Lubricating oils

United States Patent Office _Patenled

2,897,152 LUBRICATING OILS John Scotchford Elliott and Eric Descamp Edwards, London, England, assignors to C· C· Wakefield & Company Limited, London, England, a British company No Drawing. Application March 4,1957 Serial No. 643,544

Claims priority, application Great Britain March 8,1956

Claims. (Cl. 252—47.5) to

This invention is for improvements in or relating _γlubricating oils and is particularly concerned with lubricating oils which are to be used under conditions which , tend to disrupt the lubricant film, which disruption more _tparticularly takes place when the pressure between the ‘ bearing surfaces is very great. There have already been provided lubricants which have a high load-carrying capacity. Such lubricants are generally known in the trade as “extreme pressure” lubricants. ,

A large number of organic compounds have been proposed for use as extreme pressure agents, including various types of organic di- and 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 on the oil. The disulphides, on the other hand, and other sulphur compounds containing relatively firmly-bound sulphur, though comparatively non-corrosive to copper, usually possess rather poor extreme pressure properties insufficient to warrant their use except in conjunction with other extreme pressure additives such as organic halogen compounds. Among this. class of compounds there have been disclosed as additives for lubricating oils various simple alkyl and aryl thiocarbonates and thiocarbamates.

It is a nobject of the present invention to provide lubricating compositions having extreme pressure properties containing additives which are considerably less corrosive to copper and cuprous materials than many known extreme pressure agents of comparable loadcarrying ability. .

It is a further object of the invention to provide lubricating compositions having improved resistance to oxidation and foam-forming.

It is yet a further object Of the invention to provide additives for turbine oils capable of increasing substantially their load-carrying capacity without at the same time increasing their tendency to oxodise or emulsify with water. .

Thus at the present time many oils used for turbine lubrication consist of specially selected mineral oil blends stabilised against oxidation by the incorporation of; antioxidant additives and containing also additives designed to protect ferrous metal parts against rusting or corrosion by, e.g. sea water. It is of course important that additional additives, incorporated in such oils for the purpose of enhancing their extreme pressure properties, should not interfere in any way with the normal functions of the two foregoing classes of additive. Many turbine oils, especially marine turbine oils used by the Admiralty, are controlled as regards oxidation stability, salt water corrosion of ferrous metals, demulsification value and corrosive action on cuprous metals, by a very rigid specification. It is necessary, therefore, that extreme pressure additives incorporated therein should not adversely affect compliance with its clauses.

Many of the more commonly employed extreme pressure additives are detrimental in one or more respects. Thus chlorine compounds generally tend to promote oxidation and are also prone to hydrolysis with the subsequent liberation of hydrochloric acid which accelerates rusting of ferrous metal parts.

Many sulphur compounds are also pro oxidant, and those which are without effect in this respect usually possess inadequate extreme pressure properties.

We have found a class of organic sulphur compounds which possess surprisingly effective extreme pressure properties and which at the same time have valuable antioxidant properties and foam-inhibiting properties, which are relatively inactive towards copper and cuprous metals and which do not increase ferrous metal corrosion or emulsification in the presence of water. . . =

According to the present invention there is provided a lubricating composition comprising a mineral lubricating oil base and a minor proportion of a compound having the formula:

¹ Ri S \r.^-S-R.COOR, where Ri and R_a are alkyl, aryl, cycloalkyl radicals or * may together form part of a ring structure, R is Ch₃,

R₍-C3H or

R,— A— Rs where R₄ and R₅ are hydrocarbon radicals, preferably CH₃, and R₃ is an alkyl, aryl or cycloalkyl radical.

It is necessary to select Rj, R₂ and R₃ so that the resulting product , is oil-soluble in the proportions in which it is to be employed. Preferably R is —CHy— and Ri, R₂ and R₃ are alkyl radicals, the sum of the carbon atoms in Ri, R₂ and R₃ being at least six.

If desired the radicals Ri, R₃ or R₃ may contain halogen substituents, but when the additives are to be employed in turbine oils, the presence of halogen is to be avoided. .

