US3252910A - Lubricants containing metal compounds of n, n'-substituted dithiooxamides - Google Patents

Description

United States Patent 0 3,252,910 LUBRICANTS CONTAINING METAL COMPOUNDS 0F N,N-SUBSTITUTED DITHIOOXAMIDES Edward A. Oberright, Woodbury, N.J., assignor to Sgocofiny Mobil Oil Company, Inc., a corporation of New or No Drawing. Filed July 1, 1963, Ser. No. 292,132 19 Claims. (Cl. 25242.7)

The present invention relates to lubricating oil compositions possessing improved characteristics.

More particularly, the invention concerns improved lubricating oil compositions containing certain complexes of N,N'-substituted dithiooxamides.

It is well known that lubricating oils are subject to oxidative degradation under conditions of use in modern combustion engines. Oxidative combustion products of an acid nature are formed in the lubricants during engine operation and exert a corrosive elfect on the metal parts with which the lubricants come in contact. In addition, these oxidative products tend to produce formations of varnish or sludge on the engine which lower its operating eificiency. In order to lessen, as far as possible, these undesirable effects, anti-oxidant compounds are added to the lubricating oils.

It is further recognized that many lubricating oils, because of their particular nature and characteristics, often possess unsatisfactory viscosity indices (V.I.), that is, viscosity changes too rapidly within the operating temperature ranges of the engine. These oils therefore also require the presence of additives which act to improve their V.I. characteristics.

According to the present invention, it has been found that it is possible to inhibit the oxidative degradation of lubricating oil compositions as Well as improve the viscosity indices thereof by adding to these compositions certain complexes of N,N-substitu'ted dithiooxamides.

Thus, by employing these complexes of N,N-substituted dithiooxamides it is possible to produce lubricating oils possessing both superior oxidation stability and improved V.I. characteristics without resorting to the use of separate anti-oxidants and V.I. improver compounds.

Accordingly, it is an object of the present invention to provide lubricating oil compositions possessing both improved anti-oxidation characteristics and improved viscosity indices.

Another object is to provide a simple and effective method for improving the oxidation resistance and the V.I. characteristics of lubricating oils.

Other objects of the invention and the advantages thereof, will become apparent from the following detailed description.

The combination anti-oxidant and V.I. improver compounds of this invention are metal complexes of N,N- disubstituted dithiooxamides.

The preparation and possible structure of these metal complexes is described by Hurd et al. at pages 4454-4458 of the Journal of the American Chemical Society, vol. 82, 1960.

Although the invention is not limited to any particular theory regarding the structure of these complexes it is believed that they have the following structural formula:

wherein M is a metal; n has a value of at least 1, preferably from 6 to 10; and R and R each represents an organic radical, either the same or diiferent, containing sufficient carbon atoms to impart oil solubility to the metal complex, which organic radical is directly attached to the nitrogen atom by a carbon atom of said organic radical containing at least one hydrogen atom.

Examples of suitable organic radicals include hydrocarbyl radicals such as saturated or olefinically-unsaturated, straight chain or branched chain aliphatic radicals, which radicals are directly attached to the nitrogen atoms through carbon atoms of these radicals containing at least one hydrogen; cycloalkyl radicals; and aralkyl radicals I which are attached to the nitrogen atoms by a non-tertiary carbon of the alkyl substituent, i.e., a carbon containing at least one hydrogen. Further examples of suitable organic radicals include hydrocarbyl' radicals of this type additionally containing at least one hydroxy, amino, 30 imino, alkoxy or carboxy group.

It will be noted from the above that aliphatic radicals which are attached to the nitrogen atoms through a tertiary carbon atom, and phenyl groups directly attached to the nitrogen atoms are excluded from the sope of R 35 and R.

The term organic radical, as used herein, is employed in its generic sense and covers both hydrocarbyl radicals per se and hydrocarbyl radicals further containing additional groups such as the aforementioned hydroxy, amino, imino, alkoxy and carboxy groups.

As some preferred examples of organic radicals which may be present as the N,N-substituted components there may be mentioned; octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, octadecenyl, cyclohexyl, benzyl, carboxyl-hexyl, hyd r-oxy-octyl, and n-oleyl propyl amine radicals.

