US2438876A

US2438876A - Mineral oil composition

Info

Publication number: US2438876A
Application number: US578562A
Authority: US
Inventors: Orland M Reiff; Jr Harry J Andress
Original assignee: Socony Vacuum Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1945-02-17
Filing date: 1945-02-17
Publication date: 1948-03-30
Anticipated expiration: 1965-03-30

Description

Patented Mar. 30," 1948 UNITED s r Orland M. Belt! and rry 3. Andreas, 3n, Woodbury, N. 3., assignors to downy-Vacuum Oil gonligpany, Incorporated, a corporation of New No Drawing.

1 gradient which will improve the oil in one or more important respects.

It is well known to those familiar with the art that mineral oil fractions refined for their various uses are in and of themselves usually deficient in one or more respects, sothat their practical utility is limited even in the particular field for which they have been refined. For example, mineral oil fractions refined foruse as lubricants have a tendency to oxidize under conditions of use with the formation of sludge or acidic oxidation products; also the lighter fractions such as gasoline and kerosene tend to oxidize with the formation of color bodies, gum, etc. In order to prevent the formation of these prod-' ucts and thereby extend'the useful life of the oil fraction, it is common practice to blend with such oil fractions an additive ingredient which will have the effect of inhibiting oxidation, such ingredients being generally known to the trade as oxidation inhibitors or sludge inhibitors, gum inhibitors, etc.

It is also the practice to add other ingredients to mineral oil fractions for the purpose of improving oiliness characteristics and the wearreducing action of such mineral oils when they Application Feb 17,1945, Serial no. 573.562

are used as lubricants, particularly when the oils are used for the purpose of lubricating metal surfaces which areengaged under extremely high pressures and at high rubbing speeds.

Other ingredients have been developed for the purpose of depressing the pour point of mineral oil fractions which have been refined for use as lubricants, such refinement leaving a certain amount of wax in the oil, which, without the added ingredient, would tend to crystallize at temperatures which would render the oil impracticable for use under low temperature condtions. Additive agents have also been developed for improving the viscosity index of lubricating oil fractions. :In the case of internal combustion engines, particularly those operating with high cylinder pressures, there is a decided tendency for the ordinary lubricating oil fractions to form, under such conditions of use, carbonaceous deposits which'cause the piston rings to become stuck in their slots and which fill the slots in the oil ring or rings, thus ,materially reducing the efliciency of the engine. Ingredients have therefore been developed which,ewhen added to the oil, will reduce the natural tendency of the 2 oil to form deposits which interfere with the function of the piston rings.

Aside from the corrosive action which attends the formation of acidic products of oxidation in mineral oil fractions of the lubricant range, it has been discovered that certain types of recently developed hard metal alloy bearing metals, such as cadmium-silver alloy bearings, are attacked by ingredients in certain types of oils, par.- ticularly oils of high viscosity index obtained by various methods of solvent-refining. This corrosive action on alloys of the above type has led to the development of corrosion inhibitors which may be used in solvent-refined oils to protect such bearing metals against this corrosive action.

In the lighter mineral oil fractions, such as those used for fuel purposes, particularly in internal combustion engines, it has been found that the combustion characteristics of the fuel may be controlled and improved by addingminor proportions of various improving agents thereto.

The various ingredients which have been developed for use in mineral oil fractions to improve such fractions in the various respects enumerated above are largely specific to their particular applications, and it has therefore been the practice to add a separate ingredient for each of the improvements which are to be effected.

It is a primary object of the present invention to provide a mineral oil composition which has been improved in one or more of the various properties enumerated above by the incorporation therein of a small quantity of a multifunctional compound or composition obtained by reacting an alkylated hydroxyaromatic compound with a phosphorus sulfide and subsequently reacting the resultant reaction product with a sulfur chloride.

We have discovered that the compounds or compositions of the class defined above, and the neutralized products or metal salts thereof, may be added in small quantities to mineral oil fractions to form mineral oil compositions or blends superior to the unblended fractions in one or more important respects, and the present ingame I may be phenol, a cresol, a xylenol, 'a naphthol,

group containing at least ten carbonatoms, and

preferably at least twenty carbon atoms, attached to a nuclear carbon atom thereof. As will be described hereinafter such alkylated hydroxy'aromatic compounds can be readily prepared by a Friedel-Crafts synthesis, using a halogenated aliphatic hydrocarbon and a hydroxyaromatic compound, or by reaction of an unsaturated aliphatic oompound (preferably of high molecular weight) or a higher alcohol and a hydroxyaromatic compound in the presence of sulfuric acid.

