidant-control grease) 14 50 Dark. Example I (N-lauroyl p-amino phenol)--- 154 220 None. Example II (N-myristoyl p-amino pheno1) 168 240 None. Example III (N-stearoyl p-amino phenol) I20 150 None. Example V (N-lauroyl p-amino phenol in ester based grease) 210 310 None. Ester basegrease (no antioxidant-control grease) .4 85 170 Dark. Mineral oil base grease with commercial ibitor A 110 184 Slight. Mineral oil base grease with commercial Inhibitor B 110 152 Dark.

One of the common failings of oxidation inhibitors is their instability to deterioration caused by sunlight. Grease compositions containing them, therefore, darken upon exposure and lose their desired light color. The experimental greases and the two grease formulations containing the commercial inhibitors were subjected to 40 hours of ultra-violet light exposure and their resulting color change reported on the following basis. Black was given a rating 'of and no color change'was rated 0; The results of this test are set out in Table III below:

Table m. ngm stability test Grease Sample Stability Rating 1 Example I (N-lauroyl p-amino phenol) Example II (N -myristoyl p-amino phenol)..- Example III (N-stearoyl p-amino phenol) Example IV (N -n-valeryl-4-amino-3 pentadeeyl phenol) Exampl)e V (N -lauroyl p-amino phenol in ester based grease Mineral oil base grease with commercial Inhibitor A Mineral oil base grease with commercial Inhibitor B UFO coco Fifty parts of a Coastal distillate having a viscosity of 55 S. U. S. at 210 F. and a viscosity indexof 50 is charged to a steam heated grease kettle and heated to about 200 to 220 F. There is then added to the heated oil about 29 parts of rapeseed oil and 4.92 parts of sodium hydroxide. When the saponification reaction is completed, l part of p-amino phenol is added along with about 13.08 parts of the same mineral oil as was origi-' nally charged to the grease kettle. The mixture is stirred thoroughly and the temperature raised to 400 to 420 F. At this point the heating is stopped and about 1 part of petroleum sulfonate is added. The mixture is then pan cooled and a lubricating grease of excellent structure stability and antioxidant characteristics is obtained. (All parts are given as parts by weight.)

It may be desired to add to the grease composition of this invention other of the well known additive materials such as tackiness agents, corrosion inhibitors, other oxidation inhibitors, detergents and the like. This may be done with impunity in the greases of this invention 6 since the acylzp-amino phenols are perfectly compatible with these additive materials.

To recapitulate briefly, this embodiment of the present invention relates to lubricating grease compositions having outstanding characteristics of oxidation resistances which comprise a lubricating oil, either natural occurring or synthetic, thickened to a'grease consistency with the metal soap of a fatty acid and which contain combined therein in a minor proportion 21 compound having the general formulawherein R is a non-benzoid group containing from 2 to 24 carbon atoms, preferably from 10 to 18 carbon atoms, and R and R are hydrogen atoms or alkyl groups. The oxidation inhibitor may be added to the grease composition at any stage of its manufacture or it may be dissolved in a naphthenic oil and added to a finished grease with working at moderate temperature.

Another embodiment of this invention relates to synthetic lubricating compositions. Particularly this invention relates to synthetic lubricating compositions having combined therein a minor amount of an N-acyl-p-aminophenol as an oxidation inhibitor and general stabilizing agent.

In an effort to obtain superior lubricating oils having specific and unusual characteristics, new synthetic lubricants have been developed. One class of materials which has attracted unusual interest as synthetic lubricants are the esters, both the simple and complex type. In gen-v eral these lubricating oils are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. Lubricants possessing such properties are of special value in the lubrication of engines which are subjected to high temperatures such as combustion turbine engines, particularly those of the propjet type. Mineral oil lubricants containing added viscosity index improvers, pour point depressors, or other highly non-volatile additives are undesirable for use in such engines because of their tendency to leave a residue which accumulates and interferes with the operation of the engine. In addition the high pour points and low flash points of such compositions are undesirable. The synthetic lubricants of the ester type are especially adaptable to use under such conditions since these lubricants contain no additive and have a desirable combination of high flash points, low pour points, and high viscosities. In addition they thus tend to leave no residue upon volatilization.