In general, the organic radicals present as the N,N'-

substituted groups contain a total of at least 5 carbons preferably from 5 to about 30 carbon atoms. 5 M may be selected from a wide variety of suitable metals. Metals from Groups I, II, VI and VIII of the Mendeleff Periodic Table, especially Group II and VIII metals are particularly suitable. Some preferred examples of such metals are silver, copper, calcium, zinc, mercury, molybdenum, nickel, cobalt, iron, ruthenium, platinum and palladium.

Briefly, the N,N'-substituted dithiooxamido metal complexes, employed according to the present invention, may be prepared by reacting at least about two equivalents of the salt, hydroxide or oxide of the desired metal, pref- J erably in the presence of a base, with an N,N'-substituted dithiooxamide of the formula:

H s H RI I(L il IR (A) wherein R and R have the above meaning. This reaction is preferably conducted in an absolute alcoholic solution at room temperature or higher. Although any soluble metal salt, hydroxide or oxide may be employed in the synthesis reaction, metal halides, metal carbonates, metal acetates and metal nitrates are preferred.

The N,N-substituted dithiooxamides of Formula A can be obtained by reacting dithiooxamide with primary amines or mixtures of primary amines. Suitable amines include, aliphatic cycloalkyl and aralkyl primary amines wherein the nitrogen of the primary amamine is attached to a carbon atom containing at least one hydrogen atom. Primary amines wherein the amino nitrogen is directly attached to a phenyl group or a tertiary carbon of a tertiary alkyl group are not suitable.

The metal complexes of the N,Nsubstituted dithiooxamides employed according to the present invention may be present as relatively pure individual compounds, or as mixtures of two or more metal complexes of this type wherein the complexes contain a variety of N,N- substituted organic radicals.

Thus, for example, when the N,N-substituted dithiooxamides used in the preparation of the instant metal complexes, are obtained by the reaction of dithiooxamide with a mixture of suitable primary aliphatic amines containing from about 8 to 18 carbon atoms, mixtures of N,N-substituted dithiooxamido metal complexes containing various aliphatic groups as the N,N'-substitutents, are obtained. The proportions of these various N,N-substituted metal complexes in the mixture generally depends on the proportions of the different primary aliphatic amines in said amine mixture. In this particular case the mixture primary aliphatic amines contains the following proportions:

For convenience, the above-described primary amine mixture is herein referred to as C C mixture, and the corresponding metal complexes of N,N'-substituted dithiooxamides obtained from N,N-substituted dithiooxamides prepared using said amine mixture, are termed metal complexes of N,N'-bis (C -C dithiooxamides.

Similarly, metal complexes obtained from N,N-substituted dithiooxamides prepared from dithiooxamide and amine compositions exhibiting an iodine value of about 60, a specific gravity at 25 C. of 0.841, and containing about 80% of diamines of the formula,

H H H R"N-C-CONH H H H H H wherein R" is derived from oleic acid and is substantially composed of the oleyl group (C are herein referred to as N,N'-bis (N-C propyl amine) dithiooxamide metal complexes.

Further details as to the preparation of the metal complexes are given in the above-mentioned Hurd et al'. article.

The metal complexes of N,N'-disubstituted dithiooxamides when added to lubricating oils act to improve the characteristics of the oils in at least two primary ways. They inhibit the deterioration of the oil due to oxidation, thus lessening or eliminating both the formation of sludge and the damage caused by the attack of acidic oxidation products on the metal surfaces to be lubricated. In addition, these metal complexes act to increase the viscosity index (V.I.) of the composition thereby reducing any changes in the viscosity of the oils normally caused by temperature variations.

The particular amounts of metal complexes added to the lubricating oils will depend on the particular nature of the base oil, the presence or absence of other additives and the uses to which the lubricating oils are to be put.

In general, from about .001% to 10%, preferably from about 0.1 to 2.0% may be used.

The N,N'-disubstituted dithiooxamido metal complexes may be advantageously employed in a variety of lubricating oil compositions.

Some examples of lubricating oils, both petroleum base oils and synthetic oils, e.g., synthetic hydrocarbon and synthetic ester, the oxidation stability and V1. of which may be improved include mineral oils from different crudes both solvent and acid refined, hydrocracked, etc. Synthetic hydrocarbon oils would include hydrogenated polyolefins, alkyl benzene, etc. Synthetic esters would include di-Z-ethylhexyl sebacate, di-octyh adipate, trimethylol propane trioctanoate, pentaerythritol tetraheptanoate, etc.