It would appear that the presence of ester groups situated in the alpha position to the dithiocarbamate group exerts an activating influence with the consequent production of extreme pressure properties substantially in excess of those obtainable by the use of the simple aliphatic or aromatic dithiocarbamates.

Examples of suitable compounds falling within , the above formula include:

n-Butyl (dimethyl dithiocarbamyl) acetate, n-Butyl (di-n-butyl dithiocarbamyl) acetate, n-Butyl (di-isopropyl dithiocarbamyl) acetate,

2,887,152 . 3

Isopropyl (di-n-butyl dithiocarbamyl) acetate, 2-ethyl hexyl (cyclopentamethylene dithiocarbamyl) acetate

S

CH_S N.C-S-CHj-C Ο Ο ΟΗ,ΟΗ.ΟΗ,ΟΗ,ΟΗ,ΟΗ, CHj—CHjc,H and n-butyl-α(-dimethyl dithiocarbamyl) isobutyrate

CH_S SCH·

N.C—S— O—COOCjHj

CJT₃ CH_S’

The additives of the present invention may be prepared by the reaction of α-chloro or α-bromo esters with alkali metal salts of dithiocarbamic acids.

The amounts of the 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 load-carrying capacity up to about 10 percent may be employed, but in general from about 0.5 percent to about 2.0 percent is contemplated, especially for use in turbine oils. When it is desired merely to impart antioxidant properties to an oil, smaller proportions of the additives may be employed, e.g. from 0.05 to 0.5. _ In a preferred form of the present invention the additives may be employed in steam turbine oils, especially in marine turbine oils.

The turbine oils to which the additives of the present invention may be added may contain additional anti- _ouoxidant additives which may be of the alkylated phenol at 140’ F. type, e.g. tertiary butyl cresol, 2:4 dimethyl-6-tertiary butyl phenol or 2:6 di-tertiary butyl-p-cresol, and will also normally contain anti-rusting additives which may be. of various types, one such class of additives being the 35 acid esters of the long chain mono-esters of polyhydric ' alcohols described in British patent specification No 643,025.

When the lubricants of the present invention are to be employed at relatively high temperatures it is desir- 40 able to include therein a copper-staining inhibitor. Thus there may be included in the lubricant a minor proportion of a mercapto-arylene-thiazole or a derivative thereof, or an alkyl thiuram disulphide, or an additive or combination of additives of the type disclosed in United States patent application Serial No. 507,147, ⁴¹now U.S. Patent No. 2,836,561. The copper-staining inhibitor is a cyclic compound capable of homolytic dissociation into free radicals

CH₃ and complying with British Admiralty Specifications OM. 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 was added—

1.5% n-butyl (dimethyl dithiocarbamyl) acetate 0.015% alkylated succinic acid type ferrous metal corrosion inhibitor

0.001% calcium petroleum sulphonate

EXAMPLE 2

A turbine oil having excellent oxidation resistance and resistance to corrosion of ferrous metals in the presence of salt water consisted of:

59% of a highly refined mineral oil having a viscosity of about 65 seconds Redwood at 140° F.

41% of a highly refined mineral oil having a viscosity of about 170 seconds Redwood at 140° F.

to which blend was added— (dimethyl dithiocarbamyl) acetate corrosion inhibitor ^x -~™1

0.001% calcium petroleum sulphonate ₃₀ This blend had a viscosity of about 85 seconds Redwood

0.1% n-butyl (dimethyl dithiocarbamyl) acetate

0.01% of an alkylated succinic acid type ferrous metal —c— c—s- A preferred subclass of inhibitors of this type are 2-mercaptobenzothiazole and its derivatives such as benzothiazole disulphide, hydroxy methyl thiobenzothiazole and 55 triphenyl methyl thiobenzothiazole, but the corresponding derivatives of other 2-mercaptothiazoles may be employed, all as disclosed in my aforementioned application Serial No. 507,147.

The additives of the present invention may, if desired, 60 be employed in conjunction with organic halogenated compounds in mineral lubricating oils to provide, for example, extreme pressure lubricants for hypoid gears. An example of a suitable organic halogenated compound is chlorinated paraffin wax which may be employed in an 65 amount from 1 to 15% by weight. Oils containing such combmations of additives are capable of withstanding higher loads than oils which contain only the sulphur compound. As already stated, however, the presence of halogen compounds in turbine oils is undesirable.

