Alkyl-substituted diphenyl ether mixture, lubricating oil, and method for producing alkyl-substituted diphenyl ether

Abstract

Provided is an alkyl-substituted diphenyl ether mixture including substitution with 2 to 10 linear or branched alkyl groups having 8 to 24 carbon atoms, wherein the mixture substantially contains no diphenyl ether including substitution with only branched alkyl groups.

Description

Alkyl-substituted diphenyl ether mixture, lubricating oil, and method for producing alkyl-substituted diphenyl ether

[0001] The present invention relates to an alkyl-substituted diphenyl ether mixture, a lubricating oil, and a method for producing alkyl-substituted diphenyl ethers. This application claims priority to Japanese Patent Application No. 2023-206192, filed December 6, 2023, and incorporates the entire contents of said Japanese Patent Application by reference.

[0002] Lubricating oil base oils (base oils) containing alkyl-substituted diphenyl ethers as their main component are known. For example, Patent Document 1 (Japanese Patent Publication No. 58-22515) discloses alkyl-substituted diphenyl ethers having three or more alkyl groups each having 10 to 20 carbon atoms. The examples in Patent Document 1 describe that an α-olefin having 12 to 16 carbon atoms was added to the diphenyl ether, and that the average number of moles of the olefin added was 3.5 to 5.2 moles.

[0003] Patent Document 2 (WO 2005 / 040081) describes a grease composition containing a mixture of alkyl-substituted diphenyl ethers having an alkyl group having 10 to 20 carbon atoms as a substituent, the number of substituents being two or more, and the 1-position addition rate of the substituents being 5% or more. Patent Document 2 also describes that the alkyl-substituted diphenyl ether disclosed therein has both excellent high-temperature properties and excellent low-temperature properties.

[0004] Patent Document 3 (WO 2022 / 172935) discloses a dinaphthyl ether compound used as a lubricating oil having excellent heat resistance. The dinaphthyl ether compound of Patent Document 3 has a substituent that is a linear or branched hydrocarbon group having 6 to 32 carbon atoms, and the substitution number is 1.0 or more and 3.0 or less.

[0005] Japanese Patent Publication No. 58-22515 International Publication No. 2005 / 040081 International Publication No. 2022 / 172935

[0006] As shown in Patent Documents 1 to 3, lubricating oils are required to have heat resistance. Lubricating oils based on a mixture of diphenyl ether compounds are known to have high heat resistance. On the other hand, highly heat-resistant lubricating oils tend to have high viscosity, and high viscosity lubricating oils can increase the torque during operation of lubricated parts. In other words, heat resistance and viscosity are in a trade-off relationship. Therefore, one of the objects of the present invention is to provide a lubricating oil that combines high heat resistance and low viscosity, as well as a diphenyl ether mixture that serves as the base oil, and to provide a method for producing the same.

[0007] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of diphenyl ethers substituted with 2 to 10 linear or branched alkyl groups having 8 to 24 carbon atoms. Here, the alkyl-substituted diphenyl ether mixture is a mixture composed solely of linear or branched alkyl-substituted diphenyl ethers. In the case of a composition containing, in addition to alkyl-substituted diphenyl ethers, unreacted substances such as phenols and additives such as antioxidants, the portion composed solely of alkyl-substituted diphenyl ethers corresponds to the alkyl-substituted diphenyl ether mixture. The mixture is substantially free of diphenyl ethers substituted solely with branched alkyl groups. This can be rephrased as saying that, in the case of a composition containing various compounds other than alkyl-substituted diphenyl ethers, the alkyl-substituted diphenyl ether mixture contained in the composition is substantially free of diphenyl ethers substituted solely with branched alkyl groups. In other words, substantially all of the numerous alkyl-substituted diphenyl ether molecules constituting the alkyl-substituted diphenyl ether mixture are not diphenyl ethers substituted solely with branched alkyl groups.

[0008] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of diphenyl ethers substituted with 2 to 10 alkyl groups having 8 to 24 carbon atoms. The mixture consists essentially of diphenyl ethers having at least one linear alkyl group. This can be rephrased as saying that, when a composition contains various compounds other than alkyl-substituted diphenyl ethers, the alkyl-substituted diphenyl ethers contained in the composition essentially have at least one linear alkyl group. In other words, substantially all of the numerous alkyl-substituted diphenyl ether molecules constituting the alkyl-substituted diphenyl ether mixture are diphenyl ethers having at least one linear alkyl group.

[0009] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a diphenyl ether mixture substituted with 2 to 10 alkyl groups having 8 to 24 carbon atoms. Of the alkyl groups contained in the diphenyl ether mixture, the proportion of alkyl groups in which the carbon at the benzylic position is a secondary carbon is 25% or more.

[0010] The method for producing alkyl-substituted diphenyl ethers according to the present disclosure comprises a diphenyl etherification step and an alkyl addition step. The diphenyl etherification step is a step of reacting an alkyl-substituted phenol having a linear alkyl group with a halogenated benzene which may be substituted with an alkyl group, or a step of reacting a halogenated benzene having a linear alkyl group with a phenol which may be substituted with an alkyl group, to obtain a diphenyl ether having a linear alkyl group. The alkyl addition step is an alkyl addition step in which an alkyl group is added to the diphenyl ether obtained in the diphenyl etherification step. These steps are carried out sequentially. The alkyl group added in the alkyl addition step has 8 to 24 carbon atoms.

[0011] The alkyl-substituted diphenyl ether mixture described above can provide a lubricating oil that combines high heat resistance and low viscosity, as well as a diphenyl ether mixture that can serve as a base oil therefor. The method for producing the alkyl-substituted diphenyl ether mixture described above can provide a lubricating oil that combines high heat resistance and low viscosity, as well as a diphenyl ether mixture that can serve as a base oil therefor.

[0012] FIG. 1 shows the results of Example 1 (Mixture 3). １ 2 is a H-NMR chart of Example 1 (Mixture 3). １３ FIG. 3 is a C-NMR chart of Example 5 (Mixture 5). １３ 4 is a DEPT-135 chart of Example 4 (Mixture 5).

[0013] [Summary of the Embodiments] First, embodiments of the alkyl-substituted diphenyl ether mixture and the method for producing alkyl-substituted diphenyl ether according to the present disclosure will be listed and described. In this specification, unless otherwise specified, the numerical range "A to B" means "A or more and B or less."

[0014] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of diphenyl ethers substituted with 2 to 10 linear or branched alkyl groups having 8 to 24 carbon atoms. The mixture is substantially free of diphenyl ethers substituted only with branched alkyl groups.

