Lubricating oil additive and lubricating oil composition containing the same

Abstract

To provide an additive for a lubricating oil, which improves extreme pressure resistance, wear resistance and antioxidant property.SOLUTION: There is provided an additive for a lubricating oil, comprising: a predetermined epoxy compound or thio-epoxy compound; and a compound that is a reaction product starting from phosphorous acid or acidic phosphorous acid ester, and is represented by the following formula (2). In the formula, X' and X" are each independently O or S, but a case where X'=X"=S is excluded, and R and R' are each independently an atomic group having H, or at least one C as a constituent atom, but a case where R=R'=H is excluded.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lubricating oil additive and a lubricating oil composition containing the same. [Background technology]

[0002] 2. Description of the Related Art Conventionally, various additives have been added (blended) to lubricating oils and used for the purpose of improving the properties of the lubricating oils (see Patent Document 1).

[0003] For example, additives used to reduce friction and wear between two surfaces of metal members and to prevent seizure are called extreme pressure additives, and such extreme pressure additives undergo chemical adsorption under lubricating conditions and react with metals by decomposition or the like to form lubricating compounds, thereby reducing friction, etc. Known examples of such extreme pressure additives include chlorine-based additives, sulfur-based additives, phosphorus-based additives, and composites thereof.

[0004] Chlorinated paraffin and chlorinated fatty acid ester are known as chlorine-based additives that function as extreme pressure additives, but these chlorine-based additives have problems such as the generation of dioxins during incineration and the generation of rust due to the released hydrochloric acid, so their use has been avoided in recent years. In addition, dilauryl phosphite, oleyl acid phosphate, etc. are used as phosphorus-based additives, and although they are excellent in terms of improving wear resistance, they have a problem that they are only used under low load because they have weak extreme pressure properties. Furthermore, sulfur-based additives and phosphorus-sulfur composite additives are excellent in extreme pressure properties and can be used under high loads, but they have inherent problems that deteriorate workability, such as poor wear resistance, poor color, and bad odor.

[0005] On the other hand, additives used to reduce friction in the boundary lubrication region are particularly called friction modifiers. Such friction modifiers are classified into phosphorus-based additives, phosphorus-sulfur-based additives, metal-based additives containing metals such as molybdenum, and the like, and for example, molybdenum dithiocarbamate and zinc dithiophosphate, which are metal-based additives, are used in engine oils and the like. However, when additives containing metals such as molybdenum dithiocarbamate are added to engine oil and used for a long period of time, the additives deteriorate, and the deteriorated additives promote the oxidation of the lubricating oil (base oil), causing the lubricating oil (base oil) to deteriorate.

[0006] As described above, the various additives that have been added to lubricating oils in the past each exhibit a desired effect when added (blended), but many of them have problems that need to be improved. For this reason, there is currently a demand for the development of new lubricating oil additives. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2020-510116 Summary of the Invention [Problem to be solved by the invention]

[0008] Under these circumstances, the present inventors have conducted intensive research into compounds useful as additives for lubricating oils, and have discovered that a reaction product obtained by using a specific epoxy compound or thioepoxy compound and phosphorous acid or an acidic phosphite as starting materials significantly improves the extreme pressure properties, wear resistance and antioxidant properties of a lubricating oil when used as an additive in a lubricating oil, thereby completing the present invention.

[0009] That is, the problem to be solved by the present invention is to provide a novel lubricating oil additive that significantly improves the extreme pressure properties, antiwear properties, and antioxidant properties of a lubricating oil. Another problem to be solved by the present invention is to provide a lubricating oil composition containing an additive having such excellent properties. [Means for solving the problem]

[0010] In order to solve such problems, the present invention provides: i) a compound selected from the group consisting of an epoxy compound of a natural fat or an ester thereof, a thioepoxy compound of a natural fat or an ester thereof, an epoxy compound of an α-olefin having a carbon number of 8 to 30, and a thioepoxy compound of an α-olefin having a carbon number of 8 to 30, A compound represented by the following general formula (1): A and, ii) Phosphorous acid or acid phosphite 、 A reaction product using the following as a starting material, a compound represented by the following general formula (2): 、 The gist of the present invention is a lubricating oil additive comprising: [ka] (In the above general formula (1), X is an oxygen atom or a sulfur atom. R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except for the case where R=R'=hydrogen atom.) [ka] (In the above general formula (2), X' and X" are each independently an oxygen atom or a sulfur atom, except when X'=X"=sulfur atom. Also, R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except when R=R'=hydrogen atom.)