• Specific examples of lubricating compositions prepared in accordance with the present invention are:

EXAMPLE 1

EXAMPLE 3

An extreme pressure hypoid rear axle lubricant, conforming to the Society of Automotive Engineers (SAE) classification grade 140, had the following approximate·, composition:

75% conventionally-refined Mid-Continent oil of viscosity about 750 seconds Redwood at 140° F.

15% solvent refined mineral oil of viscosity 150 seconds Redwood at 140° F.

8% chlorinated paraffin wax (approx. 40% chlorine) 2% n-butyl (di-n-butyl dithiocarbamyl) acetate , r EXAMPLE 4

A turbine oil having enhanced load-carrying capacity good resistance to oxidation and corrosion of ferrous metals in presence of salt water, good resistance to foaming and improved resistance to the corrosion of copper 50 ^a°“,^cuP^rous metals at elevated temperatures, consisted of the composition of Example 1, to which was added— 0.1% benzothiazole disulphide 0.1% zinc di-n-butyl dithiocarbamate

The preparation of n-butyl (dimethyl dithiocarbamyl) acetate is illustrative of the general method of preparing the compounds of the present invention.

Preparation of n-butyl (dimethyl dithiocarbamyl) acetate . To absolution of 279 grams (1.85 mols) of n-butyl monochloracetate in an equal volume of alcohol was added very slowly with vigorous stirring at room temperature 940 mis. (2.3 mols) of 30.9% w./w. aqueous solution of sodium dimethyl dithiocarbamate expanded With an equal volume of alcohol. An exothermic reaction took place and sodium chloride separated together with a heavy oily liquid. The reaction was completed by warming the mixture to 70° C. Distilled water was now added to dissolve the sodium chloride, and the product, which crystallised on standing and scratching was filtered off.

The yield was 375 grams (87% of theoretical). M.P

A turbine oH having otanoed ioad-ettaing petotan ethel

Other esters prepared from the corresponding chloraceand sodium dithiocarbamates included:

Ethyl (dimfffbyl dithiocarbamyl) acetate, crystalline solid, M.P. 61° C.

Isopropyl (dimethyl dithiocarbamyl) acetate, solid (percent S, 28.6; theoretical, 28.9% )

Isobutyl (dimethyl dithiocarbamyl) acetate, crystalline solid , .,

Isopropyl (di-n-butyl dithiocarbamyl) acetate, low melting solid (percent N, 4.34; theoretical, 4.74) n-Butyl (di-n-butyl dithiocarbamyl) acetate, light amber liquid (percent S, 20.3; theoretical, 20.1) ,

2-ethyl hexyl (cyclopentamethylene dithiocarbamyl) acetate, amber oil (percent S, 16.0; theoretical, 19.3)

Phenyl (di-n-butyl dithiocarbamyl) acetate, brown oil (percent S, 18.2; theoretical, 18.9) n-Butyl «(dimethyl dithiocarbamyl) isobutyrate (percent

S, 21.8; theoretical, 24.3)

3,897,162 with a rubbing ratio of 3.4 to 1, loading being applied manually in increments of 5 lb. (scale reading) every 10 seconds until failure took place.

The additives were dissolved in a mineral oil blend such as “Oil B” which consisted of 80% of a solvent-refined mineral oil having a viscosity of about 150 seconds Redwood at 140° F. and 20% of a solvent-refined mineral oil having a viscosity of about 65 seconds Redwood at 140° F.

A very similar base oil, oil A, consisted of the two mineral oils described in Example 1 in 80:20 ratio. Oil A had a viscosity index of about 60 whereas oil B had a viscosity index of 95-100.

In certain blends marked with an asterisk an alkylated succinic acid type ferrous metal corrosion inhibitor was also present. . .

The results of load-carrying tests are summarized in Table 1.

TABLE 1

Test No.

Base on

Additives, present.

Percent sulphur provided by the additive

Four-hall machine tests

Load, Kg., at incipient seizure

Weld point, Kg.

