EP0377358B1 - Nitrogen-bearing additives having antioxidant properties, and lubricant compositions comprising same - Google Patents

Description

The present invention relates to the preparation of new oxidation inhibitor additives and their use in lubricating compositions. It is known that lubricating oils and in particular crankcase oils intended for internal combustion engines contain various additives which serve to improve their performance. Some of these additives are used to protect the oil from oxidation caused by high temperatures or by certain metal ions dispersed in the oil.

This degradation of the lubricant is linked to the thermal and oxidative decomposition of the oil and the additives. It gives rise to the formation and deposition of carbonaceous substances on the walls of the piston. If these deposits become too large, they can initiate a gumming or seizing of the piston and increase the wear of the moving metal parts. It is therefore important to limit the degradation of lubricants as best as possible by using effective antioxidant additives at economically reasonable concentrations.

The protection of lubricants by various organic additives is widely described. These compounds are generally distinguished according to their mode of action, on the one hand free radical inhibitors (hindered phenols, aromatic amines, phenothiazines ...), and on the other hand the products which break down hydroperoxides or peroxides ( metallic dithiocarbamates or dithiophosphates, phosphites, thioethers ...).

Metallic deactivators are also known which prevent the metal ions present in the oil or on the surfaces from initiating self-oxidation of lubricant. These products act by complexing of metals.

Among all these compounds, aromatic amines and more particularly phenothiazine derivatives are the most effective because they act according to several mechanisms, decomposition of hydroperoxides, electronic transfer agents, metal chelation and oxygen acceptors.

Thus, US-A-2 781 318 describes the use in synthetic lubricants of alkylphenothiazines, the alkyl groups of which are carried by the aromatic carbons of phenothazine.

US Pat. No. 3,536,706 mentions the use of phenothiazines substituted on the aromatic rings by tertiary alkyl groups of 4 to 12 carbon atoms or by aryl groups.

US Pat. No. 3,803,140 suggests the use of teralkylated derivatives of N-alkyl or N-alkenyl phenothiazines. However, the teralkylated derivatives of phenothiazines which are unsubstituted on nitrogen are preferred.

US-A-3,344,068 describes the use of antioxidants derived from aromatic amines in synthetic ester lubricants. These additives can be N-alkylphenothiazines substituted on aromatic rings with at least one alkyl group.

US-A-3,376,224 claims antioxidants derived from phenothiazine substituted by an alkoxymethyl group on the nitrogen atom.

Patent application WO-A-88 02007 describes the preparation and use of N-alkylthioalkylphenothiazines obtained by condensation of a phenothiazine and an alkylthioalkanol. The presence of a sulfur atom strengthens the antioxidant power of the phenothiazine thus substituted.

We have found that the properties of antioxidant additives containing aromatic nitrogen can be improved by the presence of an aminoalkylated chain.

The solubility of these additives in lubricants of synthetic or mineral origin is considerably improved.

The presence of an amine function makes it possible to introduce other functions into the molecule to reinforce its antioxidant power or to confer on it other useful properties.

où:

• Ar et Ar′ sont reliés entre eux pour former avec l'azote auquel ils sont rattachés une structure hétérocyclique aromatique choisie dans le groupe formé par la phénothiazine, l'imidazole, le benzimidazole, le triazole ou le benzotriazole
• R et R′ identiques ou différents représentent un radical alkylène, linéaire ou ramifié en C₂ à C₁₈, de préférence en C₂ à C₆ et avantageusement en C₃, éventuellement substitué par un halogène ou un groupe - OH ou - NH₂
• X représente un atome d'oxygène, de soufre ou un groupe -NH-
• a est un nombre entier entre 0 et 5 et de préférence entre 0 et 2,
• y est choisi dans le groupe formé par
  
          - NR₁R₂   (II)
  
  où R₁ et R₂, identiques ou différents représentent un atome d'hydrogène ou un radical alkyle, alkényle, cycloalkyle ou arylalkyle en C₁ à C₁₂
  
          - N = CH - Ar₁   (III)
  
  où: Ar₁ est un radical aryle renfermant au moins un groupement phénolique choisi dans le groupe formé par le phénol, le terbutylphénol, le diterbutyl-2,4-phénol, le diteramyl-2,4-phénol, le diterbutylparacrésol, le dodécylphénol, le dodécylphénol sulfurisé, le catéchol, le bêtanaphtol ou le résorcinol,
  
          - NR₁ - CO - Ar₁ et   (IV)
  
  
  
  où R₃ représente un atome d'hydrogène ou avantageusement un oligomère d'une oléfine en C₂ à C₅ dont la masse moléculaire est comprise entre 500 et 3000 et de péférence entre 800 et 1500.

