DE69324746T2 - Antioxidants for highly monounsaturated vegetable oils - Google Patents

Abstract

An antioxidant in high monounsaturated oils is described in order to prepare a composition having utility in hydraulic fluids. The composition comprises: (A) at least one animal, vegetable or synthetic triglyeride oil, (B) at least one alkyl phenol, and optionally (D) a metal deactivator. In another embodiment, the composition comprises the above (A) and (B) with (C) at least one aromatic amine, and optionally (D) as described above.

Description

The present invention relates to an antioxidant composition for triglyceride oils having at least 70% monounsaturated content. Triglyceride oils containing this antioxidant composition can be used in hydraulic fluids, two-stroke internal combustion engines, gear oils, passenger car engine oils and as lubricants for machines in the food sector.

Oxidation stability is an important requirement for all lubricants, regardless of their use. Degradation by autoxidation is catalysed to a large extent by traces of metal ions (particularly copper and iron) which are dissolved when the lubricant comes in contact with a metal surface. Organic compounds, particularly those comprising relatively long chain hydrocarbon radicals and especially those containing unsaturated moieties, undergo autoxidation when brought into contact with oxygen. This in turn leads to deterioration of the base material, often leading to an increase in overall acidity, formation of varnish-like residues, discolouration, loss of physical properties such as tensile strength for resins or elasticity for elastomers, reduction in effectiveness, polymerisation rancidity and/or odour.

In general, various additives are added to lubricating oils, hydraulic fluids and greases to improve the performance properties of these lubricants. In particular, there is a need for additives that effectively reduce oxidation and aging of the lubricant and thus significantly extend the service life of the lubricant.

US-PS 5,102,567 (Wolf, April 7, 1992) relates to a lubricating oil provided for the lubrication of parts such as bearings, gears and sliding devices, particularly in food processing equipment. The food-grade lubricating oil provides oxidation stability, thermal and hydrolytic stability; protects against rusting and corrosion; protects against wear and prevents foaming and is resistant to the formation of sludge.

US-PS 4,115,288 (Schmitt, September 19, 1978) relates to a lubricating composition comprising a major amount of a lubricating oil or grease and, as an antiwear agent, a minor amount of a substituted 1,2,3-triazole of the general formula

in which the radicals R₁ and R₂ are independently selected from the group consisting of an alkyl group containing 1 to 18 carbon atoms; an aryl group such as phenyl; a hydrogen atom and the group

and wherein at least one of R₁ and R₂ is other than hydrogen and wherein n is an integer from 5 to 15.

U.S. Patent No. 4,746,448 (Kenmochi et al., May 24, 1988) provides a cold rolling oil for steels comprising (A) 40 to 90 weight percent of a monoester of an aliphatic carboxylic acid having 12 to 22 carbon atoms and an aliphatic alcohol having 1 to 12 carbon atoms, (B) 0.5 to 10 weight percent of at least one of a dimer acid and a polymerized acid of a higher aliphatically unsaturated acid having 16 to 20 carbon atoms, (C) 2 to 40 weight percent of a polyester having a molecular weight of 750 to 7500, and (D) 0.1 to 10 weight percent of a polymer compound having nitrogen atoms in a molecule having a molecular weight of 1000 to 100,000.

According to the invention there is provided an antioxidant composition comprising a major amount of

(A) at least one vegetable triglyceride oil of the general formula

in which the radicals R¹, R² and R³ are aliphatic hydrocarbyl groups with at least 70% monounsaturated character and contain 8 to 24 carbon atoms, and a lower amount of antioxidant of

(B) at least one alkylphenol of the general formula

in which the radical R⁴ is an alkyl group containing 1 to 24 carbon atoms, a is 2 and the position para to the OH group is free, and optionally

(D) a metal deactivator selected from

(1) a benzotriazole of the general formula

in which the radical R�8 is a hydrogen atom or an alkyl group having 1 to 24 carbon atoms,

(2) a phosphatide of the general formula

in which the radicals R⁹⁰ and R¹⁰ are aliphatic hydrocarbyl groups containing 8 to 24 carbon atoms, and G is selected from

and

(3) a carbamate of the general formula

in which the radical R¹¹ is an alkyl group containing 1 to 24 carbon atoms, phenyl or alkylphenyl, where the alkyl group contains 1 to 18 carbon atoms, the radicals R¹² and R¹³ are hydrogen atoms or an alkyl group containing 1 to 6 carbon atoms, with the proviso that the radicals R¹² and R¹³ are not both hydrogen atoms,

