JPWO2013008487A1 - Pentaerythritol tetraester - Google Patents

Abstract

The present invention is a mixed ester of pentaerythritol and carboxylic acid, and the carboxylic acid contains isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms The pentaester of pentaerythritol used for refrigerating machine oil etc. which has the outstanding low-temperature fluidity | liquidity, the outstanding stability, etc. is provided.

Description

  The present invention relates to a tetraester of pentaerythritol used for industrial lubricating oil such as refrigerator oil.

  Lubricating oils used in industrial lubricating oils such as refrigeration oils are required to have excellent low-temperature fluidity and various stability improvements for use in low-temperature environments such as winter or cold regions. Examples of the stability include thermal stability, oxidation stability, oxidation / hydrolysis stability, and the like. In addition, equipment that uses the lubricating oil is required to improve various durability such as wear resistance and fatigue resistance, and to improve energy saving performance.

  Patent Document 1 contains an ester obtained by reacting pentaerythritol, 3,5,5-trimethylhexanoic acid, isobutyric acid and adipic acid in a molar ratio of 1: 1: 2.5: 0.25. Although the liquid composition is described as being useful as a cooling liquid for refrigerators and air conditioners, the low-temperature fluidity and stability of the ester are not satisfactory.

Japanese Patent Laid-Open No. 6-25690

  An object of the present invention is to provide a pentaester of pentaerythritol used for refrigerating machine oil or the like having a good balance between excellent low temperature fluidity and excellent stability.

The present invention provides the following [1] to [5].
[1] A mixed ester of pentaerythritol and carboxylic acid, wherein the carboxylic acid contains isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms. Tetraester of pentaerythritol.
[2] The tetraester of pentaerythritol according to [1], wherein the carboxylic acid comprises isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms.
[3] The tetraester of pentaerythritol according to [1] or [2], wherein the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is butyric acid.
[4] The tetraester of pentaerythritol according to [1] or [2], wherein the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is pentanoic acid.
[5] The tetraester of pentaerythritol according to any one of [1] to [4], wherein the kinematic viscosity at 100 ° C. is in the range of 4.6 to 8.2 mm ² / sec.

  According to the present invention, a tetraester of pentaerythritol used for refrigerating machine oil or the like having a good balance of excellent low temperature fluidity and excellent stability can be provided.

  The tetraester of pentaerythritol of the present invention is a mixed ester of pentaerythritol and a carboxylic acid containing isobutyric acid, 3,5,5-trimethylhexanoic acid and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms. is there. Here, the tetraester of pentaerythritol means a compound obtained by esterification using a plurality of carboxylic acids that form an ester with respect to pentaerythritol.

The “mixed ester” as used in the present invention includes the following (i) to (vi):
(I) Tetraester of pentaerythritol in which the constituent carboxylic acid in the same molecule includes isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms (ii) in the same molecule Tetraester of pentaerythritol containing two selected from the group consisting of isobutyric acid, 3,5,5-trimethylhexanoic acid, and linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms (iii) pentaerythritol (Iv) Tetraester of carboxylic acid containing isobutyric acid (iv) Pentaerythritol and carboxylic acid containing 3,5,5-trimethylhexanoic acid (v) Linear chain of 4 to 7 carbon atoms with pentaerythritol Tetraester with carboxylic acid containing aliphatic monocarboxylic acid (vi) Above (i) to ( And a mixture of two or more tetraesters selected from the group of the following formulas (provided that the carboxylic acid constituting the mixed ester is isobutyric acid, 3,5,5-trimethylhexanoic acid, and a carbon number of 4 to 7 linear aliphatic monocarboxylic acids).
The pentaerythritol tetraester of the present invention may contain a pentaerythritol triester as an impurity.

  The carboxylic acid constituting the mixed ester may contain other carboxylic acids other than isobutyric acid, 3,5,5-trimethylhexanoic acid, and linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms. . Other carboxylic acids include, for example, linear aliphatic monocarboxylic acids such as acetic acid, propionic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, 2-methylbutyric acid, 3-methylbutyric acid, 2,2, -dimethylpropanoic acid, 2-ethylbutyric acid, 2-methylpentanoic acid, 4-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethyl-2-methyl Butyric acid, 2,2-dimethylpentanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid, 2-ethyl-2-methylpentanoic acid, 2-methyloctanoic acid, 2,2-dimethylheptane Examples thereof include branched aliphatic monocarboxylic acids such as acid, isotridecanoic acid and isostearic acid.

