EP0695291A1

EP0695291A1 - Bismuth dithiocarbamates and their use as additive for lubricants

Info

Publication number: EP0695291A1
Application number: EP94913165A
Authority: EP
Inventors: Bernard 8 Spring Vale Tury
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1993-04-20
Filing date: 1994-04-20
Publication date: 1996-02-07
Also published as: AU6541994A; CA2160669A1; WO1994024100A1; JPH08508993A

Abstract

Certain bismuth tris-(di-organic substituted dithiocarbamate) salts are useful as extreme pressure (EP) additives in oils and greases. The bismuth compounds have EP properties which are as good as or better than those of the corresponding analogous antimony compounds which have previously been suggested and used as EP additives in lubricants. Some of the bismuth compounds, particularly where the substitution includes C6 alkyl or longer, or branched alkyl groups, are novel compounds.

Description

Bismuth d1th1ocarbamates and their use as additive for lubricants

This invention relates to organic bismuth compounds and their use as extreme pressure lubricant additives in oils and greases.

In some types of gears and particularly heavily loaded bearings where both high pressure and high rubbing velocities are present, it is difficult to maintain a thin film of lubricant between the gear or bearing surfaces. When this thin film breaks, the mating metal surfaces become susceptible to increased wear. This is particularly marked in bearings where the mating metal surfaces can weld together. When the weld shears under the relative motion of the surfaces, particles of metal are removed which further damage the metal surfaces of the gears and bearings and can seriously impairing performance.

In order to overcome such problems, special compounds have been developed as extreme pressure (commonly referred to as EP) additives for lubricant oils and greases. Thus, US 3139405 discloses the use of antimony salts of dialkyldithiocarbamic acids as EP additives, especially antimony dipentyl- and dihexyl- dithiocarbamates. This patent states that these two compounds impart "amazingly high load- bearing capacity" to lubricants and this is stated to be surprising and unexpected since various other metallic salts of dialkyldithio¬ carbamic acids tested alongside the antimony compounds impart only moderate or low load bearing capacities to lubricants or are ineffective e.g. by being insoluble. These other compounds include two short chain linear alkyl, di-butyl and di-amyl (di-n_-pentyl) , bismuth tris-dialkyldithiocarbamates. The antimony compounds described in US 3139405 have been successfully used as EP additives for many years and are commercially available e.g. under the trade name Vanlube 73. However, none of the antimony dialkyldithio- carbamates is ideal; some exhibit low solubility and/or poor stability in typical lubricant systems and, furthermore, antimony salts are toxic and can cause health and environmental problems.

In contrast to the teaching of US 3139405 we have now found that certain bismuth salts of dialkyldithiocarbamic acids are useful as EP additives for lubricants, such as oils and greases. Some of these bismuth compounds give superior results as EP additives and/or better compatibility and/or stability in the lubricant as compared with their antimony analogues.

Accordingly, the present invention provides a compound of the formula (I) :

[ Ri.R² - N - C(S) - S - ]₃ Bi (I)

where each R¹ and R² is, independently, Cι_i2 alkyl, C₇_i2 aralkyl optionally substituted by C*L_I2 alkyl, cyclohexyl optionally substituted by C]__i2 alkyl; or

R*¹- and R² together with the nitrogen atom to which they are attached form a heterocyclic ring optionally substituted by Cι_-j_2 alkyl, with the proviso that R¹ and R² are not both ethyl, n-butyl or ti-pentyl.

Preferably, R¹ is C^*j__i2 alkyl, C₇_i2 aralkyl optionally substituted by Cι_i2 alkyl or cyclohexyl optionally substituted by Cι_-j_2 alkyl; and R² is C6_i2 alkyl, 07.12 aralkyl optionally substituted by C1.12 alkyl, cyclohexyl optionally substituted by C-j__i2 alkyl, isopropyl, isobutyl, tertiary butyl or branched pentyl.

When R¹ or R² represents or includes alkyl, the alkyl group may be linear or branched. Examples of alkyl are methyl, ethyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, 1-methyl- pentyl, 2-ethylbutyl, 2-ethylhexyl and 1-methylhexyl.