In the past it has been found that the synthetic lubricant of the ester type, while extremely desirable due to their low pour points, high flash points and high viscosities, are somewhat unstable to light and have a tendency to corrode the metal of bearing surfaces. These undesirable results flow from the formation of corrosive materials formed on oxidation of the lubricant occurring under the conditions of high shear and high temperature to which they are subjected during normal operation.

It has now been found that these undesirable qualities may be removed by the addition to the synthetic oil as oxidation inhibiting-stabilizing agents, certain members of the family of the N-acyl-p-amino phenols.

' The lubricating compositions of this invention consist essentially of a synthetic lubricating oil of the ester type, either complex esters or simple esters, and a minor amount, sufficient to improve the oxidation resisting characterisiic thereof, of an N-acyl-p-amino phenol.

THE SYNTHETIC LUBRICATING on.

The lubricant used as a base for the improved compositions of' this invention may be any of the synthetic lubricating oils known to the art. IThese known, types include long chain esters of monobasic acids, polybasic acids, mono! and polyhydroxy alcohols, polymerized esters, ethers, ether esters, ester ethers, alkylated aromatics, polymerized cracked wax, and the like. Of these various types of synthetic lubricants, the synthetic esters, either simple or complex, are preferred, and are used in the formation of the preferred embodiment of this invention.

The synthetic esters operablein the preferred embodiment of this invention are those esters, distillable or not distillable, which are formed by the interaction of two or more of the following compounds:

( 1) Monohydric alcohols (2) Monobasic acids (3) Dibasic acids (4) Glycols (5) Polyhydric alcohols (6) Polybasic acids When at least one polyfunctional alcohol and at least one polyfunctional acid are employed, the resulting ester is known to the art as a complex ester. Diesters of dibasic acids, or single esters of monobasic acids are referred to as simple esters.

Especially preferred among the simple esters are those esters having the formula where R and R are alkyl groups, alike or different and contain from 1 to 20 carbon atoms, in a straight or branched chain, and where x is an integer from 2 to 10, preferably 4 to 8. These esters include those prepared from the following acids:

Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acid Azelaic acid Sebacic acid Brassylic acid Pentaldecanedicarboxylic acid Tetracosanedicarboxylic acid The C -C alkenylsuccinic acids listed above are prepared by condensing olefins' or mixtures of olefins with maleic anhydride.

The complex esters contemplated by this invention are grouped under the following types:

Type I.-Mnobasic acid-glycol-dibasic acid-glycolmonobasic acid.-This complex ester may be considered to have the following structural formula:

wherein R and R are the alkyl radicals of the monobasic acids; R and R are the alkyl radicals from the glycols; and R is the alkyl radical from the dibasic acid.

The esters of this type are prepared by admixing the calculated amounts of the various compounds and carrying out a straightforward esterification of the reaction. The reaction conditions are continued with an occasional sample of the product being tested for acidity until the minimum acidity is attained.

Type II.-Alcohol-dibasic acid-glycol-dibasic acid-alcohol.-This material may be represented by the following formula:

R OO-C+-R -C-OO- R -O--OC-R -CO--O--R wherein R and R are the combining radicals of the alcohol; R and R are the alkyl radicals of the diabasic acids; and R is the alkyl radical of the glycol.

"8 These esters are prepared in the manner'similar to those of Type I.

Type III. Alcohol dibasic acid glycol monobasic acidr- -These esters are prepared by reacting a dibasic acid and a glycol under such conditions that one hydroxyl group of the glycol combines with one carboxyl group of the dibasic acid, in other words, so that a half ester is formed. This half ester is then reacted with a molar proportion each of an aliphatic alcohol and a monobasic acid. These materials may be said to have the general formula:

wherein R and R are the combining alkyl radicals of the alcohol; R and R the alkyl radicals of the dibasic acid; and R is the alkyl radical of the glycol.

It will be noted that the esters of Type IV have the same structural formula as Type II. However, these complex esters are prepared by reacting an alcohol with a dibasic acid under such conditions that a half ester is formed and reacting two moles of such an ester with one mole of a glycol.