[0011] The lubricating oil additive according to the present invention as described above In one preferred embodiment of the present invention, the natural oil is beef tallow, lard, fish oil, soybean oil, safflower oil, rapeseed oil, castor oil or olive oil. In another preferred embodiment of the present invention, the ester of the natural oil is a methyl ester, ethyl ester, butyl ester, octyl ester, ester with glycol or ester with polyalcohol. In yet another preferred embodiment of the present invention, the compound A is an epoxidized soybean oil octyl ester or a C12-14 α-olefin epoxide.

[0012] On the other hand, the gist of the present invention is also a lubricating oil composition containing 1 to 50% by weight of the lubricating oil additive according to any one of the above-mentioned embodiments.

[0013] In a first preferred embodiment, such a lubricating oil composition contains a sulfur compound in an amount of 1 to 20% by weight.

[0014] In a second preferred embodiment, the lubricating oil composition of the present invention contains an antioxidant in a proportion of 0.01 to 10% by weight. Effect of the Invention

[0015] As described above, the lubricating oil additive according to the present invention contains a compound having a novel structure that is not used in conventional additives. Therefore, when the additive of the present invention is blended with a lubricating oil, the compound having the novel structure advantageously improves the wear resistance, extreme pressure properties, and antioxidant properties of the lubricating oil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The lubricating oil additive according to the present invention is a reaction product obtained by reacting a compound represented by the following general formula (1) with phosphorous acid or an acid phosphite ester as starting materials, the reaction product finally containing a compound represented by the following general formula (2). [ka] (In the above general formula (1), X is an oxygen atom or a sulfur atom. R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except for the case where R=R'=hydrogen atom.) [ka] (In the above general formula (2), X' and X" are each independently an oxygen atom or a sulfur atom, except when X'=X"=sulfur atom. Also, R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except when R=R'=hydrogen atom.) In the above general formulas (1) and (2), examples of the atomic group having at least one carbon atom as a constituent atom constituting R and / or R' include a hydrocarbon group and an atomic group bonded to an epoxy group in allyl glycidyl ether (CH2=CHCH2OCH2-), etc.

[0017] In producing the compound represented by the above general formula (2), first, the compound represented by the above general formula (1) is prepared. The compound represented by the above general formula (1) is included in the category of epoxy compounds or thioepoxy compounds, and examples of the compound represented by the general formula (1) used in the present invention include compounds derived from natural fatty acids, compounds derived from α-olefins, glycidyl ethers, and compounds derived from glycidyl ethers.

[0018] Specifically, the compound derived from natural fatty acid used in the present invention is an epoxy compound or thioepoxy compound of natural fats and oils or their esters, and can be exemplified by the compound represented by the above general formula (1). Examples of natural fats and oils include beef tallow, lard, fish oil, soybean oil, safflower oil, rapeseed oil, castor oil, olive oil, etc., and examples of the esters of natural fats and oils include the methyl esters, ethyl esters, butyl esters, octyl esters, esters with other alcohols, esters with glycols, and esters with polyalcohols of the various natural fats and oils shown above. By epoxidizing such natural fats and oils or their esters according to a conventionally known standard method, such as a method using hydrogen peroxide, etc., an epoxy compound usable in the present invention can be obtained. In addition, by thioepoxidizing such epoxy compounds according to a conventionally known standard method, such as a method using thiourea or thiocyanate (rhodanate), a thioepoxy compound usable in the present invention can be obtained.

[0019] In addition, the compound derived from α-olefin used in the present invention can be an epoxy compound or a thioepoxy compound of an α-olefin having 8 to 30 carbon atoms, which is represented by the above general formula (1). More specifically, an epoxy compound usable in the present invention can be obtained by epoxidizing an α-olefin having 8 to 30 carbon atoms obtained by polymerization of ethylene or dehydrogenation of paraffin according to a standard method. In addition, a thioepoxy compound usable in the present invention can be obtained by thioepoxidizing such an epoxy compound according to a standard method.