When Rl or R² is aralkyl it is preferably benzyl or phenylethyl, optionally substituted in the phenyl ring by C-*__i2 alkyl. The phenyl ring may contain more than one alkyl group, but preferably carries one alkyl group which is preferably present in the 4-position. An example of an alkyl substituted aralkyl group is 4-methylbenzyl.

When R¹ or R² is alkyl substituted cyclohexyl, the cyclohexyl ring may contain more than one alkyl substituent. However, when substituted by alkyl, it is preferably a singly alkyl substituent, which is preferably in the 4-position. Examples of such substituted cyclohexyl groups are 4-methylcyclohexyl, 4-propylcyclohexyl, 4-butyl- cyclohexyl, 4-isopropylcyclohexyl, 4-tertiary butylcyclohexyl and 4-nonylcyclohexyl. When R¹ and R² together with the nitrogen atom to which they are attached form a heterocyclic ring, the ring preferably contains 6 atoms as in morpholino, piperazino or piperidino. Where the ring is piperazino, both nitrogen atoms may carry a dithiocarbamyl radical whereby there is the possibility that the resulting bismuth salt is polymeric. However, it is preferred that one of the nitrogen atoms of the piperazino ring is substituted by Cι_**_2 alkyl, especially Cι_β alkyl and more especially 0-^. alkyl.

When R¹ or R² is alkyl substituted aralkyl or cyclohexyl or R¹ and R² together with the nitrogen atom to which they are attached form an N-alkyl piperazino ring, the alkyl group is preferably C-^.β alkyl, and especially C . alkyl and may be linear or branched.

It is preferred that R¹ and R² are both linear or branched Cι_i2 alkyl, and it is especially preferred that at least one of R¹ and R² is, or contains, branched alkyl since such compounds are easier to formulate and dissolve in oils and greases than when R¹ and R² are both linear alkyl. Generally, we have obtained good results when R¹ or R² and desirably R¹ and R² are not both linear short chain (C*L_5) alkyl groups and this forms a particular aspect of the invention. R¹ and R² can be mixed groups, particularly of groups of the same carbon chain length e.g. mixed pentyl groups.

Although R¹ and R² may be different, they are preferably the same because of the greater availability of symmetrical secondary amines from which the dialkyldithiocarbamic acids are conveniently derivable. In this context, 'symmetrical secondary amines' include amines made with mixed alkyl groups, especially of the same chain length as in secondary (mixed pentyl) amine.

The bismuth salts may be made from the single dialkyldithio¬ carbamic acid or may be made from a mixture of such acids. When the bismuth salt is made from a mixture of dialkyldithiocarbamic acids the three dialkyldithiocarbamic acid radicals in formula (I) are not the same. In certain circumstances it is beneficial to use a mixture of acids since compatibility of the EP additive in a lubricant system such as an oil or grease can be increased.

The dialkyldithiocarbamic acids can be made by methods known in the art. However, since some dialkyldithiocarbamic acids are unstable, they are generally made as a salt which exhibits greater stability. The salt may be formed with an amine or an alkali metal. In one preferred method, the salt is formed with an amine and is typically made by reacting an excess of a secondary amine of the formula R-*-R²NH with carbon disulphide in an appropriate organic solvent. The amount of amine used is preferably, 10 moles, more preferably 5 moles and especially 2 moles per mole of carbon disulphide. Such a method is described for example in Mέm. services Chim 6tat, (Paris), 34., 411-12 (1948). Preferred solvents are inert to the reactants and include ketones such as acetone. The reaction is facile and is generally carried out at temperatures below 60°C, preferably below 20°C and especially below 10°C. In another preferred method, stoichiometric amounts of the amine and carbon disulphide are reacted together, and the dialkyldithiocarbamic acid then converted to a salt, e.g. an alkali metal salt, by addition of a base, e.g. an alkali metal hydroxide.