The alkylated hydroxyaromatic compound. such as an alkylated phenol or an alkylated naphthol, is reacted with a phosphorus sulfide. preferably Pass, and the resultant product is then reacted with a sulfur chloride.

As indicated hereinabove, the product resulting from the reaction of the sulfur chloride with the alkylated hydroxy-aromatic compoundphosphorus sulfide reaction product can be employed as such, or the metal salts of the final reaction products can be employed. The acidic product obtained from the sulfur chloride reaction may be converted to its corresponding metal salt by reaction with a suitable metal compound such as a hydroxide or an alcoholate.

f the foregoing compositions or compounds, particularly preferred herein are the oil-soluble or oil-miscible metal salts of diaryl sulfides (selenides and tellurides) of alkyl-substituted diaryl dithiophosphoric acids, which may be represented by the general formula:

in which T represents an aromatic nucleus; It represents at least one oil-solubilizing alkyl group attached to an aromatic nucleus T and contains at least ten carbon atoms, and preferably contains at least twenty carbon atoms; 11. represents the number of R. groups substituted on an arcmatic nucleus T, and is a whole number from 1 to 4; 2 represents sulfur, selenium and tellurium, :0 represents the number of atoms in said 2 and is a whole number from 1 to 4; and M represent in are those now comm" ciallyavailabie as the cerium and yttrium groups, namely, a mixture of praseodymium, neodymium, samarium, europlum,v gadolinium. terb um, dysprosium, holmium, erbium, thalliumand lutecium.

While all of the foregoing metals are contemplated as metal constituents (M) in the metal salts of this invention, particular preference is given to barium and tin.

As indicated above, the oil-solubilizing alkyl groups (R) are preferably those which contain at least twenty carbon atoms.- While each oilthe hydrogen equivalent of a metal.

The aromatic nucleus T in the compounds represented by general Formula I may be monoor'polycyclic typical of which arebenzene, naphthalene and anthracene.

The metal substituent, M, in general Formula I may be broadly classified as follows: The alkali metals, lithium, sodium, potassium, rubidium and caesium; the alkaline earth group, beryllium, magnesium, calcium, strontium and barium; the metals zinc, cadmium and mercury, scandium, yttrium, lanthanum; aluminum, gallium, indium, thallium, titanium, zirconium, cerium, thorium, germanium, tin and lead; vanadium, columbium and tantalum; arsenic, antimony and bismuth; chromium, molybdenum. tungsten and uranium; rhenium, manganese, iron, cobalt and nickel; ruthenium, rhodium and palladium; osmium, indium and platinum.

Some of the rare earth metals are recited above; other rare earth metals suitable for the formation of the metal salts contemplated heresolubilizing group of this type may be attached to only one aromatic nucleus T as shown in general formula I, it is also contemplated that this group may be a polyvalent aliphatic hydrocarbon group attached to separate aromatic nuclear groups (T). Compounds in which the oil-solubilizing alkyl groups may be polyvalent are included under the following general formula repin which T, 2,-M and a: have the same significance indicated above; I?! represents at least two aliphatic or alkyl radicals or groups, each of which is attached to at least one aromatic nucleus T, 0 representing the valence of the aliphaticradicals R'. which may be one to two; and 11 represents a whole number from one to two, and indicates the total number of groups present-in the molecule represented by general Formula II, and which are attached to the allphatic groups represented by R' through the valence 'v.

As to the possible number of R' groups going to makeup a single molecule, this will vary with the extent to which it is desired to efiect substitutions of the aromatic nuclei with oil-solubilizlng aliphatic groups for obtaining the desired properties in the product and is, of course, lim-' ited by the number of valences on the aromatic nuclei which are available for substitution. It will be apparent to those skilled in the art that the maximum possible number of R groups which can be attached to a single-aromatic nucleus will vary as the nucleus is monoor polycyclic and also as the nucleus is otherwise substituted. It will also be apparent that available valences on the nuclei may all be attached to oil-solubilizing polyvalent aliphatic groups.

