JP7684558B2 - Diester Compounds - Google Patents

Description

The present invention relates to a diester compound that can be used in lubricant base oils for power transmission (particularly lubricant base oils for traction drives).

In recent years, with the advancement of the digital information society, the demands for precision from printers and copiers are increasing. In particular, high rotational precision, low vibration and low noise are required for the motor section, which is required for highly accurate paper feeding. When gear systems are used as the power transmission method for these rotating parts, large vibrations and noise are generated, so traction drives, which cause less vibration and noise, are widely used.

In addition, with the widespread use of industrial robots, traction drives are now used in joints that require precise movement. Other applications of traction drives include continuously variable transmissions for industrial equipment, aircraft generators, and rotor speed control for helicopters. In order to increase the amount of power transmitted, efforts have been made to enlarge the traction drives, but there is a tendency for the amount of heat generated to increase as the contact area increases.

Lubricant base oils for traction drives are preferably those with a high traction coefficient to enhance power transmission performance, and alicyclic hydrocarbon compounds have been proposed. Examples include dicyclohexyl compounds such as 2-methyl-2,4-dicyclohexylpentane, and dimerized norbornanes (Patent Documents 1 and 2).

However, alicyclic hydrocarbon compounds such as 2-methyl-2,4-dicyclohexylpentane tend to have low flash points of 200°C or less, which is not always sufficient in fields where heat resistance and safety are important, such as those used in large traction drives.

In addition, ester compounds have been proposed as lubricant base oils for traction drives with high flash points. For example, alicyclic diester compounds such as 1,2-cyclohexanedicarboxylate di(cyclohexylmethyl) are listed (Patent Document 3).

However, alicyclic diester compounds, such as 1,2-cyclohexanedicarboxylate di(cyclohexylmethyl), tend to have high pour points of -20°C or higher, which is not necessarily sufficient for use in areas where low-temperature operation is important, such as aircraft, helicopters, and automobiles.

In Patent Document 4, diesters of neopentyl glycol and cyclohexane carboxylic acid, diesters of neopentyl glycol and methylcyclohexane carboxylic acid, and diesters of neopentyl glycol and a mixture of cyclohexane carboxylic acid and methylcyclohexane carboxylic acid (molar ratio of acids: 1:1) are given as examples of traction fluids, but there is no description or suggestion regarding low-temperature fluidity, flash point, or traction coefficient at high temperatures, so they are not necessarily sufficient as lubricant base oils for traction drives.

Japanese Unexamined Patent Publication No. 47-7664 Japanese Patent Application Publication No. 3-95295 International Publication No. 2018/008667 Japanese Patent Application Publication No. 62-153393 (Japanese Patent Publication No. 6-31365)

The present invention aims to provide a diester compound that is useful as a lubricant base oil for power transmission (particularly, a lubricant base oil for traction drives).

The inventors have found that the diester compound represented by the general formula (1) has a high traction coefficient and flash point, and good low-temperature fluidity, and is useful as a lubricant base oil for power transmission (particularly, a lubricant base oil for traction drives). The present invention was completed through further investigation based on this knowledge.

That is, the present invention provides the following diester compounds:

［式中、Ｒ^１及びＲ^２は、同一又は異なってそれぞれ炭素数１～４の直鎖状若しくは分岐鎖状のアルキル基を表す。］
で表されるジエステル化合物。 [Section 1]
General formula (1)

[In the formula, R ¹ and R ² are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms.]
A diester compound represented by the formula:

[Section 2]
The diester compound according to [Item 1], wherein R ¹ and R ² in the general formula (1) are the same or different and each is a methyl group, an ethyl group, or an n-butyl group.

[Section 3]
The diester compound according to [Item 1], wherein R ¹ and R ² in the general formula (1) are each a methyl group.

The diester compound of the present invention has the characteristics of a high traction coefficient (60°C, 140°C) and flash point, and good low-temperature fluidity, and therefore can be suitably used as a lubricant base oil for power transmission (particularly, a lubricant base oil for traction drives).

1 is an IR spectrum of bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) obtained in Example 1. 1 is a ¹ H-NMR spectrum of bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) obtained in Example 1.