Type V.M0n0basic acid-glycol-dibasic acid-glycolmonobasic acid-These synthetic esters may be said to have the general formula:

wherein R and R are the alkyl radicals of the monobasic acid; R and R are the alkyl radicals of the glycol; and R is the alkyl radical of the dibasic acid.

It will be noted that these synthetic esters are the same as those appearing above under Type I except that this type is prepared by reacting a monobasic acid with a glycol under such conditions that a half ester is formed and reacting two moles of such ester with one mole of a dibasic acid.

The alcohols used in forming the esters set out above, either the simple or the complex type, include the follow ing:

Methyl alcohol Ethyl alcohol n-Butyl alcohol n-Hexyl alcohol n-Octyl alcohol 2-ethylhexyl alcohol Cetyl alcohol Oleyl alcohol Ethylene glycol mono-n-butyl ether Ethylene glycol mono-Z-ethylbutyl ether Ethylene glycol mono-Z-ethylhexyl ether Ethylene glycol mono-tert.-octyl ether ,B-n-Butylmercaptoethanol S-terL-octylmercaptoethanol B-n-dodecylmercaptoethanol Diethylene glycol mono-n-butyl ether Diethylene glycol mono-2-ethylbutyl ether Diethylene glycol mono-Z-ethylhexyl ether Propylene glycol mono-butylthioether Propylene glycol mono-tert.-octyl thioether Propylene glycol mono-n-dodecyl thioether n-Butylmercaptoethoxyethanol Tert.-octylmercaptoethoxyethanol n-Dodecylmercaptoethoxyethanol 7 '9 n-Butylrnercaptopropoxypropanol Tert.-octylmercaptopropoxypropanol n-Dodecylmercaptopropoxypropanol Propylene glycol mono-n-butyl ether Dipropylene glycol monomethyl ether Dipropylene glycol monoethyl ether Dipropylene glycol mono-n-butyl ether Tripropylene glycol monomethyl ether Tripropylene glycol monoethyl ether Tripropylene glycol mono-n-butyl ether Propylene glycol 'monoisopropylether Dipropylene glycol monoisopropyl ether Tripropylene glycol monoisopropyl ether Many of the above listed ether alcohols, formed by the reaction of ethylene oxide or propylene oxide with aliphatic alcohols, are known in the industry as Dowanols, Carbitols, or Cellosolves.

A group of alcohols especially adapted for use in connection with the present invention are the so-called x0 alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products. Materials such as diisobutylene and C olefins are suitable for this purpose; also higher and lower molecular weight olefinic materials are sometimes employed. The alcohols obtained in this manner normally have a branched chain structure.

Among the monobasic acids which may be employed in the preparation of the esters of the present invention, the following may be listed as illustrative:

Acetic acid Propionic acid Butyric acid Valerie acid Caproic acid Caprylic acid Laurie acid Palmitic acid Stearic acid Oleic acid fl-Methoxypropionic acid fi-Ethoxypropionic acid fi-TerL-octoxypropionic acid fi-Ethylmercaptopropionic acid fi-TerL-octylmercaptopropionic acid B-TerL-dodecylmercaptopropionic acid Any of the various 0x0 acids The glycols employed in preparing the esters of the present invention include ethylene glycol and any of the parafiinic homologues of the same containing up to 18' carbon atoms. These may include, for example, ethylene glycol, propylene glycol, butylene glycols, pinacone, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and the like. Since the glycols may also contain oxygen or-sulfur atoms, compounds such as diethylene glycol, triethylene glycol, the polyethylene glycols of the formula:

wherein nvis 1 to 2 6, and .the polypropylene glycols of the general formula: V I

where either R, or R is a methyl group and the other is hydrogen, and where n is 1 to 20, may likewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include such eompounds as thiodiglycol and 1,2-bis (2-hydroxyethylmercapto) ethane. There a150 may be used glycols con- 7 taining both oxygen and sulfur in similar linkages; such a compound is bis-2-(2-hydroxyethoxy) ethyl sulfide.