The antioxidant additives containing an aromatic nitrogen, according to the invention, are characterized in that they correspond to the general formula:

or:

• Ar and Ar ′ are linked together to form with the nitrogen to which they are attached an aromatic heterocyclic structure chosen from the group formed by phenothiazine, imidazole, benzimidazole, triazole or benzotriazole
• R and R ′, identical or different, represent an alkylene radical, linear or branched in C₂ to C₁₈, preferably in C₂ to C₆ and advantageously in C₃, optionally substituted by a halogen or a group - OH or - NH₂
• X represents an oxygen or sulfur atom or a group -NH-
• a is an integer between 0 and 5 and preferably between 0 and 2,
• is chosen from the group formed by
  
  - NR₁R₂ (II)
  
  where R₁ and R₂, identical or different, represent a hydrogen atom or a C₁ to C₁₂ alkyl, alkenyl, cycloalkyl or arylalkyl radical
  
  - N = CH - Ar₁ (III)
  
  where: Ar₁ is an aryl radical containing at least one phenolic group chosen from the group formed by the phenol, terbutylphenol, diterbutyl-2,4-phenol, diteramyl-2,4-phenol, diterbutylparacresol, dodecylphenol, sulfurized dodecylphenol, catechol, betanaphthol or resorcinol,
  
  - NR₁ - CO - Ar₁ and (IV)
  
  
  
  where R₃ represents a hydrogen atom or advantageously an oligomer of a C₂ to C₅ olefin whose molecular mass is between 500 and 3000 and preferably between 800 and 1500.

Preferably, phenothiazine derivatives are used.

Ar and Ar ′ may be substituted by alkyl or aryl radicals, preferably C₁ to C₁₂ or by hydroxyl, alkoxy, alkylthio or even halogen groups.

R₁ and R₂ advantageously represent a hydrogen atom or a C₁ to C₄ alkyl radical.

According to another aspect of the invention R₁ is a hydrogen atom and R₂ represents an arylalkyl radical, of general formula -CH₂ - Ar₁ where Ar₁ with the abovementioned meaning.

The introduction of the phenolic group Ar₁ strengthens the antioxidant power of the additive. Preferably, 2,6-diterbutyl-phenol or sulfurized dodecylphenol is used.

These additives can be prepared by any known method.

One obtains, for example, the additives where Y = - NR₁R₂ by alkylation of phenothiazine, imidazole, benzimidazole, triazole or benzotriazole. The use of other heterocycles can be envisaged, provided that the heterocycle has a nitrogen atom which can be alkylated.

Acrylamide, chloroacetamide, iodoacetamide, acrylonitrile or chloro-3-propionitrile are good alkylation reagents. The alkylation reaction is followed by the hydrogenation of the nitrile or amide groups.

It is possible, for example, to condense phenothiazine with acrylonitrile under cyanoethylation conditions with an amount of acrylonitrile greater than the theoretical amount in the presence of an alkaline catalyst such as Triton B (benzyltrimethylammonium hydroxide) in methanolic solution such as describes NLSMITH (J. Org. Chem. 15, 1129, 1950). The intermediate is then reduced to N-aminopropylphenothiazine, by catalytic hydrogenation in an autoclave under pressure of hydrogen and ammonia. If a> 1 several successive reactions are necessary.

Another method consists in reacting an epoxide, such as ethylene oxide or propylene oxide with the aromatic nitrogen, followed by an aminolysis of the alcohol intermediate by treatment with ammonia or with an amine of general formula R₁-NH-R₂ where R₁ and R₂ have the above meaning.

It is of course possible to obtain compounds where a> 1 by successive reactions with several molecules of epoxides, or mixtures of epoxides.

If R₂ is an arylalkyl radical containing at least one phenolic OH, the Mannich reaction is advantageously used for its synthesis.

The Mannich base is obtained by the reaction of a compound of general formula (I) where Y = -N R₁R₂ and where at least one of the groups R₁ or R₂ is a hydrogen atom with a phenol having at least one active hydrogen in its molecule and an aldehyde.