［式中、Ｒ^１及びＲ^２は、同一又は異なってそれぞれ炭素数１～４の直鎖状若しくは分岐鎖状のアルキル基を表す。］
で表されるジエステル化合物であり、動力伝達用潤滑油基油として好適に用いることができる。 The diester compound of the present invention is represented by the general formula (1)

[In the formula, R ¹ and R ² are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms.]
and can be suitably used as a lubricating base oil for power transmission.

In the general formula (1), R ¹ and R ² may be the same or different and each may be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, or a tert-butyl group. Of these, a methyl group, an ethyl group, or an n-butyl group is preferable, and a methyl group is particularly preferable.

Specific examples of the diester compounds represented by the general formula (1) include, for example, bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-ethyl-2-methylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-methyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-methyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-methylpropyl), Bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-sec-butyl-2-methylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-methylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-tert-butyl-2-methylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-diethylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-ethyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-ethyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-ethylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-sec-butyl-2-ethylpropyl), bis (3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-ethylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-tert-butyl-2-ethylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-di-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isopropyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-sec-butyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-tert-butyl- 2-n-propylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-diisopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-sec-butyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-tert-butyl-2-isopropylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-di-n-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-sec-butylpropyl), bis(3-methylcyclohexanecarboxylic acid) -1,3-(2-isobutyl-2-n-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-tert-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-di-sec-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-sec-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-sec-butyl-2-tert-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-diisobutylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-isobutyl-2-tert-butylpropyl), bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-di-tert-butylpropyl). Among these, bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) and bis(3-methylcyclohexanecarboxylic acid)-1,3-(2-n-butyl-2-ethylpropyl) are preferred.

The above diester compounds can be used alone or in mixtures of two or more types as the lubricant base oil for power transmission.

［式中、Ｒ^１及びＲ^２は前記に同じ。］
一般式（１）で表されるジエステル化合物は、例えば、式（２）で表されるカルボン酸（３－メチルシクロヘキサンカルボン酸）と、一般式（３）で表されるジオールとを、酸触媒（例えば、硫酸、ｐ－トルエンスルホン酸等）の存在下、加熱して副生する水を除去しながら脱水縮合させて製造することができる。また、酸触媒を、無機金属触媒（例えば、酸化スズ等）や有機チタン触媒（例えば、テトラ－ｎ－ブトキシチタン等）に変更して同様の方法で製造することもできる。
また、一般式（１）で表されるジエステル化合物は、式（２）で表されるカルボン酸と、一般式（３）で表されるジオールとを、縮合剤（例えば、ジシクロヘキシルカルボジイミド、カルボニルジイミダゾール等）の存在下、反応させて製造することもできる。
また、一般式（１）で表されるジエステル化合物は、式（２）で表されるカルボン酸を、酸ハライド（例えば、酸クロライド等）、混合酸無水物、活性エステル等の反応性の高い誘導体に変換した後、塩基（例えば、トリエチルアミン、４－（Ｎ，Ｎ?ジメチルアミノ）ピリジン、ピリジン等）の存在下、一般式（３）で表されるジオールを反応させて製造することもできる。
また、一般式（１）で表されるジエステル化合物は、式（２）で表されるカルボン酸と低級（炭素数１～４）アルコール（例えば、メタノール、エタノール等）とを反応（エステル化）させて低級アルキルエステルとした後、これを一般式（３）で表されるジオールとエステル交換反応させて製造することもできる。
上記反応式１で示される反応は、その反応の種類に応じて公知の反応条件に従い又は準じて実施することができる。 The method for producing the diester compound represented by the general formula (1) is not particularly limited. For example, the diester compound represented by the general formula (1) can be produced by reacting a carboxylic acid represented by the formula (2) or a derivative thereof with a diol represented by the general formula (3), as shown in reaction formula 1. Here, examples of the derivative of the carboxylic acid represented by the formula (2) include highly reactive derivatives such as acid halides (e.g., acid chlorides, etc.), mixed acid anhydrides, and active esters, and lower (1 to 4 carbon atoms) alkyl esters.