' may be pure compounds satisfying the general formula representation 11 above, or may be mixtures of such compounds. In synthesizing the preferred oil-improving agents of the present invention, however, the final oil-improving product is normally or usually a mixture of different compounds corresponding to different values of v-and y and to different numbers of aliphatic groups R". This will be more apparent from the following discussion, and illustrations, of the synthesis of the metal salts contemplated herein:

It will also be understood that the preferred oilimproving metal salts of this invention, represented by general Formulae Iand II above, may be characterized by the presence of substituent aeeasro groups other than those already shown. For example, the aryl nuclei may carry other groups such as halogen. hydroxyl, alkoxy, aroxy. aralhl, 'aryl, nltro, nitroso, ket'o, ether alcohol and ester. The methods for introducingsuch groups are known to those familiar with the art.

While the preferred metal salts oi. the diaryl sulfides, selenides and tellurides of alkyl-substituted diaryl dithiophosphoric acids are contemplated broadly by the present invention, the aryl sulfides of this class are particularly preferred.

For this reason, the preparation of said diaryl sulfides will be described at length hereinbelow. It will be understood, however, that the corresponding selenides and 'tellurides can be similarly prepared from the existing selenides and tellurides corresponding to the sulfides. such as the sulfur halides. used in the preparation of the diaryl sulfides described above.

The preferred metal salts of diaryl sulfides of alkyl-substituted diaryl dithiophosphoric acids are prepared from alkylated hydroxyaromatic compounds or alkyl halides and hydroxyaromatic compounds, phosphorus pentasulfides .(PaSs), sulfurizing agents and suitable metal compounds. For example, a hydroxyaromatic compound may be alkylated with one or more alkyl groups (R) and then reacted with P255 to form an alkyl substituted diary] dithiophosphoric acid. The acid so obtained may be directly reacted with a suitable sulfurizing agent, such as elemental sulfur or a sulfur halide, to form the corresponding sulfide of said alkyl-substitute'd diaryl dithiophosphoric acid; or, the acid may be first converted to its corresponding alkali metal salt by reaction with an alkali metal, and then reacted with said suliurizing agent. The indirect procedure through the alkali metal salt is preferred.

PilSii followed by removal of the Friedel-Crafts' complex, provides a particularly stable dithiophosphoric acid. This is discussed in detail in our copending application Serial No. 489,086, filed May 29, 1943 (now Patent No. 2,386,207 dated pounds may be accomplished in various ways.-

such as by a Friedel-Crafts synthesis, using a halogenated aliphatic hydrocarbon, or by reaction with unsaturated high molecular weight aliphatic compounds or higher alcohols in the presence of H2804 as a catalyst. The Friedel-Crafts type of elkylation reaction is particularly well adapted to the step or preparing the alkylated hydroxyaromatic compounds from which the improving agents contemplated herein are synthesized, inasmuch as it affords 'a convenient means of controlling the desired degree of alwlation. and. accordingly, the desired degree of oil-solubility.

In this reaction an appropriate mono-or polychlorine-substituted aliphatic compound or material is reacted with'the desired hydroxyaromatlc compound in the presence of a catalytic amount of aluminum chloride. Pure or substantially pure monoor poly-chlorine substituted compounds may be used. However, as will be readily understood, since it is usually extremely difficult to prepare or obtain high molecular weight aliphatic hydrocarbons in a pure or subhydrocarbons contemplated herein as preferred sources for the alkyl or aliphatic substituent R' in general. Formula II above, may be pure or mixedcompounds typified by those which characterize the heavier products of petroleum, such as heavy petroleum oils of the lubricant type, petrolatum and crystalline petroleum wax or other compounds or materials which will result in relatively long-chain aliphatic substituents. Particular preference is given to petroleum wax characterized by a melting point not substantially less than about 120 F. (49 C.) molecular weight. of about 350 and at least about twenty carbon atoms in their molecules.

For example, a wax-substituted phenol prepared by a Friedel-Crafts procedure (such as that October 9,1945). The dithiophopsphoric acid formed by this procedure is then converted to the desired metal salt by the manner outlined above, and the desired metal salts obtained are also particularly stable.