  The content of other carboxylic acids in the carboxylic acid containing isobutyric acid, 3,5,5-trimethylhexanoic acid and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is determined by the tetraerythritol tetrapentaerythritol of the present invention. The ester may be in a range that does not impair excellent properties such as low-temperature fluidity, stability, or compatibility with a difluoromethane refrigerant. Molar ratio of other carboxylic acid to the sum of isobutyric acid, 3,5,5-trimethylhexanoic acid and linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms [other carboxylic acid / (isobutyric acid, 3,5 , 5-trimethylhexanoic acid and linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms) ratio] is preferably in the range of 0/100 to 5/100.

  In the present invention, the carboxylic acid constituting the mixed ester is more preferably composed of isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms. .

  Specific examples of the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms constituting the tetraester of pentaerythritol of the present invention include butyric acid, pentanoic acid, hexanoic acid, and heptanoic acid. Pentanoic acid is preferred. When the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is butyric acid or pentanoic acid, the tetraester of pentaerythritol of the present invention is compatible with difluoromethane refrigerant in a wide range of concentrations, viscosity-temperature characteristics, low temperature flow Excellent properties such as stability, low temperature properties, and stability are particularly well balanced.

  When the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms constituting the tetraester of pentaerythritol of the present invention is butyric acid or pentanoic acid, butyric acid for the sum of isobutyric acid and 3,5,5-trimethylhexanoic acid Alternatively, the molar ratio of pentanoic acid [(butyric acid or pentanoic acid) / (isobutyric acid and 3,5,5-trimethylhexanoic acid) ratio] is preferably in the range of 10/100 to 300/100.

  When the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms constituting the tetraester of pentaerythritol of the present invention is heptanoic acid, heptanoic acid with respect to the sum of isobutyric acid and 3,5,5-trimethylhexanoic acid The molar ratio [heptanoic acid / (isobutyric acid and 3,5,5-trimethylhexanoic acid) ratio] is preferably in the range of 20/100 to 100/100.

  The ratio (mol%) of isobutyric acid to the sum of all carboxylic acids constituting the tetraester of pentaerythritol of the present invention is preferably in the range of 5 to 55 mol% in terms of low-temperature characteristics and stability. More preferably, it is in the range of 40 mol%, and even more preferably in the range of 15-40 mol%.

  The tetraesters of pentaerythritol of the present invention include, for example, pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid, linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms, and other if desired It can manufacture by making it react with carboxylic acid at 120-250 degreeC for 5 to 60 hours.

  A catalyst may be used in the reaction, and examples of the catalyst include mineral acids, organic acids, Lewis acids, organic metals, solid acids and the like. Specific examples of the mineral acid include hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, nitric acid and the like. Specific examples of the organic acid include p-toluenesulfonic acid, benzenesulfonic acid, butanesulfonic acid, propanesulfonic acid, ethanesulfonic acid, methanesulfonic acid and the like. Specific examples of the Lewis acid include boron trifluoride, aluminum chloride, tin tetrachloride, titanium tetrachloride and the like. Specific examples of the organic metal include tetrapropoxy titanium, tetrabutoxy titanium, tetrakis (2-ethylhexyloxy) titanium, and the like. Specific examples of the solid acid include a cation exchange resin.

  The sum of the amount of isobutyric acid used, the amount of 3,5,5-trimethylhexanoic acid, the amount of linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms and the amount of other carboxylic acids used It is preferable that it is 1.1-1.4 times mole with respect to the hydroxyl group of pentaerythritol.

  A solvent may be used in the reaction, and examples of the solvent include hydrocarbon solvents such as benzene, toluene, xylene, hexane, heptane, isohexane, isooctane, isononane, and decane.

  It is preferable to carry out the reaction while removing water produced by the reaction from the reaction mixture. When water generated by the reaction is removed from the reaction mixture, isobutyric acid and / or a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms may be removed from the reaction mixture at the same time.