OXIDATION INHIBITOR-.STABTLIZING AGENT I -In order to prepare the lubricating oil compositions of thisinve ntion the synthetic oils as described above are 16 blended with a minor amount, suficieiit to improve the stabilityand oxidation resistance characteristics thereof, of an N-acyl p-aminophenol. These phenols have the following general formula:

wherein R represents an alkyl group having from 1 to 8 carbon atoms; wherein R and R alike or different, are hydrogen atoms or alkyl groups containing from 4 to 15 carbon atoms per molecule.

The general formula above is subject to the following limitations 1) If the aromatic ring is substituted; that is, if R; or R are alkyl groups, R may have from 1 to 8 carbon atoms, but the sum of R+R +R must be at least 9 and not more than 17.

(2) If the aromatic ring is unsubstituted; that is, R; and R are hydrogen atoms then R may be an alkylgroup of from 3 to 8 carbon atoms per molecule.

Of the various N-acyl p-aminophenols operable in this invention, it is preferred to use those materials wherein R and R are hydrogen and R is an alkyl group having from 3 to 8 carbon atoms. Those compositions wherein R is an alkyl group having more than 10 carbon atoms tend to thicken the synthetic oil and if R is 1 or 2, the phenol is insoluble in mineral oils or soluble in water.

Exemplary of the preferred compounds may be mentioned the following:

N-acetyl-p-amino phenol N-butyryl p-arninophenol N-caprylyl-p-aminophenol N-propionyl-p-aminophenol N-n-acetyl-4-amino-3-pentadecyl phenol N-n-valeryl-4-amino-3-pentadecyl phenol N-n-propionyl-4-amino-3-pentadecyl phenol N-n-valeryl-4-amino-2,6,ditertiary butyl phenol N-n-caproyl-4-amino-2-hexyl phenol The preparation of three of the amino phenols are set out in detail below:

Preparation of N-acetyl-p-amin0phen0l.-One mole of p-aminophenol is dissolved in 1 liter of water containing 70 g. glacial acetic acid and the mixture heated with 120 g. of acetic anhydride on a steam bath for one hour. After cooling to room temperature the crystals which separate are recrystallized from hot water and melt at 167 -168 C.

Preparation of N-batyryl-p-aminophenol.One mole of p-aminophenol was mixed with 1.5 moles of n-butyric acid and cc. xylene. This mixture was refluxed for 5 hours in a 1 liter round bottom flask equipped with a condenser and watertrap using a hemispherical mantle. A water layer of 29.4 cc. was obtained in the water take-- off trap. The yield was 168.7 g. of product distilling in a short path still at 218-231 C. at -1 mm. The product melted, after three crystallizations from a mixture of acetic acid and water, at 131 C. Analysis for nitrogen gave 7.69% compared to a calculated 7.81%.

Preparation of N caprylyl-p-aminophenol.One-half mole of caprylic acid was mixed with 0.5 mole of paminophenol and 100 cc. xylene in a 1 liter flask equipped with'a water takeofi and reflux condenser. After refluxing for 6 hours 7.4 cc. of water was removed or 82% of the may beleft in solution by dissolving all but a minor:

amount of the product. V V The compounds may also be prepared in such manner that the desired N-acyl p-a'minophenols' may be formed in situ. Thisprepamfionmay be accomplished in the following manner; To a heated oil solution there is added the calculated amount of a p-aminophenol. The desired acid or acid chloride is then added, the formation of the N-acyl-p-aminophenols taking place upon the addition of the acidic constituent. After the reaction is completed the mixture is stripped with heating and water is removed.

The amounts of the N-acyl-p-aminophenols combined with the synthetic lubricating oil to form the compositions of this invention will vary between about 0.1% to about Table I V.-Oxidatin inhibitors in di-Z-ethylhexyl sebacate [0.5 wt. percent concentration] N-butyryl N-acetyll- Corrosion/Oxidation Stability (250 F.) None p-amiuo amino-.8- Phenothlazme phenol pentadecyl phenol Weight change, MgJcmfi:

Copper 0 +0.06 Steel 0. Aluminum Alloy" 0. Magnesium Alloy 0. Cadmium Plated SteeL +0.00. Visible Gorrosion' opper Purple. Steel Do. Aluminum Alloy. Do. Magnesium Alloy Do. Cadmium Plated Steel. Do. Oil Loss, percent 6 0.88. Viscosity Change at 100 F., percent +0.16. Neutralization Number Increase 0.02. I Separation and Guinminc Sl. Separation. Oxidation Rate: ml. 02 absorbed in 4 su cessive minute periods of 392 F 0-0-0-0.