Examples of the hydroxyaromatic compounds which may be used as startingmaterial for the alkylation reaction are: phenol, resorcinol, hydroquinone, catechol, cresol, xylenol, hydroxydiphenyl, benzylphenol, ph'enyl-ethyl-phenol, phenol resins, methyl hydroxydiphenyl, guaiacol, alphaand beta-naphthol, methyl alphaand methyl beta-naphthol, tolyl naphthol, xylyl naphthol, benzyl naphthol, anthranol, phenyl methyl naphthol, phenanthrol, monomethyl ether of catechol. anisole, beta-n-aphthyl methyl ether, chlorphenol and the like. Preference in general ated hydroxyaromatic compounds to designate (A) the number of atomic proportions of chicrine in chlor-aliphatic material reacted with one 1 mol of hydroxyaromatic compound in the Friedel- Crafts reaction, and (B) the chlorine content of the chlor-aliphatic material. In the above example A=3 and B=l6. This same designation wfll also apply to the oil improving agents, of

this invention. derived 'from these alkylated hydroxyaromatic compounds.

It will be apparent that the wax" substituent of a "wax-phenol,". such as the illustration used is to the monohydroxyphenols otherwise unsubabove, is a wax hydrocarbon group and is distingulshed from the hydrocarbon material known as wax by the loss of one or more hydrogen atoms.

The alkylated hydroxyaromatic compounds obtained by the Friedel-Crafts reaction may then be reacted with P235 as outlined in application Serial No. 390,586, filed April 26, 1941, in which one of the present inventors, 0. M. Bleifl, is a co-inventor. Also the reaction with P235 to form t the corresponding alkyl-substituted dithiophosphoric acid may be carried out by the novel procedure described in our copending application Serial No. 489,086, filed May 29, 1943 (now Patent No. 2,386,207 dated October 9, 1945); in this procedure an alkyl halide, as a chlorwax, and a hydroxyaromatic compound are reacted in the presence of a Friedel-Crafts catalyst, and the Friedel-Crafts reaction mixture (containing said catalyst) is then reacted with P285 followed by removal of the Friedel-Crafts catalyst, or corresponding complex.

The alkyl-substituted dithiophosphoric acid obtained by the foregoing procedures may then be converted to their corresponding alkali metal salts by reaction with an alkali metalor alkali metal compound, before conversion to their sulfides. Similarly, the acid per se may be converted to the corresponding sulfide by reaction with a. sulfurizing agent. The sulfur halides are preferred for forming the desired monoand poly-disulfides; sulfur monochloride, for example, forming the disulfide, and sulfur dichloride forming the monosulfide; The higher sulfides, such as the triand tetra-sulfides can be prepared by using an appropriate amount of elementary sulfur in combination with sulfur monochloride in this reaction. A'somewhat more expensive means may also be employed for'forming the tetrasulfldes, such means involving reacting an alkyl tetrasulfide, such as tertiary butyl tetrasulfide, with the disulfide formed from suifur mono-chloride.

To prepare the final products, the preferred improving agents contemplated herein, the diaryl sulfides of alkyl-substituted diaryl dithiophosphoric acids obtained above are substituted with metal. This substitution with metal may be accomplished through the use of a metal hydroxide, particularly for the formation of the alkali metal salts, and through the use of a metal alcoholate.

The synthesis of the preferred improving agents of this invention will be better understood from the following illustrative examples wherein the preparation of typical metal salts is described.

EXAMPLE 1 BARIUM Saar or rm: Drsutrma or WAx-suasrrru'rsn Drrnam Drrmorr-rosrnoarc Acm (3-14) (a) Preparation of chlorwaa:

Petroleum wax of A. S. T. M. melting point of 126 F. (52 C.) was chlorinated by introducing chlorine at about 150.F. (0. 65 C.) until 14% by weight of chlorine was absorbed.