Mean wear (mms) at

Mean Hertz load

100 Kg.

150 Kg.

SAESOD test failure load (lbs.)

I.— 2..-. 3—. 4—. 5-. 6—. 7—. 8—.

10.4. 11— 12-. 13—

A*

B*

B*

B B

B B

B B B* n-Butyl (dimethyl dithiocarbamyl) acetate (0.75%)----------------n-Butyl (dimethyl dlthiocarhamyl) acetate. (1.0%)-----------------n-Butyl (dimethyl dithiocarbamyl) acetate (1.5%)--—-..........ή-Butyl (dl-n-butyl dithiocarbamyl) acetate (2.0%)- -------.........

Isopropyl (di-n-hiityl dlthiocarhamyl) acetate (2 0%)---------------Phenvl (di-n-butyl dithiocarbamyl) acetate (2.15%)--—--2-ethyl hexyl (cyciopentamethylene dlthiocarhamyl) ^aaatate (²-⁵%> n-Butyl a (^tUyl dithiocarbamyl)..^------------β-Chloroethyl (di-n-hutyl dlthiocarhamyl)acetate (2.0%) ——S-n-hexyl di-n-butyl dithiocarbamate ti-92%)-----------------------S-n-hexyl di-n-butyl dithiocarbamate (1.2o%)----------------------Di-benzyl disulphide (1.0%)----------------------------------------Nil 0.20 0.26 0.39 0.40 0.40 0.40 0.40 0.36. 0.40 0.40 0.26 0.26

32/36 95/100 95/100

90/95 86/90 90/95

110

120 85/130 95/100 75/80 75/80 60/70

105

220

210

190

200/220

230

220

250

260

230

200

170

260

2.9

1.9

1.8

1.4

1.9

1.7

0.5

0.5 0.6 0.7 1.8

2.0

1.0

2.2

2.2

2.0

2.1

2.0

2.0

2.0

1.8

1.8

2.1

2.5

1.5

Ϊ30 ΪΪ0 Ϊ20

140

120

135

Tn an attempt to prepare β-chloroethyl (di-n-butyl di- thiocarbamyl) acetate from β-chloroethyl monochloracetate and sodium di-n-butyl dithiocarbamate, an amberoil was obtained containing 8.7% Cl (theoretical, 11.1%). This evidently consisted of a mixture of compounds, some of the terminal chlorine atoms having been replaced.

Of the foregoing compounds, the first three listed were not soluble to the extent of 1.0 percent m mineral oil blend A, as used in the majority of the tests herein de^sc^^e^m_Onstrate the effectiveness of the compounds used in the compositions of the present invention as extreme pressure agents, tests were carried out on the well Imown four-ball machine similar to that described by Boerlage in “Engineering,” 13th July 1933, volume 136, page 46 This apparatus comprised four steel balls arranged in the form of a pyramid. The top ball was held m a.chuck attached to a spindle rotating at approximately 1500 r p m. and pressed against the three bottom balls clamped in a stationary ball holder. The balls were immersed in the oil to be tested. Tests were normally run for one minute at a series of different loads, but in certain cases supplementary tests were carried out for a duration of ten seconds, the “Mean Hertz Load being calculated by the standard procedure described in U.S. Federal Specification W-L-791d Method 650.3 (1950) .

Certain tests were also carried out on the well known Society of Automotive Engineers (S.A.E.) Testing Machine described by Neely in the “Journal of the Society of Automotive Engineers,” volume 39, page 293 (193°)’ by a modified procedure known as the S.A.h.-b.u.u. test, described by McTurk in Wright Aeronautical Development Centre (W.A.D.C.) Technical Report 53-88, page , (1953), published by the U.S. Department of Commerce Office of Technical Services. In this test procedure, the S.A.E. machine was operated at 1000 r.p.m.

In Table 1 tests 2 to 10 summarize the load-carrying properties of a vairety of lubricating oils prepared in accordance with the present invention, from which it will be seen that in all cases the load-carrying capacity of the base oil (test 1) is greatly increased by the presence of organic dithiocarbamyl acetates. Tests 11 and 12, give comparative figures obtained with a simple conventional organic dithiocarbamate, while test 13 quotes similar figures for dibenzyl disulphide, a well known extreme pressure additive known to be among the most effective of the simple organic disulphides.