5.0% by weight based on the weight of the total composition. It is preferred to use from about 0.02% to 2.0% by weight.

The preparation of the synthetic lubricating oils used in formulating the compositions of this invention is accomplished by known procedures with which the artis familiar and does not constitute a part of this invention.

Oil blends containing the amino phenols are prepared by simply admixing the phenoiic material in the desired amount with the base oil and heating the' mixture to a temperature slightly above the melting point of the phenol.

Various blends according to the concept of this invention were prepared and tested as follows:

(A) Blends using as a base oil di-2-ethylhexyl sebacate:

(a) A blend of di-Z-ethylhexyl sebacate containing combined therein 0.5 by weight of N-butyryl-p-aminophenol was prepared by admixing the phenol with the oil, heating to about 135 C. and cooling. A brilliant solution was obtained.

(1)) A blend of di-Z-ethylhexyl sebacate containing 0.5% by weight of N-n-acetyl-4-amino-3-pentadecy1 pheml was prepared by heating a mixture of the two com-. ponents to about 135 C. and cooling. A clear solution resulted.

The two compositions preparedas indicated above were submitted to the following determinations:

(l) Corrosion oxidation stability test:

This test, described in detail in Military Specification MIL-O-608'l, consists briefly in submerging five metal plates of known area and weight in a bath cc. of the. sample being tested. The sample is then raised to a temperature of 250 F., and oxygen is bubbled through the bath. At the end of 168 hours test time the metal plates are removed, the color change is observed, and the weight change per square centimeter calculated. The percentage of oil sample loss is determined, the percent change in viscosity at 100 F. noted, the neutralization number tested and, the. change calculated. The oil sample is alsoobserved for separationland guniming.

(2) Oxidation adsorption test:

a This test was carried; outaccording to a method simia cant:

An examination of the data in Table IV above clearly points out the excellent oxidation stabilityi characteristics of the compositions of this invention. The butyryl derivative of the p-aminophenol of blend A(a) gives almost perfect results in the very stringent tests described in detail above. Only 0.01 mg./cm. of weight change was detected in the case of magnesium alloy and all of the visible corrosion results were satisfactory. The N- acetyl-4-amino-3 pentadecyl phenol of blend A(b) showed a loss of 0.07 mg./cm. in the case of the copper plate, the others being satisfactory; All of the visible corrosion tests were passing. The phenothiazine compound, the best available inhibitor heretofore known, showed weight changes of +0.06 in the case of both copper and the cadmium plated steel samples. These results are still within the satis factory range but are not as satisfactory as either of the two experimental inhibitors. This compound failed all of the visible corrosion tests.

In the determination of the percent of oil lost during thetest, none was shown by either A(a) or A(b), the compositions ofinvention, whereas the phenothiazine solution showed a loss of 0.88%. In the other tests the three compositions showed outstanding results, only the phenothiazine slightly separating after the test period. No oxygen was absorbed by either of the compositions in the stringent oxygen adsorption test.

The data of Table IV above, particularly the low amount of test plate weight loss and the lack of visible corrosion points out that the compositions of this invention are very useful as metal deactivators and are particularly desirable in compositions that come in contact with metals, such as insulation materials and transformer oils and the like. There may also be added to the compositions materials such as 2-amino benzenethiol, amine type antioxidants containing metal deactivators, and the like to enhance the metal deactivation effect of the N a-am n Phn 1 (B) Blends using as a base oil a complex ester lubri- A complex'estenlubricating oil.prepared from 8.8 mols of rspoctylalcohol, 4.4 mols of triethylene glycol and 8.0 12. 9. 1.95 ad i cid nd ha ng a or u a e sn ise Table V.Oxidatin inhibition in complex ester lubricants [0.5 wt. percent concentration] No Inhibi- N -butyryl Corrosion] Oxidation Stability (250F.) tor p-aminophenol Wt. change mgJcm z Copper -.11 None N n 0. Aluminum Alloy .05..- Do. Magnesium Alloy 4.11-- 0.06. Cadmium Plated Steel 20.90. 0.02.