(b) Preparation ofdithiophosphoric acid of waxphenol (3-14) 8 about 175 C. and the mixture was stirred for about one hour at this temperature to complete the reaction. The product at this stage was the cated by the decrease in the amount of ms evolved: however, the reaction mixture was heated longer to insure completion of the reaction. about C., and water was carefully added to decompose the aluminum chloride complex. The color .of the reaction mixture was lightened at this point by the addition of 5 grams of zinc dust. Small amounts of butanol were added to break emulsions formed on the addition of water. Several washings with water were required to obtain a water extract free of aluminum chloride. The product was filtered through Hi-Flo, and the butanol distilled from the filtrate by using reduced pressure. The product obtained was a 1:3 blend in mineral oil, which contained 0.6% phosphorus and 1.0% sulfur, and'had a (0) Preparation of the disulfide 0 dithiophosphoric acid of war-phenol (3-14) One hundred grams of the mineral oil blend obtained in (b) were reacted with 34 grams of a butanol solution of sodium butylate, which was formed by dissolving 1.13 grams of metallic sodium in 33 grams of butanol. The reaction mixture was heated for one hour at 100 C., then cooled to room temperature (about 20-25 C.), and 3.33 grams of sulfur monochloride were added at a rate slow enough to avoid appreciable rise in temperature, thereby avoiding discoloration of the product. This reaction mixture was stirred for about one hour at about 20-25 C., and the reaction product formed therein was the disulfide of dithiophosphoric acid of wax-phenol (3-14), also described as the disulfide of waxsubstituted diphenyl dithiophosphoric acid (3-14).

(d) Preparation of barium salt of (c) Eight grams of barium hydroxide octahydrate (Ba(OH)z.8H2O) were added to the reaction mixture obtained in (c) and the resulting mixture was heated to about 150 C. After stirring the mixture at this temperature for about one hour in order to remove all of the water of reaction, the temperature was then lowered to about 80 0., followed by adding 3.73 grams of barium oxide (BaO) dissolved in methanol in order to introduce more barium. Part 01' the methanol was distilled off during the introduction of the solution; the temperature was then raised to C. to completely remove the methanol. The reaction mixture was then filtered with the aid of Hi-Flo to obtain the finished prod- The reaction mixture was then cooled to earners Barron SALT or ran 'I'nraasunms orwax-Sussnrurnn Drrnnnrr. Drrarornosrnoarc Acm (3-14) (a) Preparationof the tetrasulfide of wax-substitilted diphenyl dithiophosphoric acid (3-14) One hundred grams of the mineral oil blend of wax-substituted diphenyl dithiophosphoric acid (3-14) obtained as described in Example 1 '(b) were reacted with 34 grams oi a butanoi solution oi sodium butylate (NS OCdHB), which was formed by dissolving 1.13 grams or metallic sodium in 33 grams'cr butanol. This reaction mixture was heated for one hour at about 100 (2., and the butanol was then distilled off. Chlorbenzene, 35 on, was added as a diluent and the reaction mixture was cooled to room temperature. Then, 1.7 grams of elementary sulfur and 3.33 grams of sulfur monochloride were added at a rate slow enough to avoid appreciable rise in temperature. The reaction mixture was stirred for about one hour to complete the formation of the tetrasulflde.

(b) Preparation of barium salt of (41) Eight grams of BaiOH'lailI-EO were added to the reaction mixture obtained in (a) and the resulting mixture was heated to about 150 C. for one hour to remove all or the water of reaction. The temperature was then lowered to about 80 0., and 3.73 grams of IBaO dissolved in methanol were added. The mixture was heated to about 125 C. to complete the reaction and to distill oil methanol. The mixture was then filtered with the aid of Hi-Flo to obtain the finished product in approximately a 1:3 blend in mineral oil.

Sramvous Saar or m Drsunmn or WAX-SUBSTI- rum Drrnam Drrmornosrnonrc Acrn (3-14) v1 (1)) were converted to the disulflde derivative of reaction with sulfur monochloride as described in 1 (c). The i'reeacid was then converted to the sodium salt by adding 1.13 grams of metallic sodium in solution in butanol, and heating the mixture to about 100 C. A butanol solution containing 4.7 grams or stannous chloride was then added and the mixture was heated to reflux temperature for about one hour to complate the formation of the stannous salt. .Butanol was then distilledofi and the remaining reaction mixture was filtered with the aid of Hi-Flo to obtain the finished product, approximately a 1:3 blend in mineral oil.

It will be apparent to those skilled in the art that the metal'salts of this invention can be obtained in the free state just as readily as they are obtained in mineral oil blends in the foregoing examples. To obtain a metalsalt per se, a

light hydrocarbon diluent, such as kerosene,-

Stoddard solvent, 'etc., is used in place 01' a mineral oil and is distilled oil before or after'the formation of the metal salt.