It Will be seen by comparing tests 2, 3, 12 and 13 that n-butyl (dimethyl dithiocarbamyl) acetate, which is. typical of the additives of the present invention, gave significantly better results on the four ball machine than both the conventional dithiocarbamates and dibenzyl disulphide, although the total amounts of added sulphur in the oils were identical in tests 3, 12 and 13 and less in test 2. In this connection it should be pointed out that the load at the point of incipient seizure and the mean Hertz load are generally believed to be the most significant of the four ball machine test results quoted.

By comparing test 11 with tests 4 to 10 (all about .40% added S) it will again be seen that the simple thiocarbamate ester was inferior to the compounds of the present invention.

When used in turbine oils, the organic dithiocarbamyl acetates not only do not adversely affect the properties of such oils but confer valuable antioxidant and antifoaming properties, thus rendering unnecessary the addi' tion of specific antioxidant and antifoaming additives.

If special load-carrying properties are not required, quite small amounts of the dithiocarbamyl acetates are sufficient to confer a degree of oxidation and foaming stability.

2,897,153

TABLE 2 ' Test . No.

14.

is.

16.

17.

18.

19.

20.

Additive

None_____________________________ n-Butyl (dimethyl dithiocarbamyl) acetate (1.5%) n-Butyl (dlmethyldithiocarbamyl) acetate (0.75%) n-Butyl (dimethyldithiocarbamyl) acetate (0.1%) n-Butyl (di-n-butyl dlthiocarbamyl) acetate (2.0%) n-Butyl (dimethyl dithiocarbamyl) acetate (1.0%),

Benzothiazole disulphide (0.1%).

As test 19+0.1% zinc di-n-butyl dithiocarbamate____

<td></td><td rowspan="2"> Acidity (milligrams KOH per gram)</td><td></td><td colspan="2"> Oxidation test</td><td></td><td colspan="2"> Foaming test (75° F.) ·</td>

<td> Base oil</td><td> Demulsification value</td><td> Acidity after oxidation (mgs. KOH per gram)</td><td> Demulsification value after oxidation</td><td> Salt water corrosion . test</td><td> Tendency (mis.)</td><td> Stability (mis.)</td>

<td> A*</td><td> 0.06</td><td></td><td rowspan="3"> Failed, u oxidant 0.11 0 11</td><td rowspan="2"> Hess antipresent.</td><td rowspan="2"> No rusting. _</td><td rowspan="5"> 490 10 Nil 110</td><td rowspan="5"> Nil (8 mins). Nil (10 secs). Nil. Nil (2 mins.).</td>

<td> A*</td><td> 0.06</td><td></td>

<td> B*</td><td> 0.06</td><td></td><td rowspan="2"> 630</td><td rowspan="2"> ——do_______</td>

<td> A·</td><td> 0.06</td><td></td><td> 0.22</td>

<td> A·</td><td></td><td></td><td> 0.08</td><td> 240</td><td></td>

<td> B*</td><td> 0.08</td><td> 150</td><td> 0.17</td><td> 600</td><td> -----do_______</td><td> 30</td><td> Nil-(1.5 mins,).</td>

<td> ’·</td><td> 0.22</td><td> 240 j</td><td> 0.11</td><td> 360</td><td> -----do_______</td><td> 400</td><td> Nil (6 mins.).</td>

Table 2 illustrates the effect of the additives on typi- temperatures, a selection of the results he-ing given in cal turbine oils containing rust inhibitors which, with the 20 Table 3.