(4) Citric acid and derivatives of citric acid of the general formula

in which the radicals R¹⁴, R¹⁵ and R¹⁴ are independently hydrocarbon groups or aliphatic hydrocarbyl groups containing 1 to 12 carbon atoms, with the proviso that that at least one of R¹⁴, R¹⁵ and R¹⁴ is an aliphatic hydrocarbyl group,

(5) a coupled phosphorus-containing amide of the general formula

in which the radicals X¹, X² and X³ are independently an oxygen atom or sulfur atom;

wherein R¹⁷ and R¹⁶ are independently a hydrocarbyl group, a hydrocarbyl-based oxy group, the hydrocarbyl portions containing from 6 to 22 carbon atoms, or a hydrocarbyl-based thio group containing from 4 to 34 carbon atoms;

in which the radicals R¹⁹9;, R²⁰, R²¹ and R²² are independently a hydrogen atom or an alkyl group having 1 to 22 carbon atoms or an aromatic, alkyl-substituted aromatic or an aromatic-substituted alkyl group having 6 to 34 atoms;

in which n is 0 or 1;

in which n' is 2 or 3;

in which the radical R²³ is a hydrogen atom; and, if n' is 2, the radical R²⁴ is selected from

wherein the radical R is an alkyl group in the form of an alkylene or alkylidene containing 1 to 12 carbon atoms and the radical R' is an alkyl, alkylene, alkylidene or carboxyl group containing 1 to 60 carbon atoms and, if n' is 3, the radical R²⁴ is

or

(6) a methyl acrylate derivative prepared by reacting equimolar amounts of a phosphoric acid of the general formula

with methyl acrylate, wherein X¹ and X² are as defined in (D)(5) and R²⁵ and R²⁶ are each independently a hydrocarbyl group, a hydrocarbyl-based thio group or, preferably, a hydrocarbyl-based oxy group, wherein the hydrocarbyl portion contains 1 to 30 carbon atoms and the residual acidity is neutralized with 1 mole of propylene oxide per 20-25 moles of phosphoric acid.

In a preferred embodiment, the invention comprises an antioxidant composition comprising a major amount of:

(A) the triglyceride oil described above with a lower antioxidant amount of

(B) at least one alkylphenol as described above,

(C) at least one aromatic amine of the general formula

in which the radical R�5 is

group and wherein the radicals R⁶ and R⁷ are independently an alkyl group having 4 to 18 carbon atoms, and optionally

(D) the metal deactivator described above.

Various preferred features and embodiments of the present invention will now be described by way of non-limiting examples.

(A) The triglyceride oil

In carrying out this invention, a triglyceride oil is used which is a vegetable oil of the general formula

Included in the triglyceride formula are aliphatic hydrocarbyl groups having at least 70% monounsaturated character and having 8 to 24 carbon atoms. The term "hydrocarbyl group" as used here means a group having a carbon atom directly bonded to the rest of the molecule. The aliphatic hydrocarbyl groups include the following:

(1) Aliphatic hydrocarbon groups, i.e. alkyl groups such as heptyl, nonyl, undecyl, tridecyl, heptadecyl; alkenyl groups having a single double bond such as heptenyl, nonenyl, undecenyl, tridecenyl, heptadecenyl, heneicosenyl; alkenyl groups having 2 or 3 double bonds such as 8,11-heptadecadienyl and 8,11,14-heptadecatrienyl. All isomers of these are included, but straight-chain groups are preferred.

(2) Substituted aliphatic hydrocarbon groups; i.e. groups containing non-hydrocarbon substituents which, in the context of this invention, do not alter the predominantly hydrocarbon character of the group. Suitable substituents are known; examples are the hydroxyl group, carbalkoxy (especially lower carbalkoxy) and alkoxy (especially lower alkoxy) groups, the term "lower" denoting groups having not more than 7 carbon atoms.

(3) Heterogroups; that is, groups which, while having a predominantly aliphatic hydrocarbon character within the context of this invention, contain atoms other than carbon present in a chain or ring which would otherwise consist of aliphatic phatic carbon atoms. Suitable heteroatoms are known and include, for example, oxygen and sulfur.

The fatty acid residues are chosen so that the triglyceride has a monounsaturated character of at least 70% and preferably at least 80%.