To demonstrate the effectiveness '01 the metal salts of the type described above in the mineral oil compositions contemplated by this invention, we have conducted several comparative testts, the results of which are listed below, with representative mineral oils alone and with the same oils blended with various representative metal salts l oi diaryl sulfides of chi-substituted diaryl ditbiophosphoric acids.

Pour

5 These tests were conducted with a mineral lubricating oil fraction having a Saybolt Universel viscosity (8. U. V.) of 67 seconds at 210 21. and an A. S. T. M. pour point of 20 F. The results for the blank oil and the oil blends are listed below in Table I.

Tablet A. 8. '1. M. Pour Test improving Agent Barium salt oi wax-substituted diphenyl dithlophosphoric acid disulflde (3-14 -25 1 arium salt oi wax-substituted di henyl dithio- 0 phosphoric acid tetrasulflde (3-14 l5 stannous salt of wax-substituted diphenyl dithiophosphoric acid disulflde -14 0 -15,

Barium salt of wax-substituted a-dinaphthyl 10 +5 dithiphosphcric acid disulflde (3-12) 25 The improvement produced by the improving agents of the present invention in the viscosity index of mineral oils to which they are added is clearly shown by the illustrative data shown in Table II.

Table II I Kinematic Per Vis.at- Compound Added cent V. I

v 100 F. 210 F.

None -1 0 80.17 4.80 79.8 Barium salt of waxsubstituted dipben yl dithiophosphorlo acid dlsulfl 0(3-14) 2 33.78 5.20 88.6

um salt of wax-substituted digglgrijvnldlthiophosphoricacid to do 3-14) 2 34.45 5.29 01.1 tannous salt of wax-substituted diphelayldithiophosphoricacid disulfl 0(3-14) 2 33.7 5.23 91.8 Barium salt of war-substituted a-dinaphthgl dithiophosphoric acid disulil a (3-12) 2 32.68 5.09 87.3

The efi'ectiveness of the preferred metal salts contemplated herein in stabilizing motor oils Table III Per cent Compound Added Oono.

u. v. M at 210/r.

None Barium salt oi. wax-substituted dipbenyl dlthiophosphorlo acid disuliid 3-14) e tannous salt of wax-substituted diphenyl dithiophosphoi'lc acid disuliide (3-1 Barium salt of wax-substituted a-dlnaphthyl dithiophosphorio acid disulflde (3-12) It will be apparent from the foregoing description that we have developed a new class 01 mineral oil compositions characterized by the presence in a minor proportion of a metal salt of a diaryl sulfide oi. an alkyl-substituted diaryl dithiophosphorlc acid as an improving agent. The

improved-properties obtained and the degree of improvement efiected in a particular property may be varied with the metal substituents and the number of sulfur atoms in the sulfide group: also by the degree of alkylation of the aryl nuclei. As to the degree of alkylation, it is important that the aryl nuclei be sumciently alkylated to provide a final product which is "soluble" or miscible" in the particular mineral oil fraction with whichit is to be blended; that is, one which will remain uniformly dispersed in the oil in sufficient amount to effect the desired improvement. The amount of improving agent used may be varied depending upon the mineral oil or mineral oil fraction with which it is blended and the' acsasvo metal salt of a diaryl-tetrasulfide of a wax-sub-v stituted diaryl dithiophosphoric acid.

6. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suflicient tostabilize said mineral oil against oxidation, of an oil-miscible metal scribed certain preferred procedures which may be followed-in the preparation of the metal salts of diaryl sulfides (selenides and tellurides) oi alkyl-substituted diaryl dithiophosphoric acids used as improving agents in the mineral oil compositions contemplated herein and have referred to various representative constituents in these salts, such procedure and examples have been used for illustrative purposes only. The invention, therefore, is not to be considered as limited by the specific examples given but includes within its scope such changes and modifications as fairly come within the spirit of the appended claims.

This application is a continuation-in-part application of our copending application Serial No. 495.766, filed July 22, 1943.

We claim:

1. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, sufflcient to stabilize said mineral oil against oxidation, of a metal salt of a diaryl sulfide of an alkyl-substituted diaryl dithiophosphoric acid, the alkyl substituent of which is an oil-solubilizing alkylgroup containing at least about ten carbon atoms.

