EP0798366A2 - Lubricant - Google Patents

Abstract

Use of benzene compounds of formula (I) as lubricant is new. In (I), 4-6 of the substituents X1-X6 = SR, SO2R or SOR, and the remaining substituents are H, Cl, F, OH, SH, R, OR,COOR or OOCR; R = optionally F-substituted 1-18C alkyl; and in this residue, ≥ 1 CH2 group can be replaced by O or S, so that O atoms are not directly connected to each other.

Description

In order to reduce wear and energy loss due to friction, machine bearings and gearboxes are known to be provided with a lubricant that enables the solid bodies that are moved against each other to be separated as completely as possible during operation. The lubricants can be divided into lubricating oils and greases.

Mineral oils and synthetic oils such as polyalkylene glycols, ester oils, phosphoric acid esters and silicones are used as lubricating oils (see overview in Ullmanns Enzykl. Der technical chemistry, 4th edition, vol. 20). Modern lubricating oils contain a number of additives that affect both the physical and chemical properties. These are, in particular, oxidation inhibitors, detergents, high-pressure additives, friction reducers, anti-foaming agents and corrosion inhibitors.

The energy losses and signs of wear occurring in a friction pairing depend in a complex manner on the material of the machine element itself, the properties of the lubricating oil, such as its viscosity and its interactions with the material, and on the pressure and speed conditions. Closed support films, such as occur in the hydrodynamic area of plain bearings or in the elastohydrodynamic area of rolling bearings, are favorable. High friction losses - and the signs of wear that correlate with them in general - occur particularly in plain bearings in the mixed friction area (cf. VDI reports 680, Das Öl als Konstruktionsement, VDI-Verlag, Düsseldorf 1988).

Lubrication with greases is widespread. These consist of a lubricating oil and a solid which is dispersed in fine form, the so-called thickener, which has only a minor influence on the tribological properties, and in primarily has the function of a reservoir for the lubricating oil.

The known lubricants are in need of improvement because many friction pairings can only be operated with high friction losses.

DE 33 32 955 gives compounds of the formula I as components for liquid-crystalline phases for electro-optical displays. DE 28 19 822 describes additions of less than 1% of tris and tetrakis [alkylthio] benzenes as antioxidants to conventional lubricants.

The object of the invention was to find a new, stable lubricant by means of which friction pairings in gears and bearings can be operated with particularly low friction losses.

worin 4,

5 oder 6 der Substituenten X₁ bis X₆ -SR, -SO₂R oder -SOR
und die übrigen Substituenten
-H, -Cl, -F, -OH, -SH, -R, -OR, -COOR oder -OOCR

sein können, worin R jeweils unabhängig voneinander einen unsubstituierten oder mehrfach durch Fluor substituierten Alkylrest mit 1 bis 18 C-Atomen bedeutet, wobei in diesem Rest eine oder mehrere CH₂-Gruppen durch -O- oder -S- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, als Schmiermittel.The object was achieved by using one or more compounds of the general formula I.

where 4,

5 or 6 of the substituents X ₁ to X ₆ -SR, -SO ₂ R or -SOR
and the other substituents
-H, -Cl, -F, -OH, -SH, -R, -OR, -COOR or -OOCR

may be in which R is independently an unsubstituted or polysubstituted alkyl radical having 1 to 18 carbon atoms, in which one or more CH ₂ groups can be replaced by -O- or -S- so that O atoms are not directly linked to each other as a lubricant.

It has surprisingly been found that the sulfur-containing lubricant according to the invention is significantly lower than conventional lubricants in gearboxes and bearings Allows friction losses.

The lubricant according to the invention may contain other compounds in addition to one or more compounds of the formula I. These can include antioxidants, such as derivatives of 2,6-di- tert -butylphenol, high-pressure additives, such as zinc dialkyl dithiophosphate, friction reducers, light stabilizers, emulsifiers or demulsifiers. However, organic compounds for varying the viscosity can also be used, such as compounds whose molecules contain benzene or naphthalene nuclei which are substituted several times by alkyl groups. If the lubricant according to the invention is a lubricating oil, these additives are present in the homogeneous liquid in a molecularly disperse form. The content of the molecularly dispersed additives in the compounds of the formula I in the lubricating oil according to the invention is at most 30%.