Visible Corrosion te Aluminum Alloy. Magnesium Alloy Cadmium Plated Steel-..

Separation and Cumming An inspection of the data of Table V above clearly points out the inhibiting effect of the N-butyryl-p-aminophenol in the complex ester type synthetic lubricant.

It is also within the concept of this invention to add other additive materials to the improved lubricating compositions of this invention. Other oxidation inhibitors, or additive agents such as detergents, pour point depressants, thickeners, sludge dispersants, extreme pressure agents, corrosion inhibitors and the like are compatible with the additive materials of invention and blends of these may be made to fit the requirements of the lubricating job for which the oil is desired.

To recapitulate briefly, this embodiment of the invention relates to new and improved lubricating oil compositions having outstanding oxidation resistance and having exceptional high and low temperature characteristics. The novel compositions comprise synthetic lubricating oils containing combined therein minor but oxidation resistance improving amounts of an N-acyl p-aminophenol. The phenolic material of these new compositions have the following general formula:

where R is an alkyl group having 1-8 carbon atoms, R, and R alike or different, are hydrogen atoms or alkyl groups containing from 4 to 15 carbon atoms, and where R and R are not both hydrogen atoms, then R+R +R must be not less than 9 nor more than 17. The preferred phenolic materials are defined by the formula above when R and R are hydrogen'and R is an alkyl group of from 3 to 8 carbon atoms.

The synthetic oil base for the compositions of the invention is of the ester type, either the simple esters or the complex esters. From 0.001% to 5.0% by weight of the phenolic material may be incorporated into the base oil, preferably from 0.01% to 2.0%.

In still another embodiment of the present invention, p-acyl aminophenols, particularly those wherein the hydrocarbon residue of the acyl group has at least two carbon atoms, are added to vegetable and animal fats, oils and their derivatives such as soaps. Butter, lard, hardened fats, coconut oil and other animal and vegetable fats, fatty acids and soaps, such as the potassium and sodium salts of the fatty acids contained in these fats and fatty oils, tend to develop an objectionable rancid odor and "14 tasteon exposure to air and, in accordance with this embodiment of the present invention, these materials are stabilized against oxidation and deterioration for long periods by addition of this class of antioxidant.

In general, the amount of anti-oxidant to be added is in the range of about 0.001 to 5.0 /b, preferably 0.01 to 0.5%. The concentration of the anti-oxidant may vary to secure protection against deterioration to a less or greater degree depending upon the nature of the fat, fatty oil, or soap in question, the nature of the acyl group. Preferred are the acyl aminophenols wherein the acyl group has from 9-19 carbon atoms.

The following examples further illustrate this embodiment of the present invention: 1

EXAMPLE VII The stabilizing effect of the inhibitor of the present invention upon animal fats was determined. The proteinaceous residue from rendering generally has been considered free from rancidity problems although almost all who store these products are aware of rancidity. The rapidly developing practice of adding animal fats to animal and poultry feeds has imposed an additional requirement for stability in animal fats. This requirement stems from the vitamin and nutrient destroying capabilities of rancid fats.

In this example, all renderings were performed in a standard design Albright-Nell dry melter. The data in the tables below were obtainedfrom rendering hog meat in the melter. The materials were well washed. In order to evaluate the effect of adding the anti-oxidant of the invention, the stability values reported were obtained by the accelerated method based on formation of volatile carbonyl compounds as reported by J. F; Neurner and L. R. Dugan, Jr. in Food'Technology, vol. 7, No. 5, 191-194 (1953).

In the table below there is shown a comparison of the stabilizing effects of several anti-oxidants upon lard; In each case, 0.01% of the stabilizer was employed.

These data clearly show the considerably greater stability of the lard stabilized with the anti-oxidant of the invention.