[0020] Further, the glycidyl ether used in the present invention can be exemplified by alkyl glycidyl ether and allyl glycidyl ether having 1 to 3 epoxy groups in the molecule. Such glycidyl ethers can be produced by reacting alcohols or phenols with epichlorohydrin according to a conventionally known standard method, and the reaction product is distilled to remove chlorine, which is advantageously used in the present invention. Moreover, such glycidyl ethers can be thioepoxidized according to a standard method to obtain thioepoxy compounds usable in the present invention.

[0021] The above-mentioned specific epoxy compound or thioepoxy compound is reacted with phosphorous acid or an acidic phosphorous acid ester as starting materials to obtain a compound (reaction product) that constitutes the lubricating oil additive according to the present invention.

[0022] As a method for ring-opening an epoxy compound to phosphorylate it, a reaction with orthophosphoric acid is known as shown in U.S. Pat. No. 2,965,657 and Japanese Patent Publication No. 48,867, but a method for ring-opening an epoxy compound with phosphorous acid or an acidic phosphite is not known. Phosphite esters are generally synthesized by reacting alcohol with phosphorus trichloride, and a phosphite triester or dialkyl phosphite is produced by this reaction. These compounds are representative compounds as phosphorus-based extreme pressure additives, but their effects are limited. Furthermore, it is not common to produce a phosphite ester using an epoxy compound and phosphorous acid, for reasons such as the fact that phosphorous acid is solid at room temperature.

[0023] Under such circumstances, the present inventors have conducted intensive research and have found that a reaction product obtained by reacting a specific epoxy compound or thioepoxy compound (a compound represented by the above general formula (1)) with phosphorous acid or an acidic phosphite as starting materials exhibits excellent effects as an additive in lubricating oils, thereby completing the present invention.

[0024] In the present invention, the acid phosphite to be reacted with a predetermined epoxy compound or thioepoxy compound can be produced, for example, by hydrolyzing dialkyl hydrogen phosphite, which is a phosphite. In this case, as the dialkyl hydrogen phosphite, a lower phosphite such as dimethyl hydrogen phosphite, diethyl hydrogen phosphite, dibutyl hydrogen phosphite, etc. is advantageously used, and 0.1 to 5 equivalents of water are added to the dialkyl hydrogen phosphite, the dialkyl hydrogen phosphite is hydrolyzed at 0 to 100°C, and the remaining water and the generated alcohol are distilled off from the reaction product to obtain the acid alkyl hydrogen phosphite, which is the acid phosphite of interest.

[0025] The acidic alkyl hydrogen phosphite thus obtained is reacted with a predetermined epoxy compound or thioepoxy compound (a compound represented by the above general formula (1)), and the resulting reaction product is washed with water and dehydrated under reduced pressure to remove the alcohol, thereby obtaining the target compound represented by the above general formula (2). The reaction temperature between the acidic alkyl hydrogen phosphite and the predetermined epoxy compound or the like is preferably set to about -20 to 120°C, more preferably 0 to 80°C. If the reaction temperature is too low, side reactions are suppressed, but the reaction rate of the main reaction is also reduced, which may result in poor efficiency. On the other hand, if the reaction temperature is too high, the reaction rate of the main reaction is increased, but at the same time, side reactions may also actively proceed.

[0026] In the present invention, the compound represented by the above formula (2) can also be obtained by using phosphorous acid instead of the above-mentioned acidic alkyl hydrogen phosphite (acidic phosphite ester). In this case, phosphorous acid is dissolved in water, a solvent, or a water-containing solvent and reacted with a predetermined epoxy compound or thioepoxy compound. The solvent used in this case not only dissolves phosphorous acid, but also contributes to the uniformity of the reaction with the epoxy compound or the like in the subsequent reaction. Examples of such a solvent include alcohols such as methanol, ethanol, propanol, and butanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as diethyl ether and dibutyl ether; glycol ethers such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol, dipropylene glycol, tripropylene glycol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monobutyl ether; and glymes such as glyme, diglyme, and triglyme. Incidentally, a solvent containing excess water is not preferably used since it may cause hydrolysis of the epoxy compound, etc. In addition, the reaction temperature between the phosphorous acid dissolved in the solvent and the predetermined epoxy compound, etc. is preferably set to about -20 to 120°C, more preferably 0 to 80°C.