[In the formula, ^R1 and ^R2 are the same as above.]
The diester compound represented by the general formula (1) can be produced, for example, by dehydration condensation of a carboxylic acid represented by the formula (2) (3-methylcyclohexanecarboxylic acid) and a diol represented by the general formula (3) in the presence of an acid catalyst (e.g., sulfuric acid, p-toluenesulfonic acid, etc.) while removing water produced as a by-product by heating. The compound can also be produced by a similar method by changing the acid catalyst to an inorganic metal catalyst (e.g., tin oxide, etc.) or an organic titanium catalyst (e.g., tetra-n-butoxytitanium, etc.).
The diester compound represented by general formula (1) can also be produced by reacting a carboxylic acid represented by formula (2) with a diol represented by general formula (3) in the presence of a condensing agent (e.g., dicyclohexylcarbodiimide, carbonyldiimidazole, etc.).
Alternatively, the diester compound represented by the general formula (1) can be produced by converting the carboxylic acid represented by the formula (2) into a highly reactive derivative such as an acid halide (e.g., an acid chloride), a mixed acid anhydride, or an activated ester, and then reacting the resulting derivative with a diol represented by the general formula (3) in the presence of a base (e.g., triethylamine, 4-(N,N-dimethylamino)pyridine, pyridine, etc.).
The diester compound represented by the general formula (1) can also be produced by reacting (esterifying) the carboxylic acid represented by the formula (2) with a lower (carbon number 1 to 4) alcohol (e.g., methanol, ethanol, etc.) to form a lower alkyl ester, and then subjecting the lower alkyl ester to a transesterification reaction with a diol represented by the general formula (3).
The reaction shown in the above reaction scheme 1 can be carried out according to or in accordance with known reaction conditions depending on the type of reaction.

［式中、Ｒ^１及びＲ^２は前記に同じ。］
式（４）で表される化合物（ｍ－トルイル酸）又はその誘導体と、一般式（３）で表されるジオールとを反応させて、一般式（５）で表される化合物を製造する反応は、上記反応式１における式（２）で表されるカルボン酸又はその誘導体と、一般式（３）で表されるジオールとを反応させて一般式（１）で表される化合物を製造する反応に従い又は準じて実施することができる。
一般式（５）で表される化合物を核水素化（還元）する反応は公知の方法を採用することができる。例えば、水素雰囲気下（常温から加圧）、還元触媒（白金、パラジウム、ニッケル、ロジウム等の遷移金属又はその酸化物、パラジウム／Ｃ等）の存在下、一般式（５）で表される化合物を還元することにより、一般式（１）で表される化合物を製造することができる。 Alternatively, the diester compound represented by general formula (1) can also be produced by reacting (esterification or transesterification) a compound represented by formula (4) (m-toluic acid) or a derivative thereof with a diol represented by general formula (3) to obtain a compound represented by general formula (5), and then hydrogenating (reducing) the aromatic ring of the compound, as shown in reaction formula 2. Here, examples of the derivative of m-toluic acid include highly reactive derivatives such as acid halides (e.g., acid chloride, etc.), mixed acid anhydrides, active esters, and lower (1 to 4 carbon atoms) alkyl esters.

[In the formula, ^R1 and ^R2 are the same as above.]
The reaction of reacting a compound represented by formula (4) (m-toluic acid) or a derivative thereof with a diol represented by general formula (3) to produce a compound represented by general formula (5) can be carried out in accordance with or in a similar manner to the reaction of reacting a carboxylic acid represented by formula (2) or a derivative thereof with a diol represented by general formula (3) in the above reaction scheme 1 to produce a compound represented by general formula (1).
A known method can be adopted for the reaction of hydrogenating (reducing) the compound represented by the general formula (5). For example, the compound represented by the general formula (1) can be produced by reducing the compound represented by the general formula (5) in a hydrogen atmosphere (from room temperature to pressure) in the presence of a reduction catalyst (a transition metal such as platinum, palladium, nickel, or rhodium, or an oxide thereof, palladium/C, etc.).

From the viewpoint of practicality such as simplicity, the method of obtaining the product by an esterification reaction between 3-methylcyclohexanecarboxylic acid and a diol represented by general formula (3) is most preferable.