  Further, isobutyric acid constituting the tetraester obtained from the difference in reactivity of isobutyric acid, 3,5,5-trimethylhexanoic acid, and linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms with respect to pentaerythritol And the molar ratio of 3,5,5-trimethylhexanoic acid to a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms may differ from that in the amount used to produce the tetraester.

  After the reaction, the pentaerythritol tetraester of the present invention is a method usually used in organic synthetic chemistry (washing with water and / or alkaline aqueous solution, treatment with activated carbon, adsorbent, etc., various chromatographic methods, if necessary) It may be purified by a distillation method or the like.

  The tetraester of pentaerythritol of the present invention has excellent low temperature fluidity, excellent stability, excellent low temperature characteristics, excellent viscosity-temperature characteristics, excellent compatibility with difluoromethane solvents, excellent lubricity and the like.

  The viscosity-temperature characteristic is a change in kinematic viscosity with respect to a temperature change of an oil agent such as a lubricating oil. Good viscosity-temperature characteristics means that the viscosity change is small with respect to temperature changes, while poor ones mean that the viscosity increases rapidly in the low temperature range and the kinematic viscosity becomes lower than expected in the high temperature range. It is a thing. Generally, this characteristic is expressed as a viscosity index, and it can be said that the higher the value, the better the viscosity-temperature characteristic. The viscosity characteristic in a low temperature region is also called low temperature fluidity, and is expressed by a pour point, a freezing point, a channel point, and the like.

  The pour point refers to the lowest temperature at which the oil agent flows when the oil agent such as lubricating oil is cooled according to the method of Japanese Industrial Standard (JIS) K2269. An oil agent with a low pour point does not deteriorate its fluidity even in low temperature environments such as in winter or in cold regions, or when operating as an evaporator in a refrigerator at low temperatures when used as refrigeration oil. It is preferable in that it does not cause malfunction of the equipment using the device.

  In addition, when storing or using an oil agent such as lubricating oil for a long period of time in a place where the temperature difference is large, an oil agent that has no volatility in the high temperature range and does not solidify or precipitate in the low temperature range is preferable. Although there is no restriction | limiting in particular as a temperature range, The oil agent which can be used stably at about -20 degreeC at about 150 degreeC in a high temperature side and low temperature side is preferable. The characteristic that solidification and precipitation do not occur in the low temperature range is defined as the low temperature characteristic. In this invention, it can suppress that a precipitate generate | occur | produces at low temperature by using C4-C7 linear aliphatic monocarboxylic acid as carboxylic acid.

  Stability includes, for example, thermal stability, oxidation stability, oxidation / hydrolysis stability, shear stability and the like in lubricating oil applications.

  Examples of lubricity include friction reduction, wear reduction, extreme pressure, and the like.

  Moreover, the tetraester of pentaerythritol of the present invention is excellent in compatibility with not only a conventional difluoromethane mixed solvent (R-410A, R-407C) but also a difluoromethane refrigerant alone. In recent years, difluoromethane refrigerant (HFC-32) has attracted attention as a refrigerant for refrigerators. Difluoromethane refrigerant has an ozone depletion coefficient of zero and a global warming potential (GWP) currently used refrigerant [R-410A (mixture of difluoromethane and pentafluoroethane), R-407C (difluoromethane and A mixture of pentafluoroethane and 1,1,1,2-tetrafluoroethane), etc.] and a coefficient of performance (COP) of R-410A, R-407C, etc. Therefore, it is a preferable refrigerant from the viewpoint of energy saving (“Lubrication Economy”, June 2004 (No. 460), p. 17). However, the conventional lubricating base oil is not sufficiently compatible with the difluoromethane refrigerant, and a lubricating base oil having excellent compatibility is required (Japanese Patent Laid-Open No. 2002-129177).

  Compatibility with difluoromethane refrigerant is generally expressed using the two-layer separation temperature. It can be said that the lower the two-layer separation temperature, the better the compatibility on the low temperature side. The compatibility of the ester with the refrigerant has a correlation with the property of the ester. In this invention, since isobutyric acid is used as carboxylic acid, the compatibility with a difluoromethane solvent is good.