Linear or cyclic alkylaldehydes or an aromatic aldehyde are used, but preferably formaldehyde or its derivatives such as paraformaldehyde, acetaldehyde or propionaldehyde.

Among the phenols, diterbutyl-2,6-phenol or sulfurized dodecylphenol will advantageously be used.

The Mannich base is generally obtained by adding 0.8 to 1.5 moles, preferably 1.2 moles of aldehyde, 0.8 to 2.5, preferably 1 mole of compound of formula (I) to one mole of phenol.

The reaction is carried out with stirring under an atmosphere of an inert gas such as nitrogen, at a temperature between 60 and 130 ° C and preferably around 100 ° C, for a time between 2 to 10 hours.

It is generally carried out in the presence of a polar solvent such as isopropanol or an aromatic solvent such as toluene or xylenes. The water formed during the reaction is removed by azeotropic entrainment.

After the reaction, it is sufficient to remove the solvent to collect the Mannich base which can be directly used in the lubricant compositions according to the present invention.

The compounds with an oxaldine or base of SCHIFF function (Y = -N = CH-Ar₁) are obtained by reaction of aldehydes of general formula Ar₁-CHO with compounds of general formula (I) where Y = NR₁R₂ and R₁ and R₂ represent a hydrogen atom.

The compound Ar₁-CHO is salicylaldehyde, terbutylsalicylaldehyde, diterbutyl-3-5-hydroxy-4-benzaldehyde or diterbutyl-3,5-hydroxy-4-phenyl-3-propionaldehyde.

The amide-function compounds (Y = -NR₁-CO-Ar₁) are obtained by reaction of an acid of general formula Ar₁ - CO₂H with compounds of general formula (I) where Y = NR₁R₂ and at least one of the groups R₁ and R₂ represents a hydrogen atom.

The compound Ar₁- CO₂H is salicylic acid, terbutylsalicylic acid, diterbutyl-3,5-hydroxy-4-phenyl-3-propionic acid.

The formation of SCHIFF bases or amides generally takes place by heating the reagents under the same operating conditions as those described for obtaining the MANNICH bases.

sont obtenus par réaction d'un dérivé de l'anhydride succinique avec un composé de formule générale (I) où Y=NR₁R₂ et R₁et R₂ représentent un atome d'hydrogène.Compounds with imide function,

are obtained by reaction of a succinic anhydride derivative with a compound of general formula (I) where Y = NR₁R₂ and R₁and R₂ represent a hydrogen atom.

The introduction of the imide function into the molecule confers dispersing properties on the additives according to the invention.

The succinic anhydride used is generally substituted by an alkyl group, preferably an oligomer.

The oligomer comes from the oligomerization of a C₂ to C₅ olefin. It has a molecular weight between 500 and 3000, and preferably between 800 and 1500. The oligomer has residual unsaturation and reacts with maleic anhydride to give the substituted succinic anhydride.

The operation is generally carried out by condensing 0.5 to 1.5 moles, preferably 1 mole of compound of formula (I) per mole of anhydride in an organic solvent such as toluene or xylenes, capable of removing the water formed in the azeotropic entrainment reaction. The reaction gives rise to the formation of amide and imide functions.

After the reaction, it suffices to remove the solvent to collect the additive which can be used in the lubricating compositions of the invention

The additive can be incorporated in natural or synthetic lubricating oils or in mixtures of such oils. By way of example, mention may be made of ordinary or refined mineral oils of paraffinic or naphthenic composition and hydrorefined oils. Synthetic oils, such as polybutenes, alkylbenzenes such as dinonylbenzenes and tetradecylbenzene, ethers or esters of polypropylene glycols, esters of polycarboxylic acids such as methyl adipate and pentaerythritol heptanoate, silicone oils such as polysiloxanes, total or partial esters of phosphoric acid, in particular the tricresylphosphate and alkylphosphoric acids are also suitable.

The concentration of additives according to the invention in the ready-to-use lubricating compositions is generally of the order of 0.01 to 10% by weight and preferably from 0.1 to 2.5% by weight.

It is possible to combine the antioxidant compounds according to the invention with other usual additives of lubricants such as corrosion inhibitors, detergents and antiwear, dispersant and defoamer additives.

The lubricant compositions containing the antioxidant compound according to the invention can be used in particular as oils for crankcases intended for internal combustion engines, as oils for crankcase, as oils for gear and to facilitate the machining of metals.

The following examples illustrate the invention without, however, limiting it.