The bismuth salts of this invention are preferably made by reacting the appropriate dialkyldithiocarbamic acid with a suitable bismuth halide such as bismuth trichloride in the presence of a suitable organic reaction medium. Generally, 1 mole of bismuth halide is used with about three moles of the dithiocarbamic acid. The organic reaction medium is desirably chosen to be a solvent for the dialkyldithiocarbamic acid and a non-solvent (or a poor solvent) for the bismuth salt to ease separation of the bismuth salt from the reaction mixture. However, if a volatile organic reaction medium is used differential solubility of the bismuth salt is less important as the solvent can be removed by evaporation and the bismuth salt purified in conventional manner, for example, by recrystallisation. Suitable solvents for the reaction of the bismuth trihalide with the dialkyldithiocarbamic acid are aliphatic hydrocarbons and chloro- hydrocarbons and, especially, ketones such as acetone. The reaction is typically carried out at temperatures below 120°C, preferably below 100°C and especially below 60°C. Where appropriate, the reaction may be carried out in a solvent at reflux.

The bismuth salts of this invention are typically pale yellow solids melting below 100°C if derived from dialkyldithiocarbamic acids^ containing linear alkyl groups, but they can be oily liquids if derived from a dialkyldithiocarbamic acid containing branched alkyl groups.

Particularly good EP properties in oils and greases have been obtained with bismuth tris-[bis-(2-ethylhexyl)dithiocarbamate] , bismuth tris-(dihexyldithiocarbamate) and bismuth tris-[di(branched pentyl)dithiocarbamate] .

As described above, the bismuth salts of this invention exhibit useful properties as EP additives in lubricating oils and greases. Some also exhibit useful antioxidant properties and superior stability to the antimony analogues, especially against light.

Thus, in a further aspect, the invention provides a composition comprising a bismuth salt of the formula I and a lubricant. The lubricant is preferably an oil or a grease.

In a further aspect, the invention provides a composition comprising a grease and compound of the formula (la):

[ Rl.R² - N - C(S) - S - ]₃ Bi (la)

where each R¹ and R² is, independently, Cι_i2 alkyl, C₇_i2 aralkyl optionally substituted by alkyl, cyclohexyl optionally substituted by C*^*__i2 alkyl; or

R¹ and R² together with the nitrogen atom to which they are attached form a heterocyclic ring optionally substituted by C-^*__i2 alkyl.

In a still further aspect, the invention provides a composition comprising an oil and a compound of the formula (lb):

[ Rl.R² - N - C(S) - S - ]₃ Bi (lb)

where each R¹ and R² is, independently, C-*__i2 alkyl, C₇_i2 aralkyl optionally substituted by C-]__-*_2 alkyl, cyclohexyl optionally substituted by C-^*__i2 alkyl; or R¹ and R² together with the nitrogen atom to which they are attached form a heterocyclic ring optionally substituted by C-j__i2 alkyl, with the proviso that when R¹ and R² are either both n-pentyl or ri-butyl the oil is not a SAE 90, high viscosity index, mineral oil having a viscosity of 87 seconds Saybolt viscosity at 210°F (equivalent to about 17 cSt at 100°C) and 1030 seconds Saybolt viscosity at 100°F (equivalent to about 190 cSt at 40°C).

One preferred class of oils are gear or engines oils having a viscosity above about 200 cSt at 40°C, more preferably above 300 and especially above 400 cSt at 40°C. Such oils preferably have a viscosity below 1500 cSt at 40°C and especially below 1000 cSt at 40°C.

Another preferred class of oils are lighter gear or engine oils having a viscosity below 180, more preferably below 150 and especially below 100 cSt at 40°C. Such oils preferably have a viscosity above 10 and especially above 20 cSt at 40°C.

The bismuth salt is typically used at a concentration of at least 0.01Z, preferably at least 0.1Z, more preferably at least 0.5Z, and especially at least 2Z by weight, based on the total weight of the lubricant. The bismuth salt may be present at a concentration up to 10Z, preferably up to 8Z, more preferably up to 6Z and especially up to 5Z by weight, based on the total weight of the lubricant.

The term oil includes oils such as those described in standard texts on lubrication such as "Schmiermittel-Taschenbuch" by Schewe- Kobak, (Huethig Verlang, Heidelburg, 1974) and in "Schmierstoffe and Verwandte Produkte" by D Klamann, (Verlage Chemie, Weinheim, 1982) and also those described in US 3139405.