This lubricating oil can be converted in a generally known manner (cf. Ullmanns Enzykl.) By adding thickeners which are not present in the form of a molecule into a lubricating grease which is also included in the present invention. Particularly suitable thickeners are lithium 12-hydroxystearate and powder made of polytetrafluoroethylene (eg microteflon powder 5µ, Dr. Tillwich GmbH, Horb). Within the scope of the present inventions, polymers serving for the formation of gels, such as so-called side chain polymers (H. Ringsdorf et al., Angew. Chem. 101 , 934 (1989) and literature cited therein), as well as inorganic solid additives, such as molybdenum disulfide, are also described or graphite, one of the thickeners. An inventive grease can contain up to 35% of such thickeners. The distinction between molecularly disperse and non-molecularly disperse substances can be made by an ultracentrifugation (for example with the Beckman L8-M ultracentrifuge at a centrifugal acceleration between 7x10 ⁵ and 6x10 ⁵ m / s ² at 25 ° C., 10 min) in a manner known per se.

The compounds of the formula I comprise the preferred sub-formulas Ia to Id (Y independently of one another means -SR, -SO ₂ R or -SOR, Z independently of one another means -H, -Cl, -F, -R, -OH, -SH, -OR, -COOR or -OOCR):

Of these, the sub-formulas Ia and Ib are particularly preferred.

Of the sulfur-containing substituents Y, -SR and -SO ₂ R are preferred, and -SR is particularly preferred. The alkyl radicals -R in the substituents Y in one and the same compound can be the same or different. It can be unbranched or branched residues. Unbranched alkyl radicals are preferred. Of these, radicals having 6 to 18 carbon atoms are preferred, in particular hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, hexadecyl and octadecyl. Of the substituents Z in the partial formulas Ia to Id, -H, -OR and -COOR are preferred, with -H being particularly preferred. The alkyl radicals -R in the substituents Z are each independent of one another and preferably unbranched. They mean in particular methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, hexadecyl and octadecyl.

• Hexakis[hexylthio]benzol
• Hexakis[heptylthio]benzol
• Hexakis[octylthio]benzol
• Hexakis[nonylthio]benzol
• Hexakis[decylthio]benzol
• Hexakis[dodecylthio]benzol
• Hexakis[tetradecylthio]benzol
• Hexakis[hexadecylthio]benzol
• Hexakis[octadecylthio]benzol
• Hexakis[2-perfluorhexyl-ethylthio]benzol

geeignet.Of the compounds of partial formula Ia, the compounds in particular are

• Hexakis [hexylthio] benzene
• Hexakis [heptylthio] benzene
• Hexakis [octylthio] benzene
• Hexakis [nonylthio] benzene
• Hexakis [decylthio] benzene
• Hexakis [dodecylthio] benzene
• Hexakis [tetradecylthio] benzene
• Hexakis [hexadecylthio] benzene
• Hexakis [octadecylthio] benzene
• Hexakis [2-perfluorohexyl-ethylthio] benzene

suitable.

und die Pentakis[alkylthio]alkoxybenzole

wovon die Verbindungen

• Pentakis[octylthio]benzol
• Pentakis[decylthio]benzol
• Pentakis[dodecylthio]benzol
• Pentakis[octylthio]octyloxybenzol
• Pentakis[octylthio]anisol

besonders geeignet sind.The preferred compounds of the partial formula Ib include the pentakis [alkylthio] benzenes

and the Pentakis [alkylthio] alkoxybenzenes

of which the connections

• Pentakis [octylthio] benzene
• Pentakis [decylthio] benzene
• Pentakis [dodecylthio] benzene
• Pentakis [octylthio] octyloxybenzene
• Pentakis [octylthio] anisole

are particularly suitable.

die 2,3,5,6-Tetrakis[alkylthio]terephthalsäurealkylester

und die 2,3,5,6-Tetrakis[alkylthio]-1,2-dialkoxy-benzole

worunter die Terephthalsäureester bevorzugt sind.The compounds of sub-formula Ic include 1,2,4,5-tetrakis [alkylthio] benzenes

the 2,3,5,6-tetrakis [alkylthio] terephthalic acid alkyl esters

and the 2,3,5,6-tetrakis [alkylthio] -1,2-dialkoxy-benzenes

among which the terephthalic acid esters are preferred.

bevorzugt.Of the compounds of partial formula Id are the phthalic acid esters

prefers.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart), and under reaction conditions which are suitable for the mentioned implementations are known and suitable.