[0015] In the past, in order to provide a diphenyl ether composition having excellent heat resistance for use as a lubricating base oil, it has been proposed to set the number and distribution of alkyl groups attached to the diphenyl ether skeleton within a specific range. It has also been proposed to set the addition form of the alkyl substituent attached to the diphenyl ether skeleton (e.g., the alkyl group addition rate at the first position) within a specific range. However, the need for heat resistance continues, and lubricating oils that combine high heat resistance and low viscosity are also desired. In light of this situation, the inventors conducted extensive research and found that a diphenyl ether mixture that does not contain diphenyl ethers substituted only with branched alkyl groups and always contains linear alkyl groups can combine low viscosity and high heat resistance. Unlike the conventional method of adding alkyl groups to diphenyl ethers as a raw material, the diphenyl ether mixture that always contains linear alkyl groups can be produced by preparing a diphenyl ether skeleton compound to which linear alkyl groups have been added in advance and then further adding alkyl groups to the skeleton compound.

[0016] The mixture according to the present disclosure is characterized by having a specific range of alkyl group substitution number and carbon number, and is substantially free of diphenyl ethers substituted only with branched alkyl groups. Due to the characteristics of its production method, the alkyl-substituted diphenyl ether mixture is not composed of uniform compounds, but is obtained as a mixture of alkyl-substituted diphenyl ether compounds with different numbers and forms of alkyl groups added. Conventional alkyl-substituted diphenyl ether compositions specify the number of alkyl groups added to the entire composition (i.e., the average number of alkyl groups added) and the form of alkyl group addition, but do not specify the specific form of each compound constituting the alkyl-substituted diphenyl ether composition. In contrast, the diphenyl ether mixture according to the present invention is characterized by being substantially free of diphenyl ethers substituted only with branched alkyl groups, in other words, the compounds constituting the diphenyl ether mixture are not diphenyl ether compounds substituted only with branched alkyl groups. Here, "substantially free" refers not only to the complete absence of diphenyl ether compounds substituted only with branched alkyl groups, but also to cases where the amount of diphenyl ethers substituted only with branched alkyl groups is so small that it is difficult to detect them when analyzed by commonly used measurement methods (e.g., NMR). Furthermore, this also includes cases where the diphenyl ether mixture contains a small amount of "diphenyl ether compound substituted with only branched alkyl groups" to the extent that it does not affect the performance as a lubricating base oil. Specifically, this means that the amount of diphenyl ether compound substituted with only branched alkyl groups contained in the alkyl-substituted diphenyl ether mixture is 2% or less of the total amount of the alkyl-substituted diphenyl ether mixture.

[0017] Without being bound by any particular theory, it is believed that the mixture according to the present disclosure has a high proportion of linear alkyl chains, which exhibit higher heat resistance than branched alkyl chains, and therefore can exhibit high heat resistance even with a small number of alkyl groups added, thereby achieving both low viscosity and high heat resistance.

[0018] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of diphenyl ethers substituted with an average of 2 to 10 alkyl groups having 8 to 24 carbon atoms. The mixture consists essentially of diphenyl ethers having at least one linear alkyl group. Here, "consisting only of" means that diphenyl ethers having at least one linear alkyl group account for 98% or more of the total amount of the alkyl-substituted diphenyl ether mixture. More preferably, diphenyl ethers having at least one linear alkyl group account for 99% or more of the total amount of the alkyl-substituted diphenyl ether mixture. As described above, it has been discovered that such diphenyl ether mixtures exhibit both low viscosity and high heat resistance.

[0019] The alkyl-substituted diphenyl ether mixture may be a mixture of diphenyl ethers substituted with an average of 2 to 5 alkyl groups. When the number of alkyl group substitutions is within this range, the alkyl-substituted diphenyl ether mixture can be obtained by combining known raw materials and production methods, and the effects of the present invention can be reliably achieved.

[0020] The alkyl-substituted diphenyl ether mixture is composed of compounds having at least one linear alkyl group, and at least one of the linear alkyl groups may be bonded to a carbon atom in a benzene ring at the o-position or m-position to an oxygen atom-bonded carbon atom. The alkyl-substituted diphenyl ether mixture composed of such compounds has high heat resistance.

[0021] The alkyl-substituted diphenyl ether mixture may have an average total number of carbon atoms of 25 or more and 100 or less in the alkyl groups of the diphenyl ether mixture.

[0022] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of diphenyl ethers substituted with 2 to 10 alkyl groups having 8 to 24 carbon atoms. Of the alkyl groups contained in the diphenyl ether mixture, the proportion of alkyl groups in which the carbon at the benzyl position is a secondary carbon is 25% or more. Methods for measuring and calculating the proportion of "alkyl groups in which the carbon at the benzyl position is a secondary carbon" in the diphenyl ether mixture are described in detail in the Examples.

[0023] The alkyl-substituted diphenyl ether mixture according to the present disclosure is produced by a different production method from conventional alkyl-substituted diphenyl ether mixtures, resulting in a high ratio of alkyl groups in which the carbon at the benzyl position is a secondary carbon, at 25% or more. Conventional alkyl-substituted diphenyl ethers are produced by using diphenyl ether as a raw material and adding alkyl groups to diphenyl ether using the Friedel-Crafts reaction. In the addition of alkyl groups via the Friedel-Crafts reaction, stochastic rearrangement occurs in the olefin compound used as the alkyl group raw material during the addition reaction. Therefore, even when an α-olefin is used as the alkyl group raw material, the ratio of alkyl groups in which the carbon at the benzyl position is a secondary carbon in the added alkyl groups does not increase and reaches a plateau. Furthermore, diphenyl ethers in which all of the substituted alkyl groups are branched alkyl groups have been produced. In contrast, the mixture according to the present disclosure is obtained by a method in which a diphenyl ether skeleton compound to which a linear alkyl group has been added is prepared in advance, and then an alkyl group is further added to the skeleton compound. As a result, an alkyl-substituted diphenyl ether mixture in which the ratio of alkyl groups in which the carbon at the benzyl position is a secondary carbon, at 25% or more, is obtained. Furthermore, the alkyl-substituted diphenyl ether compound produced has at least one linear alkyl group. That is, the diphenyl ethers contained in the alkyl-substituted diphenyl ether mixture may consist essentially of diphenyl ethers having at least one linear alkyl group. The diphenyl ether mixture according to the present disclosure achieves both low viscosity and high heat resistance.

[0024] The alkyl-substituted diphenyl ether mixture is a mixture of diphenyl ethers substituted with 2 to 5 alkyl groups, and at least one of the linear alkyl groups may be a linear alkyl group bonded to a carbon atom in a benzene ring at the m-position to which an oxygen atom is bonded.

[0025] The lubricating oil according to the present disclosure is a lubricating oil containing the above-described diphenyl ether mixture.