The acid value of the diester compound represented by general formula (1) is preferably 0.1 mgKOH/g or less, more preferably 0.05 mgKOH/g or less. When the acid value is 0.1 mgKOH/g or less, the heat resistance of the diester compound represented by general formula (1) itself tends to be improved, and such a preferable range also has a favorable effect on improving the thermal oxidation stability of the base oil containing the diester compound represented by general formula (1). Examples of methods for reducing the acid value include a method of allowing the reaction to proceed sufficiently, a method of neutralizing with an alkaline component in a post-treatment process and washing with water (for example, a method of washing (neutralizing) with an aqueous alkaline solution and washing with water), and a method of adsorption treatment with activated alumina.

The hydroxyl value of the diester compound represented by general formula (1) is preferably 2 mgKOH/g or less, more preferably 1 mgKOH/g or less. When the hydroxyl value is 2 mgKOH/g or less, the hygroscopicity of the diester compound represented by general formula (1) itself tends to be lower and the heat resistance tends to be improved. In such a preferred range, the water resistance and thermal oxidation stability of the base oil containing the diester compound represented by general formula (1) are also improved. Examples of methods for reducing the hydroxyl value include a method of allowing the reaction to proceed sufficiently and a method of distilling off the raw material alcohol component in the post-treatment process under reduced pressure (for example, a method of distilling off the excess raw material alcohol that can be distilled under reduced pressure or normal pressure).

The diester compound represented by the general formula (1) can be used as a lubricant base oil for power transmission (particularly, a lubricant base oil for traction drives). The present invention also discloses a lubricant base oil for power transmission (particularly, a lubricant base oil for traction drives) containing the diester compound represented by the general formula (1).

The traction coefficient (60°C) of the power transmission lubricant base oil is usually 0.080 or more, and preferably 0.090 or more. In this specification and claims, the traction coefficient (60°C) is a value measured by the method described in the examples below.

The traction coefficient (140°C) is usually 0.075 or more, and preferably 0.085 or more. In this specification and claims, the traction coefficient (140°C) is a value measured by the method described in the Examples below.

The low-temperature fluidity of a power transmission lubricant base oil can be evaluated, for example, by the pour point. From the viewpoint of low-temperature operability, the pour point of a lubricant base oil is usually -30°C or lower, and preferably -35°C or lower. In this specification and claims, the pour point is a value measured by the method described in the examples below.

From the viewpoint of storage stability and ease of handling, the flash point of a power transmission lubricant base oil is usually 185°C or higher, and preferably 200°C or higher. If it is lower than 185°C, there are many restrictions on handling due to the risk of ignition. In this specification and claims, the flash point is a value measured by the method described in the examples below.

Examples of lubricating base oils for power transmission include lubricating base oils for power transmission with a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.085 or more, a pour point of -30°C or less, and a flash point of 185°C or more; lubricating base oils for power transmission with a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.075 or more, a pour point of -35°C or less, and a flash point of 185°C or more; lubricating base oils for power transmission with a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.075 or more, a pour point of -30°C or less, and a flash point of 200°C or more; lubricating base oils for power transmission with a traction coefficient (60°C) of 0.080 or more, a traction coefficient (140°C) of 0.075 or more, a pour point of -35°C or less, and a flash point of 200°C or more. Further, lubricating base oils for power transmission having a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.085 or more, a pour point of -35°C or less, and a flash point of 185°C or more; lubricating base oils for power transmission having a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.085 or more, a pour point of -30°C or less, and a flash point of 200°C or more; lubricating base oils for power transmission having a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.075 or more, a pour point of -35°C or less, and a flash point of 200°C or more are preferred, and lubricating base oils for power transmission having a traction coefficient (60°C) of 0.090 or more, a traction coefficient (140°C) of 0.085 or more, a pour point of -35°C or less, and a flash point of 200°C or more are particularly preferred.

Power transmission lubricant base oils containing the diester compound represented by general formula (1) have high traction coefficients (60°C, 140°C) and flash points, and good low-temperature fluidity, making them suitable for use as power transmission lubricant base oils, particularly as lubricant base oils for traction drives.

The power transmission lubricant base oil containing the diester compound represented by the general formula (1) may contain other base oils that can be used in combination (hereinafter referred to as "combined base oils"). In other words, the power transmission lubricant base oil containing the diester compound represented by the general formula (1) includes only the diester compound represented by the general formula (1) and a mixture of the diester compound represented by the general formula (1) and a combined base oil. Hereinafter, the power transmission lubricant base oil may be referred to as "base oil".

