JP2017105717A - Method for decreasing by-product of coupling reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method with which a deboronized-hydrogenated product of an aromatic boronic acid compound, being a by-product of a target compound, can be decreased, in the target compound of a Suzuki-Miyaura coupling reaction using the aromatic boronic acid compound in the presence of a palladium catalyst, in which the target compound is required to have extremely high purity with regard to application and quality control thereof.SOLUTION: In a production method of a Suzuki-Miyaura coupling reaction product, which is a production method of the coupling reaction product, and which includes: a step of subjecting a mixture of an aromatic boronic acid compound substituted by a triazine or the like, an aromatic halogen compound or an aromatic triflate compound, a palladium catalyst, and a reaction solvent to a coupling reaction by heating; and a step of obtaining a product precipitated in the previous step by filtration, operations from the start of heating to the completion of filtration are performed without further adding a solvent different from the reaction solvent to the mixture.SELECTED DRAWING: None

Description

  The present invention relates to a method for reducing a coupling reaction by-product and a method for producing a coupling reaction compound using the method.

  In the production of an aromatic compound by a coupling reaction of an aromatic boronic acid compound and an aromatic halogen compound, a poor solvent such as water is added to the reaction solution at the end of the coupling reaction in order to improve the yield of the target compound. It has been conventionally practiced to add, precipitate the target product dissolved in the reaction solution, and separate and purify the precipitated compound (for example, Patent Document 1).

JP2015-027986

  As a result of the study by the inventors, when a poor solvent is added to the reaction solution at the end of the coupling reaction between the aromatic boronic acid compound and the aromatic halogen compound or aromatic triflate compound, a by-product (aromatic boronic acid is simultaneously formed with the target product. It was found that a deboronic acid / hydrogen adduct of the compound) was precipitated. The target product of the coupling reaction is required to be extremely high in terms of its use and quality control, and the above-mentioned by-products are required to be reduced as much as possible. Therefore, the present inventors examined the separation of the above-mentioned by-product from the target product, and since the by-product has close physical properties to the target product, conventionally known purification methods such as recrystallization and sublimation. It was found that separation of the by-product by means of was difficult, and a solution to the problem of reducing the by-product was sought.

  More specifically, the inventors have the following general formula (1)

(In the formula, Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or 4 to 20 carbon atoms. A heterocyclic aromatic group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
BOL represents a boronic acid group or a boronic acid ester group. )
As a result of various investigations and detailed analyzes of the coupling reaction using the compound represented by formula (2), the following general formula (3) in which BOL of the general formula (2) is desorbed and hydrogenated

(In the formula, the definition of each substituent is the same as in the general formula (1)).
As a problem, it was found that a by-product represented by the formula (1) was generated and hindered purification of the target product.

  In order to solve such problems, an object of the present invention is to reduce the above-mentioned by-products and obtain a high-purity target product.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors filtered the obtained crystal without performing a conventional operation of adding a poor solvent such as water to a reaction solution. As a result, it was found that the content of the by-product in the reaction target product can be efficiently reduced and an extremely high-purity target compound can be produced, and the present invention has been completed.

  That is, the present invention performs a step of heating the mixture of the aromatic boronic acid compound represented by the general formula (1) and the aromatic halogen compound or aromatic triflate compound, the palladium catalyst and the reaction solvent to cause a coupling reaction. , A method for producing a coupling reaction product, wherein a step of obtaining the product precipitated by the step by filtration is performed, wherein the reaction solvent is added to the mixture for the operation from the start of the heating until the filtration is completed. It has been found that the above-mentioned problems can be solved by a method for producing a coupling reaction product, which is performed without additional addition of different solvents, and the present invention has been completed.

  Hereinafter, the present invention will be specifically described.

  The present invention provides the following general formula (1)

(In the formula, Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or 4 to 20 carbon atoms. A heterocyclic aromatic group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
BOL represents a boronic acid group or a boronic acid ester group. )
A mixture of an aromatic boronic acid compound, an aromatic halogen compound or an aromatic triflate compound, a palladium catalyst, and a reaction solvent represented by the following: A method for producing a coupling reaction product including a step of obtaining by filtration, wherein a solvent different from the reaction solvent is additionally added to the mixture for the operation from the start of heating to the end of filtration of the reaction solution It is the manufacturing method of the coupling reaction product characterized by performing without performing.

  Preferably, the aromatic halogen compound or aromatic triflate compound is represented by the following general formula (2):

(Where
Ar ³ represents a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
HAL represents a halogen element or a triflate group. )
A coupling reaction product represented by the following general formula (4):

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
Ar ³ each independently represents a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom). )
A by-product produced as a by-product in the coupling reaction is represented by the following general formula (3):

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH. )
It is a compound represented by these manufacturing methods characterized by the above-mentioned.

  Although it does not specifically limit as an aromatic boronic acid compound in this invention, The aromatic compound which has a general well-known boronic acid or boronic acid ester can be used. The aromatic boronic acid compound represented by the above general formula (1) is preferable as the aromatic boronic acid compound in that the effect of the present invention is remarkable.

In the aromatic boronic acid compound represented by the general formula (1), Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group is substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom). Or a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).

In Ar ¹ , the alkyl group having 1 to 4 carbon atoms is not particularly limited, and examples thereof include a methyl group, an ethyl group, a normal propyl group, a normal butyl group, an isopropyl group, and a t-butyl group. It is done. Among these, a methyl group is more preferable because the compound is stable.

In Ar ¹ , the aromatic hydrocarbon group having 6 to 20 carbon atoms is not particularly limited, and examples thereof include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a phenanthryl group, an anthracenyl group, a pyrenyl group, Or a triphenylenyl group etc. are mentioned. Among these, a phenanthroyl group or an anthracenyl group is preferable in terms of high purification efficiency of by-products.

In Ar ¹ , the heterocyclic aromatic group having 4 to 20 carbon atoms is not particularly limited, and examples thereof include a pyridyl group, a pyrimidyl group, a pyrazyl group, a quinolyl group, an isoquinolyl group, and a phenanthrolinyl group. Is mentioned.

Ar ¹ is preferably a phenanthroyl group, anthracenyl group, pyrenyl group, triphenylenyl group, pyridine group, pyrimidyl group, pyrazyl group (these groups are substituted with a methyl group or a fluorine atom in that it is easy to reduce by-products. It may be a phenanthroyl group, an anthryl group, a pyridyl group, or a pyrimidyl group (these groups may be substituted with a methyl group or a fluorine atom).

In the aromatic boronic acid compound represented by the general formula (1), each Ar ² is independently an aromatic hydrocarbon group having 6 to 20 carbon atoms (the group is an alkyl group having 1 to 4 carbon atoms or Which may be substituted with a fluorine atom).

In Ar ² , the aromatic hydrocarbon group having 6 to 20 carbon atoms is not particularly limited, and examples thereof include a phenyl group, a biphenyl group, a naphthyl group, an anthracenyl group, and a triphenylenyl group. Among these, a phenyl group, a biphenyl group, and a naphthyl group are preferable, and a phenyl group is more preferable in terms of high purification efficiency of by-products.

In Ar ² , the alkyl group having 1 to 4 carbon atoms is not particularly limited, and examples thereof include a methyl group, an ethyl group, a normal propyl group, a normal butyl group, an isopropyl group, and a t-butyl group. It is done. