US2836561A - Lubricating oils - Google Patents

Description

United States 2,836,561 LUBRICATING OILS John Scotchford Elliott and Eric Descarnp Edwards, London, England, assignors to C. C. Wakefield & Company Limited, London, England, a British company No Drawing. Application May 9, 1955 Serial No. 507,147 Claims priority, application Great Britain May 17, 1954 7 Claims. (Cl. 252-316) This invention is for improvements in or relating to lubricating oils, and has particular reference to lubricating oils having extreme pressure properties, and to cutting oils and metal working oils.

A large number of organic compounds have been pro posed for use as extreme pressure agents, including various types of organic diand polysulphides, and the corresponding derivatives of selenium. While the higher polysulphides are very effective in increasing the film rupture strength of the oil in which they are dissolved, they tend to be inherently unstable, corrosive, especially to copper and cuprous materials, and to exert a pro-oxidant effect upon the oil.

The potential corrosiveness of a sulphur-bearing organic compound towards cuprous metals is dependent both on the chemical structure of the compound and on the temperature at which it is employed. Thus, in general, monosulphides are less corrosive than disulphides which, in turn, are less corrosive than the trior higher polysulphides; aromatic polysulphides, in which the sulphur is directly linked to aromatic nuclei, are less corrosive than the corresponding aliphatic compounds, while the corrosiveness of any particular sulphide group can be appreciably influenced by the presence of other neighbouring groups.

Generally speaking the effectiveness of sulphur-bearing organic compounds as extreme pressure additives for lubricating oils depends upon the ease with which they reak down, yielding sulphur which then reacts with the metal forming a sulphide film which prevents welding at high loads. Thus, for example, the triand tetrasulphides will provide reactive sulphur at lower temperatures than the corresponding disulphides, and consequently are more effective extreme pressure additives. Their corrosiveness to copper and cuprous metals, however, is a serious drawback, precluding their use in certain circumstances.

It is an object of the present invention to provide extreme pressure lubricants containing organic dior polysulphides, or their selenium analogues, which are normally corrosive to copper at 300 F. or below, in which the corrosiveness to copper or cuprous alloys is inhibited by the addition of a novel combination of inhibitors.

It has already been proposed in United States patent specification No. 2,414,257 to inhibit the copper staining tendencies of lubricants containing active sulphur by the addition of a minor proportion of a mercapto-arylene thiazole or a derivative thereof, or an alkyl thiuram monoor disulphide.

We have now found that the staining of copper and cuprous metals by lubricants containing organic diand polysulphides orv their selenium analogues can be inhibited to an outstanding and unexpected degree by the conjoint use of two additives of different types. These are: (a) a cyclic compound containing the group 'i3-SH as part of a ring structure or a derivative thereof capable of homolytic dissociation into free radicals aren't 0 N as part of a ring structure or a derivative thereof capable of homolytic dissociation into free radicals t (LS N and (b) a zinc, cadmium or iron salt of an organic dithiocarbamic acid.

More specifically additive (a) is a compound of general formula A-B in which A is a radical containing the group and B is a radical attached to the sulphur atom, of such nature that the compound AB dissociates homolytically at elevated temperatures yielding free radicals. Thus, B may be H, CH OH, -C(C H or it may be the same as A.

We have found that if B is a group, such as benzyl, butylaceto or dioctyl ammonium, which encourages heterolytic dissociation, the compound is relatively ineffective as an inhibitor of copper staining.

A preferred sub-class of inhibitors of this type are 2- mercaptobenzothiazole B l G and its derivatives such as benzothiazole disulphide, hydroxymethyl thiobenzothiazole and triphenyl methyl thiobenzothiazole, but the corresponding derivatives of other Z-mercaptothiazoles may be employed, for example, those having the general formula where R and R may be the same or different and represent hydrogen or hydrocarbon radicals, e. g., 2-mer capto-4-methyl-5-isopropyl thiazole. Examples of other types of additive containing the group l (J-SH as part of a ring structure are the Z-mercapto-oxazoles containing the group the Z-mercaptoimidazoles containing the group the Z-rnercaptothiazines containing the group or isomers thereof and the Z-mercaptothiazolines.containing the group It is to be understood that the foregoing examples are merely illustrative of the more readily available types of compounds falling within category (a), and the invention is not intended to be restricted to these types. Itis also to be understood that derivatives of these mercapto com- ,pounds may be employed, which dissociate homolytically yielding free radicals, e. g., the disulphides.