[0026] The method for producing alkyl-substituted diphenyl ethers according to the present disclosure includes a diphenyl etherification step and an alkylation step. The diphenyl etherification step is a step of reacting an alkyl-substituted phenol having a linear alkyl group with a halogenated benzene that may be substituted with an alkyl group, or a step of reacting a halogenated benzene having a linear alkyl group with a phenol that may be substituted with an alkyl group, to obtain a diphenyl ether having a linear alkyl group. The alkylation step is an alkylation step in which an alkyl group is added to the diphenyl ether obtained in the diphenyl etherification step. These steps are performed sequentially. The alkyl group added in the alkylation step has 8 to 24 carbon atoms. The alkyl-substituted diphenyl ether mixture obtained by this production method combines high heat resistance and low viscosity and is suitable as a base oil for lubricating oils.

[0027] In the method for producing an alkyl-substituted diphenyl ether, the alkyl-substituted phenol having a linear alkyl group may be an alkyl-substituted phenol having a linear alkyl group bonded at the m-position to the carbon atom to which an oxygen atom in a benzene ring is bonded. According to this configuration, by combining commonly used raw materials and a production method, it is possible to obtain an alkyl-substituted diphenyl ether mixture that has both high heat resistance and low viscosity at a practically reasonable cost.

[0028] [Specific Example of Embodiment] The alkyl-substituted diphenyl ether mixture according to the present disclosure will now be described more specifically.

[0029] [Compounds Constituting the Alkyl-Substituted Diphenyl Ether Mixture] The alkyl-substituted diphenyl ether mixture according to the present disclosure is a mixture of alkyl-substituted diphenyl ether compounds, and the alkyl-substituted diphenyl ether compounds constituting the alkyl-substituted diphenyl ether mixture are substantially free of diphenyl ethers substituted only with branched alkyl groups. Here, "substantially free" specifically means that diphenyl ethers substituted only with branched alkyl groups account for 2% or less of the total amount of the alkyl-substituted diphenyl ether mixture. More preferably, diphenyl ethers substituted only with branched alkyl groups account for 1% or less of the total amount of the alkyl-substituted diphenyl ether mixture.

[0030] The alkyl-substituted diphenyl ether mixture according to the present disclosure consists essentially of diphenyl ether compounds having at least one linear alkyl group. This means that the diphenyl ether compounds having at least one linear alkyl group account for 98% or more of the total amount of the alkyl-substituted diphenyl ether mixture. More preferably, the proportion of diphenyl ether compounds having at least one linear alkyl group relative to the total amount of the alkyl-substituted diphenyl ether mixture is 99% or more. The compound constituting the alkyl-substituted diphenyl ether mixture is a compound represented by the following general formula (1): R in general formula (1) may substitute for a hydrogen atom on either of the two benzene rings. (In formula (1), R's may be the same or different and are linear or branched alkyl groups having 8 to 24 carbon atoms, at least one of R's is a linear alkyl group, 1≦a≦10, and a is an integer.)

[0031] The alkyl-substituted diphenyl ether mixture is substantially composed of compounds represented by general formula (1). Here, "consisting substantially of compounds represented by general formula (1)" not only refers to cases where 100% of the compounds contained in the alkyl-substituted diphenyl ether mixture are compounds represented by general formula (1), but also includes cases where, when the alkyl-substituted diphenyl ether mixture is analyzed by a commonly used measurement method (e.g., NMR), the amount of compounds other than the diphenyl ether compound represented by general formula (1) is so small that it is difficult to detect them. Furthermore, it also includes cases where compounds other than the diphenyl ether compound represented by general formula (1) are contained in such small amounts that they do not affect the performance of the diphenyl ether mixture as a lubricating base oil. Specifically, 98% or more of the diphenyl ether compounds contained in the alkyl-substituted diphenyl ether mixture are compounds represented by general formula (1). It is more preferable that 99% or more of the diphenyl ether compounds contained in the alkyl-substituted diphenyl ether mixture are compounds represented by general formula (1).

[0032] In general formula (1), R's may be the same or different and are alkyl groups having 8 to 24 carbon atoms, with 1≦a≦10. The alkyl groups represented by R's may be linear or branched alkyl groups, but at least one of the R's is a linear alkyl group.

[0033] Specific examples of R include linear alkyl groups such as octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, icosyl, docosyl, and tetracosyl groups. Examples of branched alkyl groups include alkyl groups such as a 1-methylundecyl group, a 1-ethyldecyl group, a 1-methyltridecyl group, a 1-ethyldodecyl group, a 1-methylpentadecyl group, a 1-ethyltetradodecyl group, a 1-methylheptadecyl group, a 1-ethyloctadecyl group, a 1-methylnonadecyl group, a 1-ethyloctadecyl group, a 2-ethylhexyl group, a 2-octyldodecyl group, a 2-decyltetradecyl group, a 2-dodecylhexadecyl group, a 1-butyl-1-methylpentyl group, a 1-butyl-1-methylheptyl group, a 1-methyl-1-pentyloctyl group, a 1-hexyl-1-methylnonyl group, a 1-heptyl-1-methyldecyl group, a 1-methyl-1-octylundecyl group, and a 1-decyl-1-methyltridecyl group.

[0034] By including an alkyl group having 8 or more carbon atoms, heat resistance can be obtained. Furthermore, by including an alkyl group having 24 or less carbon atoms, the viscosity does not become excessively high, and an alkyl-substituted diphenyl ether mixture that achieves both low viscosity and heat resistance can be obtained.

[0035] The linear alkyl group that is one of the Rs is not limited as long as it is an alkyl group having 8 to 24 carbon atoms, but is preferably an alkyl group having 12 to 18 carbon atoms, specifically, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl. The linear alkyl group possessed by the compound represented by general formula (1) may be one type, or may have two or more types of linear alkyl groups. Furthermore, one of the Rs is preferably a linear alkyl group bonded at the o-position or m-position relative to the carbon atom to which the oxygen atom in the benzene ring is bonded, and more preferably a linear alkyl group bonded at the m-position.

[0036] a represents the number of alkyl groups substituted on the diphenyl ether skeleton, and is 1≦a≦10, and preferably 2≦a≦5. The a alkyl substituents (R) may all be linear alkyl groups, or a mixture of linear and branched alkyl groups may be present. The a alkyl substituents (R) may be substituted on the same or different benzene rings of the two benzene rings.

[0037] [Alkyl-substituted diphenyl ether mixture] The alkyl-substituted diphenyl ether mixture is a mixture of compounds represented by the above general formula (1), and is represented by the following general formula (2). (In formula (2), R's may be the same or different and are linear or branched alkyl groups having 8 to 24 carbon atoms, at least one of R's is a linear alkyl group, 2≦x≦10, and x is a real number.) Here, x is the average value of the alkyl groups (average alkyl substitution number) possessed by the diphenyl ether compounds constituting the alkyl-substituted diphenyl ether mixture. The alkyl-substituted diphenyl ether mixture may contain a mono-alkyl-substituted diphenyl ether compound as long as the average alkyl substitution number is 2 or more.