Compounds of the sub-formulas Ia and Ib are obtained by reacting hexachlorobenzene or pentachlorobenzene or hexafluorobenzene or pentafluorobenzene with a sodium alkylthiolate RSNa in an aprotic solvent, N, N-dimethylformamide, N-methyl-2-pyrrolidinone or preferably tetraethylene glycol dimethyl ether at 50 to 180 ° C. For this purpose, the thiolate is first prepared in one of the solvents mentioned from the mercaptan RSH with sodium hydride or sodium amide. Instead of a pure mercaptan RSH, mixtures of mercaptans can also be used, so that a mixture of compounds which are included in the sub-formulas is formed. It is assumed within the scope of the invention that the reactivity of the various thiolates towards the halogenobenzenes is the same, so that the compounds have a random substitution pattern for the various alkylthio groups. Mixtures of this type are distinguished by particularly low melting points, which results in a low pour point which is advantageous compared to known lubricants (definition see Ullmanns Enzykl.).

It has surprisingly been found that the lubricant according to the invention is excellently suitable for the lubrication of gears and machine bearings. It has also surprisingly been found that lower friction losses can be achieved in internal combustion engines when using the lubricating oil according to the invention as an engine oil than when using conventional mineral and synthetic oils. This is particularly noticeable by the lower fuel consumption of motors used in racing with a rotation frequency of> 8000 rpm.

The favorable lubricating properties and the extraordinarily favorable low vapor pressures with relatively low viscosity values also result in advantageous applications for the compounds of the formula I as lubricating oils for bearings in turbomolecular pumps and oil rotary vacuum pumps.

The following examples are intended to illustrate the invention without limiting it. Before and after, percent means percent by mass.

example 1

69.1 g (2.89 mol) of sodium hydride are added to 800 ml of absolute tetraethylene glycol dimethyl ether (tetraglyme) under dry nitrogen. A solution of 421 g (2.89 mol) of n-octyl mercaptan in 1200 ml of tetraglyme is added dropwise to the suspension over the course of 2 hours. The mixture is then stirred for a further 1/2 hour and 124.4 g (0.436 mol) of hexachlorobenzene are added. It is heated to 130-135 ° C and stirred at this temperature for 20 hours with exclusion of moisture. After cooling, the reaction flask is equipped with a distillation attachment. The solvent is largely distilled off in vacuo (oil rotary pump) at a bath temperature of 130 ° C. The residue is cooled and a total of 1 liter of 5% hydrochloric acid is added dropwise and then rapidly. The resulting emulsion is first extracted with 600 ml and then twice with 200 ml of diethyl ether. The combined organic phases are extracted three times with 75 ml of saturated NaCl solution and once with 100 ml of water and then dried with MgSO ₄ . After the ether has been distilled off, the oily crude product of 426 g is mixed with 500 ml of acetone. After briefly refluxing, the cloudy mixture becomes a clear solution from which a yellowish white crystalline sediment is formed overnight at -25 ° C. The supernatant brown solution is poured off and the crystals are dissolved in a further 500 ml of acetone. After a total of 3-fold crystallization carried out in the same way, the crystals are melted and the oil is freed from volatile additives in vacuo (0.2 mbar) at 200 ° C. Yield: 378 g (92% of theory) of hexakis [octylthio] benzene, melting point -6 ° C, viscosity at 20 ° C 120 mm ² / s, at 40 ° C 51 mm ² / s, vapor pressure at 20 ° C <10 ^-8 mbar.

The isotropic melt can be subcooled to about -10 ° C (polarization microscopic observation in a heating table from Lincam).

A lubricant A, consisting of 99% of this compound and 1.0% of the high pressure additive Irgalube 349 (Ciba-Geigy Ltd.) was compared on various devices with conventional lubricants:
a) In a two-disk test stand for measuring the coefficient of friction µ under elastohydrodynamic conditions (TU Munich, see K. Michaelis et al., Proc. 10th Intern. Coll. Tribology - Solving Friction and Wear Problems, Vol. 2, p . 1363-75, 1996) a coefficient of friction µ of 0.012 was measured at a Hertzian pressure of 1000 N / mm ² , a lubricant temperature of 60 ° C, a total speed of the disks of 16 m / s and a slip of 20% (definition see K. Michaelis). In comparison, the commercial oil M100 (mineral oil base ISO VG 100) has a µ of 0.031. Based on known relationships, particularly low friction losses in gear transmissions and worm gears can be derived from this result.
b) A ball screw drive 40x20 was used in a test stand for ball screws (University of Karlsruhe, see D. Spath et al. Annals of the CIRP Gen. Assembly, Vol. 44/1, Enschede 1995) to determine the friction behavior in the mixed friction area and in the hydrodynamic area (Linear ball bearing) from Deutsche Star (single nuts with four-point contact, ball diameter 6 mm, preload force 3.5 kN (Def. See Spath et al.) Operated with lubricant A. At a temperature of the ball screw drive of 20 ° C the friction torque was measured as a function of the speed (all definitions see Spath et al.) The transition from mixed friction to hydrodynamic friction takes place at the speed n _ü , at which, according to generally known law, the smallest achievable friction torque is displayed at the same time (in Nm) between n _ü and the high speed of 1500 min ^-1 is due to the internal friction in the lubricant Standard oil Tellus C100 (mineral oil, shell) gives the following Values. Tellus C100 0.88 Nm (n _ü = 40 min ^-1 ), 1.75 Nm (1500 min ^-1 ) Lube oil A 0.25 (n _ü = 40 min ^-1 ), 0.70 Nm (1500 min ^-1 )