The oil is preferably a mineral oil or a synthetic oil or a mixture of such oils. Examples of synthetic oils include polyalkylene glycols; poly(alpha-olefins) ; esters, especially phthalates; perfluoroalkylethers and silicones.

Preferred lubricants are industrial oils especially gear and hydraulic oils.

The oil may contain other additives which are generally incorporated in fluid lubricant, such as metal passivating agents, viscosity index improvers, pour point depressants, dispersing agents, ^• detergents, and other additives providing protection against wear, extreme pressure, corrosion, rusting and oxidation.

The grease is preferably a mineral or synthetic oil as described above which has been thickened by the addition of a gelling agent. The gelling agents may be a soap, such as a lithium soap, a lithium complex soap, a non-soap gelling agent such as a clay, a carbon black, a silica or a polyurea which is preferably incorporated into the oil in finely divided form. The clay is preferably surface coated with an organic material to aid dispersion in the oil, such as a quaternary ammonium compound. Where the grease is based on a silicone oil, the non-soap gelling agent is preferably silica, especially fused silica having an average particle diameter below one μm.

Metals which benefit from protection by the bismuth salt include iron and copper and especially alloys such as steel and brass. As disclosed above, bismuth salts of the formulae (I), (la) and (lb) has been found particularly effect as an EP additive in a lubricant where the metals are in frictional contact and form part of a gear or bearing.

Accordingly in a further aspect, the invention provides the use of a compound of one of the formula (I), (la) and (lb) as an EP additive for a lubricant, especially an oil or a grease.

In a yet further aspect, the invention provides a metal surface, particularly a gear and especially a bearing which is treated with a bismuth salt of one of the formula (I), (la) and (lb) or a lubricant composition containing a bismuth salt of one of the formula (I), (la) and (lb).

The invention further includes a method of lubricating one or more surfaces, especially of mating metal surfaces, which comprises including in a lubricant, particularly a lubricating oil or grease, for the one or more surfaces a bismuth salt of one of the formula (I), (la) and (lb), particularly in an amount of from 0.1 to 10Z by weight of the lubricant. The invention is further illustrated in the following examples in which all parts are by weight unless stated to the contrary.

Materials

BDAC bismuth tris-(di-ιι-pentyldithiocarbamate) made in Comparative

Synthesis Example C.

BDAC (mixed) is bismuth tris-[di-(mixed pentyl isomers)dithio- carbamate] made in Synthesis Example 3.

BDHC is bismuth tris-(dihexyldithiocarbamate) made in synthesis

Example 1

BDHC is bismuth tris-(dihexyldithiocarbamate)

BDEHC is bismuth tris-[di-(2-ethylhexyl)dithiocarbamate]

ADHC is antimony tris-(dihexyldithiocarbamate) made in Comparative

Synthesis Example A.

ADAC is antimony tris-(dipentyldithiocarbamate) made in Comparative

Synthesis Example B

ADAC (mixed) is antimony tris-[di-(mixed pentyl isomers) dithiocarbamate] made in Comparative Synthesis Example D

Vanlube 73 is a commercially available antimony tris-(dialkyldithio- carbamate) EP additive from Vanderbilt Company, New York USA.

Synthesis Example 1

Bismuth tris-(dihexyldithiocarbamate)

a) dihexyldithiocarbamic acid dihexylamine salt

Carbon disulphide (13 g; 0.17 mol) dissolved in acetone (75 ml) was slowly added over 20 minutes, with stirring to a solution of dihexylamine (63.02 g; 0.34 mol) in acetone (75 ml) keeping the temperature below 5°C. The acetone solution (193.8 g) was stirred for a further 30 minutes and was used directly in the preparation of the bismuth salt described below without isolation of the acid.

b) bismuth tris-(dihexyldithiocarbamate) (BDHC)

The solution of dihexyldithiocarbamic acid salt in acetone (96.9 g) was stirred with anhydrous bismuth trichloride (7.89 g; 0.025 mol), and then heated to reflux at 56°C for about 30 minutes. The product separated as a yellow solid. Most of the acetone was removed by distillation to leave the product as a yellow slurry. Water (250 ml) was added and the solid filtered off, washed with water (200 ml) followed by methanol (100 ml). The product was finally recrystallised from ethanol. Yield: 20.76 g (74Z of theory); mp 79.8 - 80.4°C.