[0038] The alkyl-substituted diphenyl ether mixture represented by general formula (2) can also be expressed by the following general formula (3). For convenience of explanation, the description will be made with reference to general formula (3). m and n in general formula (3) represent the R alkyl groups contained in the diphenyl ether compounds constituting the alkyl-substituted diphenyl ether mixture. １ , R ２ is the average number of alkyl groups (average number of alkyl substitutions) belonging to each of the groups R １ and R ２ may be bonded to the same benzene ring or to different benzene rings of the two benzene rings. (In formula (3), R １ are linear alkyl groups having 8 to 24 carbon atoms, which may be the same or different, and R ２ is R １and m and n are linear or branched alkyl groups having 8 to 24 carbon atoms, which may be the same or different, and are 1≦m, 0≦n, and 2≦m+n≦10, where m+n is a real number.

[0039] The alkyl-substituted diphenyl ether mixture is an alkyl group R consisting of a straight-chain alkyl group. １ R １ Specific examples of R include linear alkyl groups among the alkyl groups listed as R, preferably alkyl groups having 12 to 18 carbon atoms, more preferably one or more selected from the group consisting of dodecyl, tridecyl, tetradecyl, pentadecyl, and hexadecyl groups. m is preferably 1 or more and 5 or less.

[0040] R ２ is R １ and R are straight-chain or branched alkyl groups having 8 to 24 carbon atoms, which may be the same or different from each other, and examples of the alkyl groups listed as R include R. ２ is 0 or more (0≦n). That is, R ２ may not be present. n is preferably 4 or less.

[0041] Preferably, m+n is 2≦m+n≦5. That is, the alkyl-substituted diphenyl ether mixture preferably has an average number of substituents of 2 to 5. Within this range, the alkyl-substituted diphenyl ether mixture becomes liquid at room temperature and can constitute a composition with physical properties suitable for use as a lubricating base oil. The number of alkyl group substitutions can be measured and calculated by the method shown in the Examples below.

[0042] In the alkyl-substituted diphenyl ether mixture according to the present disclosure, the average number of carbon atoms in the alkyl group (the average number of carbon atoms in one alkyl group) is preferably 8 to 20. The average number of carbon atoms in the alkyl group is a real number representing the average number of carbon atoms per alkyl group in the compounds contained in the alkyl-substituted diphenyl ether mixture. The average number of carbon atoms in the alkyl group can be measured by the method shown in the Examples below.

[0043] The lower limit of the average total carbon number of the alkyl groups in the alkyl-substituted diphenyl ether mixture of the present invention (the sum of the carbon numbers of the alkyl groups in one molecule of alkyl-substituted diphenyl ether is referred to as the total carbon number of the alkyl group; the average value of the total carbon numbers of the alkyl groups in the alkyl-substituted diphenyl ether mixture is referred to as the average total carbon number of the alkyl groups) is 16 or more, preferably 25 or more, and more preferably 30 or more. The upper limit of the average total carbon number of the alkyl groups in the mixture is 240 or less, preferably 100 or less, more preferably 70 or less, and even more preferably 60 or less. The average total carbon number of the alkyl groups in the alkyl-substituted diphenyl ether mixture is a real number calculated from the average carbon number of the alkyl groups and m + n.

[0044] The number average molecular weight of the alkyl-substituted diphenyl ether mixture according to the present disclosure is preferably about 500 to 1000. A large number average molecular weight tends to provide excellent heat resistance, but the kinematic viscosity tends to be excessively large. A small number average molecular weight tends to provide low kinematic viscosity, but the heat resistance tends to be poor. If the number average molecular weight is within the above range, an alkyl-substituted diphenyl ether mixture having low viscosity and excellent heat resistance can be obtained. The number average molecular weight of the alkyl-substituted diphenyl ether mixture can be determined by the following formula, as shown in the examples below. １ This is a value measured using H-NMR. Note that, hereinafter, the number average molecular weight may be simply referred to as "average molecular weight."

[0045] In the alkyl-substituted diphenyl ether mixture according to the present disclosure, the proportion of secondary carbons at the benzyl position of the alkyl group in the alkyl-substituted diphenyl ether (referred to as the secondary carbon ratio) is preferably 25% or more, more preferably 35% or more, and even more preferably 38% or more. The alkyl-substituted diphenyl ether mixture according to the present disclosure is composed of diphenyl ether compounds having at least one linear alkyl group, and the benzyl position carbon of the linear alkyl group attached to the benzene ring is always a secondary carbon. Without being bound by theory, a high secondary carbon ratio in the alkyl-substituted diphenyl ether mixture makes it less likely to undergo oxidation reactions with oxygen in the air at high temperatures, thereby making it less likely to evaporate. This is thought to enable the mixture to exhibit high heat resistance even with a small number of alkyl groups, contributing to the achievement of both low viscosity and high heat resistance. The upper limit of the secondary carbon ratio in the benzyl group is not particularly limited, and may be 100% or less, 70% or less, or 55% or less.

[0046] [Production Method] The method for producing the alkyl-substituted diphenyl ether mixture described above is not particularly limited, but the following production method is preferred. That is, the method for producing an alkyl-substituted diphenyl ether according to the present disclosure includes a diphenyl etherification step and an alkyl addition step. The diphenyl etherification step is a step in which an alkyl-substituted phenol having a linear alkyl group is reacted with a halogenated benzene which may be substituted with an alkyl group, or a halogenated benzene having a linear alkyl group is reacted with a phenol which may be substituted with an alkyl group, to obtain a diphenyl ether having a linear alkyl group. From the viewpoint of material availability, it is preferred to obtain a diphenyl ether having a linear alkyl group by reacting an alkyl-substituted phenol with a halogenated alkyl benzene which may be substituted with an alkyl group.

[0047] The diphenyl etherification step is a step of synthesizing a diphenyl ether, which serves as a skeleton to which an alkyl group is added. As a raw material in this diphenyl etherification step, an alkyl-substituted phenol having a linear alkyl group or a halogenated benzene having a linear alkyl group is used. Since the linear alkyl group is preserved regardless of the subsequent reaction steps, the final alkyl-substituted diphenyl ether compound also has the linear alkyl group that was possessed by the raw material compound. Therefore, regardless of the form of the alkyl group added in the alkyl addition step performed following the diphenyl etherification step, a diphenyl ether compound having at least one linear alkyl group can be obtained. The linear alkyl group derived from the raw material compound is represented by the general formula (2), R １ The raw material used as the alkyl-substituted phenol having a linear alkyl group is not particularly limited, but from the viewpoint of heat resistance, it is preferable to use, for example, hydrogenated cardanol (a substituted phenol having an alkyl group with 15 carbon atoms at the m-position).