When the tetraester of pentaerythritol of the present invention is used in refrigerating machine oil, the kinematic viscosity at 100 ° C. of the tetraester is preferably in the range of 4.6 to 8.2 mm ² / sec, and preferably 5.0 to 7. More preferably, it is in the range of 0 mm ² / sec.
Further, the viscosity index of the ester is preferably 89 or more.

  When the tetraester of pentaerythritol of the present invention is used in refrigerating machine oil, if the residual amount of hydroxyl groups in the tetraester is large, the refrigerating machine oil becomes cloudy at a low temperature and undesired phenomena occur such as blocking the refrigeration cycle capillary device Therefore, the hydroxyl value of the mixed ester is preferably 10 mgKOH / g or less, and more preferably 5 mgKOH / g or less.

  The pentaerythritol tetraester of the present invention is used for refrigeration machine oils, engine oils, gear oils, motor oils used in hybrid cars and electric cars, grease, metal parts cleaning agents, plasticizers, etc. Can do.

  Examples of the refrigerating machine oil using the pentaerythritol tetraester of the present invention include a refrigerating machine oil containing a pentaerythritol tetraester and an additive for lubricating oil. In the refrigerating machine oil using the tetraester of pentaerythritol of the present invention, the tetraester is used as a lubricating oil base oil.

  Examples of additives for lubricating oil include antioxidants, wear reducing agents (antiwear agents, anti-seizure agents, extreme pressure agents, etc.), friction modifiers, acid scavengers, metal deactivators, and antifoaming agents. And the like which are usually used as lubricating oil additives. The content of these additives is preferably 0.001 to 5% by weight in the refrigerating machine oil.

  You may use together the tetraester of the pentaerythritol of this invention, and another lubricating base oil. Examples of other lubricating base oils include mineral oils and synthetic base oils.

  Examples of the mineral oil include paraffinic crude oil, intermediate crude oil, and naphthenic crude oil. Further, refined oils obtained by refining them by distillation or the like can also be used.

  Synthetic base oils include, for example, poly-α-olefins (polybutene, polypropylene, α-olefin oligomers having 8 to 14 carbon atoms, etc.), aliphatic esters (fatty acid monoesters, polyhydric alcohols) other than the tetraesters of the present invention. Fatty acid ester, aliphatic polybasic acid ester, etc.), aromatic ester (aromatic monoester, aromatic ester of polyhydric alcohol, aromatic polybasic acid ester, etc.), polyalkylene glycol, polyvinyl ether, polyphenyl ether, alkylbenzene , Carbonate, synthetic naphthene and the like.

  The tetraester of pentaerythritol of the present invention is excellent in the ability to dissolve additives for lubricating oil such as metal deactivators such as benzotriazole and silicone antifoaming agents. The additive for lubricating oil is used by being dissolved in the lubricating oil, for example, in order to extend the life of the lubricating oil, equipment using the lubricating oil, and the like. The lubricating oil additive generally has low solubility in pentaerythritol ester (Japanese Patent Laid-Open No. 10-259394). Benzotriazole has low solubility in mineral oil and / or synthetic oil (Japanese Patent Laid-Open No. 59-189195). However, for example, the solubility (25 ° C.) of benzotriazole in tetraester 4 (described later in Example 4) and tetraester 10 (described later in Example 10), which are tetraesters of pentaerythritol of the present invention, is 0.031 g / g and 0.024 g / g, which show high solubility of benzotriazole in all pentaesters of pentaerythritol. The pentaerythritol tetraester of the present invention has excellent low-temperature fluidity and excellent wear resistance when benzotriazole is dissolved.

EXAMPLES Hereinafter, although an Example, a comparative example, and a test example demonstrate this invention further more concretely, it is not limited to a following example.
The nuclear magnetic resonance spectrum was measured by the following measuring instrument and measuring method.
Measuring instrument: GSX-400 (400 MHz) manufactured by JEOL Ltd.
Measurement method: ¹ H-NMR, standard (tetramethylsilane), solvent (CDCl ₃ )

  The nuclear magnetic resonance spectrum was measured for each of the tetraesters of pentaerythritol produced in Examples 1 to 12 below, and isobutyric acid, 3,5,5-trimethylhexanoic acid, and carbon atoms of 4 to 4 in the tetraester of pentaerythritol were measured. The molar ratio of 7 to the linear aliphatic monocarboxylic acid was calculated by the following formula.