2. An improved mineral oil composition comprising a mineral oil having admixed therewith a'mi'nor proportion sufflcient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt of a diaryl sulfide of an alkyl-substituted diaryl dithiophosphorie acid, the alkyl substituent thereof, having at least twenty carbon atoms.

3. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suflicient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt 01 a diaryl sulfide of a wax-substituted diaryl dithiophosphoric acid.

4. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportionysuflicient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt of a diaryl disulfide of a wax-substituted diaryl dithiophosphoric acid.

salt of a disulfide of a wax-substituted vdiphenyl dithiophosphoric acid.

7. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suiiicient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt of a tetrasulfide of a wax-substituted diphenyl dithiophosphoricacid. 2 .8. An improved mineral oilcomposition comprising a mineral oil having admixed therewith a minor proportion, sufiicient to stabilize said mineral oil against oxidation, of an oil-miscible barium salt'of the disulfide of a wax-substituted diphenyl dithiophosphoric acid.

9. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion. suflicient to stabilize said mineral oil against oxidation, of an oil-miscible stannous salt of the disulfide of a wax-substituted diphenyl dithiophosphoric acid.

10. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suilicient to stabilize said mineral oil against oxidation, of an oil-miscible 1 barium salt of the tetrasulfi'de 01 a wax-substituted diphenyl dithiophosphoric acid.

11. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suflicient to stabilize said mineral oil against oxidation, of an intimate mixture 01' oil-soluble metal salts .of diaryl sulfides of alkyl-substituted diaryl dithiophosphori acids, said metal salts in said mixture differing from each other with respect to the nature of the alkyl substituents, the said alkyl substituents being attached to the aryl nuclei and having at least twenty carbon atoms.

12. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, sufilcient tstabilize said mineral oil against oxidation, or an intimate mixture of oil-soluble metal salts or diaryl sulfides of aikyl-substituted diaryl dithiophosphoric acids, said metal salts in said mixture difiering from each other with respect to the nature of the alkyl substituents, the said alkyl substituents being attached to the aryl nuclei and comprising essentially aliphatic hydrocarbon groups having a composition corresponding substantially to the difl'erent aliphatic hydrocarbons contained in parafiln wax.

13. An improved mineral oil composition comrising a mineral oil having admixed therewith a minor proportion, sufiicient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt having the general formula:

in which: '1' represents an aromatic nucleus; It

represents at least one oil-solubilizing alkyl group 13 I 14. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, suflicient to stabilize said mineral 011 against oxidation, of an oil-miscible metal salt having the general formula:

in which: T represents an aromatic nucleus; R," represents at least two polyvalent hydrocarbon groups, each of said groups having at least twenty carbon atoms and a'valence 12 from 1 to 2; a: is a whole number from 1 to 4; M represents the hydrogen equivalent of a metal and y is a whole number from 1 to 2.

15. An improved mineral oil composition comprising a mineral oil having admixed therewith a minor proportion, from about 5 per cent to about 1 per cent, of a metal salt of a diaryl sulfide of an alkyl-substituted diaryl dithiophosphoric acid,

14 a. minor proportion, sufflclent to stabilize said mineral oil against oxidation, of an oil-miscible metal salt of a diphenyl sulfide of an alkyl-substituted diphenyl dithiophoshoric acid, the alkyl substituent thereof, having at least 20 carbon atoms.

18. An improved mineral oil composition com-- prising a mineral oil having admixed therewith a minor proportion, sufiicient to stabilize said mineral oil against oxidation, of an oil-miscible metal salt of a diphenyl sulfide of a wax-substituted diphenyl dithiophosphoric acid.

19. An improvement agent for hydrocarbon lubricating oils comprising a, neutralized. diaryi sulfide of an alkyl substituted diaryl dithiophosphoric acid, said alkyl substituent containing at least ten carbon atoms.

ORLAND M. REIFF. HARRY J. ANDRESS, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,772,386 Derby Aug. 5, 1930 1,949,629 Romieux Mar. 6, 1934 2,265,851 Matheson Dec. 9, 1941 2,316,081 Loane Apr. 6, 1943 2,316,083 Macharen Apr. 6, 1943 2,316,087 Gaynor Apr. 6, 1943 2,362,624 Gaynor Nov, 14, 1944