[0048] The diphenyl etherification step is not particularly limited, but the following synthesis method using the Ullmann reaction can be employed. For example, hydrogenated cardanol is mixed with copper iodide in the presence of a base to perform nitrogen substitution, and bromobenzene is added dropwise to obtain a diphenyl ether having a linear alkyl group. The molar ratio of hydrogenated cardanol to bromobenzene may be in the range of 10:1 to 1:10. The reaction temperature may be 100 to 200°C. A solvent may be used from the standpoint of reactivity and reaction efficiency. Examples of solvents that can be used include dimethyl sulfoxide and N-methyl-2-pyrrolidone. Examples of bases that can be used include alkaline compounds such as potassium carbonate, potassium phosphate, potassium hydroxide, sodium hydroxide, and sodium hydride. The amount of base added may be 1 to 10 equivalents per equivalent of the phenol hydroxyl group. In the above example, copper iodide is used as the catalyst, but other catalysts such as copper chloride and copper bromide can also be used. The amount of catalyst added may be, for example, 0.1 to 1 equivalent per equivalent of the phenol hydroxyl group.

[0049] The alkylation step, which follows the diphenyl etherification step, adds an alkyl group to the diphenyl ether obtained in the diphenyl etherification step. The alkyl group added in the alkylation step has 8 to 24 carbon atoms. The alkylation step utilizes the Friedel-Crafts reaction and can be carried out under known conditions or with known equipment. For example, a diphenyl ether having a linear alkyl group can be reacted with a linear or branched olefin using aluminum chloride or the like as a catalyst to obtain an alkyl-substituted diphenyl ether mixture. The amount of olefin added to the diphenyl ether can be determined depending on the number of alkyl groups desired to be added to the diphenyl ether. For example, when adding two olefins to the diphenyl ether, the amount of olefin added to the diphenyl ether (molar ratio) can be 1:1 to 1:3. The reaction temperature for the alkylation reaction can be 40 to 130°C. From the perspective of reactivity and reaction efficiency, a solvent may be used. Examples of solvents that can be used include nitrobenzene and dichloromethane. When a catalyst is used, the catalyst can be appropriately selected from, for example, iron bromide, zirconia sulfate, etc. The amount of catalyst added may be, for example, 0.0046 to 20% by mass based on the olefin.

[0050] After the alkylation step, the reaction mixture is usually distilled to remove unreacted compounds, etc., thereby recovering the alkyl-substituted diphenyl ether mixture of the present invention.

[0051] [Base Oil for Lubricating Oil] The alkyl-substituted diphenyl ether mixture according to the present disclosure can be used as a base oil for lubricating oils, either alone or in combination with other compounds or compositions. In addition to the alkyl-substituted diphenyl ether mixture according to the present disclosure, the lubricating oil composition can be blended with mineral oils, as well as synthetic oils such as α-olefin oligomers, polyol esters, diesters, polyalkylene glycols, silicone oils, modified silicone oils, alkyl diphenyl ether oils, multiple alkylate cyclopentane oils, and silahydrocarbon oils, to further improve its performance or, if necessary, to impart additional performance, within a range that does not impair the effects of the present invention. Furthermore, various additives such as antioxidants, extreme pressure agents, friction modifiers, metal deactivators, antifoaming agents, thickeners, colorants, and thickeners can be blended alone or in combination as needed.

[0052] The additive may be any antioxidant commonly used in lubricating oils, including, for example, phenolic compounds, amine compounds, phosphorus compounds, and sulfur compounds.

[0053] Examples of extreme pressure agents include phosphorus-based compounds and sulfur-based compounds. Examples of friction modifiers include molybdenum-based compounds such as molybdenum dithiocarbamate and fatty acid derivatives such as glycerin monostearate. Examples of metal deactivators include benzotriazole-based, tolyltriazole-based, thiadiazole-based, and imidazole-based compounds. Examples of antifoaming agents include polyacrylates and styrene ester polymers. Examples of thickeners include inorganic compounds such as metal soaps (e.g., lithium soap), silica, graphite, and clays (e.g., hectorite or bentonite), and organic compounds such as polyurea, polyether ether ketone, and polyphenyl sulfide.

[0054] When a lubricating oil composition contains an alkyl-substituted diphenyl ether mixture according to the present disclosure, the content of the alkyl-substituted diphenyl ether mixture is preferably about 50 to 100 mass% of the entire lubricating oil composition (total mass) from the viewpoint of ensuring heat resistance. In this case, the content of additives and the like in the lubricating oil composition is preferably about 50 to 0 mass%.

[0055] Furthermore, the alkyl-substituted diphenyl ether mixture according to the present disclosure can also be used as an additive to a lubricating oil composition. In such cases, the content of the alkyl-substituted diphenyl ether mixture is preferably about 1 to 49 mass% of the entire lubricating oil composition (total mass). Furthermore, the alkyl-substituted diphenyl ether mixture according to the present disclosure can be used as a component of high-temperature lubricating oils and heat-resistant greases.

[0056] The lubricating oil composition, high-temperature lubricating oil, and heat-resistant grease are suitable for use as bearing lubricants, lubricants for impregnated bearings, grease base oils, refrigeration oils, plasticizers, etc. In particular, they can be suitable for use as various lubricating oils used under high-temperature conditions, such as bearing oils, hydrodynamic bearing oils, oil-impregnated bearing oils, grease base oils, oil-impregnated plastic oils, gear oils, jet engine oils, heat-insulating engine oils, gas turbine oils, automatic transmission oils, vacuum pump oils, hydraulic fluids, etc. Furthermore, since the alkyl-substituted diphenyl ether mixture according to the present disclosure also has excellent radiation resistance, it is believed that it can also be suitable for use as a radiation-resistant lubricating oil or radiation-resistant grease.

[0057] EXAMPLES The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] [Measurement Method] 1. NMR The compounds and mixtures synthesized in the examples and comparative examples were identified using NMR. The method for calculating the number of alkyl group substitutions and the carbon number at the benzyl position of the alkyl group in the synthesized mixture will be described later. NMR measurements were performed using the following equipment and measurement conditions. Equipment: JNM-ECX series FT NMR equipment, 400 MHz, manufactured by JEOL Ltd. Solvent: None Temperature: 70°C Measurement conditions: １ H-NMR: Number of scans: 8 times１3 C-NMR: Scan count 1024 times DEPT-135: Scan count 512 times, angle 135°

[0059] 2. GC The progress of the reaction was confirmed using gas chromatography. The reaction was judged to have progressed when a new peak was generated on the higher boiling point side than the raw material. ・Apparatus: GC-2010Plus, manufactured by Shimadzu ・Column: Ultra ALLOY Capillary Column UA17-15W-0.25F (30m x 0.250mm 0.10 Micron), manufactured by Frontier Laboratories Ltd. ・Vaporization chamber temperature: 350°C ・Injection method: Total injection ・Temperature conditions: 50°C to 350°C, heated at 12.5°C / min, then held at 350°C for 15 minutes ・Carrier gas: Nitrogen (column flow rate: 1.48mL / min)