Examples of base oils that can be used in combination include mineral oils (hydrocarbon oils obtained by refining petroleum), poly-α-olefins, polybutenes, alkylbenzenes, alkylnaphthalenes, alicyclic hydrocarbon oils, animal and vegetable oils, organic acid esters (excluding the diester compounds represented by general formula (1)), polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, alkylphenyl ethers, and silicone oils. At least one of these can be used in combination as appropriate.

The content of the diester compound represented by general formula (1) in the power transmission lubricant base oil containing the diester compound represented by general formula (1) is usually 70 mass% or more, preferably 90 mass% or more, more preferably 95 mass% or more, and particularly preferably 98 mass% or more.

The content of the combined base oil in the power transmission lubricant base oil containing the diester compound represented by general formula (1) is usually 30 mass% or less, preferably 10 mass% or less, more preferably 5 mass% or less, and particularly preferably 2 mass% or less.

The diester compound represented by the general formula (1) can be suitably used in a power transmission lubricant containing the power transmission lubricant base oil. In order to improve the performance of the power transmission lubricant, at least one of additives such as an antioxidant, metal detergent, ashless dispersant, oiliness agent, antiwear agent, extreme pressure agent, metal deactivator, rust inhibitor, viscosity index improver, pour point depressant, antifoam agent, hydrolysis inhibitor, thickener, corrosion inhibitor, and color stabilizer can be appropriately blended into the base oil. The amount of these additives is not particularly limited as long as the effects of the present invention are achieved.

Here, in this specification and claims, the range of the amount of additives to be blended may be specified using the expression "with respect to the base oil," such as "0.01 to 5 mass% with respect to the base oil." In this case, "base oil" is used to mean either a base oil consisting of only the diester compound represented by general formula (1) or a base oil consisting of a mixture of the diester compound represented by general formula (1) and a combined base oil. In addition, in the example of "0.01 to 5 mass% with respect to the base oil," this is synonymous with 0.01 to 5 mass parts with respect to 100 mass parts of base oil.

By appropriately combining a thickener with a power transmission lubricant base oil containing a diester compound represented by general formula (1), it can be made into a "grease."

Thickeners include metal soap-based thickeners, complex metal soap-based thickeners, and non-soap-based thickeners.

Among the above, from the viewpoints of heat resistance, water resistance, and shear stability, lithium soap, lithium complex soap, and urea compounds are suitable as thickeners, with urea compounds being particularly preferred.

These thickeners can be used alone or in combination of two or more, and there are no particular limitations on the amount added as long as the desired effect is achieved.

Examples of corrosion inhibitors include sodium sulfonate and sorbitan ester, which are usually added at about 0.1 to 3.0 mass% to the base oil.

Examples of color stabilizers include substituted hydroquinone and furfural azine, and are usually added at about 0.01 to 0.1% by mass to the base oil.

The power transmission lubricating oil containing the diester compound represented by general formula (1) thus obtained is suitable as a lubricating oil for traction drives because it contains a base oil with a high traction coefficient and flash point and excellent low-temperature fluidity, as described above.

The power transmission lubricant base oil containing the diester compound represented by general formula (1) and the diester compound represented by general formula (1) can be added to a power transmission lubricant (particularly a traction drive lubricant) to improve the traction coefficient of the power transmission lubricant. Therefore, they can be used as a traction coefficient improver.

Power transmission lubricating oils containing the diester compound represented by general formula (1) have high power transmission performance, low vibration and noise generation, and a high flash point, and therefore can be used as lubricating oils for traction drives, that is, power transmission devices consisting of two or more rotating bodies. Devices that employ such traction drives include, for example, motors, transmissions, generators, reducers, etc., of automobiles, ships, aircraft, precision instruments, robots, etc.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The physical and chemical properties of the lubricating base oil and lubricating oil composition in each example were evaluated by the following methods. Reagents were used for compounds not specifically mentioned.