Isobutyric acid / 3,5,5-trimethylhexanoic acid / linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms = integrated value of peak X / integrated value of peak Y / (integrated value of peak Z / 2)
Here, the peak X corresponds to a hydrogen atom peak on the methine group in isobutyric acid, the peak Y corresponds to a hydrogen atom on the methine group in 3,5,5-trimethylhexanoic acid, and the peak Z has 4 to 4 carbon atoms. 7 corresponds to the peak of the hydrogen atom on the methylene group at the α-position of the carbonyl group in the linear aliphatic monocarboxylic acid No. 7.

The nuclear magnetic resonance spectrum was measured for the ester of pentaerythritol produced in Comparative Example 1 below, and the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and adipic acid in the ester of pentaerythritol was determined by the following formula: Calculated by
Isobutyric acid / 3,5,5-trimethylhexanoic acid / adipic acid = integrated value of peak X / integrated value of peak Y / (integrated value of peak W / 4)
Here, the peak X and the peak Y have the same meaning as described above, and the peak W corresponds to the peak of a hydrogen atom on the α-position methylene group of the carbonyl group in adipic acid.

[Example 1]
[Tetraesters of pentaerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) of 71/29/33 (tetra Production of ester 1)
As an adsorbent, Kyoward 500 manufactured by Kyowa Chemical Industry Co., Ltd. was used.
As activated carbon, Shirahige P manufactured by Nippon Enviro Chemicals was used.
In a reactor equipped with a Dean-Stark trap, 327 g of pentaerythritol (2.4 mol, manufactured by Guangei Perstorp), 650 g of isobutyric acid (7.4 mol, manufactured by Tokyo Chemical Industry), 365 g of 3,5,5-trimethylhexanoic acid ( 2.3 mol, manufactured by Kyowa Hakko Chemical Co., Ltd.) and 162 g of butyric acid (1.8 mol, manufactured by Wako Pure Chemical Industries, Ltd.) were charged, and the mixture was degassed by bubbling nitrogen at room temperature for 30 minutes while stirring the mixture. .
The mixture was then stirred at 138-230 ° C. for 30 hours with nitrogen bubbling. After the reaction, the reaction product was stirred at 218 ° C. for 1 hour under a reduced pressure of 0.7 kPa to distill off unreacted carboxylic acid in the reaction product. The reaction product was washed at 85 ° C. for 1 hour with 400 mL of an alkaline aqueous solution containing sodium hydroxide twice as much as the acid value of the reaction product. The reaction product was then washed 3 times with 400 mL of water at 88 ° C. for 1 hour. Subsequently, the reaction product was dried by stirring at 106 ° C. for 1 hour under a reduced pressure of 1.1 kPa while performing nitrogen bubbling.
To the reaction product, 5.0 g of adsorbent (corresponding to 0.5% by weight of the reaction product) and 9.9 g of activated carbon (corresponding to 1.0% by weight of the reaction product) are added, and nitrogen bubbling is performed. The reaction product was stirred at 104 ° C. for 2 hours under a reduced pressure of 1.1 kPa, and then filtered using a filter aid to obtain 822 g of tetraester 1.

[Example 2]
[Tetraester of pentaerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid (ratio of isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid) of 62/38/57 (tetra Production of ester 2)]
The molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) was 1 / 1.80 / The tetraester 2 was obtained in the same manner as in Example 1 except that the amount was 1.20 / 1.80.

[Example 3]
[Tetraester of pentaerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) of 34/66/95 (tetra Production of ester 3)]
The molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) is 1 / 0.72 / The tetraester 3 was obtained in the same manner as in Example 1 except that it was 1.68 / 2.40.

[Example 4]
[Tetraester of pentaerythritol having a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid (ratio of isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid) of 34/66/41 (tetra Production of ester 4)]
The molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) was set to 1 / 1.20 / The tetraester 4 was obtained in the same manner as in Example 1 except that the ratio was changed to 2.00 / 1.60.

[Example 5]
[Tetraesters of pentaerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) of 24/76/42 (tetra Production of ester 5)]
The molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and butyric acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / butyric acid ratio) is 1 / 0.90 / The tetraester 5 was obtained in the same manner as in Example 1 except that the ratio was 3.00 / 0.90.