'e. g., 2-mercapto-4-methyl thiazole,Z-mercaptobenzoxazole and Z-mercaptobenzimidazole, have not. The latter two compounds, however, may be used in certain synthetic lubricants, e. g., di(2-ethyl hexyl) sebacate, if desired. Mineral oil-soluble compoundscontaining oxa zole and imidazole rings can, however, be obtainedby choosing suitable'alkyl or alkylated aromatic substituents. The most effective compounds appear to be those containing a benzo radical adjacent to, the heterocyclic nucleus.

Additive (b) is a metal salt of an organic 'dithiocarbamic acid having the general formula t /VNC-S M R2 7 z where R 'and R may be the same or different and repre-' sent preferably hydrocarbon'radicals although either R or R may be H, or' may together form part of a ring structure, M is zinc, cadmium or iron, and x is the valency of M. a

Specific examples of additives of this type are:

Zinc diethyl dithiocarbarnate Zinc di-n-butyl'dithiocarbamate Zinc di (methyl cyclopentamethylene) dithiocarbamate Cadmium di n-butyl dithiocarbamate Ferric di n-butyl dithiocar'bamate Zinc mono-octyl dithiocarbamate Cadmium pentamethylene dithiocarbamate Whereas the inhibitors ofgroup (a) are in themselves effective inhibitors of copper staining by active sul- .phur, the compounds of group (b) are of little or no value otherwise be possible. furthermore, it has been found 1 f that the more effective inhibit orsof group (a) when used aloneprotect the metal from-sulphur attack by forming face. a

The extreme: pressure additives employed in the lubri- 4 on the surface a'coarse yellowish-brown film of the copper complex which is capable of being removed by rubbing with consequent loss in Weight of the metal. By the conjoint use of the two types of additive, howeven'it is often possible to obtain a bright untarnished copper surcating compositions of the present invention contain the group Cs,..-se,,o l l\ where m is 0, 1, 2,3 or 4 and n is 0, l, 2 or 3 the sum of m and n being not less than 2 and not greater than 4, the carbon atoms being attached to other carbon atoms or to hydrogen or halogen atoms. a

More specifically these compounds may be simple or ganic di, tri or tetrasulphides, di'or tri-selenides or sulphoselenides. They may be aliphatic, aromatic or alicyclic compounds which may be unsubstituted or substituted by e. g., halogen atoms, nitro groups, hydroxyl groups or ester groups. Alternatively, they'may be cyclic compounds in which the sulphur and/0r selenium-containing groups form part 'of a ring structure.

Alternatively, the extreme pressure additives may be complex compounds or mixtures of compounds obtained, for example, by sulphurisinga wide variety of unsaturated organic compounds such as lard oil, sperm oil, oleine, tallow, 'wool fat or various terpene derivatives.

, The precise chemical structure of these compounds is not known with certainty. It'is known,'however, that when one or less than one molecular proportionof sulphur per olefinic linkage is employed in sulphurising an unsaturated organic compound, the'product'is generally non-corrosive towards copper at 300 F. or higher; it is believed that in such. materials the sulphur is presentas mono-sulphide linkages. When higher amounts of sulphur are used, however, products are obtained having varying degrees of chemical activity towards copper, depending upon the amount of sulphur used and tempertaure of sulphurizing; It is believed in these latter compounds diand polysulphide linkages exist which may form bridges between the molecules or be present in cyclic structures.

The amounts of the extreme pressure additives employed will depend upon the purpose for which the oil is to be used. Any quantity from the minimum sufficient to impart a substantial increase in film rupture strength up to about 10 percent maybe employed, but in general from about 0.5 percent to about 2.0 percent is contemplated, especially for use in turbine oils.

Specific examples of the extreme pressure additives employed in the present invention are:

Dibenzyl disulphide Dibenzyl trisulphide V I Di(3 carbomethoxy-4-hydroxyphenyl) polysulphides as described. in United States patent specification No.

, Sulphuri'zed sperm oil Di(n-butyl) dithiodiace tate Di(n-butyl) trithiodiacetate Di n-butyl tetrathiodiacetate Di n-butyl diselenodiacetate tetrathiacyclo-octane Halogenated derivatives of the foregoing may also be employed.

It will be understood that the present invention applies' I not only to lubricants containing a-dior polysulphide or.

selenium analogue as the sole extreme pressure additive,

but also to lubricants containingadditionally other addi tives known to confer extreme pressure properties such as organic halogenated compounds and organic phosphorus compounds. A large number of such compounds are known to the art. V 1 7 In one application of the present invention an extreme U pressure lubricant for the lubrication of hypoid gears comprises a mineral lubricating oil, an organic dior polysulphide compound (or selenium analogue) of the type hereinbefore described, and an organic halogenated compound e. g., a chlorinated paraflin wax, together with the two additives of types (a) and (b) to inhibit staining of copper and cuprous metals.