<Compounds used>
Cyclohexane carboxylic acid: Sigma-Aldrich Corporation; 2-Methyl-cyclohexane carboxylic acid: Sigma-Aldrich Corporation; 3-Methyl-cyclohexane carboxylic acid: Sigma-Aldrich Corporation; 4-Methyl-cyclohexane carboxylic acid: Sigma-Aldrich Corporation; 2,2-Dimethyl-1,3-propanediol: Tokyo Chemical Industry Co., Ltd.; Diisodecyl adipate: New Japan Chemical Co., Ltd. Product name: "Sanso Cizer DIDA"
Mineral oil Y: NOF Corporation product name "Polybutene 0N"

(a) Acid Value (AV)
Measurements were performed in accordance with JIS K2501 (2003) with a detection limit of 0.01 mg KOH/g.

(b) Hydroxyl Value (OHV)
The measurement was performed in accordance with JIS K0070 (1992) with a detection limit of 0.1 mg KOH/g.

[Measurement of physical properties of lubricant base oil]
(c) Traction Coefficient The maximum traction coefficient was measured when testing was performed using the following device and conditions, and this was taken as the traction coefficient (60° C., 140° C.).
[Measurement conditions]
Equipment: Ball-on-ring type friction tester (Phoenix Tribology TE54 model)
Test piece shape: upper test piece (25 mm diameter sphere), lower test piece (50 mm diameter ring)
Test piece material: SUJ2
Slip rate: 5%
Sample temperature: 60°C, 140°C
Load: 150N
<Evaluation of traction coefficient (60°C)>
A: 0.090 or more B: 0.080 or more and less than 0.090 C: less than 0.080 <Evaluation of traction coefficient (140°C)>
A: 0.085 or more B: 0.075 or more but less than 0.085 C: Less than 0.075

(d) Low temperature fluidity test (pour point)
The pour point was measured in accordance with JIS-K-2269 (1987).
<Evaluation of low temperature fluidity>
A: -35℃ or lower B: -35℃ to -30℃ or lower C: -30℃ or higher

(e) Flash point: Measured in accordance with JIS K2265 (Cleveland open cup).
<Flash point evaluation>
A: 200°C or higher B: 185°C or higher but less than 200°C C: Less than 185°C

(f) Kinematic Viscosity Kinematic viscosity was measured at 40° C. and 100° C. in accordance with JIS-K-2283 (2000).

(g) Evaluation of power transmission lubricant base oils In evaluating the traction coefficient, low temperature fluidity and flash point of a power transmission lubricant base oil, a C of 1 or more is rated as unsuitable, a B of 2 or less (other ratings of A) is rated as good, and a B of 1 or less (other ratings of A) is rated as particularly good.

<Infrared absorption spectrum (IR spectrum)>
The IR spectrum of the obtained diester compound was measured by the ATR method (attenuated total reflection method) using an infrared spectrometer (Spectrum 400 manufactured by PerkinElmer Japan Co., Ltd.).

<Proton Nuclear Magnetic Resonance Spectrum ( ¹ H-NMR)>
¹ H-NMR of the obtained diester compound was carried out by dissolving it in deuterated chloroform and then measuring it by ¹ H-NMR (500 MHz) using a nuclear magnetic resonance apparatus (DRX-500 manufactured by Bruker).

[Example 1]
In a 1-liter four-neck flask equipped with a stirrer, a thermometer, and a water fractionation receiver with a condenser, 532.6 g (3.75 mol) of 3-methyl-cyclohexane carboxylic acid, 177.2 g (1.70 mol) of 2,2-dimethyl-1,3-propanediol, 0.6 g of tin oxide, and 30 g of xylene as an entrainer were charged, and the flask was replaced with nitrogen, and then the temperature was gradually raised to 230 ° C. While adjusting the degree of vacuum so that xylene was refluxed, the generated water distilled with the theoretical amount of generated water (30.7 g) as a target was removed in the water fractionation receiver, and an esterification reaction was performed. After the reaction was completed, the remaining 3-methyl-cyclohexane carboxylic acid and xylene were removed by distillation under reduced pressure to obtain an esterified crude product. Next, the obtained esterified crude product was neutralized with 1.5 times the equivalent of an aqueous solution of caustic soda relative to the acid value, and then repeatedly washed with water until it became neutral. Magnesium sulfate was added to the resulting esterified crude product for dehydration, and the magnesium sulfate was then removed by filtration to obtain 487.8 g (1.38 mol) of bis(3-methylcyclohexanecarboxylate)-1,3-(2,2-dimethylpropyl).
The acid value of the obtained diester compound was 0.01 mgKOH/g or less, and the hydroxyl value was 1 mgKOH/g or less. The IR spectrum and ¹ H-NMR spectrum of bis(3-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) were measured and are shown in Figures 1 and 2. The peak at about 7.27 ppm in ^{the 1} H-NMR spectrum is the peak of residual protons in the solvent, deuterated chloroform.

IR (cm ^-1 ): 2927, 2857, 1731, 1475, 1457, 1379, 1303, 1275, 1255, 1216, 1173, 1134, 1088, 1045, 1024, 1006, 972, 936, 880, 853, 744, 701

The physical properties of the diester compound when evaluated as a power transmission lubricant base oil (A) are shown in Table 1.

[Comparative Example 1]
Table 1 shows the physical properties of diisodecyl adipate when it was evaluated as a power transmission lubricating base oil (a).

[Comparative Example 2]
The physical properties of mineral oil Y when evaluated as a power transmission lubricant base oil (b) are shown in Table 1.

[Comparative Example 3]
In the same manner as in Example 1, except that 521.6 g (4.07 mol) of cyclohexane carboxylic acid was used instead of 3-methyl-cyclohexane carboxylic acid, 514.2 g (1.58 mol) of bis(cyclohexane carboxylic acid)-1,3-(2,2-dimethylpropyl) was obtained.
The acid value of the obtained compound was 0.01 mgKOH/g or less, and the hydroxyl value was 1 mgKOH/g or less. The physical properties of the compound when evaluated as a power transmission lubricant base oil (c) are shown in Table 1.

[Comparative Example 4]
Bis(2-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) was obtained in an amount of 476.4 g (1.35 mol) in the same manner as in Example 1, except that 3-methyl-cyclohexanecarboxylic acid was replaced with 532.6 g (3.75 mol) of 2-methyl-cyclohexanecarboxylic acid.
The acid value of the obtained compound was 0.01 mgKOH/g or less, and the hydroxyl value was 1 mgKOH/g or less. The physical properties of the compound when evaluated as a power transmission lubricant base oil (d) are shown in Table 1.

[Comparative Example 5]
Bis(4-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) was obtained in an amount of 497.4 g (1.41 mol) in the same manner as in Example 1, except that 3-methyl-cyclohexanecarboxylic acid was replaced with 532.6 g (3.75 mol) of 4-methyl-cyclohexanecarboxylic acid.
The acid value of the obtained compound was 0.01 mgKOH/g or less, and the hydroxyl value was 1 mgKOH/g or less. The physical properties of the compound when evaluated as a power transmission lubricant base oil (e) are shown in Table 1.
In addition, since the values of the kinetic viscosity (40°C and 100°C) of this diester compound are in good agreement with those of the sample of Example A2 of Patent Document 4, the sample of Example A2 of Patent Document 4 is recognized to be bis(4-methylcyclohexanecarboxylic acid)-1,3-(2,2-dimethylpropyl) of this Comparative Example 5.

From Table 1, it can be seen that the power transmission lubricant base oil of the present invention described in Example 1 has a high traction coefficient (60°C) of 0.090 or more and a high traction coefficient (140°C) of 0.085 or more, a pour point of -30°C or less, and a high flash point of 200°C or more.

Power transmission lubricant base oils containing the diester compound represented by general formula (1) have a high traction coefficient, a high flash point, and good low-temperature fluidity, and can therefore be suitably used as power transmission lubricant base oils (particularly lubricant base oils for traction drives) for automobiles, ships, aircraft, precision instruments, and the like.

Claims (3)

General formula (1)

[In the formula, R ¹ and R ² are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms.]
A diester compound represented by the formula: 2. The diester compound according to claim 1, wherein R ¹ and R ² in the general formula (1) are the same or different and each is a methyl group, an ethyl group, or an n-butyl group. The diester compound according to claim 1, wherein R ¹ and R ² in the general formula (1) are each a methyl group.

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