[0060] 3. HPLC Diphenyl ether compounds with different molecular weights were separated using HPLC. The abundance ratio of diphenyl ether compounds with different alkyl substitution molar numbers was calculated from the obtained peak areas. Apparatus: Agilent Technologies, 1220 InfinityLC Developing solvent: CHCl ３ : acetonitrile = 50:50 Column: TSKgel ODS-100V 5 μm 4.6 mm × 15 cm, manufactured by Tosoh Corporation Flow rate: 1.00 mL / min Detector: UV 254 nm

[0061] [Preparation of Alkyl-Substituted Diphenyl Ether Mixture] [Skeleton Synthesis 1] Synthesis of m-Pentadecyl Diphenyl Ether Hydrogenated cardanol (Cardolite, NC-510) (30 g, 0.18 mol), bromobenzene (23.0 g, 0.15 mol), potassium carbonate (27.6 g, 0.2 mol), copper(I) iodide (1.9 g, 0.10 mol), and N-methylpyrrolidone (160 mL) were added and heated with stirring at 170°C for 7 hours. The progress of the reaction was monitored by GC. Potassium carbonate was removed by filtration, and the filtrate was subjected to adsorption treatment with activated clay and hydrotalcite. Unreacted components, solvent, and by-products were removed by distillation, yielding 18.1 g of Skeleton Compound 1 as a white solid. The yield was 26%. １Using H-NMR, the skeleton compound 1 was identified as m-pentadecyl diphenyl ether.

[0062] [Skeleton Synthesis 2] Synthesis of o-hexadecyl diphenyl ether (1) Grignard reaction: A flask was charged with Mg (10 g, 1.68 eq relative to o-phenoxybenzaldehyde), iodine (1 grain, approximately 0.02 g), THF (1 M relative to o-phenoxybenzaldehyde), and pentadecyl bromide (98.7 g, 1.4 eq relative to o-phenoxybenzaldehyde) in a dropping funnel. The mixture was heated to 70°C while adding pentadecyl bromide dropwise from the dropping funnel. After the addition was complete, the mixture was stirred at 70°C for 1 hour and then allowed to cool to room temperature to synthesize the Grignard reagent. A separate flask was charged with o-phenoxybenzaldehyde (48 g, 1.0 eq) and THF (2 M), and the Grignard reagent was added dropwise to the flask with stirring at room temperature. After the dropwise addition was completed, the progress of the reaction was confirmed by TLC, and the reaction was quenched with 1M HCl, followed by extraction with ethyl acetate. The solvent was removed by distillation, yielding 107 g of a yellow, transparent crude product. (2) Reduction Reaction The crude product obtained in (1), dichloromethane (0.5 M relative to o-phenoxybenzaldehyde), and triethylsilane (56.3 g, 2.0 eq relative to o-phenoxybenzaldehyde) were added and cooled with ice water. Trifluoroborane ether complex (69 g, 2.0 eq relative to o-phenoxybenzaldehyde) was added dropwise thereto, and after the dropwise addition was completed, the progress of the reaction was confirmed by TLC. NaHCO ３ The reaction mixture was quenched with aq, and the solvent was removed by distillation to obtain a yellow, transparent crude product. This was then purified by column chromatography (AcOEt / Hex 1:50 to 1:1) to obtain 16.9 g of framework compound 2 as a white solid in an 18.2% yield. １ Using H-NMR, the framework compound 2 was identified as o-hexadecyl diphenyl ether.

[0063] [Skeleton Synthesis 3] Synthesis of m-hexadecyl diphenyl ether The same reaction procedure as in Skeleton Synthesis 2 was carried out, except that o-phenoxybenzaldehyde was changed to m-phenoxybenzaldehyde (50 g). 13.8 g of Skeleton Compound 3 was obtained as a white solid. The yield was 14.3%.１ Using H-NMR, the framework compound 3 was identified as m-hexadecyl diphenyl ether.

[0064] [Synthesis of Alkyl-Substituted Diphenyl Ether Mixtures] Alkyl-substituted diphenyl ether mixtures 1 to 11 were obtained using skeleton compounds 1 to 3 or diphenyl ether as starting materials. Specifically, the skeleton compound or diphenyl ether in the amounts listed in Tables 1 to 3 and aluminum chloride (2.8% by mass relative to the olefin) were added to a flask and stirred at 85°C. The olefin listed in Tables 1 to 3 was added dropwise thereto, and after the addition was completed, the mixture was stirred at 85°C for 2 hours. The mixture was allowed to cool to room temperature and then subjected to adsorption treatment with activated clay, Kyoward™. Low-boiling substances such as unreacted skeleton compound were removed by vacuum distillation to obtain liquid mixtures 1 to 11. Mixture 11 was obtained by synthesizing compound 4 as described above to obtain mono-substituted hexadecanyl diphenyl ether (abundance ratio 100%, solid, compound 4), an intermediate of mixture 11, and then further synthesizing compound 4 as described above.

[0065] Tables 1 to 3 show, for each of Mixtures 1 to 11, the type of skeletal compound, the type of olefin added to the skeletal compound, the amount added (equivalents) and the amount charged (g), as well as the appearance, yield, and yield of the resulting diphenyl ether mixture.

[0066]

[0067]

[0068]

[0069] The following olefins were used as shown in Tables 1 to 3: 1-octene: Linearene 8 manufactured by Idemitsu Kosan Co., Ltd. 1-dodecene: Linearene 12 manufactured by Idemitsu Kosan Co., Ltd. 1-hexadecene: Linearene 16 manufactured by Idemitsu Kosan Co., Ltd. 2-octyl-1-dodecene: HS Dimer A-20 manufactured by Toyokuni Oil Mills Co., Ltd. 1-chlorododecane: manufactured by Tokyo Chemical Industry Co., Ltd. Diphenyl Ether: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0070] [Confirmation and Evaluation of Mixtures] In addition to the mixtures 1 to 11 obtained above, the following compositions were prepared as comparative examples 3 to 5. These compositions are generally used as lubricating base oils. Comparative example 3: Spectra Syn 10 and Spectra Syn 40 manufactured by ExxonMobil were mixed at a kinematic viscosity of 100 mm at 40°C. ２ The materials were mixed so as to obtain a ratio of 1:1 / s. Comparative Example 4: Trimellitic acid ester PRIO1943 manufactured by Cargill Japan Comparative Example 5: Polyol ester FG100 manufactured by ZSCHIMMER Furthermore, as Comparative Example 2, Skeleton Compound 1 (m-pentadecyl diphenyl ether) was prepared.

[0071] For alkyl-substituted diphenyl ether mixtures 1 to 11 shown in Tables 1 to 3 and the compositions of Comparative Examples 2 to 5, the type and number of alkyl substitutions, the abundance ratio of 2,3-substituted alkyl diphenyl ether compounds (the abundance ratio of di-substituted alkyl diphenyl ethers and tri-substituted alkyl diphenyl ethers relative to the entire mixture), the average carbon number of the substituted alkyl group, molecular weight, and the ratio of secondary, tertiary, and quaternary carbons at the benzyl position of the alkyl group were measured and calculated. The results are summarized in Tables 4 to 6. Details of the methods for calculating the number of alkyl groups added and the carbon series at the benzyl position of the alkyl group are described below.

