EP0184713A2 - Stabilized lubricants on the basis of a polyether - Google Patents

Abstract

Stabilized lubricants based on polyethers contain diphenylamine derivatives of the formula <IMAGE> in which R¹ is hydrogen, a straight-chain or branched C4 to C12 alkyl group, a straight-chain or branched C4 to C12 alkylene group, a C7 to C12 aralkyl group, a C7 to C12 Aralkylene group, a C5 to C12 cycloalkyl group optionally substituted by C1 to C6 alkyl, alkenyl, cycloalkyl or cycloalkenyl or a C5 to C12 cycloalkenyl group optionally substituted by C1 to C6 alkyl, alkenyl or cycloalkenyl, but not a hydrocarbon group derived from a terpene, in the ortho or para position to the respective N atom, n is an integer from 1 to 29 and Y is a bifunctional radical -A- and optionally also a bifunctional radical -B- , in each case in the ortho or para position to the N atoms, where -A- is a straight-chain or branched C4 to C12 alkyl radical, a C7 to C12 alkyl radical or a C5 to C12 cycloalkyl radical optionally substituted by C1 to C6 alkyl or cycloalkyl, but not a hydrocarbon radical derived from a terpene, and <IMAGE>, where R² is hydrogen, C1 to C6 alkyl or C5 to C6 cycloalkyl stands and wherein -B- has a proportion of 0 to 50 mol% of Y and optionally further additives.

Description

The present invention relates to polyether-based lubricants stabilized with special diphenylamine derivatives.

Polyether-based lubricants are known. They are characterized by excellent lubricity, good viscosity behavior, high flash point, low volatility, low pour point and low impact on metals and sealing materials. They can be used over a wide temperature range, for example from -20 to + 220 ° C. Because of these properties, lubricants based on polyether are used in particular as hydraulic fluids, brake fluids, metalworking fluids, lubricants for compressors and refrigeration machines and as bearing and gear oils for thermally and mechanically highly stressed units in the paper, textile and plastics industries.

However, polyether-based lubricants often have insufficient thermal and oxidation stability and therefore do not always meet all the requirements placed on high-quality lubricants.

In order to improve the properties of lubricants based on polyethers, additives have already been proposed, such as aromatic amines, e.g. Phenyl-ctnaphthylamine, phenothiazine derivatives and certain diphenylamine derivatives (see Ullmann's Encyclopedia of Industrial Chemistry, 4th edition, volume 20, page 510, DE-OS 22 11 805 and DE-OS 28 06 133).

However, the known additives acting as stabilizers do not meet all the requirements with regard to the stabilization of lubricants based on polyether. Despite this stabilization, one can recognize an oxidative degradation of the lubricants by the relatively rapid drop in their viscosity. In addition, with prolonged use of the lubricants stabilized in this way at higher temperatures, a considerable loss is observed due to the evaporation of volatile degradation products.

enthalten, in der

• R Wasserstoff, eine geradkettige oder verzweigte C₄ bis C₁₂-Alkylgruppe, eine geradkettige oder verzweigte _C4 bis C₁₂-Alkylengruppe, eine _C7 bis C₁₂-Aralkylgruppe, eine C₇ bis C₁₂-Aralkylen- gruppe, eine gegebenenfalls durch C₁ bis C₆-Alkyl, -Alkenyl, -Cycloalkyl oder -Cycloalkenyl substituierte C₅ bis C₁₂-Cycloalkylgruppe oder eine gegebenenfalls durch C₁ bis C₆-Alkyl, -Alkenyl oder -Cycloalkenyl substituierte C₅ bis C₁₂-Cyclo- alkenylgruppe, nicht jedoch eine von einem Terpen abgeleitete Kohlenwasserstoffgruppe, in ortho- oder para-Stellung zum jeweiligen N-Atom bedeutet,
• n für eine ganze Zahl von 1 bis 29 steht und
• Y für einen bifunktionellen Rest -A- und gegebenenfalls zusätzlich für einen bifunktionellen Rest -B-, jeweils in ortho- oder para-Stellung zu den N-Atomen steht, wobei
  -A- einen geradkettigen oder verzweigten C₄ bis ^C ₁₂-Alkylrest, einen C₇ bis C₁₂-Aralkylrest oder einen gegebenenfalls durch C₁ bis C₆-Alkyl oder -Cycloalkyl substituierten C₅ bis C₁₂-Cycloalkylrest, nicht jedoch ein von einem Terpen abgeleiteter Kohlenwasserstoffrest, und
  