EXAMPLE 1 (preparation of N (aminopropyl) phenothiazine).

In a reactor containing 100 g (0.5 mole) of phenothiazine and 530 g (10 moles) of acrylonitrile, and cooled to a temperature below 10 ° C., 2.5 ml of a 40% methanolic solution are added dropwise benzyltrimetyl ammonium hydroxide. The whole is heated at 80 ° C. for 1 hour 30 minutes. The excess acrylonitrile is then removed by vacuum distillation. The solid is isolated and recrystallized twice from acetone. Phenothiazinyl-10 propionitrile is obtained with a yield of 66% (83.9 g, mp 156-157 ° C).
50.6 g of this nitrile are placed in a Soxhlet apparatus and are continuously extracted with 1000 ml of ethyl ether containing 16 g of lithium aluminum hydride. After 72 hours of reaction, the ethereal solution is treated successively with 16ml of water, 12ml of 25% sodium hydroxide and twice 50ml of water. After filtration of the insoluble salts, N-aminopropylphenothiazine is obtained after drying and distillation of the ether (Rt = 70%).

EXAMPLE II (Mannich base with diterbutyl-2-6-phenol).

2.56 g (0.01 mole) of N-aminopropylhenothiazine and 1.96 g (0.01 mole) of diterbutyl-2,6-phenol and 100 ml of ethanol are introduced into a 250 ml reactor with stirring. The mixture is left stirring for 10 minutes at room temperature, then 0.33 g (0.011 mole) of paraformaldehyde is added. The whole is brought to reflux for 24 hours and then left at room temperature for another 96 hours. The solid is separated by filtration, washed with ethanol and dried in an oven at 100 ° C (m = 2.31 g, Rt 51%).

EXAMPLE III (Mannich base with sulfurized dodecylphenol).

• a) Dans un réacteur contenant 500g de dodécylphénol, on introduit sous agitation, sous atmosphère d'azote et en maintenant la température entre 20 et 30°C, 141,5g de S₂Cl₂ en une heure environ. Après addition complète, le mélange est chauffé 1 heure à 150°C, puis 1 heure à 180°C et 1 heure à 200°C en maintenant un courant d'azote pour éliminer le chlorure d'hydrogène. On laisse refroidir sous agitation, en maintenant un léger courant d'azote (Le produit obtenu a une teneur en soufre de 10,3%).
• b) Dans un réacteur de 250ml on introduit sous agitation 2,56g (0,01 mole) de N-aminopropylphénothiazine, 2,93g (0,005 mole) de dodécylphénol sulfurisé (IIIa) et 200ml d'éthanol. On laisse 5 minutes à température ambiante sous agitation puis on additionne 0,33g de paraformaldéhyde et on porte à reflux 8 h.

L'eau formée est éliminée avec le solvant au fur et à mesure de sa formation, on laisse ensuite refroidir. Après 2 jours à température ambiante, le précipité obtenu est filtré puis dissous dans le dichlorométhane. Après filtration et élimination du solvant, on recueille 1,3g d'une poudre marron.
Par spectroscopie IR on vérifie la présence de la bande d'adsorption du doublet de l'azote à 3300cm¹ caractéristique du produit attendu.

• a) Into a reactor containing 500 g of dodecylphenol, 141.5 g of S₂Cl₂ are introduced in approximately one hour with stirring, under a nitrogen atmosphere and maintaining the temperature between 20 and 30 ° C. After complete addition, the mixture is heated for 1 hour at 150 ° C., then 1 hour at 180 ° C. and 1 hour at 200 ° C. while maintaining a stream of nitrogen to remove the hydrogen chloride. The mixture is allowed to cool with stirring, while maintaining a slight stream of nitrogen (the product obtained has a sulfur content of 10.3%).
• b) 2.56 g (0.01 mole) of N-aminopropylphenothiazine, 2.93 g (0.005 mole) of sulfurized dodecylphenol (IIIa) and 200 ml of ethanol are introduced into a 250 ml reactor. It is left for 5 minutes at room temperature with stirring, then 0.33 g of paraformaldehyde is added and the mixture is brought to reflux for 8 h.

The water formed is removed with the solvent as it is formed, then allowed to cool. After 2 days at room temperature, the precipitate obtained is filtered and then dissolved in dichloromethane. After filtration and removal of the solvent, 1.3 g of a brown powder are collected.
By IR spectroscopy we verify the presence of the adsorption band of the nitrogen doublet at 3300cm¹ characteristic of the expected product.