For example, a triglyceride comprising only an oleic acid residue has an oleic acid content of 100% and consequently a monounsaturated content of 100%. If the triglyceride is composed of acid residues such as 70% oleic acid, 10% stearic acid, 5% palmitic acid, 7% linoleic acid and 8% hexadecanoic acid, the monounsaturated content is 78%. It is also preferred that the monounsaturated character comes from an oleic acid residue, i.e., R¹CO, R²CO and R³CO is the oleic acid residue. The preferred triglyceride oils are high (at least 70%) oleic acid triglyceride oils. Typical high oleic vegetable oils used in the present invention are high oleic safflower oil, high oleic corn oil, high oleic canola oil, high oleic sunflower oil, high oleic soybean oil, high oleic cottonseed oil, and high oleic palm oil. A preferred high oleic vegetable oil is high oleic sunflower oil from Helianthus SP, available from SVO Enterprises Eastlake, Ohio as Sunyl® high oleic sunflower oil.

(B) The alkylphenol

Component (B) is at least one alkylphenol of the general formula

in which the radical R⁴ is an alkyl group having 1 to 24 carbon atoms and a has the value 2. The radical R⁴ preferably contains 4 to 18 carbon atoms and in particular 4 to 12 carbon atoms. The radical R⁴ can be either straight-chain or branched-chain, with branched-chain being preferred. The position para to the OH group is free.

Component (B) is an alkylphenol, but mixtures of alkylphenols can be used. Preferably, the phenol is a butyl-substituted phenol with two t-butyl groups. The t-butyl groups occupy the 2,6-position, ie the phenol is sterically hindered:

(C) The aromatic amine

Component (C) is at least one aromatic amine of the general formula

in which the residue R&sup5; represents the group

and wherein R⁶ and R⁷ are independently an alkyl group having 4 to 18 carbon atoms.

In a particularly advantageous embodiment, component (C) comprises an alkylated diphenylamine such as the nonylated diphenylamine of the formula

(D) The metal deactivator to be used if necessary

An optional metal deactivator may be used, the metal deactivator being selected from:

(1) a benzotriazole,

(2) a phosphatide,

(3) a carbamate,

(4) citric acid or its derivatives, or

(5) a coupled phosphorus-containing amide.

(D)(1) Benzotriazole

A suitable metal deactivator is a benzotriazole compound of the general formula

in which the radical R⁸ is a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 24 carbon atoms, preferably 1 to 12 carbon atoms and in particular 1 carbon atom. If the radical R contains 1 carbon atom, the benzotriazole compound is a tolyltriazole of the formula

Tolyltriazole is available under the trademark Cobratec TT-100 from Sherwin-Williams Chemical.

(D)(2) The phosphatide

Other metal deactivators are the phosphatides of the general formula

in which the radicals R⁹ and R¹⁰ are aliphatic hydrocarbyl groups having 8 to 24 carbon atoms and the radical G is selected from

Preferably, the remainder G

so that the phosphatide is lecithin. Particularly effective phosphatides are soybean lecithin, corn lecithin, peanut lecithin, sunflower lecithin, safflower lecithin and rapeseed lecithin.

(D)(3) The carbamate

A third suitable metal deactivator are the carbamates of the general formula

in which the radical R¹¹ is an alkyl group having 1 to 24 carbon atoms, phenyl or alkylphenyl, where the alkyl group contains 1 to 18 carbon atoms. Preferably the radical R¹¹ is an alkyl group having 1 to 6 carbon atoms. The radicals R¹² and R¹³ are hydrogen atoms or an alkyl group having 1 to 6 carbon atoms, with the proviso that the radicals R¹² and R¹³ are not both a hydrogen atom.

(D)(4) Citric acid and its derivatives

A fourth suitable metal deactivator is citric acid or derivatives of citric acid of the general formula

in which the radicals R¹⁴, R¹⁵ and R¹⁵ are independently hydrogen atoms or aliphatic hydrocarbyl groups having 1 to 12 carbon atoms, with the proviso that at least one of the radicals R¹⁵ and R¹⁵ is an aliphatic hydrocarbyl group and preferably 1 to contains 6 carbon atoms.