[0072] Furthermore, the kinematic viscosity, viscosity index (VI), and heat resistance test results (evaporation rate, viscosity increase, and acid value change) were carried out for the alkyl-substituted diphenyl ether mixtures 1 to 11 and the compositions of comparative examples 2 to 5 shown in Tables 1 to 3. The measurement and evaluation methods were as follows. The results are summarized in Tables 4 to 6.

[0073] [Measurement of Physical Properties of Compositions and Heat Resistance Test] 1. Kinematic Viscosity and Viscosity Index The kinematic viscosity and viscosity index (VI) of the resulting mixtures and compositions were measured in accordance with JIS K 2283. ２ When the VI was 115 or more, the viscosity was evaluated as being sufficiently low.

[0074] 2. Heat Resistance Test A heat resistance test was conducted by placing 5.0 g of sample in a 33 mm diameter petri dish and leaving it in a constant temperature bath at 180°C for 500 hours. The weight, viscosity, and acid value of each sample before the heat resistance test and after 500 hours had elapsed were measured. Using the measured values ​​before the heat resistance test as the reference, the evaporation rate, viscosity increase rate, and acid value change were calculated using the following formulas. The viscosity was measured at 40°C using a Brookfield digital viscometer DV2T. The acid value was measured in accordance with JIS K2501. Evaporation rate (%) = 100 x (mass before heating - mass after heating) / mass before heating Viscosity increase rate = viscosity after heating (mm ２ / s) / Viscosity before heating (mm ２ / s) When the viscosity increase ratio was less than 12, it was evaluated as good. Acid value change (mg KOH / g) = acid value after heating - acid value before heating When the oxidation change was less than 11 (mg KOH / g), it was evaluated as good.

[0075]

[0076] Example 1 (Mixture 3) shown in Table 4 is a mixture in which an alkyl group is added to Skeleton Compound 1 (m-pentadecyl diphenyl ether), and its production method results in a diphenyl ether mixture consisting of diphenyl ether compounds having at least one linear alkyl group. Comparative Example 1 (Mixture 10) is a mixture in which 1-chlorododecane is added to diphenyl ether, and the number of alkyl groups added (m + n) is 2.6, and the secondary carbon ratio is 5%. In Comparative Example 1, the proportion of compounds in which all substituted alkyl groups are branched alkyl groups, i.e., all carbons at the benzyl position are tertiary carbons, is (0.95)^. ２．６ = 88%, which suggests the presence of diphenyl ether compounds substituted only with branched alkyl groups. Comparative Example 2 is Skeleton Compound 1 (m-pentadecyl diphenyl ether), and the number of added alkyl groups is 1. None of Comparative Examples 3 to 5 are diphenyl ether mixtures.

[0077] As shown in Table 4, Example 1 had good kinematic viscosity and viscosity index (VI). It was thought that torque could be kept low when Example 1 was used as a lubricant. The evaluation results for heat resistance were also good. In contrast, the heat resistance test results for Comparative Example 1 showed a large viscosity increase ratio and acid value change, resulting in inferior heat resistance compared to Example 1. Comparative Example 2 was a mixture of white solids, and kinematic viscosity could not be measured. All of Comparative Examples 3 to 5 solidified in the heat resistance test (180°C x 500 hours), resulting in inferior heat resistance compared to Example 1.

[0078]

[0079] Regarding Examples 2 to 4 shown in Table 5, Example 2 (Mixture 6) is a mixture in which an alkyl group is added to Skeleton Compound 2 (o-hexadecyl diphenyl ether), Example 3 (Mixture 7) is a mixture in which an alkyl group is added to Skeleton Compound 3 (m-hexadecyl diphenyl ether), and Example 4 (Mixture 4) is a mixture in which an alkyl group is added to Skeleton Compound 1 (m-pentadecyl diphenyl ether). Based on their production method, they are diphenyl ether mixtures composed of diphenyl ether compounds having at least one linear alkyl group. Comparative Example 6 (Mixture 11) is a mixture in which 1-hexadecene and 1-dodecene are added to diphenyl ether. The number of alkyl groups added (m+n) was 2.5, and the secondary carbon ratio was 0%, confirming that the compound was one in which all of the substituted alkyl groups had a branched structure. Comparative Example 7 (Mixture 8) is a mixture in which 1-dodecene and 1-tetradecene are added to diphenyl ether, and since the number of added alkyl groups (m+n) was 2.9 and the secondary carbon ratio was 0%, it was confirmed that the compound was one in which all of the substituted alkyl groups had a branched structure.

[0080] As shown in Table 5, Examples 2 to 4 were good in both kinematic viscosity and viscosity index (VI). The evaluation results for heat resistance were also good. In contrast, the heat resistance test results for Comparative Example 6 showed a large viscosity increase ratio and acid value change, resulting in poor heat resistance. Comparative Example 7 had a viscosity index (VI) of less than 115. The heat resistance was also poor.

[0081]

[0082] Examples 5 to 7 shown in Table 6 are all mixtures in which an alkyl group is added to Skeleton Compound 1 (m-pentadecyl diphenyl ether). Due to their manufacturing method, they are diphenyl ether mixtures composed of diphenyl ether compounds having at least one linear alkyl group. In Example 5, a branched alkyl group is added to Skeleton Compound 1. In Example 6, an alkyl group having 8 carbon atoms is added to Skeleton Compound 1. In Example 7, an alkyl group having 8 carbon atoms is added to Skeleton Compound 1, and the amount added is greater than in Example 6. In Example 7, the abundance ratio of 3,4-substituted ADE compounds (the abundance ratio of 3-substituted ADE and 4-substituted ADE relative to the total ADE mixture) was 66%. Comparative Example 8 (Composition 9) is a mixture in which 2-octyl-1-decene is added to diphenyl ether. Since only a branched alkyl group is added, the mixture is composed solely of branched alkyl-substituted diphenyl ether compounds. Furthermore, since the number of alkyl groups added (m+n) was 2.1 and the secondary carbon ratio was 23%, the majority of compounds had tertiary or higher carbon atoms at the benzyl position of the alkyl group.