EXAMPLE IV

20 g (0.1 mol) of phenothiazine and 4.1 g of sodium amide in 200 ml of toluene are heated to reflux with stirring. After one hour, this previously cooled solution is poured into 250 ml of bis (chloro-2-ethoxy) -1.2 ethane. The whole is heated at reflux for 4 hours. The toluene and the excess of di- (chloro-2-ethoxy) -1.2 ethane are evaporated.
The residue is taken up with 200 ml of a 30% aqueous ammonia solution and 100 ml of methanol and the whole is maintained at 60 ° C. for 72 hours. The alcohol is eliminated and the product is extracted with twice 150 ml of toluene. The organic phase is washed with twice 50 ml of water and dried over magnesium sulfate. After evaporation of the solvent, a product consisting mainly of (amino-2-ethoxy) -2- (phenothiazinyl-2-ethoxy) ethane is recovered.

EXAMPLE V

In this example, the stability to oxidation of lubricating compositions containing an additive of the invention is evaluated. The tests are carried out at 160 ° C., using a pressurized oxygen bomb in the presence of a metal catalyst, a fuel catalyst and water so as to partially simulate the conditions under which the oil can be submitted in a gasoline engine.
The metal catalyst is a mixture of soluble naphthenates of Pb, Cu, Fe, Mn and Sn.
The oxidation stability of lubricants is assessed by measuring the induction time, that is to say the time interval between the start of the test and the rapid drop in pressure in the bomb.
The longer this induction time, the more effective the antioxidant additives used in the composition of the lubricants.

Claims (9)

1. Additives to lubricating oils having an anti-oxidant effect comprising an aromatic nitrogen, characterised in that they correspond to the general formula

   

   wherein:
   Ar and Ar′ are connected to one another so as to form with the nitrogen to which they are linked an aromatic heterocyclic structure selected from the group comprising phenothiazine, imidazole, benzimidazole, triazole or benzotriazole;

   - R and R′, which may be identical or different, represent a C₂ to C₁₈ linear or branched alkylene radical, optionally substituted by a halogen or a -OH or -NH₂ group;

   - X represents an oxygen or sulphur atom or a -NH - group; and

   - a is an integer between 0 and 5 and Y is selected from the group formed by
   
           - N R₁R₂   (II)
   
   wherein:
   R₁ and R₂, which may be identical or different, represent a hydrogen atom or a C₁ to C₁₂ alkyl, alkenyl, cycloalkyl or arylalkyl radical;
   
           - N - CH - Ar₁   (III)
   
   wherein:
   Ar₁ is an aryl radical containing at least one phenolic group selected from the group comprising phenol, p-terbutylphenol, diterbutyl-2,4-phenol, diteramyl-2,4-phenol, diterbutyl-paracresol, dodecylphenol, sulphurised dodecylphenol, catechol, beta-naphthol or resorcinol
   
           - NR₁ - CO - Ar₁   (IV) and
   
   

   

   wherein:
   R₃ is a hydrogen atom or an oligomer of a C₂ to C₅ olefin of which the molecular weight is between 500 and 3000 and is preferably between 800 and 1500.
2. Additives according to Claim 1, characterised in that R and R′, which may be identical or different, represent a C₁₂ to C₆, advantageously a C₃, linear or branched alkylene radical.
3. Additives according to Claim 1 or 2, characterised in that a is an integer between 0 and 2.
4. Additives according to Claim 1, characterised in that R₁ and R₂, which may be identical or different, represent a hydrogen atom or a C₁ to C₄ alkyl radical.
5. Additives according to Claim 1, characterised in that R₁ represents a hydrogen atom and R₂ represents an aryl alkyl radical having the general formula -CH₂-Ar₁.
6. Additives according to Claim 5, characterised in that the aryl radical Ar₁ is diterbutyl 2,4-phenol or sulphurised dodecylphenol.
7. Additives according to Claim 1, characterised in that the aromatic heterocyclic structure is phenothiazine.
8. Lubricating composition characterised in that it contains a natural or synthetic lubricating oil and 0.01 to 10 weight %, preferably 0.1 to 2.5 weight %, of an additive according to any one of Claims 1 to 7.
9. Composition according to Claim 8, characterised in that it comprises further additives conventional in lubricants such as corrosion inhibitors, detergents and anti-wear, dispersant and anti-foaming additives.