(D)(5) The coupled phosphorus-containing amide

The fifth suitable metal deactivator is a coupled phosphorus-containing amide which is a statistical mixture of compounds of the general formula

X¹ and X² are independently an oxygen atom or sulfur atom, and preferably a sulfur atom, whereas X³ is an oxygen atom or sulfur atom, and preferably an oxygen atom. R¹⁷ and R¹⁸ are each independently a hydrocarbyl group, a hydrocarbyl-based thio group, or preferably a hydrocarbyl-based oxy group, with the hydrocarbyl portion containing from 6 to 22 carbon atoms. The hydrocarbyl portion of R¹⁷ and R¹⁸ generally contains from 1 to 34 carbon atoms. When R¹⁷ is hydrogen and R²⁴ is methylene, R¹⁷ and R¹⁸ will contain from 6 to 12 carbon atoms to provide sufficient oil solubility. The hydrocarbyl portion of R¹⁷ and R¹⁸ may independently have alkyl character or aromatic character. Although the hydrocarbyl portion of both R¹⁷ and R¹⁸ may be of the same type of hydrocarbyl group, i.e., both alkyl or both aromatic, often one such group may be alkyl and the remaining group may be aromatic. Various coupled phosphorus-containing amide compounds may be prepared by reacting a mixture of two or more different reactants, each containing a hydrocarbyl group and an aromatic hydrocarbyl group (R¹⁷ and R¹⁸). The same or different compounds are coupled using different R²⁴ coupling groups to form a random mixture of coupled compounds, or they are reacted with different compounds to form different R²⁴ functional groups. to provide therein.

The hydrocarbyl group of R¹⁷ and R¹⁸ is preferably an alkyl group having from 6 to 22 (more preferably 8 to 12) carbon atoms. Examples of such groups include hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, octadecyl, behenyl and the like, including all isomers thereof. Should the hydrocarbyl groups R¹⁷ or R¹⁸ be aromatic, they may be phenyl or naphthyl groups. Frequently they will have an alkyl substituent Thus, the alkyl-substituted aromatic group may contain from 0, ie, phenyl, to 28 carbon atoms, and preferably from 7 to 12 carbon atoms. Whenever a mixture of the coupled phosphorus-containing amide compounds is used which contains significant or effective amounts of the R¹⁷ or R¹⁸ alkyl-type substituents, the aromatic substituent may preferably contain from 6 to 12 carbon atoms in its alkyl group, ie, the alkyl-substituted aromatic substituent. This is because, although the solubility of phenyl or lower alkyl substituted aromatic compounds can be quite low, the overall solubility in a lubricant composition can generally be increased to a desired level by the use of the R¹⁷ and R¹⁸ hydrocarbyl groups which are alkyl groups and/or by the use of R²³ and/or R²⁴ groups containing a large number of carbon atoms. The use of lower alkyl compounds, e.g., having less than 6 carbon atoms in the above R¹⁷ and R¹⁸ radicals, with a methylene group as the R²⁴ radical is undesirable with respect to oil solubility.

In the alkyl-substituted aromatic group, the aromatic is preferably phenyl, while the alkyl group may be as described above. Specific examples of such alkyl groups on the aromatic nucleus include methyl, ethyl, propyl, butyl, pentyl, heptyl, octyl, decyl, behenyl and the like, including isomers thereof.

Accordingly, specific examples of mixed hydrocarbyl (R¹⁷ and R¹⁸) portions of substituents include tolyl and octyl, tolyl and hexyl, isobutylphenyl and amyl, phenyl and isooctyl, and the like. Mixed hydrocarbyl (R¹⁷ and R¹⁸) substituents are also ensured when cresylic acids are used to form the phosphorus portion of the coupled phosphorus-containing amide compound. The sources, types and variety of cresylic acids are known. The number of different molecular units in the mixture is further increased by the different R²⁴ coupling groups, as indicated above for coupled phosphorus-containing amides with n' equal to 2 or 3.

When X¹ and X² are sulfur atoms, and especially when X² is a sulfur atom, the alkylhydrocarbyl substituent (R¹⁷ or R¹⁸) contains 6 or more carbon atoms. However, when X¹ or X² are oxygen atoms, and especially when X² is an oxygen atom, the alkylhydrocarbyl substituent (R¹⁷ or R¹⁸) contains 6 to 12 carbon atoms.