[0083] As shown in Table 6, Examples 5 to 7 exhibited good kinematic viscosity and viscosity index (VI). The heat resistance evaluation results were also good. The evaporation rates for Examples 6 and 7 were 25.0% and 14.8%, respectively. While there are no comparative examples in which alkyl-substituted diphenyl ethers having alkyl group carbon numbers comparable to those of Examples 6 and 7 were synthesized by conventional manufacturing methods, the results of Examples 1 to 5 and Comparative Examples 1 and 6 to 8 suggest that the secondary carbon ratios of the mixtures synthesized by conventional manufacturing methods are lower than those of Examples 6 and 7. Therefore, the evaporation rates of Examples 6 and 7 are presumed to be superior to those of alkyl-substituted diphenyl ethers synthesized by conventional technology. In contrast, Comparative Example 8 exhibited a viscosity index (VI) of less than 115. Furthermore, the heat resistance was also poor. In particular, comparing Example 5 and Comparative Example 8, both contained branched alkyl groups and had an alkyl group addition molar number of 2.1. However, Example 5, which was composed of a compound having a linear alkyl group, clearly exhibited superior viscosity characteristics and heat resistance.

[0084] [Calculation of the number of alkyl groups added] This will be explained using Example 1 (Mixture 3) as an example. １ An overview of H-NMR is shown. １ From the H-NMR chart, the peak integral ratios representing the hydrogens bonded to the aromatic ring, the benzyl carbon of the alkyl group, and the alkyl group excluding the benzyl position are calculated. The a to c shown in Figure 1 correspond to the following: Hydrogens bonded to the aromatic ring: the integral ratio from 6.5 to 7.5 ppm is taken as a (a is the reference, a = 1); Hydrogens bonded to the benzyl carbon of the alkyl group: the integral ratio from 2.2 to 3.4 ppm is taken as b; Hydrogens bonded to the alkyl group excluding the benzyl position: the integral ratio from 0.7 to 1.7 ppm is taken as c; and the number of protons in the added alkyl chain is taken as d. For example, when adding 1-octene, the alkyl chain to be added is C ８ H １７ Therefore, d = 17. The number of alkyl additions is calculated using the following formula: Number of alkyl additions = 10 x (b + c) / (b + c + a x d)

[0085] When alkyl groups with different carbon numbers are added, the calculation is as follows: The number of protons of the alkyl group added by the Friedel-Crafts reaction is defined as d'. The number of protons of the straight-chain alkyl group that was previously bonded to the diphenyl ether before the Friedel-Crafts reaction is defined as e. The number of added alkyl groups that were previously bonded to the diphenyl ether is defined as f. Number of added alkyls = f + ((10 - f) x (b + c) - a x e) / (b + c + a x d')

[0086] [Calculation of the series number of the alkyl benzyl carbon] (1) When adding a linear olefin, as shown in Figure 2 １３ From the C-NMR chart, the peak integral ratios representing the β carbons of the aromatic ring and alkyl group are calculated, and the alkyl group benzyl carbon series is calculated. A1 and A2 shown in Figure 2 correspond to the following: Aromatic ring: The integral ratio from 152 to 160 ppm is taken as A1 (A1 is the reference, A1 = 1). β carbon of alkyl group: The integral ratio from 31.0 to 32.0 ppm is taken as A2. Secondary carbon ratio = (A2 / A1) ÷ number of alkyl additions × 100 Tertiary carbon ratio = 100 - secondary carbon ratio

[0087] (2) Addition of branched olefins Figures 3 and 4 show the results of Example 5 (Mixture 5). １３ The C-NMR and DEPT-135 overview are shown. １３ By comparing the C-NMR and DEPT-135 spectra, peaks of secondary carbon, tertiary carbon, and quaternary carbon appearing at 32.0 to 36.0 and 38.0 to 50.0 ppm were identified. １３ Of the peaks in the C-NMR range of 35.0 to 40.2 ppm, the integral ratio of secondary carbon was designated B1, the integral ratio of tertiary carbon B2, and the integral ratio of quaternary carbon B3, and the carbon series at the benzyl position of the alkyl group was calculated using the following formulas: Secondary carbon ratio = (B1 / (B1+B2+B3)) x 100 Tertiary carbon ratio = (B2 / (B1+B2+B3)) x 100 Quaternary carbon ratio = (B3 / (B1+B2+B3)) x 100

[0088] The present invention is intended to cover a wide range of applications, including those related to the present invention, including those related to the present invention.

Claims

1. A mixture of diphenyl ethers substituted with 2 to 10 linear or branched alkyl groups having 8 to 24 carbon atoms, said mixture being substantially free of diphenyl ethers substituted only with branched alkyl groups.

2. A mixture of diphenyl ethers substituted with 2 to 10 alkyl groups having 8 to 24 carbon atoms, said mixture consisting essentially of diphenyl ethers having at least one linear alkyl group.

3. The alkyl-substituted diphenyl ether mixture according to claim 1 or 2, wherein the diphenyl ether mixture is a diphenyl ether mixture substituted with 2 to 5 alkyl groups.

4. The alkyl-substituted diphenyl ether mixture according to claim 1 or 2, wherein at least one of the linear alkyl groups is bonded at the o-position or m-position to the carbon atom to which the oxygen atom in the benzene ring is bonded.

5. The alkyl-substituted diphenyl ether mixture according to claim 1 or 2, wherein the average total number of carbon atoms in the alkyl groups of the diphenyl ether mixture is 25 or more and 100 or less.

6. A diphenyl ether mixture substituted with 2 to 10 alkyl groups having 8 to 24 carbon atoms, wherein the ratio of alkyl groups in which the carbon at the benzylic position is a secondary carbon among the alkyl groups contained in the diphenyl ether mixture is 25% or more.

7. The alkyl-substituted diphenyl ether mixture according to claim 6, wherein the diphenyl ethers contained in the alkyl-substituted diphenyl ether mixture consist essentially of diphenyl ethers having at least one linear alkyl group.

8. The alkyl-substituted diphenyl ether mixture according to claim 7, wherein the alkyl-substituted diphenyl ether mixture is a mixture of diphenyl ethers substituted with 2 to 5 alkyl groups, and at least one of the linear alkyl groups is a linear alkyl group bonded at the m-position to the carbon atom in the benzene ring to which the oxygen atom is bonded.

9. A lubricating oil comprising the alkyl-substituted diphenyl ether mixture of claims 1, 2 or 6.

10. A method for producing an alkyl-substituted diphenyl ether, comprising sequentially carrying out a diphenyl etherification step of reacting an alkyl-substituted phenol having a linear alkyl group with a halogenated benzene which may be substituted with an alkyl group, or a halogenated benzene having a linear alkyl group with a phenol which may be substituted with an alkyl group, to obtain a diphenyl ether having a linear alkyl group, and an alkyl addition step of adding an alkyl group to the diphenyl ether obtained in the diphenyl etherification step, wherein the number of carbon atoms of the alkyl group added in the alkyl addition step is 8 to 24.

11. The method for producing alkyl-substituted diphenyl ethers according to claim 10, wherein the alkyl-substituted phenol having a straight-chain alkyl group is an alkyl-substituted phenol having a straight-chain alkyl group bonded at the meta-position to the carbon atom in the benzene ring to which the oxygen atom is bonded.

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