Elemental analysis:- Theory 47.3ZC; 7.9ZH; 4.2ZN, 19.4ZS; 21.1ZBi

Found 47.3ZC; 7.9ZH; 4.2ZN; 18.8ZS; 20.5ZBi

Comparative Synthesis Example A

Antimony tris-(dihexyldithiocarbamate) (ADHC)

The preparation of Synthesis Example 1(b) was repeated, but substituting antimony trichloride (5.63 g; 0.025 mol) for the bismuth trichloride. The antimony salt was obtained as a pale yellow crystalline solid. Yield: 15.84 g (62Z theory); mp 69.6 - 71.2°C.

Elemental analysis:- Theory 51.9ZC; 8.7ZH; 4.7ZN; 21.3ZS; 13.5ZSb

Found 52.0ZC; 8.3ZH; 4.7ZN; 20.4ZS; 13.5ZSb

Synthesis Example 2

Bismuth tris-[di-(mixed pentyl isomers) dithiocarbamate] (BDAC mixed)

Synthesis Example 1 was repeated, but substituting dipentylamine based on mixed pentyl isomers containing about 80Z branched pentyl groups (53.5 g; 0.34 mol; from Aldrich Chemicals) for the dihexylamine used in Synthesis Example 1. The bismuth tris-[di(mixed pentyl isomers) dithiocarbamate] was obtained as yellow solution in acetone. The product was recovered by distilling off the acetone and washing with methanol (4 x 200 ml) to remove excess amine. The methanol, which formed an upper layer, was decanted and the residual oily product dissolved in methylene chloride. This was washed with a water/methanol mixture (80:20) (4 x 40 ml). The methylene chloride solution was then dried over anhydrous sodium sulphate, screened and the methylene chloride evaporated to give the title product as a yellow oily liquid which slowly solidified on standing to yield a waxy solid.

Yield: 12.5 g (55.3Z of theory).

Elemental analysis:- Theory 3.7ZC; 7.3ZH; 4.6ZN; 21.2ZS;

Found 43.6ZC; 7.1ZH; 4.5ZN; 19.3ZS

Synthesis Example 3

Bismuth tris-[di-(2-ethylhexyl)dithiocarbamate] (BDEHC) Synthesis Example 2 was repeated, but substituting di-2-ethylhexylamine (25 g; 0.34 mol) for the mixed isomer dipentylamine used in Synthesis Example 2. The bismuth tris- (di-2-ethylhexyldithiocarbamate) was obtained as a yellow solution in acetone. The product was recovered by distilling off the acetone. Methanol (200 ml) was added and the mixture cooled to 0°C. The upper solution was decanted off and the product washed further with methanol (3 x 100 ml). A check of the decanted solution on the last washing indicated the absence of further amine. The residual oily product dissolved in methylene chloride, washed three times with water/ methanol mixture (80:20) (total volume 100 ml), dried over anhydrous sodium sulphate, filtered and the methylene chloride evaporated to give the title product as an orange oily liquid. Yield: 20.2 g (70Z of theory).

Comparative Synthesis Example B

Antimony tris-(di-rι-pentyldithiocarbamate) (ADAC)

Di-n-pentyldithiocarbamic acid salt was prepared as described in Example 1(a), but substituting di-n-pentylamine (53.5 g; 0.34 mol; from Aldrich Chemicals) for the dihexylamine.

The antimony salt was prepared by the method described in comparative Example A, but substituting di-n-pentyldithiocarbamic acid for the dihexyldithiocarbamic acid. The title product was obtained as a pale yellow solid. Yield : 13 . 7 g ( 67Z of theory ) ; mp 70.2 - 71.0°C .

