Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic sulfur compound
Reexamination Certificate
2001-07-05
2003-04-15
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic sulfur compound
C508S570000, C568S025000, C568S058000, C044S435000
Reexamination Certificate
active
06548462
ABSTRACT:
The invention relates to novel bisphenylthio compounds and their use as lubricants.
In order to reduce the wear and the energy loss due to friction, machine bearings and gears are known to be provided with a lubricant which, during operation, permits as complete separation as possible of the solid bodies moving against one another. The lubricants may be divided into lubricating liquids and lubricating greases. Conventional lubricating liquids in use are mineral oils obtained from petroleum, synthetic oils, such as polyalkylene glycols, ethylene polysulphides, ester oils or phosphoric acid esters, and silicone oils (Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A15, page 423 et seq., VCH Weinheim 1990). Mesogenic liquids, i.e. liquids which form thermotropic liquid crystalline phases and can be; transformed from a low-viscosity into a high-viscosity phase, and vice versa, in the lubricating gap (U.S. Pat. No. 5,160,451) are also known. In general, a liquid is referred to as mesogenic if it can form one or more liquid crystalline phases under specific conditions (pressure, temperature, shearing, surface interactions). The relationships between chemical structure and the arrangement of the molecules in such phases and the temperature range in which such phases can occur is known (e.g. H. Kelker, R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim 1980; C. Destrade et al., Mol. Cryst. Liq. Cryst. Vol. 106, 121 (1984). Lubrication with lubricating greases is widely used. These lubricating greases consist of a lubricating liquid and, dispersed therein in fine form, a solid, the so-called thickener which has only a slight effect on the tribological properties and is primarily a reservoir for the lubricating liquid. In addition, very low-viscosity organic substances, such as fuels for spark-ignition engines (petrol) and diesel engines (diesel fuel), can also be considered as lubricants, which is clear from the known effect of the fuel on the wear of nozzle valves of fuel injection nozzles. Solutions and emulsions of organic compounds in water also serve as lubricants, in particular as so-called cooling lubricants in the machining of metallic workpieces.
The energy losses and wear phenomena occurring in a friction pairing—these are generally solid bodies separated by a lubrication gap and moving against one another—depend in a complex manner on the material of the machine element itself, on the properties of the lubricating oil, such as its viscosity and its interactions with the material, and on the pressure and velocity conditions. Continuous supporting films, as occur, for example, in the hydrodynamic region of sliding bearing or in the elastohydrodynamic region of roller bearings, are advantageous. High frictional losses, characterized by the generally customary coefficients of friction, and the wear phenomena generally correlated with them occur particularly in sliding bearings in the case of so-called boundary friction and mixed friction (cf. Ullmann's Encycl.).
In addition to the ethylene polysulphides, inter alia hexakis-, pentakis- and tetrakis[alkylthio]benzenes are known as sulphur-containing lubricants (DE 196 11 466). The latter compounds are distinguished by particularly good lubricating properties. Owing to their tendency to form discotic phases under atmospheric pressure at temperatures as low as in the range from 0 to −10° C., and in particular such phases which are characterized by a particularly high degree of ordering of the molecules and very high viscosities, these lubricants are not suitable for machine bearings which have to be supplied with a liquid medium at temperatures down to −40° C. by a continuous flow process.
It was an object of the invention to provide sulphur compounds which have the advantageous frictional and wear properties of the above-mentioned alkylthiobenzenes but, even at low temperatures, exhibit no transition to a liquid crystalline phase disadvantageous for the flowability.
The object was achieved by providing the compounds, according to the invention, of the general formula I
in which
X
1
to X
5
in each case independently of one another represents H, Cl, F, OH, SH, R, —OR and —SR, R being an organic radical having 1 to 18 C atoms which may be an alkyl or alkenyl radical which may also contain —O— or —S— instead of one to four nonneighbouring CH
2
groups and may also be monosubstituted or polysubstituted by —OH, —SH or halogen, or a phenyl, cyclohexyl or cyclohexylmethyl radical which is unsubstituted or substituted by one to 3 alkyl groups having a total of 1 to 9 C atoms, in which in each case a CH
2
group may be replaced by —O—, with the proviso that at least 3 of the radicals X
1
to X
5
are —SR,
Y
1
to Y
5
in each case independently of one another have the meaning stated for X
1
to X
5
and
z denotes an &agr;,&ohgr;-alkylene group having 2 to 18 C atoms in which one to 3 CH
2
groups may also be replaced by —O— or —S—, or a 1,4-cyclohexanedimethyl group
or a single bond.
It was found that the compounds according to the invention are suitable as lubricants which permit particularly small frictional losses in friction pairings and surprisingly are flowable at low temperatures.
The molecules of the compounds of the formula I contain two phenyl rings which are linked via a bridge containing at least two S atoms. Altogether, at least 8 S atoms are contained in the molecule, each phenyl ring being linked to at least 4 S atoms. Preferred compounds are those in which both phenyl groups are each linked to at least 5 S atoms, particularly preferably those in which both phenyl groups are each linked to 6 S atoms.
The substituents X
1
to X
5
and, in each case independently of one another, Y
1
to Y
5
are preferably —SR, —H or —SH. The radical R preferably designates an alkyl radical having 1 to 18 C atoms, in which one to four nonneighbouring CH
2
groups may also be replaced by —O— or —S— and which may be substituted by —OH or —SH. Straight alkyl chains are particularly preferred, very particularly those having 6 to 12 C atoms.
The group Z preferably contains 2 to 10 C atoms. Particularly preferred here are straight-chain &agr;,&ohgr;-alkylene groups. The 1,4-clohexanedimethyl group is also preferred.
The formulae Ia to If are examples of compounds according to the invention:
The preparation of the compounds of the formula I is carried out by generally known methods of synthetic chemistry, as described, for example, in R. C. Larock, Comprehensive Organic Transformations, VCH Publishers, Inc. (1989) and in Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme Verlag, Stuttgart.
Compounds of the formula I are preferably prepared by first producing, from a mixture of the thiols RSH and HS—Z—SH, in an aprotic solvent, such as N-methyl-2-pyrrolidinone, N,N-dimethylformamide or tetramethyleneglycol dimethyl ether, by reaction with sodium amide or sodium hydride, the corresponding sodium thiolates, which are then converted into mixtures of compounds of the formula I by addition of halobenzenes, such as hexa-, penta- or tetrachlorobenzene, or the corresponding fluorine compounds, in a substitution reaction at temperatures between 50° C. and 180° C.
If mixtures of the thiols RSH, such as, for example, mixtures selected from the compounds octadecylthiol, hexadecylthiol, tetradecylthiol, dodecylthiol, decylthiol, nonylthiol, octylthiol, heptylthiol, hexylthiol, pentylthiol, butylthiol, propylthiol, ethylthiol and methylthiol, are used, mixtures of numerous compounds of the formula I with a randomly distributed arrangement of the various substituents RS are formed. By selecting the alkyl chain length of the thiols used and their proportions, it is possible to influence the viscosity and flow behaviour at low temperatures.
If, in the reactions mentioned, less than the stoichiometric amount of metal thiolates is chosen, compounds of the formula I having halogen substituents can be obtained.
The introduction of the —SZS— bridge can al
Eidenschink Rudolf
Kretzschmann Holger
Dunn Michael L.
McAvoy Ellen M.
Nematel Dr. Rudolph Eidenschink
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