In another application of the invention a turbine oil having extreme pressure properties comprises a mineral lubricating oil and an extreme pressure additive of the type described in United States patent specification No. 2,691,000 having the general formula:

where R is an alkyl, aryl or cycloalkyl radical, X is sulphur or selenium and n is 2, 3 or 4 when X is sulphur, and 2 or 3 when X is selenium, together with additives of types (a) and (b) hereinbefore described, to inhibit staining of copper and cuprous metals. Mixed sulphoselenides conforming to the above general formula are included within the scope of the invention.

While the present invention is particularly concerned with lubricating compositions having a mineral lubricating oil base, it is also applicable to lubricants consisting wholly or predominantly of fatty oils, e. g., castor oil or rapeseed oil, and to synthetic lubricants such as dicarboxylic acid diesters, e. g., di(Z-ethyl hexyl) sebacate, and polyglycol ethers.

In carrying out the present invention, the organic dior polysulphide extreme pressure additive is present in sufiicient quantity to impart extreme pressure properties to the oil while the inhibitors may each be present in amounts ranging from about 0.01 to about 1.0 percent. In general the best results are obtained by the use of the two inhibitors in approximately equal amounts.

The present invention also includes an additive for use in a lubricating composition, containing as an extreme-pressure additive an organic dior polysulphide or their selenium analogues, to inhibit the copper or cuprous metal staining properties of the extreme-pressure additive, which additive comprises a mixture of (a) a cyclic compound containing the group N as part of a ring structure or a derivative thereof capable of homolytic dissociation into free radicals N and (b) a zinc, cadmium or iron salt of an organic dithiocarbamic acid.

The following examples are illustrative of compositions prepared in accordance with the present invention: EMMPLE I An extreme pressure hypoid rear axle lubricant, con forming to the Society of Automotive Engineers (S. A. E.)

classification grade 90, was prepared having the following approximate composition:

% conventionally refined Mid-Continent oil of viscosity about 700 seconds Redwood at F.

15.91% solvent refined mineral oil of viscosity seconds Redwood at 140 F.

8% chlorinated paraffin wax (approx. 40% chlorine) 0.5% di(3-carbomethoxy 4-hydroxyphenyl) polysulphides prepared as described in Example 4 of United States patent specification No. 2,388,047

0.25% di(3-carbomethoxy-4-hydroxyphenyl) thioether 0.14% Z-mercaptobenzothiazole 0.20% zinc di-n-butyl dithiocarbarnate EXAMPLE II A synthetic lubricant having extreme pressure properties consisting of di(2ethyl hexyl) sebacate, having dissolved therein:

1.0% di( 3-carbomethoxy-4-hydroxyphenyl) disulphide (prepared as described in Example 2 of United States patent specification No. 2,388,047

0.1% benzothiazole disulphide 0.1% zinc diethyl dithiocarbamate EXAMPLE III An extreme pressure turbine oil conforming to British Admiralty specification O. M. 100 was prepared, consisting of approximately:

75% of a mineral oil having a viscosity of about 170 seconds Redwood at 140 F.

25% of a solvent refined mineral oil having a viscosity of about 65 seconds Redwood at 140 F.

to which blend was added:

1.5% di-n-butyl trithiodiacetate 0.1% benzothiazole disulphide 0.1% zinc di-n-butyl dithiocarbamate 0.07% ethylene glycol mononaphthenate acid phthalate (ferrous metal corrosion inhibitor) 0.001% calcium petroleum sulphonate EXAMPLE IV A cutting oil was prepared consisting of:

40% conventionally refined naphthenic base oil of viscosity about 140 seconds Redwood at 140 F.

45% mineral oil of viscosity about 50 seconds Redwood at 140 F.

10% sulphurised olein 5% chlorinated paraffin wax (approx. 40% chlorine) to which blend was added:

0.1 Z-mercaptobenzothiazole 0.1% zinc di-n-butyl dithiocarbamate The sulphurised olein used in this example contained about 24% sulphur and Was prepared by heating olein with sulphur at a temperature of about 170 to 200 C.

for a period of about 40 minutes and then heating the product with further sulphur at a slightly lower temperature, e. g. to C. I

Table 1 Percentage Appearance of copper strips after of inhibitor Test No. Inhibitor ((1) Percent (b) (zinc di-n-butyl dithio- 3 hours 24 hours carbamate) None None Smooth black. Black, much flaking of copper sulphide. do 0.2 .do Black, considerable flaking. Benzothiazole disulphide 0.2 None Dullcopper.-. Dtrk glrlplwn, with surace .-..do 0.1 0.1 Bright copper- Light peacock stain.