The compositions of the present invention may, of

course, also contain effective quantities of various typical additives, normally used in lubricating oils which are designed to improve the oil compositon in other respects, such as detergents, rust inhibitors, pourpoint improvers, etc.

The following specific embodiments will serve to further illustrate the present invention.

PREPARATION OF N,N-DISUBSTITUTED DI- THIOOXAMIDE METAL COMPLEX The preparation of the zinc complex of N,N-dioctadecyl dithiooxamide is given as illustrative of a suitable method for the preparation of the metal complexes.

An absolute ethanol solution of two equivalents of ZnCl and four equivalents of triethylamine is filtered, warmed to 60 C. and added dropwise to a well-stirred, absolute ethanol solution of one equivalent of purified N,N-dioctadecyl dithiooxamide which is maintained at 70 C. during the addition period. The resulting product is both an oil and a tan solid. The oil readily solidifies upon cooling. The product, including the additional material gained on concentration of the mother liquor, is triturated, washed with acetone and Soxhlet-extracted with ethanol for 24 hours and then dried under vacuum (about .1 mm. 65 F.).

Upon analysis this product contains: 4.5% N, 8.6% S and 9.8% Zn.

Some examples of other suitable metal complexes and their respective metal, sulfur and nitrogen contents, whe e available, are as follows:

Examples 1-11 The oil compositions shown in the following Table 1 are prepared.

In order to determine the effect of the metal complexes on the viscosity characteristics of the oil compositions, the K.V. of each composition is obtained at 5 F. and 210 F. and the viscosity index (V.I.) is calculated therefrom.

The initial and final neutralization numbers (N.N.) for each oil composition are reported in Table 2.

TABLE 1.-MEIAL COMPLEXES AS V.I. AGENTS Additive Initial Example Cone.

No. Composition (weight percent) K.V. at K.V. at V.I.

Base Oil A 8.91 62. 98 111 Base Oil A plus Zn Complex of N,N-dioctadecyl dithiooxamide-.. 3.0 19. 19 103. 9 147 1. 5 11. 54 72. 7 139 i 0.75 9. 30 65.9 123 Base Oil A plus Zn Complex of N,N'-Bis (Cs-01B) dithiooxamiden 3. 67.25 767.0 123 do 1. 21. 19 210. 0 118 do 0.75 11. 42 83.1 126 Base Oil B 5. 44 34. 03 104 Base Oil B plus Zn Complex of N ,N-dioctadecyl dithiooxamide. 3. 0 23. 78 299. 8 122 8.-.- 1.5 10.53 87. 28 111 9 0.75 7.42 52. 92 110 10 Base Oil B plus Zn Complex of N ,N-(C -Cia) dithiooxamido 1. 5 25. 87 277 118 11 do 0. 75 12. 01 109. 9 106 l A SAE grade, solvent-refined oil having a K.V. of 8.91 cs. at 210 F. and 62.98 cs. at

1 Illend of 80% mid-continent distillate and 20% naphthenic distillate containing 3.3%

barium sulionate and 3.3% barium phenate.

From the viscosity indices reported in Table 1, it will be noted that the metal complexes improve the V.I. of each of the oil compositions.

Examples 12-24 The oil compositions shown in Table 2 are prepared by admixing the dithiooxamido metal complexes and various base oil stocks.

CATALYTIC OXIDATION TEST In order to determine the effectiveness of these metal complexes in inhibiting the oxidation of the oils, the com- The difference between the initial N.N. of the oil and the N.N. of the oil after being subjected to oxidation according to the test procedure is an -indication of the ing no metal complex.

tralization number than the corresponding oils contain- These low final neutralization numbers indicate that that the oils of the present invention containing N,N'-disubstituted dithiooxamido metal complexes possess superior resistance to oxidative degradation.

TABLE 2.OATALYTIC OXIDATION TEST AT 325 F. FOR 24 HOURS Additive Neut. N 0. Example Composition Cone.