TABLE 3

[Tests recorded in this table were 24 hours duration, the base oil used throughout being oil B*J

<td rowspan="2"> Test No.</td><td rowspan="2"> Additives present</td><td colspan="5"> Appearance of copper strips at— i . ..</td>

<td> 100° 0.</td><td> 110° 0.</td><td> 120° C.</td><td> 130° O.</td><td> 140° σ.</td>

<td> 21_____ 22—</td><td> n-Butyl (dimethyl dithiocarbamyl) acetate (0.75%). As test No. 214-0.1% benzothiazole</td><td> Light brown/peacock stain.</td><td> Dark peacock/ magenta.</td><td rowspan="2"> Dark peacock brown; 10% black. Orange brown powdery deposit. Patch of yellow deposit.</td><td> Dark brownblack patch.</td><td> Dark peacock, black at one end. ---------</td>

<td> 23—</td><td> disulphide. As test No. 22+0.1% zinc di-n-butyl dithiocarbamate.</td><td> Reddish brassy stain.</td><td> Light golden brown.</td><td> Light peacock with powdery light brown deposit.</td><td> Powdery light-------- brown deposit.</td>

There was no stain of the copper the absence of copper deactivators.

at 100° O. by n-butyl (dimethyl dlthiocarbamyl) acetate In concentrations up to at least 1.5%, in addition of a suitable antioxidant, would comply with British Admiralty Specification O.M. 100.

In test 17 the foaming test was carried out using as base oil the higher viscosity component of oil A without rust inhibitors.

The methods employed for determining the various values quoted above were standard methods described in “Standard Methods for Testing Petroleum and its Products,” and having the following references:

Acidity I.P. 1/53 Method A (page 12, 1943 edition) Demulsification value I.P. 19/51 (page 117, 1951 edition) Oxidation test I.P. 114/53 P (page 395, 1953 edition) Salt water corrosion test I.P. 135/51 (page 390, 1951 edition) (modified to comply with O.M. 100 specification) Foaming stability I.P. 146/55 T (page 266, 1956 edition) (sequence 1 only quoted in the above table)

It will be seen from Table 2 that dithiocarbamyl acetates function effectively as antioxidants even in quite low concentrations, thus enabling turbine oils to satisfy the oxidation requirements of O.M. 100 specification (0.20 mg. KOH per gram maximum after oxidation test) without the addition of any other oxidation inhibitors

By comparing tests 15 to 17 and 19 with test 14, it will be seen that they also function effectively as inhibitors of foaming. In test 20, the presence of zinc di-n-butyl dithiocarbamate evidently interfered with this effect.

Other properties of the oils, such as acidity, demulsification value and salt-water corrosion resistance were unaffected by the addition of the dithiocarbamylacetates.

In order to determine the effect of the lubricating oils of the present invention on copper at various temperatures, a series of tests were carried out in which strips of clean electrolytic quality copper foil 2 inches long and inch wide were immersed in the oils in test tubes and heated in an oven for various periods of time at different

From Table 3 it will be seen that n-butyl (dimethyl dithiocarbamyl) acetate, which is typical of the additives of the present invention, is very mild in its action towards copper at temperatures of the order of 100 to 110° C. such as are encountered in steam turbines. Further improvement, particularly at the higher temperatures, may be obtained by including benzothiazole disulphide or a combination of this compound with zinc di-n-butyl dithiocarbamate.

A turbine oil complying with British Admiralty Specification O.M. 100 and consisting of base oil B containing 1.0% n-butyl (dimethyl dithiocarbamyl) acetate together with rust inhibitors as in Example 1 and copper deactivators as in Example 4 was subjected to a test on the well known Institution of Automobile Engineers (I.A.E.) 314'' Centres Gear Machine described by Mansion in the Journal of the Institute of Petroleum, volume 38, page 633 (1952). This machine was operated at 4000 r.p.m. using En. 34 gears, with an oil temperature of 70° C. The average failure load was 93 lbs;, a typical O.M. 100 turbine oil without load-carrying additive failing at 29 lbs.

To illustrate the use of dithiocarbamyl acetates in extreme pressure lubricants suitable for hypoid gears, the composition of Example 3 was tested on the four’ball machine (standard one minute run), the weld-point being 490-500 kg. and the mean wear scar diameter at 100, 200, 300 and 400 kg. load being respectively 0.5 1.2 1.7 and 2.3 mms.

A commercially available hypoid gear oil having approximately the same viscosity and complying with U.S. Army Specification MIL-L-2105 welded at 400 kg., the mean wear scar diameter at 100, 200 and 300 kg. load being respectively 0.4, 1.5 and 2.0 mms. '