Hydlroxymethylthiobenzothia- 0.2 None Light; brown. As No. 3.

zo e. 6 do 0.1 0.1 Light peacock Medium brown/peacock. 7 2-Mercapto-4,6,6 trimethyl-1,3,6 0.2 None Purple brown. Black, considerable flak- H thiazine. ing. 8 d0 D. 1 0.1 Light brown} Light brown with some peacock. dark patches.

7 Test results in this table illustrate the effect of adding zinc di-n-butyl dithiocarba'mate to a lubricating oil consisting of the same mineral oil blend as in Example 111, containing 1.5% di-n-butyl trithiodiacetate, to which various copperstain inhibitors of type (a) had been added.

The tests were carried out by immersing clean copper strips, polished with carborundum powder, in the oils contained in l" test-tubes. The test-tubes were placed in an oil bath which was maintained at the desired temperature in an oven. The oils were heated at 100 C. for 24 hours.

Table 2 Percentage Appearance of copper strips aiter of inhib- Test Inhibitor ((1) Percent itor (b) 7 No. (zinc di-ubutyl 3 hours 24 hours dithio' carbamate) 9 2-Mercapto-benzoxazole. 0. 2 None Patches 12f black, brown and Smooth black.

' peacoc 10 .do 0.1 0. 1 Bright, brassy with a little Light peacock.

light peacock stain. 11 2-1vIercapto-benzimidazole 0. 2 None Brown with black patches- AsNo. 9. 12 clo 0.1 0.1 As No. 10 As No.10.

In this table a typical synthetic lubricant, di(2-ethy-l hexyl) sebacate was employed, containing 1.5% di-nbut only those of zinc, cadmium and iron proved to be effective.

Table 4 Percent of Percent of Appearance oi copper after Test Sulphur or selenium benzotln'azinc No. compound Percent zole dibutyl disul dithio- 3 hours 24 hours phide carbamate 21 Dibenzyl trisulphi deuu 1. 5 None None Black, flaky Black, much flaking. 22 do. 1. 5 0. 2 None Light peacock Do. 23 1. 5 None 0. 2 Smooth black- Do. 24 1. 5 0. 1 0. 1 Bright copper- Smooth black. 25 1.0 None None Dark'brown Black, slightly flaky.

acetate.

1. 0 0. 2 None Greenish brown Dark brown, patchy. 1. 0 None 0. 2 Peacock Dark peacock. 1. 0 0.1 0.1 Bright copper Bright copper with brown patches. 29 4.7 dimethyl-4,7 di 1. 0 None None Very dark brown. Black, flaky.

(2dimethyl propyD- 1,2,5,6 tetrathia-cyclooctane. 30 1.0 0. 2 None Very light peacock- Do. 31 1. 0 None 0. 2 Brown Do. 32 1. 0 0.1 Bright copper Smooth black.

butyl trithiodiacetate, the temperature being 100 C. as

before. a e

The results in Table 4 illustrate the variety of organic diand polysulphides and their selenium analogues which Table 3 Percentage Appearance of copper after- 'lestv of ben- Inhibitor (1)) Percent No. zothiazole disulphide 3 hours 24 hours 1 None None Smoothblack Black, much flaking of copper sulphide. 3 0.2 -do Dull copper Dark brown with surface film. 13 0.1 do. Light brown Dark brown, dull with small black patches. 14 0.1 Zigc dimethyl dithiocar- 0.1 Bright copper..- Bright copper.

amate. 15 0.1 Zinc diethyl dlthiocarbam- 0.1 l0 Light brown with patch- 7 mate. 1 es of bright copper. 16 V 0.1 Cadmium dibutyl dithio- 0.1 .....(10 Almost bright copper.

carbamate. 17 0.1 Cadmium pentamethylene 0.1 do Brown/peacock.

dithiocarbamate. 18 0.1 Ferric dlbutyl dithiocar- 0.2 do Brightorange.

bamate. 19 0.1 Nickel dibutyl dithioear- 0.2 Dull copper Very dark brown with bamate. surface film. 20 0.1 Piperidine cyclopentameth- 0.1 Darkbrown,black Dark brown, blackllaky ylene dithiocarbamate. patches. patches. p

The results in Table -3 illustrate the efiect of adding may be inhibited by the combination of additives of the various dithiocarbamates to armineral oil blend as in 75 present invention. 7 r a The compounds were dissolved in the same mineral oil blend as used in Table 1, the test being of 24 hours duration at 100 C.