Elemental Analysis:- Theory 48.4ZC; 8.1ZH; 5.1ZN; 23.5ZS; 14.9ZSb

Found 48.7ZC; 8.3ZH; 5.1ZN; 23.1ZS; 14.4ZSb

Comparative Synthesis Example C

Bismuth tris-(di-n-pentyldithiocarbamate) (BDAC)

The title compound was made by the method described in Example 1(a) and (b), but substituting di-n_,-pentylamine (53.5 g; 0.34 mol; from Aldrich Chemicals) for the dihexylamine. The product was obtained as a yellow solid. Yield: 16.2 g (71Z of theory); mp 69 - 70°C.

Elemental Analysis:- Theory 43.7ZC; 7.3ZH; 4.6ZN; 21.2ZS; 23.1ZB1

Found 44.2ZC; 7.5ZH; 4.6ZN; 21.3ZS; 22.7ZB1

Comparative Synthesis Example D

Antimony tris-[di-(mixed pentyl isomers) dithiocarbamate] (ADAC mixed) Example 3 was repeated, but substituting antimony trichloride for bismuth trichloride as described in Comparative Example A. The product was isolated as a yellow oily liquid. Yield: 12.96 g (63.3Z of theory).

Elemental Analysis:- Theory 48.3ZC; 8.1ZH; 5.1ZN; 23.4ZS

Found 48.8ZC; 7.9ZH; 5.1ZN; 22.6ZS

Application Example 1

Various bismuth tris-(dithiocarbamates) , and certain antimony tris-(dithiocarbamates) as controls, were added to samples of a highly refined neutral petroleum based base oil having a viscosity of approximately lOOcSt at 40°C to give an additive concentration of 0.0035 mol. (100 g oil)^-1. These samples were subjected to a four ball test according to British Institute of Petroleum test IP 239 and the load at which welding occurred was measured. A control containing no ^• EP additive was included. The additives, concentrations and welding loads are set out in Table 1 below.

The results show that the bismuth tris-(dialkyldithiocarbamates) are effective EP additives in the petroleum based oil.

Application Example 2

Various antimony and bismuth tris-(dithiocarbamates) were evaluated as EP additives at a concentration of 0.0035 mol. (100 g oil)"--- as described in Application Example 1 and the loading determined at which welding occurred. The results show that the bismuth tris-(dialkyldithiocarbamates) are effective EP additives in the petroleum based oil. It is particularly notable that antimony tris-(dipentyldithiocarbamate) made from linear dipentylamine (ADAC) and from mixed isomers of dipentylamine (ADAC mixed) behave very similarly as EP additives in the petroleum based oil. These antimony salts behave very similarly as EP additives to Vanlube 73. Remarkably, the bismuth salts BDAC, BDAC (mixed) and BDHC all exhibit superior properties as EP additives in the oil. this is contrary to the teachings of US 3139405 which demonstrates that both bismuth tris- (dipentyldithiocarbamate) and bismuth tris-(dibutyldithiocarbamate) ^• are significantly inferior to the antimony analogues.

Application Example 3

Various antimony and bismuth tris-(dithiocarbamates) were evaluated as EP additives in a lithium hydroxystearate soap thickened grease. The base grease had a total soap content of 9.4Z by weight, lithium 0.22Z and glycerol 0.6Z, which was dispersed in a refined mineral oil derived from North West European crude having a specific gravity of 0.88, a viscosity of 576 seconds Saybolt at 100°F (about 120 cSt at 40°C) and 67 seconds Saybolt at 210°F (about 12 cSt at 100°C), a viscosity index of 95, closed flash point of 480°F (250°C) and pour point of -15°F (-26°C). The compounds listed in Table 3 below were mixed into the grease, with heating as necessary, to distribute the compound uniformly throughout the grease, to give a concentration of 0.0035 mol. (100 g grease)^-1. The results of four ball testing as described in application Example 1 is included in Table 3. These results indicate that the bismuth salts exhibit similar performance in this grease to the antimony analogues. This is unexpected from the teachings of US 3139405.

Application Example 4

Application Example 1 was repeated using a lighter mineral oil, Vitrea 22 (from Shell) having a viscosity of about 24 cSt at 40°C. The results are set out in Table 4 below. These show that the bismuth salt exhibits a similar relative advantage over the antimony analogue as established for the oil described in Application Example 1.