EXAMPLE VIII In this example there is illustrated the stabilizing etfect of the p-acyl amino-phenol upon a vegetable oil. Olive oil was held at 50% humidity and at F. and the odor determined at the end of 100 hours. Again, 0.01% of various anti-oxidants were employed to stabilize the oil being tested.

Antioxidant Odor after 100 hours 0 ontrnl 4 Butylated hydroxyanisole 1 2, 6 di-tertiary butyl p-cresol 1 p-lauroyl aminophenol 0 Citric aeid 4 4= Bad odor. 1 Very faint rancid odor. 0=San1e odor as original oil.

EXAMPLE IX Lauroyl p-aminophenol has also been found to stabilize light colored soap chips made with soy bean fatty acids. In this test, 10 grams of soap chips at 100% humidity are held in a 200 cc. sealed glass jar at 100 F. The soap -15 containing 0.02% of the stabilizer was rancid 'in 24 hours by this test, while that containing 0.05% was rancid in 7 days. The un'stabilized soap was rancid in 8-12 hours.

EXAMPLE X In this example, samples of hydrogenated cotton seed oil were stabilized with p-acyl aminophenols and the resistance to oxidation measured by the Norma-Hoffman oxidation bomb test described previously.

Hours of Pif'essuro Drop Sample lbs. 10 lbs. lbs.

Unstabillzed +0.05% lauroyl p-amluophenol 120 240 +0.51% stearoyl p-amlnophenol 100 176 212 These data show that hydrogenated vegetable oils are rendered stable to oxidation even under the relatively severe conditions of this test.

What is claimed is:

1. A lubricating grease composition consisting essentially of a lubricating oil thickened to a grease consistency with a grease making metal soap of a fatty acid having combined therein a minor, but oxidation resistance improving amount, of a compound having the formula-- wherein R is an alkyl group having from 10 to 18 carbon 16 atoms and R and R" are alkyl groups containing from 4'to '15 .carbon atoms. 4

3. A lubricatinggrease composition consisting essentially of a mineral lubricating oil thickened to a grease consistency'with the sodium soap of rapeseed oil having combined therein from 0.25% to 2% by weight of N- lauroyl p-amino phenol. 1

4. A lubricating grease composition consisting essentially of a mineral lubricating oil thickened to a grease consistency with the sodium soap ofrapeseed oil having combined therein from 0.25% to 2% by weight of N- myristoyl p-amino phenol. V p

5. A lubricating grease composition consisting essentially of a mineral lubricating oil thickened to a grease consistency with the sodium soap of rapeseed oil having combined therein from 0.25 to 2% by Weight of N- stearoyl p-ainino phenol.

6. Alubricating grease composition consisting essentially of di-2-ethyl hexyl sebacate thickened to a grease consistency with the lithiurn'soap of stearic acid and having combined therein from 0.25 to 2% by weight of N- lauroyl p-amino phenol.

7. A process for the preparation of a lubricating grease composition having outstanding oxidation resistance properties which comprises adding to a heated lubricating oil a saturated fatty acid, adding to the mixture a quantity of a metallic hydroxide sufficient to form the desired amount of a grease making metal soap of the said fatty acid and to leave a portion of the said acid unreacted, adding to the mixture a quantity of an amino phenol suificient to react With said unreacted acid and form the desired amount of acyl p-amino phenol, and stripping the resulting mixture of water to form a stabilized grease composition.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,456 Lan Kelma Dec. 5, 1933 2,360,631 Zimm er et a1 Oct. 17, 1944 2,604,450 Morway et al July 22, 1952 2,604,452 Morway et al. July 22, 1952 2,625,557 Cottle et al. July 22, 1952 2,629,666 Morway et al. Feb. 24, 1953 2,642,397 Morway et a1. June 16, 1953 2,654,722 Young et al Oct. 6, 1953

Claims

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH A GREASE MAKING METAL SOAP OF A FATTY ACID HAVING COMBINED THEREIN A MINOR, BUT OXIDATION RESISTANCE IMPROVING AMOUNT, OF A COMPOUND HAVING THE DORMULA