  bedeutet, wobei R² für Wasserstoff, C₁ bis C₆-Alkyl oder C₅ bis C₆-Cycloalkyl steht und wobei -B- einen Anteil von 0 bis 50 Mol-% an Y hat. In der Formel (I) steht
• R¹ vorzugsweise für Wasserstoff, Benzyl, Styryl, α--Methylstyryl, tert.-Butyl, tert. Amyl, Isononyl, Cyclohexyl, Isooctyl, Methylcyclohexyl oder einen der Reste
  
  
  
  jeweils in ortho- oder para-Stellung zum jeweiligen N-Atom, besonders bevorzugt für Wasserstoff,
  
  
  oder α-Methylstyryl, jeweils in ortho- oder para-Stellung zum jeweiligen N-Atom, und ganz besonders bevorzuqt für Wasserstoff,
• n vorzugsweise für eine ganze Zahl von 1 bis 19 und besonders bevorzugt für eine ganze Zahl von 1 bis 12,
• Y in der Bedeutung von -A- vorzugsweise für
  
  
  
  und in der Bedeutung für -B- vorzugsweise für -CH₂-. Der Anteil von -B- an Y beträgt vorzugsweise 0 bis 40 Mol-%. Besonders bevorzugt steht Y nur für -A- in der Bedeutung von
  
  Die erfindungsgemäß stabilisierten Schmierstoffe auf der Basis von Polyethern können Diphenylaminderivate der Formel (I) beispielsweise in Mengen von 0,1 bis 10 Gew.-%, bezogen auf die Mischung enthalten. Vorzugsweise beträgt diese Menge 0,2 bis 5 Gew.-%.

Stabilized lubricants based on polyethers have now been found, which are characterized in that they have diphenylamine derivatives of the formula

included in the

• Group R is hydrogen, a linear or branched C ₄ to C ₁₂ alkyl group, a linear or branched _C4 to C ₁₂ alkylene group, a _C7 to _C12 aralkyl group, a C ₇ to C ₁₂ -Aralkylen-, an optionally by C ₁ to C ₆ alkyl, alkenyl, cycloalkyl or cycloalkenyl substituted C ₅ to C ₁₂ cycloalkyl group or an optionally by C ₁ to C ₆ alkyl, alkenyl or cycloalkenyl-substituted C ₅ to C ₁₂ cyclo- alkenyl group, but does not mean a hydrocarbon group derived from a terpene, ortho or para to the respective N atom,
• n stands for an integer from 1 to 29 and
• Y stands for a bifunctional radical -A- and optionally additionally for a bifunctional radical -B-, in each case in the ortho or para position to the N atoms, where
  -A- a straight-chain or branched C ₄ to ^C ₁₂ alkyl radical, a C ₇ to C ₁₂ aralkyl radical or a C ₅ to C ₁₂ cycloalkyl radical optionally substituted by C ₁ to C ₆ alkyl or cycloalkyl, but not one of a terpene derived hydrocarbon residue, and
  
  means, where R ^{2 is} hydrogen, C ₁ to C ₆ alkyl or C ₅ to C ₆ cycloalkyl and where -B- has a proportion of 0 to 50 mol% of Y. In formula (I) stands
• R ^{1 is} preferably hydrogen, benzyl, styryl, α-methylstyryl, tert-butyl, tert. Amyl, isononyl, cyclohexyl, isooctyl, methylcyclohexyl or one of the radicals
  
  
  
  each in the ortho or para position to the respective N atom, particularly preferably for hydrogen,
  
  
  or α-methylstyryl, in each case in the ortho or para position to the respective N atom, and very particularly preferably for hydrogen,
• n preferably for an integer from 1 to 19 and particularly preferably for an integer from 1 to 12,
• Y in the meaning of -A- preferably for
  