N 0. (weight percent) Initial Final Base Oil A 1 10 12 Base Oil A plus Zn Complex of N,N- 3. 0

dioctadecyl dithiooxamide. 1% do 1. 0 l4 dn 8. 3 15 Base Oil A plus Zn Complex of N,N-bis 0. 2. 8

(Ce-C15) dithiooxamide. 16. do 0.15 2. 3 17- rlr 0.15 1.9 Base Oil C 2 0.13 3. 3 18 Base Oil C plus 00 Complex of N,N- 0. 20 0. 20

diodecyl dithiooxamide. Base Oil D 3 0. 18 35. 4 19 Base Oil D plus Zn Complex of N,N- 0. 1 0.38

dioctadecyl dithiooxamide. 20. do 0. 38 21 do 0.63 22 Base Oil D plus Zn Complex of N,N-bis 0. 25

(CB-Cl!) dithiooxamido. 23 (in 0.50 24.. rln 0. 38

1 See Table 1. 2 Trimethylolpropane triootanoate. Di-2-ethyl hexyl sebacate.

positions of Examples 12-24 are subjected to a catalytic oxidation test.

According to this procedure, 25 cc. of the test oil is placed in .a 200 x 25 mm. test tube with 15.6 sq. in. of sandblasted iron wire, 0.78 sq. in. of polished copper wire, 0.87 sq. in. of polished aluminum wire, and 0.167 sq. in. of polished lead surface. Dry air is passed through the sample at the ratio of 10 liters per hour while the samples are heated in an aluminum block bath for a period of 24 hours at a temperature of 325 F.

Examples 25-32 The metal complexes are admixed With a synthetic ester base oil comprising di-2-ethylhexyl sebacate in the 0 amounts shown in Table 3.

The resulting oil compositions are then subjected to the catalytic oxidation test described above.

The initial and final neutralization numbers, and the initial and final K.V. at 210 F. for each of the oil sampics is determined and reported in Table 3.

It will be noted that the neutralization number of the blank oil containing no metal complex increases from 0.18 to 35.4, whereas the oils containing the metal complexes exhibit significantly superior oxidation stability as evidenced by the slight diiference between their initial and final neutralization numbers.

TABLE 3.CATALYTIC OXIDATION TEST AT 325 F. FOR 24 HOURS Additive Neut. No. K.V. at 210, cs. Example Composition Cone.

No. (weight percent) Initial Final Initial Final Base Oil D 1 0.18 35. 4 3. 35 6. 27 25 Base Oil D plus Zn Complex of N,N- 0.5 0.05 0.8 3. 40 3. 41

blS(Ca-Cis) dithiooxamide. 26 do 0. 25 0. 05 1. 0 3. 38 3. 40 27 Base Oil D plus Zn Complex of N,N- 0.5 0.45 0.8 3.37 3. 55

bis(N-C1s propyl amine) dithiooxamide. 2s (In 0.25 0. 20 14. 3 3. 35 4. 30 29 Base Oil D plus Co Complex of N,N- 0.5 0.10 0.50 3. 88 3. 40

bis(dehydroabietyl) dithiooxamide. do 0.25 0.10 0. 50 3.37 3. 39 31 Base Oil D plus Ni Complex 0! N ,N- 1. O 0. 0.8 3. 42 3.51

bis(dehydroabietyl) dithiooxamide. i2 rln 0. 5 0.15 0.5 3. 38 3. 39

1 Di-2-ethylhexyl sebacate.

Examples 33-40 metal of said complex 18 selected from the class consist- Eight oil compositions containing the metal complexes are prepared.

These oils are then subjected to the catalytic oxidation test described above. The results obtained including the amount of lead lost from the lead surface is reported in Table 4.

ing of Groups I, II, VI and VIII of the Mendeleff Periodic Table and wherein the N,N'-di-substituted group is an organic radical selected from the group consisting of hydrocarbyl radicals and substituted hydrocarbyl radicals directly attached to the nitrogen atom by a carbon atom containing at least one hydrogen atom, and which TABLE 4.CATALYTIC OXIDATION TEST AT 825 F. FOR 24 HOURS Additive Neut. No. K.V. at 210, cs. Lead Example Composition Cone. Loss,

NO. (weight) mg.

percent) Initial Final Initial Final Base Oil A 1 0. 10 12. 8 8. 38 17. 85 200 33 Base Oil A plus Zn Complex of N,N-b1s (oleyl) 2.0 0. l0 3. 5 8. 80 9. 09 7.0

dithiooxamide. 34 dn 1.0 0.10 2.8 8. 55 9.27 15. 5 35 Base Oil A plus Zn Complex of N,N-bis (N-C 1. 0 0.70 3.0 8. 47 10. 92 4. 9

propyl amine) dithiooxamide. 36-- o 0.5 0. 5. 3 8. 43 11. 25 3. 5 37.. Base Oil A plus Co Complex of N,N'-b1s (dehy- 2.0 0.15 1.3 8.83 9. 36