Each of R¹⁹9;, R²⁰, R²¹ and R²² can independently be a hydrogen atom or a saturated hydrocarbyl group having up to 22 carbon atoms. The saturated hydrocarbyl group can be an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 4 to 22 carbon atoms, or an aromatic group, an aromatic-substituted alkyl group or an alkyl-substituted aromatic group having 6 to 34 carbon atoms. Preferably, R¹⁹9;, R²⁰, R²¹ and R²² are hydrogen atoms or methyl groups, with hydrogen atoms being particularly preferred. Examples of specific alkyl groups R¹⁹9, R²⁰, R²¹ and R²² include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, etc., and isomers thereof, whereas examples of specific aromatic groups include phenyl, tolyl, naphthyl, heptylphenyl, nonylphenyl, dodecylphenyl, wax-substituted phenyl and the like. With respect to the R²¹-C-R²² group, n may have the value 0 or 1. Preferably, n has the value 1.

In the amide portion of the molecule, R²³ may be a hydrogen atom or an alkyl group having 1 to 22 carbon atoms, with a hydrogen atom being particularly preferred. Examples of specific alkyl groups include methyl, ethyl, propyl, butyl, etc., including the various isomers thereof.

A particularly preferred embodiment of (D)(5) involves a statistical mixture (ie, compounds each containing different substituent groups providing a plurality of different compounds) of different phosphorus-containing amide compounds coupled or bonded to one another through different R²⁴ groups, with the proviso that for a general coupled phosphorus-containing amide whose mixture contains some compounds with n' equal to 2, the R²⁴ radical is

Any such statistical mixture is likely to contain some coupled amide compounds of coupled phosphorus-containing amides in which R24 is methylene. When R24 is methylene, R17 and R18 must generally contain more than 6 carbon atoms to maintain good oil solubility.

If n' has the value 2, the residue R²&sup4; is selected from

and if n' has the value 3, the remainder R²&sup4;

wherein R is independently hydrogen or an alkyl group, alkylene or alkylidene having 1 to 12 carbon atoms and R' is hydrogen or an alkyl or carboxyalkyl group, alkylene or alkylidene having 1 to 60 carbon atoms, R is preferably methylene and R' is preferably an alkyl group having 1 to 28 carbon atoms. When R and R' are linking groups, they may be alkylene and/or alkylidene groups, i.e. the bond may be vicinal and/or geminal.

The following illustrates the preparation of these coupled phosphorus-containing compounds. All parts and percentages are by weight unless otherwise indicated.

Example (D)(5)-1

To a mixture of 1775 parts (4.26 equivalents) of O,O-di-isooctyldithiophosphoric acid and 980 parts of toluene are added 302 parts (4.26 equivalents) of acrylamide under a nitrogen atmosphere. The reaction mixture warms to about 56ºC and 77 parts (2.33 equivalents) of paraformaldehyde and 215 parts (0.11 equivalents) of paratoluenesulfonic acid hydrate are added. Heating is continued at reflux (92-127ºC) while 48 parts of water are removed. After cooling the mixture to 100ºC, 9.2 parts (0.11 equivalents) of sodium bicarbonate are added and cooling is continued to about 30ºC. Reduced pressure (20 mbar (15 mm Hg)) is applied and the solvent toluene is removed by raising the temperature to 110ºC. The residue is filtered through a filter aid and the filtrate is the desired product. The product contains 6.86% P (6.74% calculated).

Example (D)(5)-2

To a mixture of 1494 parts (3.79 equivalents) of O,O-di-isooctyldithiophosphoric acid and 800 parts of toluene are added, under a stream of nitrogen, 537 parts (3.79 equivalents) of a 50% aqueous acrylamide solution over a period of 1 hour. The reaction mixture warms to about 53ºC and 64 parts (1.93 equivalents) of paraformaldehyde and 18 parts (0.095 equivalents) of paratoluenesulfonic acid hydrate are added. Heating is continued under reflux (91-126ºC) for 4 hours while collecting 305 parts of water. The mixture is cooled to about 90ºC and 7.6 parts (0.095 equivalents) of 50% aqueous sodium hydroxide solution are added. Cooling is continued to about 30ºC and reduced pressure is applied (20 mbar (15 mm Hg)). The solvent toluene is removed by raising the temperature to 110ºC. The residue is filtered through a filter aid and the filtrate is the desired product. The product contains 6.90% P (6.75% calculated) and 2.92% N (2.97% calculated).

Example (D)(5)-3

To a mixture of 984 parts (1.30 equivalents) of O,O-p-di-dodecylphenyldithiophosphoric acid and 575 parts of toluene are added 100 parts (0.65 equivalents) of methylenebisacrylamide under a stream of nitrogen. The reaction mixture warms to about 40ºC and it is heated at 80-85ºC for 2 hours. After cooling the mixture to 30ºC, a reduced pressure (20 mbar (15 mm Hg)) is applied and the solvent toluene is removed by raising the temperature to 100ºC. The residue is filtered through a filter aid and the filtrate is the desired product. The product contains 4.09% P (4.31% calculated).