[0027] In addition, when an epoxy compound is used as the compound represented by the general formula (1), the compound represented by the general formula (2) finally obtained is an acidic phosphite ester. This acidic phosphite ester can be used as a lubricating oil additive as it is, but it can also be used as a lubricating oil additive in the form of a neutral salt, taking into consideration corrosion of metal members to which the lubricating oil is used and hydrolysis in the lubricating oil. For example, it can be used in the form of a metal salt with zinc, calcium, copper, molybdenum, etc., or in the form of a salt with amines such as ethylenediamine, diethylenetriamine, butylamine, octylamine, cocoamine, oleylamine, and beef tallow amine. In addition, the acidic phosphite ester represented by the general formula (2) can be neutralized with sodium hydroxide, potassium hydroxide, etc., as well as alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine, and the reaction product generated by such neutralization can be used as a water-decomposable lubricating oil additive.

[0028] In preparing the lubricating oil composition according to the present invention, the lubricating oil base oil to which the compound represented by the above general formula (2) is added as an additive is not particularly limited, and it is possible to appropriately use conventionally known mineral oils, synthetic oils, and even mixed oils thereof. The lubricating oil composition is prepared according to a conventionally known method, for example, by adding an additive to a lubricating oil base oil and mixing them.

[0029] In preparing the lubricating oil composition, the compound represented by the above general formula (2) is used in a quantitative proportion such that the content in the composition is 1 to 50% by weight so that the effect of blending (adding) such a compound can be advantageously enjoyed.

[0030] In addition to the compound represented by the above general formula (2), the lubricating oil composition may also contain sulfur compounds, antioxidants and various other additives that have been conventionally added to lubricating oils, so long as they do not impair the object of the present invention.

[0031] Examples of sulfur compounds that can be used in the present invention include sulfide compounds such as sulfurized olefins, sulfurized esters such as sulfurized fats, etc. When such sulfur compounds are blended into a lubricating oil composition, the sulfur compounds are used in a quantitative ratio such that the content of the sulfur compounds in the composition is 1 to 20% by weight in order to advantageously enjoy the effects of blending (adding) the compounds.

[0032] Examples of antioxidants that can be used in the present invention include ashless antioxidants such as phenols and amines, and metal antioxidants such as copper and molybdenum. When such antioxidants are blended into the lubricating oil composition, they are used in a quantitative ratio such that the content of the antioxidant in the composition is 0.01 to 10% by weight in order to advantageously enjoy the effects of blending (adding) the antioxidant.

[0033] In the lubricating oil composition obtained as described above, the compound represented by the above general formula (2) contained therein has a characteristic molecular structure, and therefore the composition has excellent extreme pressure properties, wear resistance and acid value inhibition properties. EXAMPLES

[0034] The present invention will be described in more detail below with reference to several examples, but it goes without saying that the present invention is not limited in any way by the description of such examples. It should be understood that the present invention can be modified, altered, improved, and the like based on the knowledge of a person skilled in the art, in addition to the following examples and the above specific description, without departing from the spirit of the present invention.

[0035] The acidic phosphite (acidic ethyl hydrogen phosphite: AEP) used in producing the compounds in the following examples was produced according to the following method.

[0036] -Production of Acid Ethyl Hydrogen Phosphite (AEP)- In a 100 mL four-neck flask, 69 g of diethyl hydrogen phosphite (manufactured by Johoku Chemical Industry Co., Ltd., product name: JP-202) and 9 g of water were placed, and these were mixed and dissolved in the flask, and the flask was heated at 50 to 60° C. for 4 hours. After the heating was completed, the flask was dehydrated under reduced pressure to obtain 55 g of acidic ethyl hydrogen phosphite (AEP, acid value: 405 mg KOH / g), which is an acidic phosphite ester.

[0037] Example 1 21 g of AEP was placed in a 100 mL four-neck flask, and the flask was heated to 50 to 60°C. 60 g of epoxidized soybean oil octyl ester (manufactured by Sanwa Synthetic Chemical Industry Co., Ltd., product name: Chemicizer T-5000) was added dropwise to the flask heated to 50 to 60°C over 1 hour. After the completion of the addition, the flask was kept at 50 to 60°C for 1 hour, and then the reaction product was removed from the flask, washed with water, and dehydrated under reduced pressure to obtain 66 g of a phosphorous ester (Example 1) having a phosphorus content of 4.4% by weight and an acid value of 78 mgKOH / g.