  
  
  and in the meaning for -B- preferably for -CH ₂ -. The proportion of -B- in Y is preferably 0 to 40 mol%. Y is particularly preferably only for -A- in the meaning of
  
  The lubricants stabilized according to the invention based on polyethers can contain diphenylamine derivatives of the formula (I) for example in amounts of 0.1 to 10% by weight, based on the mixture. This amount is preferably 0.2 to 5% by weight.

in der

• R¹ die bei Formel (I) angegebene Bedeutung hat
• mit bifunktionellen Verbindungen der Formeln (III) bis (V)
  
  
  
  
  in denen
• Y die bei Formel (I) angegebene Bedeutung hat und
• Hal für ein Halogenatom steht
  oder mit aus den Verbindungen der Formeln (III) bis (V) durch Abspaltung von HHal, H₂0 oder HCOOH abgeleiteten Olefinen, in Gegenwart einer starken Säure (pK_s-Wert kleiner als 2) bei 50 bis 300°C umsetzt.

Diphenylamine derivatives of the formula (I) are known per se. They can be prepared, for example, by using diphenylamine and / or diphenylamine derivatives of the formula (II)

in the

• R ^{1 has} the meaning given for formula (I)
• with bifunctional compounds of the formulas (III) to (V)
  
  
  
  
  in which
• Y has the meaning given for formula (I) and
• Hal represents a halogen atom
  or from the compounds of formulas (III) to (V) by elimination of HHal, H ₂ 0 or HCOOH derived olefins, in the presence of a strong acid is reacted _(pK a less than 2) at 50 to 300 ° C.

in der

• R³ und R⁴ gleich oder verschieden sein können und für Wasserstoff oder C₁ bis C₁₂-Alkyl stehen, und/oder Polymere aus Tetrahydrofuran und/oder Blockpolymere und/oder statistische Polymere aus verschiedenen Epoxiden der Formel (VI) und/oder Tetrahydrofuran. Vorzugsweise enthalten die Schmierstoffe auf Polyetherbasis Homo- und/oder Mischpolymere aus Ethylen- und Propylenoxid.

Lubricants based on polyether are also known per se (see, for example, RC Gunderson and AW Hardt "Synthetic Lubricants", Reinhold Publishing Corp. New York, 1962, pages 61 ff.). They generally contain polymers of epoxides of the formula (VI)

in the

• R ³ and R ^{4 can be the} same or different and represent hydrogen or C ₁ to C ₁₂ alkyl, and / or polymers made of tetrahydrofuran and / or block polymers and / or statistical polymers made of different epoxides of the formula (VI) and / or tetrahydrofuran . The polyether-based lubricants preferably contain homo- and / or mixed polymers of ethylene and propylene oxide.

Such polyethers are generally oils which have molecular weights of, for example, 500 to 20,000. They preferably have molar masses of 1000 to 7000. They can be prepared by methods known per se, for example by an alkali-catalyzed or acid-catalyzed polymerization of the cyclic ethers, it being possible to use monoalcohols, polyalcohols or amines as starter molecules. The OH end groups of the polyethers thus produced can be closed by a conventional alkylation or acylation, i.e. be converted into ether or ester end groups.

Polyethers which are particularly suitable for the stabilization according to the invention are oils with molecular weights of 500 to 20,000, preferably with molecular weights of 1,500 to 7,000, which are obtained by alkali-catalyzed addition of propylene oxide and optionally ethylene oxide to alcohols, for example ethanol, butanol, propanediol, glycerol, trimethylolpropane or Pentaerythritol. Other polyethers which are particularly suitable for the stabilization according to the invention are oils with molecular weights of 500 to 10,000, preferably 1000 to 7000, which are preferably acid-catalyzed copolymerization of at least two substances from the group consisting of ethylene oxide, propylene oxide, tetrahydrofuran and epoxides with 6 to 20 8 to 12 carbon atoms.

• a) Diphenylaminderivate der Formel (VII)
  
  
  in der
  • R⁵ und R⁶ gleich oder verschieden sein können und für Wasserstoff, C₁ bis C₁₂-Alkyl oder C₇ bis C₁₂-Alkaryl, vorzugsweise für Isooctyl und/oder Styryl, stehen,
  • Z für Schwefel und
  • m für 0 oder 1 steht,
• b) Metalldesaktivatoren vom Typ der Salicylidenamine der Formel (VIII)
  
  
  in der
  • X für einen zweibindungen, gegebenenfalls stickstoffhaltigen, aliphatischen Rest, vorzugsweise für -(CH₂)₂-,
    
    -(CH₂)₃-,
    
    
    -(CH₂-CH₂-NH)_m-CH₂-CH₂ mit m = O bis 5, vorzugsweise mit m = 1, steht,
• c) weitere Stabilisatoren auf der Basis aromatischer Amine, wie Phenyl-α-naphthylamin, 4-Isopropylaminodiphenylamin, N,N'-Dicyclohexyl-p-phenylendiamin und/oder 4-Isohexyl-aminodiphenylamin,
• d) phenolische Antioxidantien, wie 2,6-Di-tert.-butyl- p-kresol, 2,6-Di-tert.-butyl-4-methoxyphenol, Methyl- und Butyl-hydrochinon, 2,2'-Methylen-bis-(6-tert.-butyl-4-methylphenol), 2,2'-Methylen-bis-(6-cyclohexyl-4-methylphenol), 1,1'-Bis-(2-hydroxy-3,5-dimethylphenyl)-butan, 2,2'-Thio-bis-(4-methyl-6-tert.-butylphenol) und 4,4'-Methylen-bis-(2,6- ditert.-butylphenyl),
• e) weitere übliche Additive wie Korrosionsinhibitoren, z.B. Bernsteinsäurehalbester, Phosphorigsäureester und Phosphorsäureester, und Verschleißschutzmittel, z.B. Stickstoff- und/oder Phosphorverbindungen wie Triarylphosphate und Mono- und Diarylphosphonate.

According to the invention with the diphenylamine For _- stabilized mel (I) polyether may additionally comprise further constituents, for example

• a) Diphenylamine derivatives of the formula (VII)
  
  
  in the
  • R ⁵ and R ^{6 may be the} same or different and represent hydrogen, C ₁ to C ₁₂ alkyl or C ₇ to C ₁₂ alkaryl, preferably isooctyl and / or styryl,
  • Z for sulfur and
  • m represents 0 or 1,
• b) metal deactivators of the salicylidene amine type of the formula (VIII)
  
  
  in the
  • X for a two bonds, optionally nitrogen-containing, aliphatic radical, preferably for - (CH ₂ ) ₂ -,
    
    - (CH ₂ ) ₃ -,
    
    
    - (CH ₂ -CH ₂ -NH) _m -CH ₂ -CH ₂ with m = O to 5, preferably with m = 1,
• c) further stabilizers based on aromatic amines, such as phenyl-α-naphthylamine, 4-isopropylaminodiphenylamine, N, N'-dicyclohexyl-p-phenylenediamine and / or 4-isohexylaminodiphenylamine,
• d) phenolic antioxidants, such as 2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-methoxyphenol, methyl and butyl hydroquinone, 2,2'-methylene bis- (6-tert-butyl-4-methylphenol), 2,2'-methylene-bis- (6-cyclohexyl-4-methylphenol), 1,1'-bis- (2-hydroxy-3,5- dimethylphenyl) butane, 2,2'-thio-bis- (4-methyl-6-tert-butylphenol) and 4,4'-methylene-bis- (2,6-ditert.-butylphenyl),
• e) further conventional additives such as corrosion inhibitors, for example succinic acid half-esters, phosphoric acid esters and phosphoric acid esters, and wear protection agents, for example nitrogen and / or phosphorus compounds such as triaryl phosphates and mono- and diaryl phosphonates.

The diphenylamine derivatives of the formula (VII) can be present, for example, in amounts of 0 to 10% by weight, based on the mixture. This amount is preferably 0.1 to 5% by weight.

The metal deactivators of the formula (VIII) can be present, for example, in an amount of 0 to 4% by weight, based on the mixture. This amount is preferably 0.5 to 2% by weight.

The other additives can, for example, each be present in amounts of 0 to 10% by weight, based on the mixture. This amount is preferably 0 to 5% by weight.

Of particular interest are stabilized lubricants based on polyethers which simultaneously contain diphenylamine derivatives of the formula (I), diphenylamine derivatives of the formula (VII) and metal deactivators of the formula (VIII), since these result in a synergistic mixture, i.e. a mixture that is better stabilized than can be expected from the individual effects of the additives.

The lubricants according to the invention can be produced in various ways. For example, diphenylamine derivatives of the formula (I) and, if appropriate, further additives can be added to polyethers in the desired proportions and, if appropriate with heating, for example at 80 to 100 ° C., dissolved therein. Another possibility is to first produce concentrates from the stabilizers using a suitable medium and to add these to the polyether lubricant to be stabilized in accordance with the desired proportions. Suitable concentrations for Such concentrates are, for example, those from 20 to 90% by weight, suitable media for their production are, for example, higher alcohols, such as 2-ethylhexanol and octaethylene glycol, but especially polyether lubricants. You can also mix the stabilizers or their concentrates first in the desired proportions and add this mixture to the lubricant to be stabilized.

In the case of the polyether-based lubricants stabilized according to the invention with diphenylamine derivatives of the formula (I), the drop in viscosity and the losses due to the evaporation of volatile degradation products are considerably less than in the case of lubricants based on polyether which have been stabilized with conventional additives.

The following examples illustrate the present invention without restricting it.

Examples example 1

A commercial polypropylene ether with a molecular weight of 5500 and started on trimethylolpropane was mixed with 2% by weight, based on the mixture, of the specified stabilizers and the mixture was tested for oxidation stability in accordance with DIN 51 352 Part 2.

The oil to be tested was aged in a glass vessel with 0.1% by weight of ferric oxide as a catalyst while introducing 15 l / h of air at 200 ° C. for 24 hours. The viscosity of the aged samples was determined at 40 ° C. and compared with the viscosity of the non-aged sample.

The closer the quotient, the greater the stability of the mixture Final viscosity Initial viscosity is 1.

Table 1 shows the stabilizers tested, and Table 2 the results obtained. The (kinetic) viscosity measurements were carried out in accordance with DIN 51562, Part 1 (Ubbelohde method).

Example 2

Aus der Tabelle 3 ist klar zu ersehen, daß der Stabilisator 4 alleine eine geringere Wirkung besitzt als die Stabilisatoren 4 + 6. Der Zusatz von Stabilisator 7 oder Stabilisator 8 erzeugt nur eine unwesentliche Verbesserung. Ein erheblicher Sprung zur höherer Wirkung erfolgt durch die Verwendung des Stabilisators 1 (erfindungsgemäß) anstelle des Stabilisators 6. Das trifft besonders für die Kombination der Stabilisatoren 4, 1 und 7 zu. Demnach bildet dieses Stabilisatorgemisch eine synergistische Mischung.Various mixtures of the stabilizers listed in Table 1 were added to the polyether used in Example 1 in such a way that the proportion of polyether in the lubricant formulation was always 98% by weight. The type and proportion of the stabilizers and the viscosities before and after aging (measured in accordance with DIN 51 352, Part 2) of the lubricant formulation are shown in Table 3.

From Table 3 it can be clearly seen that the stabilizer 4 alone has a lower effect than the stabilizers 4 + 6. The addition of stabilizer 7 or stabilizer 8 produces only an insignificant improvement. A significant jump to a higher effect is achieved by using stabilizer 1 (according to the invention) instead of stabilizer 6. This is particularly true for the combination of stabilizers 4, 1 and 7. Accordingly, this stabilizer mixture forms a synergistic mixture.

Example 3

In this example, different lubricating oil formulations based on polyether were compared with regard to their thermo-oxidative resilience. The evaporation losses that occur in the hot air stream at a certain temperature were measured.

For this purpose, 3 cm ^{3 of} the sample were placed in a quartz crucible, a liquid surface of 3.7 cm ^{2 being} formed. The crucible with the sample was then stored in the heating furnace, through which air heated to the test temperature flowed. The weight loss of the sample was determined gravimetrically as a function of time (see Table 4, data in% by weight).

The lower the evaporation losses at a certain temperature as a function of time, the better the resilience of the lubricating oil formulation.

Table 4 shows good resistance to degradation for all products at the lower temperatures and short exposure times. At higher temperatures and especially with long exposure times, the formulations according to the invention prove to be significantly more stable. Also noteworthy is the low or even constant loss of evaporation of samples A and B over a period of 3 hours with increasing temperatures.

Despite this significantly improved effect of the polyethers stabilized according to the invention, the amount of stabilizer applied is significantly less than in comparative experiment C.

• A = 94 Gew.-% Polyether auf Basis von Propylenoxid (Molgew. 4.500)
  • 2 Gew.-% Diphenylkresylphosphat
  • 2,4 Gew.-% Stabilisator Nr. 4 (siehe Beispiel 1)
  • 1,2 Gew.-% Stabilisator Nr. 1 (siehe Beispiel 1)
  • 0,4 Gew.-% Stabilisator Nr. 7 (siehe Beispiel 1)
• B = 94 Gew.-% Polyether auf Basis von Propylenoxid (Molgew. 4.000) und Stabilisator wie bei A.
• C = 93 Gew.-% Polyether auf Basis von Propylenoxid (MG 5.000) und 7 Gew.-% einer handelsüblichen Stabilisatorformulierung (LP 1655 der Hoechst AG) gemäß dem Stand der Technik.
• D = 100 Gew.-% einer handelsüblichen Schmierölformulierung (Glygole 30) auf Polyetherbasis, die als hochtemperaturbeständiges Schmieröl eingeführt ist.

Explanations to Table 4

• A = 94% by weight of polyether based on propylene oxide (molecular weight 4,500)
  • 2% by weight diphenyl cresyl phosphate
  • 2.4% by weight of stabilizer No. 4 (see example 1)
  • 1.2% by weight of stabilizer No. 1 (see example 1)
  • 0.4% by weight of stabilizer No. 7 (see example 1)
• B = 94% by weight of polyether based on propylene oxide (molecular weight 4,000) and stabilizer as in A.
• C = 93% by weight of polyether based on propylene oxide (MW 5,000) and 7% by weight of a commercially available stabilizer formulation (LP 1655 from Hoechst AG) according to the prior art.
• D = 100% by weight of a commercially available lubricating oil formulation (Glygole 30) based on polyether, which is introduced as a high-temperature-resistant lubricating oil.

Claims (10)

1. Stabilized lubricants based on polyethers, characterized in that they contain diphenylamine derivatives of the formula (I)

included in the R ^{1 is} hydrogen, a straight-chain or branched ^C ₄ to C ₁₂ alkyl group, a straight-chain or branched C ₄ to C ₁₂ alkylene group, a C ₇ to C12 aralkyl group, a C ₇ to C ₁₂ aralkylene group, one optionally by C ₁ to C ₆ alkyl, alkenyl, cycloalkyl or cycloalkenyl substituted C ₅ to C ₁₂ cycloalkyl group or an optionally by C ₁ to C ₆ alkyl, alkenyl or cycloalkenyl-substituted C ₅ to C ₁₂ cycloalkenyl group, but does not mean a hydrocarbon group derived from a terpene, ortho or para to the respective N atom, n stands for an integer from 1 to 29 and Y represents a bifunctional radical -A- and optionally additionally a bifunctional radical -B-, in each case in the ortho or para position to the N atoms, where -A- is a straight-chain or branched C ₄ to C ₁₂ alkyl radical, a C ₇ to C ₁₂ aralkyl radical or a C ₅ to C12 cycloalkyl radical optionally substituted by C ₁ to C ₆ alkyl or cycloalkyl, but not a hydrocarbon radical derived from a terpene, and

means, where R ^{2 is} hydrogen, C ₁ to C ₆ alkyl or C ₅ to C ₆ cycloalkyl and where -B- has a proportion of 0 to 50 mol% of Y. 2. Stabilized lubricants according to claim 1, characterized in that R for hydrogen, benzyl, styryl, α-methylstyryl, tert-butyl, tert. Amyl, isononyl, cyclohexyl, isooctyl, methylcyclohexyl or one of the radicals

each in the ortho or para position to the respective N atom n for an integer from 1 to 19 and Y in the meaning of -A- for

and in the meaning for -B- stands for -CH ₂ -. 3. Stabilized lubricants according to claims 1 and 2, characterized in that they contain 0.1 to 10 wt .-% of a diphenylamine derivative of the formula (I), based on the mixture. 4. Stabilized lubricants according to claims 1 to 3, characterized in that they contain polymers of epoxides of the formula (VI)

in the _R ³ and _R ^{4 can be the} same or different and represent hydrogen or C ₁ to C ₁₂ alkyl, and / or polymers made of tetrahydrofuran and / or block polymers and / or statistical polymers made of different epoxides of the formula (VI) and / or tetrahydrofuran contain. 5. Stabilized lubricants according to claims 1 to 4, characterized in that they contain polyethers in the form of oils with molecular weights of 500 to 20,000. 6. Stabilized lubricants according to claims 1 to 5, characterized in that they additionally contain diphenylamine derivatives of the formula (VII)

in the _R ⁵ and _R ^{6 can be the} same or different and represent hydrogen, C ₁ to C ₁₂ alkyl or C ₇ to C ₁₂ alkaryl, Z for sulfur and m represents O or 1
and metal deactivators of the salicylidene amine type of the formula (VIII)

in the X represents a two bonds, optionally nitrogen-containing, aliphatic radical. 7. Stabilized lubricants according to claim 6, characterized in that they contain diphenylamine derivatives of the formula (VII) in an amount of 0.1 to 5% by weight and metal deactivators of the formula (VIII) in an amount of 0.5 to 2%. -%, each based on the mixture. 8. Stabilized lubricants according to claims 1 to 7, characterized in that they additionally contain further stabilizers based on aromatic amines, phenolic antioxidants, corrosion inhibitors and / or wear protection agents. 9. Stabilized lubricants according to claim 8, characterized in that they each contain the substances mentioned in amounts of 0 to 10% by weight, based on the mixture. 10. A process for the preparation of stabilized lubricants, characterized in that diphenylamine derivatives of the formula (I)

in the R ^{1 is} hydrogen, a straight-chain or branched ^C ₄ to C ₁₂ alkyl group, a straight-chain or branched C ₄ to C ₁₂ alkylene group, a C ₇ to C ₁₂ aralkyl group, a C ₇ to C ₁₂ aralkylene group, one optionally by C ₁ to C ₆ alkyl, alkenyl, cycloalkyl or cycloalkenyl substituted C ₅ to C ₁₂ cycloalkyl group or an optionally by C ₁ to C ₆ alkyl, alkenyl or -Cycloalkeriyl substituted C ₅ to C ₁₂ cycloalkenyl group , but not a hydrocarbon group derived from a terpene, in the ortho or para position to the respective N atom, n stands for an integer from 1 to 29 and Y stands for a bifunctional radical -A- and optionally additionally for a bifunctional radical -B-, in each case in the ortho or para position to the N atoms, where
-A- a straight-chain or branched C ₄ to C ₁₂ alkyl radical, a C ₇ to C ₁₂ aralkyl radical or a C ₅ to C ₁₂ cycloalkyl radical optionally substituted by C ₁ to C ₆ alkyl or cycloalkyl, but not one of a terpene derived hydrocarbon residue, and

means, where R ^{2 is} hydrogen, C ₁ to C ₆ alkyl or C ₅ to C ₆ cycloalkyl and where -B- has a proportion of 0 to 50 mol% of Y, adds and dissolves therein with heating.