Example (D)(5)-4

A reaction vessel is charged with 820 parts of toluene and 930 parts (2.32 equivalents) of an O,O-dialkyldithiophosphoric acid prepared from a mixture of 20 mole percent isobutyl alcohol and 80 mole percent 2-ethylhexyl alcohol. To this mixture is added 178.6 parts (1.16 equivalents) of methylenebisacrylamide under a stream of nitrogen. The mixture warms to about 65°C and is heated for 2 hours at about 80-85°C. After cooling to 50°C, a reduced pressure (40 mbar (30 mm Hg)) is applied. The toluene solvent is removed by raising the temperature to 115°C. The residue is filtered through a filter aid. filtered and the filtrate is the desired product. The product contains 7.30% P (7.28% calculated).

Example (D)(5)-5

To a mixture of 305 parts of toluene and 611 parts (1.82 equivalents) of an O,O-dialkyl-substituted dithiophosphoric acid prepared from a mixture of 20 mole percent phenol and 80 mole percent isooctyl alcohol are added 258 parts (1.82 equivalents) of a 50% aqueous acrylamide solution over a period of 20 minutes under a nitrogen atmosphere. After an initial warming to 60°C, 32.1 parts (0.97 equivalents) of paraformaldehyde and 7.3 parts (0.038 equivalents) of paratoluenesulfonic acid hydrate are added. The mixture is heated to reflux (91-127°C) for 2 hours while 131 parts of water are removed. The mixture is cooled to 80ºC and 3.1 parts (0.038 equivalents) of 50% aqueous sodium hydroxide solution are added. Cooling is continued to a temperature of 50ºC and a reduced pressure (40 mbar (30 mm Hg)) is applied. The toluene solvent is removed by raising the temperature to 110ºC. The residue is filtered through a filter aid and the filtrate is the desired product. The product contains 7.09% P (7.42% calculated).

Example (D)(5)-6

To 1017 parts (3.0 equivalents) of O,O-di-4-methyl-2-pentyldithiophosphoric acid are added 213 parts (3.0 equivalents) of acrylamide under nitrogen. The reaction mixture is allowed to warm to 65ºC and is held at 65-75ºC for 1-3 hours. The product is filtered through a filter aid and the filtrate is the desired product. The product contains 7.65% P (7.82% calculated), 3.51% N (3.50% calculated) and 16.05% S (16.06% calculated).

Example (D)(5)-7

To 614 parts (1.5 equivalents) of O,O-diisooctyldithiophosphoric acid are added 213 parts (1.5 equivalents) of a 50% aqueous acrylamide solution. The reaction mixture is heated to 65ºC and held at 70ºC for 2 hours. While the temperature is raised to 90ºC, a reduced pressure (27 mbar (20 mm Hg)) is applied. The residue is filtered through a filter aid and the filtrate is the desired product. The product contains 6.67% P (6.60% calculated), 2.94% N (2.97% calculated) and 14.50% S (13.60% calculated).

Example (D)(5)-8

To 1340 parts (3.41 equivalents) of O,O-diisooctyldithiophosphoric acid are added 242 parts (3.41 equivalents) of acrylamide under nitrogen. The reaction mixture is heated to 60ºC and is maintained at 65-70ºC for 1 hour. To this mixture are added 400 parts of toluene, 14 parts of potassium carbonate and 307 parts (3.58 equivalents) of 35% aqueous formaldehyde. The mixture is heated under a nitrogen atmosphere for 16 hours at 35-40ºC. To this mixture are added 18.2 parts of glacial acetic acid.

Example (D)(5)-9

Water is removed from the product of Example (D)(5)-8 under reflux for 6 hours using a Dean-Stark trap. After 234 parts of water are collected (at a temperature of 120ºC), the mixture is cooled to 30ºC. While the temperature is raised to 115ºC, a reduced pressure (40 mbar (30 mm Hg)) is applied. The mixture is filtered through a filter aid and the filtrate is the desired product. The product contains 6.71% phosphorus.