[0038] Example 2 In a 100mL four-neck flask, 10g of reagent phosphorous acid (purity: 97%) and 20g of 2-propanol were placed, mixed in the flask, and dissolved. Next, the flask was heated to 50-60°C, and 40g of epoxidized soybean oil octyl ester (product name: Chemicizer T-5000) was dropped into the heated flask over 1 hour. After the flask was kept at 50-60°C for 1 hour after the end of the dropwise addition, the reaction product was removed from the flask, washed with water, and dehydrated under reduced pressure to obtain 45g of a phosphorous acid ester (Example 2) having a phosphorus content of 4.0% by weight and an acid value of 69mgKOH / g.

[0039] Example 3 21 g of AEP was placed in a 100 mL four-neck flask, and the flask was heated to 50 to 60°C. 31.5 g of C12-14α-olefin epoxide (manufactured by DIC Corporation, product name: EpoCizer M-24) was added dropwise over 1 hour into the flask heated to 50 to 60°C. After the completion of the addition, the flask was kept at 50 to 60°C for 1 hour, and then the reaction product was removed from the flask, washed with water, and dehydrated under reduced pressure to obtain 38 g of a phosphite ester (Example 3) having a phosphorus content of 6.0 wt% and an acid value of 101 mgKOH / g.

[0040] Example 4 21 g of AEP was placed in a 100 mL four-neck flask, and the flask was heated to 50 to 60° C. 43 g of glycidyl ether of C12-13 mixed alcohol (manufactured by Yokkaichi Synthetic Co., Ltd., product name: EPOGOSE EN) was added dropwise to the flask heated to 50 to 60° C. over 1 hour. After the completion of the addition, the flask was kept at 50 to 60° C. for 1 hour, and then the reaction product was removed from the flask, washed with water, and dehydrated under reduced pressure to obtain 49 g of a phosphite ester (Example 4) having a phosphorus content of 5.1% by weight and an acid value of 88 mgKOH / g.

[0041] --Example 5-- In a 1000 mL four-neck flask, 480 g of methanol, 2 g of glacial acetic acid, and 76 g of thiourea were placed, and the methanol in the flask was mixed and dissolved while heating to 50 to 60°C. After dissolution, 390 g of epoxidized soybean oil octyl ester (product name: Chemicizer T-5000) was added to the flask, and the reaction was allowed to proceed in the flask for 12 hours at 50 to 60°C. After 12 hours, the reaction product was removed from the flask, washed with water, and dehydrated to obtain 403 g of thioepoxidized soybean ester (TESO) with a sulfur content of 6.5 wt%.

[0042] 21 g of AEP was placed in a 100 mL four-neck flask, and the flask was heated to 50 to 60°C. 75 g of TESO was added dropwise to the flask heated to 50 to 60°C over 1 hour. After the completion of the dropwise addition, the flask was kept at 50 to 60°C for 1 hour, and the reaction product was removed from the flask, washed with water, and dehydrated under reduced pressure to obtain 84 g of a mixture (Example 5) consisting of 1) phosphite ester a, 2) a compound in which the atom at the position corresponding to X' in the general formula (2) of the present invention is a sulfur atom and the atom at the position corresponding to X" is an oxygen atom in the phosphite ester a, and 3) a compound in which the atom at the position corresponding to X' in the general formula (2) of the present invention is an oxygen atom and the atom at the position corresponding to X" is a sulfur atom in the phosphite ester a. The phosphorus content of the mixture was 4.1% by weight, the sulfur content was 5.2% by weight, and the acid value of the mixture was 61 mgKOH / g.