The compound used in tests 29 to 32 was prepared by treating diisobutylene (2 mols) in benzene solution with sulphur monochloride (1 mol) and reacting the product with alcoholic sodium disulphide to yield a product containing about 30% sulphur, consisting principally of the above compound.

3. The turbine oil of claim 1 in which said dithiocarbamate is cadmium di-n-butyl dithiocarbamate.

4. The turbine oil of claim 1 in which said dithiocarbamate is ferric di-n-butyl dithiocarbamate.

5. A lubricating composition comprising a lubricant base selected from the group consisting of mineral lubricating oil and a dicarboxylic acid diester lubricating oil and a minor proportion, sufficient to impart extremepressure properties to the lubricant, of a compound capa- T able 5 Percent of Percent of Test N o. Sulphur compound Percent 2-mercapzinc dibutyl Appearance of copper after tobenzodithiocar- 18 hours thiazole bamate 33 Di-tertiary butyl disulphide 2. None None Black, very flaky. 34 do 2. 0 0.2 None Darl: hbrown-black flaky pa 0 cs. 35 do 2. 0 0. 1 Orange with dull deposit. 36 Sulphurized sperm oil 5.0 None None Very dark brown, flaky. 5.0 0.2 None Do. 5. 0 None 0. 2 Do. 5. 0 0. 0.1 Brown/peacock, slightly flaky.

Table sets out the results of further tests which were ble of releasing reactive sulphur selected from the group carried out in the same base oil blend, but for 18 hours consisting of organic disulphides and polysulphides, to-

at 275 Fv gether with from 0.01 to 1.0 percent of an organic com- Table 6 Appearance of copper after- Test N 0. Oil Composition 3 hours 24 hours 40 Composition of ExampleI Bright gold Golden.

41 Composition of Example I Peacock, with dark Brown/peacock with without the zinc di-n-butyl spots. black spots. dithiocarbamate.

42 Composition of Example IV... Bright copper with Darkpeacock-smooth with dark spots. black 111 places.

43 Composition of Example IV Dark peacock Black, flaky.

without the zinc di-n-butyl dithiocarbamate, but with an extra 0.1% of 2-mercapt0benzothiazole.

It will be understood that the foregoing tests are designed to demonstrate the superiority of the miXed additives of types (a) and (b) as compared with either type used alone. At higher temperatures, or in the presence of more active sulphur compounds, it may be necessary to use more than the 0.1-0.2 percent of the additives quoted in the above examples, provided that compounds are selected having adequate solubility in the lubricating oil base. On the other hand, in other circumstances, e. g., to inhibit staining of copper at room temperature, quite small amounts of inhibitors, below 0.1 percent, may be sufiicient.

We claim:

1. A turbine oil comprising mineral oil containing from 0.5 to 2.0 percent of a compound selected from the group consisting of di(n-butyl) dithiodiacetate and di(nbutyl) trithiodiacetate, together with from 0.05 to 0.2 percent of benzothiazole disulphide and from 0.05 to 0.2 percent of an organic dithiocarbamate selected from the group consisting of zinc, cadmium and iron dithiocarbamates.

2. The turbine oil of claim 1 in which said dithiocarbamate is zinc di-n-butyl dithiocarbamate.

in which n is an integer from 2 to 4 inclusive.

7. The lubricating composition of claim 5 in which said derivative of said organic compound is benzothiazole disulphide.

References Cited in the file of this patent UNITED STATES PATENTS 2,211,798 Story et al Aug. 20, 1940 2,414,257 Evans et a1 Jan. 14, 1947 2,629,694 Woods et a1. Feb. 24, 1953 2,691,000 Elliott Oct. 5, 1954 2,713,558 Schmitz July 19, 1955

Claims (1)

1. A TURBINE OIL COMPRISING MINERAL OIL CONTAINING FROM 0.5 TO 2.0 PERCENT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DI(N-BUTYL) DITHIODIACETATE AND DI(N BUTYL) TRITHIODIACETATE, DISULPHIDE AND FROM 0.05 TO 0.2 PERCENT OFBENZOTHIAZOLE DISULPHIDE AND FROM 0.05 TO 0.2 PERCENT OF AN ORGANIC DITHIOCARBAMATE SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM AND IRON DITHIOCARBAMATES.