(D)(6) The methyl acrylate derivative

The last remaining metal deactivator is a methyl acrylate derivative formed by the reaction of equal molar amounts of a phosphoric acid of the general formula

with methyl acrylate, wherein X¹ and X² are as defined above in (D)(5) and R²⁵ and R²⁶ are independently a hydrocarbyl group, a hydrocarbyl-based thio group or, preferably, a hydrocarbyl-based oxy group, the hydrocarbyl moiety containing 1 to 30 carbon atoms. Preferably R²⁵ and R²⁶ are hydrocarbyl-based oxy groups, the hydrocarbyl group containing 1 to 12 carbon atoms and X¹ and X² are sulfur atoms. Since the reaction does not proceed to completion, the remaining acidity is neutralized with propylene oxide.

In the preparation of (D)(6), methyl acrylate is added to the phosphoric acid and at the end of this addition propylene oxide is added. For every 20-25 moles of phosphoric acid, 1 mole of propylene oxide is used.

The following illustrates the preparation of the methyl acrylate derivative. All parts and percentages are by weight unless otherwise indicated.

Example (D)(6)-11

To 2652 parts (9.04 equivalents) of an O,O-dialkyldithiophosphoric acid prepared from a mixture of 65 mole percent isobutyl alcohol and 35 mole percent isoamyl alcohol are added 776 parts (9.04 equivalents) of methyl acrylate. The methyl acrylate is added dropwise and the temperature is raised from 60ºC to 93ºC. The ingredients are held at this temperature for 6 hours and then cooled to 35ºC whereupon 23 parts (0.04 equivalents) of propylene oxide are added dropwise. The ingredients are filtered to give a product with a phosphorus content of 7.54% (8.12% calculated).

RBOT test

The rotating bomb oxidation test (RBOT) is a relatively short test procedure for the oxidation stability of oils.

The RBOT test is a rapid method for assessing the oxidation stability of lubricating oils. In this test, the oil sample, water and a copper catalyst coil are placed in a covered glass container which is placed in a bomb equipped with a pressure gauge. The bomb is charged with oxygen to a pressure of 6.41 bar (90 psi), placed in an oil bath thermostatted at 150ºC and rotated at 100 rpm. The pressure in the bomb is continuously monitored. Initially, the pressure increases rapidly due to the increase in temperature, typically to about 13.6-14.3 bar (190-200 psi). The pressure remains relatively constant until the oil breaks down. The bomb "life" of the sample is the time in minutes measured from the start of the test until the pressure drops by 1.78 bar (25 psi) from the maximum pressure achieved. A 10-foot (3 m) long, 14 AWG (1.63 mm) diameter, purified copper coil is typically used in the test. The longer the "life," the more stable the oil formulation (i.e., the more effective the antioxidant).

The composition according to the invention comprising components (A) and (B) and optionally (D) or (A), (B) and (C) and optionally (D) are suitable for hydraulic fluids, two-stroke engines with internal combustion, gear oils, car engine oils and as lubricants for machines in the food sector. The composition according to the invention comprises a major amount of (A) and a minor amount of (B) and optionally (D) or a major amount of (A) and a minor amount of (B) and (C) and optionally (D). A major amount means an amount of more than 50%. Consequently, 51%, 75% and 99% are major amounts. A minor amount is an amount less than 50%. Examples of minor amounts are 1%, 25% and 49%. The ranges of components (A), (B), (C) and (D) are given below in parts by weight.

In addition to components (A), (B), (C) and (D), other components may be present in this composition.

The components of the invention are mixed together according to the above ranges to obtain solutions. Table I below shows non-limiting examples of the preparation of the composition of the invention. All parts are by weight. When the triglyceride oil, component (A), is designated by a number such as Sunyl® 80 high oleic sunflower oil, this means that the oleic acid residue of the triglyceride is 80%. In some examples, more than one triglyceride oil is used. For example, 80 parts of Sunyl® 90 are mixed with normal sunflower oil containing 20% oleic acid residues to obtain a sunflower oil mixture with 76% oleic acid residues. TABLE I EXAMPLE NUMBERS

Claims (13)