[0043] On the other hand, as comparative examples, the following compounds which have been conventionally used as additives for lubricating oils were prepared. Comparative Example 1: Dilauryl hydrogen phosphite (manufactured by Johoku Chemical Industry Co., Ltd.) Comparative Example 2: Oleyl acid phosphate (manufactured by Johoku Chemical Industry Co., Ltd.) Comparative Example 3: Zinc dialkyldithiophosphate (ZDTP, manufactured by Chevron Japan Co., Ltd.) Comparative Example 4: Activated sulfur ester (manufactured by DIC Corporation, product name: Dyloop)

[0044] For the compounds or mixtures according to Examples 1 to 5 and Comparative Example 2, the compounds or mixtures were neutralized with 1 equivalent of oleylamine or octylamine relative to the acid value of each compound, while the compounds according to Comparative Examples 1, 3 and 4 were used as they were, and an evaluation test of seizure resistance and abrasion resistance test were carried out. Specifically, in each test, a ▲Sota type four-ball friction tester was used in accordance with the method specified in JIS-K-2519:2017 "Lubricant-load capacity test method", and 1) for seizure resistance, the seizure load (kgf) was measured with the change in test load per minute being 1 kgf, and 2) for abrasion resistance test, a load of 5 kgf was applied to the sample and the test ball for 5 minutes, the wear scar diameter formed on the surface of the three test balls was measured, and the average of those measured values ​​was calculated. The seizure load (kgf) measured in this way and the average value (mm) of the calculated wear scar diameter are shown in Table 1 below.

[0045] In addition, a predetermined amount of a phosphate ester-based lubricating oil additive (product name: ADEKA Eco Royal AWP, manufactured by ADEKA Corporation) and a predetermined amount of any of Examples 1 to 5 and Comparative Examples 1 to 4 were added to a polyol ester for lubricating oils (base oil, product name: Unistar HP-281R, manufactured by NOF Corporation) to prepare nine types of lubricating oil compositions containing 0.5% by weight of the phosphate ester-based additive and 0.5% by weight of the compound or mixture according to the Examples, etc. The kinematic viscosity (mm 2 The kinematic viscosity (mm 2 The change rate of the kinetic viscosity was calculated from the following formula: The measurement results and calculation results are shown in Table 1 below. (ν2 / ν1)×100=[rate of change](%) (formula) In the above formula, ν1 is the kinetic viscosity (mm 2 / s), and ν2 is the kinetic viscosity (mm 2 / s).

[0046] [Table 1]

[0047] As is clear from the results in Table 1, the additives according to the present invention (Examples 1 to 5) impart excellent extreme pressure properties to the lubricating oil due to their high seizure load, impart excellent wear resistance to the lubricating oil due to their short wear scar diameter, and further impart excellent oxidation prevention properties to the lubricating oil due to their small rate of change in kinetic viscosity.

Claims

1. A lubricating oil additive comprising: i) a compound A selected from the group consisting of epoxy compounds of natural fats and oils or their esters, thioepoxy compounds of natural fats and oils or their esters, epoxy compounds of α-olefins having 8 to 30 carbon atoms, and thioepoxy compounds of α-olefins having 8 to 30 carbon atoms, the compound A being represented by the following general formula (1): and ii) a reaction product using as starting materials phosphorous acid or an acidic phosphite ester, the compound being represented by the following general formula (2): 【Chemistry 1】 (In the above general formula (1), X is an oxygen atom or a sulfur atom. R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except for the case where R=R'=hydrogen atom.) 【Chemistry 2】 (In the above general formula (2), X' and X" are each independently an oxygen atom or a sulfur atom, except when X' = X" = a sulfur atom. Also, R and R' are each independently a hydrogen atom or an atomic group having at least one carbon atom as a constituent atom, except when R = R' = a hydrogen atom.)

2. The lubricating oil additive according to claim 1, wherein the natural oil is beef tallow, lard, fish oil, soybean oil, safflower oil, rapeseed oil, castor oil or olive oil.

3. An additive for lubricating oil as described in claim 1 or claim 2, wherein the ester of natural fats and oils is a methyl ester, ethyl ester, butyl ester, octyl ester, ester with glycol or ester with polyalcohol of natural fats and oils.

4. The lubricating oil additive according to claim 1, wherein compound A is an epoxidized soybean oil octyl ester or a C12-14 α-olefin epoxide.

5. A lubricating oil composition comprising the lubricating oil additive according to any one of claims 1 to 4 in an amount of 1 to 50% by weight.

6. 6. The lubricating oil composition according to claim 5, which contains 1 to 20% by weight of the sulfur compound.

7. The lubricating oil composition according to claim 5 or 6, which contains an antioxidant in a proportion of 0.01 to 10% by weight.

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