Example 2

In the manner shown in Example 1, 6.9 g of NaH (289 mmol) in 80 ml of tetraglyme, a solution of 11.0 g of hexyl mercaptan (96.3 mmol), 13.7 g of octyl mercaptan (96.3 mmol) and 16.3 g of decyl mercaptan (96.3 mmol) in 120 ml of tetraglyme and 12.4 g of hexachlorobenzene (43.6 mmol) produced a mixture of hexakis [alkylthio] benzenes. However, the crude product is not crystallized, but is purified by column chromatography (200 g of silica gel 60 (Merck), petroleum ether-toluene mixture). The solvent is first spun off and the residue is freed from volatile impurities at 200 ° C. and in an oil pump vacuum at 0.2 mbar.

The mixture is examined without the addition of additives in the test bench described in Example 1b. In the speed range from 0 to 1500 min ^-1, lower friction torques result than with the Tellus C 100 reference oil.

Example 3

In the manner shown in Example 1, 5.8 g of NaH (241 mmol), 80 ml of tetraglyme, a solution of 46.7 g of dodecyl mercaptan (241 mmol) in 120 ml of tetraglyme and 10.9 g (43.6 mmol) Pentachlorobenzene Pentakis [dodecylthio] benzene produced. Yield: 40 g (80% of theory), melting point 36 ° C.

Pentakis [octylthio] benzene (melting point 12 ° C.) was prepared in the same manner and with the same molar ratios, starting from pentachlorobenzene and octyl mercaptan.

In the test bench described in Example 1b, the compound showed lower coefficients of friction at 60 ° C. in the speed range from 0 to 1500 min ⁻¹ than the comparative oil Tellus C 100 at the same temperature.

Example 4

A mixture of 75% hexakis [octylthio] benzene with 25% of the low-viscosity compound 4-trans- (4-propyl-cyclohexyl) ethyl-benzene in the test bench listed in Example 1b likewise gave more favorable frictional moments under the conditions mentioned there than with the oil Tellus C 100.

Example 5

10.0 g of the liquid mixture of compounds of the general formula I from Example 2 are mixed with 0.2 g of the antioxidant 2,6-di- tert -butyl-4-methylphenol and 1.0 of the high-pressure additive zinc-dibutyl- dithiophosphate added. 3.0 g of the polytetrafluoroethylene powder Hostafon TF 9202 (Hoechst AG) are stirred into the lubricating oil which has formed as a homogeneous liquid after briefly stirring at room temperature. The suspension is treated at room temperature in a commercially available ultrasound bath (20 KHz, 200 W) for 30 minutes. The resulting grease has a thickener content of 21.1%.

Claims (5)

Use of compounds of the general formula I

wherein 4, 5 or 6 of the substituents X ₁ to X ₆
-SR, -SO ₂ R or -SOR
and the other substituents
-H, -Cl, -F, -OH, -SH, -R, -OR, -COOR or -OOCR can be, where R in each case independently of one another is an unsubstituted or polysubstituted alkyl radical having 1 to 18 carbon atoms, in which one or more CH ₂ groups can be replaced by -O- or -S- so that O atoms are not directly linked to each other as a lubricant. Use of compounds according to claim 1, wherein all 6 substituents are X ₁ to X ₆ -SR, as a lubricant. Use of compounds according to claim 1, wherein 5 substituents are X ₁ to X ₆ -SR, as a lubricant. Use of compounds according to one of the preceding claims, in which R each independently of one another denotes an unbranched alkyl radical having 1 to 18 carbon atoms, as a lubricant. Use of compounds according to one of the preceding claims as engine oil in internal combustion engines which have a piston frequency of> 8000 Z / min.