1. Antioxidant composition for triglyceride oils comprising a major amount of (A) at least one vegetable triglyceride oil of the general formula in which R¹, R² and R³ are aliphatic hydrocarbyl radicals with at least 70% monounsaturated character and contain 8 to 24 carbon atoms, and a lower amount of antioxidant of (B) at least one alkylphenol of the general formula in which R⁴ is an alkyl radical containing 1 to 24 carbon atoms, a is 2 and the position para to the OH group is free, and optionally (D) a metal deactivator selected from (1) a benzotriazole of the general formula in which R⁸ is a hydrogen atom or an alkyl radical having 1 to 24 carbon atoms, (2) a phosphatide of the general formula in which R⁹⁰ and R¹⁰ are aliphatic hydrocarbyl radicals containing 8 to 24 carbon atoms, and G is selected from (3) a carbamate of the general formula in which R¹¹ is an alkyl radical containing 1 to 24 carbon atoms, phenyl or alkylphenyl where the alkyl radical contains 1 to 18 carbon atoms, R¹² and R¹³ are hydrogen atoms or an alkyl radical containing 1 to 6 carbon atoms, with the proviso that R¹² and R¹³ are not both hydrogen atoms, (4) Citric acid and derivatives of citric acid of the general formula in which R¹⁴, R¹⁵ and R¹⁶ are independently hydrocarbon or aliphatic hydrocarbyl radicals containing 1 to 12 carbon atoms, with the proviso that at least one of R¹⁴, R¹⁵ and R¹⁶ is an aliphatic hydrocarbyl radical, (5) a coupled phosphorus-containing amide of the general formula in which X¹, X² and X³ are independently an oxygen atom or sulfur atom; wherein R¹⁷ and R¹⁸ are independently a hydrocarbyl group, a hydrocarbyl-based oxy group, wherein the hydrocarbyl moieties contain from 6 to 22 carbon atoms, or a hydrocarbyl-based thio group containing from 4 to 34 carbon atoms; in which R¹⁹9;, R²⁰, R²¹ and R²² are independently a hydrogen atom or an alkyl group having 1 to 22 carbon atoms, or an aromatic, an alkyl-substituted aromatic or an aromatic-substituted alkyl group having d to 34 atoms; in which n is 0 or 1; in which n' is 2 or 3; in which R²² is a hydrogen atom; and if n' is 2, R²⁴ is selected from wherein R is an alkyl radical in the form of an alkylene or alkylidene containing 1 to 12 carbon atoms and R' is an alkyl, alkylene, alkylidene or carboxy radical containing 1 to 60 carbon atoms and if n' is 3, R²⁴ is or (6) a methyl acrylate derivative prepared by reacting equimolar amounts of a phosphoric acid of the general formula with methyl acrylate, wherein X¹ and X² are oxygen or sulfur atoms and R²⁵ and R²⁶ are each independently a hydrocarbyl-based hydrocarbyl, thio or oxy group, wherein the hydrocarbyl portion contains from 1 to 30 carbon atoms and the residual acidity is neutralized with one mole of propylene oxide per 20 to 25 moles of phosphoric acid. 2. The composition of claim 1, wherein the vegetable triglyceride oil is an ester of at least one straight chain fatty acid and glycerin, wherein the fatty acid contains about 8 to 22 carbon atoms. 3. A composition according to claim 1 or claim 2, wherein the monounsaturated fatty acid is oleic acid. 4. A composition according to any preceding claim, wherein a is 2 and R⁴ contains 1 to 8 carbon atoms. 5. A composition according to claim 4, wherein the alkylphenol has the general formula in which R4 is t-butyl. 6. A composition according to any one of the preceding claims, wherein R⁸ is a hydrogen atom or an alkyl radical containing 1 to 8 carbon atoms. 7. A composition according to claim 6, wherein R⁸ is methyl. 8. A composition according to any preceding claim, wherein R⁶ and R⁷ are nonyl radicals. 9. A composition according to any preceding claim, wherein X¹ and X² are sulfur atoms and R²⁵ and R²⁶ are hydrocarbyl-based oxy radicals, the hydrocarbyl radical containing from 1 to 12 carbon atoms. 10. Composition according to one of the preceding claims, containing 75-99 parts by weight of (A), 0.1-10 parts by weight of (B) and optionally 0-2 parts by weight of (D). 11. Composition according to one of claims 1 to 9, further comprising (C) at least one aromatic amine of the general formula in the R&sup5; and R6 and R7 are alkyl radicals containing 4 to 18 carbon atoms. 12. Composition according to claim 11, containing 75-99 parts by weight of (A), 0.1-10 parts by weight of (B), 0.1-10 parts by weight of (C) and optionally 0-2 parts by weight of (D). 13. A process for preparing a composition according to any preceding claim comprising mixing together a major amount of (A) the vegetable triglyceride oil and a minor amount of (B) the alkylphenol and optionally (D) the metal deactivator and (C) the aromatic amine.