droabietyl) dithiooxamide. 38 do 1. 0 0.15 3. 8 8. 59 10. 39 Base Oil A plus Ni Complex of N,N'-bls (dehy- 2. 0 0.35 3.8 8.87 10.61

droabietyl) dithiooxamide. 40 n 1. 0 0. 25 4. 5 8. 57 11. 28

1 See Table 1.

From a comparison of the initial and final neutralization numbers and initial and final K.V. values of the base oil alone and the base oils containing the metal complexes, it will be noted that these latter oil compositions exhibit both superior oxidation stability and more constant viscosity characteristics. In addition, it is noted that in the case where the base oil alone is employed, 200 mg. of metal are lost from the lead surface due to the corrosive action of the oxidation products formed in the oil. However, in the oil compositions of Examples 33-36 which contained the metal complexes, the formation of oxidation products is inhibited to such an extent that only from 3.5 to 16 mg. of metal are lost.

Although the present invention has been described by reference to certain preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention.

Having thus described the invention what it is desired to secure and claim by Letters Patent is:

1. A lubricating composition comprising a major proportion of a lubricating oil and a minor proportion sufiicient to improve the oxidation stability and viscosity index thereof of at least one oil soluble metal complex of an N,N-organo-di-substituted dithiooxamide wherein the organo radical is selected from the group consisting of organic radical contains sufiicient carbon atoms to render the N,N'-di-substituted dithiooxamido metal complex oilsoluble.

3. The lubricating composition of claim 2, wherein said organic radicals contain from 5 to about 30 carbon atoms.

4. The lubricating composition of claim 2, wherein the organic radical is a hydrocarbyl radical containing at least one member selected from the class consisting of hydroxy, amino, imino, alkoxy and carboxy groups.

5. The lubricating composition of claim 2, wherein the organic radical is an aliphatic radical.

6. The lubricating composition of claim 2, wherein the organic radical is a cycloalkyl radical.

7. The lubricating composition of claim 2, wherein the organic radical is an aralkyl radical.

8. The lubricating composition of claim 2, wherein the metal component of said metal complex is a Group II metal.

9. The lubricating composition of claim 2, wherein the metal component of said metal complex is a Group VIII metal.

10. The lubricating composition of claim 2, wherein the N,N-di-substitutcd dithiooxamido metal complex is present in an amount from about 0.001 to about 10% by weight.

11. The lubricating composition of claim 2, wherein the lubricating oil is a mineral oil.

12. The lubricating composition of claim 2, wherein the lubricating oil is a synthetic ester oil.

13. The lubricating composition of claim 2, wherein the lubricating oil is a synthetic hydrocarbon oil.

14. A lubricating oil composition comprising a major proportion of a lubricating oil and from about 0.001 to about 10% by weight of N,N-dioctadecyl dithiooxamido ZlIlC.

15. A lubricating oil composition comprising a major proportion of a lubricating oil and from about 0.001 to about 10% by weight of N,N'-dioleyl dithiooxamido zinc.

16. A lubricating oil composition comprising a major proportion of a lubricating oil and from about 0.001 to about 10% by weight of N,N'-bis(dehydroabietyl) dithiooxarnido cobalt.

17. A lubricating oil composition comprising. a major proportion of a lubricating oil and from about 0.001 to about 10% by weight of N,N-didodecyl dithiooxamido 20 cobalt.

18. A lubricating oil composition comprising a major .symmetrical-N,N'-hydrocarbyl radical and a symmetrical- N,N-substituted hydrocarbyl radical.

References Cited by the Examiner UNITED STATES PATENTS 4/1940 Reifi 25242.7 10/1949 Watson et al. 252--47 OTHER REFERENCES Martell et al., Chemistry of the Metal Chelate Compounds (1952), p. 503.

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner.

Claims (1)

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF A LUBRICATING OIL AND A MINOR PROPORTION SUFFICIENT TO IMPROVE THE OXIDATION STABILITY AND VISCOSITY INDEX THEREOF OF AT LEAST ONE OIL SOLUBLE METAL COMPLEX OF AN N,N''-ORGANO-DI-SUBSTITUTED DITHIOOXAMIDE WHEREIN THE ORGANO RADICAL IS SELECTED FROM THE GROUP CONSISTING OF HYDROCARBYL RADICALS AND SUBSTITUTED HYDROCARBYL RADICALS.