Table 1

Additive concentration Weld load

(Zw/w) (kgf)

BDHC 3.42 510

BDEHC 4.0 380

ADHC 3.12 310

ADAC 2.83 370

Control _ 150

Table 2

Additive concentration Weld load

(Zw/w) (kgf)

ADAC 2.83 370

ADAC (mixed) 2.83 370

Vanlube 73 6.40 330

BDAC 3.13 560

BDAC (mixed) 3.13 610

BDHC 3.42 510

Control . 150

Table 3

Additive concentration Weld load (Zw/w) (kgf)

ADAC 2.83 330

ADAC (mixed) 2.83 350

Vanlube 73 6.4 340

BDAC 3.13 360

BDAC (mixed) 3.13 300

BDHC 3.42 380

Control _ 130

Table 4

Additive concentration Weld load

(Zw/w) (kgf)

ADAC mixed 2.83 240

BDAC mixed 3.13 370

Claims

1 A compound of the formula (I):

[ R---.R² - N - C(S) - S - ]₃ Bi (I)

where each R¹ and R² is, independently, C₁_₁2 alkyl, C₇_i2 aralkyl optionally substituted by C**__i2 alkyl, cyclohexyl optionally substituted by Cι_i2 alkyl; or

R¹ and R² together with the nitrogen atom to which they are attached from a heterocyclic ring optionally substituted by ^cl-12 alkyl, with the proviso that R¹ and R² are not both ethyl, n-butyl or n-pentyl.

2 A compound as claimed in claim 1 wherein R² is C5_i2 alkyl, C₇_i2 aralkyl optionally substituted by C-j__i2 alkyl, cyclohexyl optionally substituted by Cι_i2 alkyl, isopropyl, isobutyl, tertiary butyl or branched pentyl.

3 A compound as claimed in either claim 1 or claim 2 wherein R¹ and R² are the same.

4 A compound as claimed in any one of claims 1 to 3 wherein at least one of R¹ and R² is, or contains, branched alkyl.

5 The compounds bismuth tris-(dihexyldithiocarbamate) , bismuth tris- [bis-(2-ethylhexyl)dithiocarbamate] , bismuth tris-[di-(mixed pentyl isomers) dithiocarbamate].

6 A composition comprising a grease and a compound of the formula (la):

[ Rl.R² - N - C(S) - S - ]₃ Bi (la) where each R^{1 ant}^ ^R2 is, independently, C]__i2 alkyl, C₇_i2 aralkyl optionally substituted by C]__i2 alkyl, cyclohexyl optionally substituted by C-^*__]_2 alkyl; or

R¹ and R² together with the nitrogen atom to which they are attached form a heterocyclic ring optionally substituted by Cι_i2 alkyl.

A composition comprising an oil and a compound of the formula (lb):

[ Rl.R² - N - C(S) - S - ]₃ Bi (lb)

where each Rl and R² is, independently, Cι_i2 alkyl, C₇_i2 aralkyl optionally substituted by Cι_i2 alkyl, cyclohexyl optionally substituted by Cι_i2 alkyl; or

R! and R² together with the nitrogen atom to which they are attached form a heterocyclic ring optionally substituted by ^cl-12 alkyl, with the proviso that when R¹ and R² are both ri-pentyl or n-butyl the oil is not an SAE 90 high viscosity index mineral oil having a viscosity of 17 cSt at 100°C and 190 cSt at 40°C.

A composition as claimed in claim 7 wherein the oil has a viscosity above 200 cSt at 40°C.

A composition as claimed in either claim 7 wherein the oil has a viscosity below 180 cSt at 40°C.

A composition as claimed in any one of claims 7 to 9 wherein at least one of R¹ and R² is, or contains, branched alkyl.

The use of a compound as claimed in any one of claims 1 to 5 as an extreme pressure additive for a lubricant for protecting metals. A metal surface which is treated with a compound as claimed in any one of claims 1 to 5 or a composition as claimed in any one of claims 7 to 10.

A metal surface as claimed in claim 12 which is a gear or bearing.