[Example 6]
[Tetraester of pentaerythritol in which the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid (ratio of isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid) is 30/70/259 (Production of tetraester 6)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 6 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was 1 / 0.38 / 0.96 / 3.46.

[Example 7]
[Tetraester of pentaerythritol in which the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid ratio) is 69/31/74 (Production of tetraester 7)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 7 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was changed to 1 / 1.92 / 0.96 / 1.92.

[Example 8]
[Tetraester of pentaerythritol in which the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid ratio) is 32/68/104 (Production of tetraester 8)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 8 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was 1 / 0.72 / 1.68 / 2.40.

[Example 9]
[Tetrapentaerythritol having a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid to pentanoic acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid ratio) of 35/65/42 Production of ester (tetraester 9)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 9 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was changed to 1 / 1.20 / 2.00 / 1.60.

[Example 10]
[Tetrapentylerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid ratio) of 40/60/11 Production of ester (tetraester 10)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 10 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was changed to 1 / 1.73 / 2.59 / 0.48.

[Example 11]
[Tetrapentylerythritol with a molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid (isobutyric acid / 3,5,5-trimethylhexanoic acid / pentanoic acid ratio) of 26/74/22 Production of ester (tetraester 11)]
Pentaic acid is used instead of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and pentanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 11 was obtained in the same manner as in Example 1 except that the ratio of pentanoic acid was changed to 1 / 0.90 / 3.00 / 0.90.

[Example 12]
[Tetraester of pentaerythritol in which the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid to heptanoic acid (ratio of isobutyric acid / 3,5,5-trimethylhexanoic acid / heptanoic acid) is 65/35/72 (Production of tetraester 12)]
Instead of butyric acid, heptanoic acid is used, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and heptanoic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / The tetraester 12 was obtained in the same manner as in Example 1 except that the ratio of heptanoic acid was changed to 1 / 1.92 / 0.96 / 1.92.

[Comparative Example 1]
[Ester of pentaerythritol in which the molar ratio of isobutyric acid, 3,5,5-trimethylhexanoic acid and adipic acid (ratio of isobutyric acid / 3,5,5-trimethylhexanoic acid / adipic acid) is 69/31/7 ( Production of ester A)
Adipic acid was used in place of butyric acid, and the molar ratio of pentaerythritol, isobutyric acid, 3,5,5-trimethylhexanoic acid and apidic acid used (pentaerythritol / isobutyric acid / 3,5,5-trimethylhexanoic acid / Ester A was obtained in the same manner as in Example 1 except that the ratio of adipic acid was 1 / 2.50 / 1.00 / 0.25.

(Test Example 1) Measurement of pour point The pour points of tetraesters 1 to 12 and ester A were measured according to the method of JIS K2269-1987 using an automatic pour point measuring device RPC-01CML (manufactured by Rouai Co., Ltd.). The results are shown in Tables 1-3.

(Test Example 2) Measurement of kinematic viscosity Using a Canon-Fenske viscometer, the kinematic viscosities of tetraesters 1 to 12 and ester A at 40 ° C and 100 ° C were measured according to the method of JIS K2283: 2000. The viscosity index was calculated according to the same method. The results are shown in Tables 1-3.

(Test Example 3) Measurement of two-layer separation temperature Two-layer separation temperatures of tetraesters 1 to 4 and 6 to 8 were measured according to the method of JIS K2211: 2009. Each 0.4 g of tetraesters 1 to 4 and 6 to 8 and 3.6 g of difluoromethane refrigerant are sealed in a pressure-resistant glass tube, and the mixture is cooled from 30 ° C. at a rate of 0.5 ° C./min. The temperature at which separation or white turbidity occurred was defined as the two-layer separation temperature. The results are shown below.

(Test Example 4) Solidification at −20 ° C., confirmation of presence or absence of precipitates (evaluation of low temperature characteristics)
Each of tetraesters 2 to 12 was placed in a 1.0 g glass container and allowed to stand for 96 hours in a thermostat set to −20 ° C. Solidification after standing and presence / absence of precipitates were visually confirmed. The results are shown below.

(Test Example 5) Measurement of RBOT life (evaluation of oxidation / hydrolysis stability and oxidation stability)
"Condition 1"
An oxidation stability test was performed according to the method of JIS K2514-1996, using a rotary cylinder type oxidation stability tester RBOT-02 (manufactured by Rouai Co., Ltd.). 49.50 g of each of tetraester 1-12 and ester A, 4,4′-methylenebis (2,6-di-tert-butylphenol) (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.25 g, IRGANOX L57 (Ciba Special) 0.25 g (manufactured by Tei Chemicals), 5 mL of water, and electrolytic copper wire (diameter 1.6 mm, length 3 m) polished with sandpaper # 400 were placed in a pressure-resistant container. Next, oxygen was injected into the pressure vessel up to 620 kPa, and the pressure vessel was placed in a thermostatic bath at 150 ° C. and rotated at 100 revolutions per minute. The time required for the pressure drop of 175 kPa from the time when the pressure in the pressure vessel reached the maximum (RBOT life) was measured. The results are shown in Tables 1-3.
In Tables 1-3, the longer the RBOT life, the better the oxidation / hydrolysis stability of the tetraester.

"Condition 2"
4,4′-methylenebis (2,6-di-tert-butylphenol), IRGANOX L57, and water were not put in a pressure vessel, and the other operations were performed in the same manner as in condition 1 above. The time required for the pressure drop of 175 kPa from the time when the pressure of the container reached the maximum (RBOT life) was measured. Here, the longer the RBOT lifetime, the better the oxidation stability of the tetraester.

(Test Example 6) Measurement of weight loss temperature (evaluation of thermal stability)
Using a thermogravimetric / differential calorimeter Tg-DTA6200 (manufactured by Seiko Instruments Inc.), 5% weight loss temperatures of tetraesters 5, 6 and 9-12 were measured under the following conditions. The results are shown in Table 4.
Measurement temperature: 40 to 420 ° C., rate of temperature increase: 10 ° C./min, atmosphere: nitrogen aeration (300 mL / min), sample container: aluminum 15 μl (open), sample amount: 3 mg

From Tables 1 to 3, the tetraesters 1 to 12 have a kinematic viscosity at 100 ° C. of 4.6 to 8.2 mm ² / sec, a viscosity index of 89 or more, and a pour point of −42.5 ° C. or less. It can be seen that the RBOT life under Condition 1 is 756 minutes or longer and has excellent oxidation / hydrolysis stability.

  From Table 4, tetraesters 5, 6 and 9 to 12 had a 5% weight loss temperature of 221.8 ° C. or higher in the measurement of Tg-DTA. It can be seen that the tetraesters of the present invention have excellent thermal stability.

  In Test Example 3, tetraesters 1 to 4 and 6 to 8 had a two-layer separation temperature of −32 ° C. or lower, and among them, tetraesters 1 to 3 and 7 were −50 ° C. or lower. It turns out that the tetraester of this invention has the outstanding compatibility with a difluoromethane refrigerant | coolant.

  In Test Example 4, tetraesters 2 to 12 did not solidify, and no deposits were confirmed. It can be seen that tetraesters 2 to 12 can be preferably used even when stored or used for a long time in a low temperature range.

  In “Condition 2” of Test Example 5, tetraester 3 had an RBOT life of 217 minutes, and tetraester 8 had an RBOT life of 247 minutes. It can be seen that the tetraester of the present invention has high oxidative stability.

  According to the present invention, a tetraester of pentaerythritol used for refrigerating machine oil or the like having a good balance of excellent low temperature fluidity and excellent stability can be provided.

Claims (5)

  A mixed ester of pentaerythritol and a carboxylic acid, wherein the carboxylic acid contains isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms. Tetraester.   The tetraester of pentaerythritol according to claim 1, wherein the carboxylic acid comprises isobutyric acid, 3,5,5-trimethylhexanoic acid, and a linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms.   The tetraester of pentaerythritol according to claim 1 or 2, wherein the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is butyric acid.   The tetraester of pentaerythritol according to claim 1 or 2, wherein the linear aliphatic monocarboxylic acid having 4 to 7 carbon atoms is pentanoic acid. The tetraester of pentaerythritol according to any one of claims 1 to 4, which has a kinematic viscosity at 100 ° C in the range of 4.6 to 8.2 mm ² / sec.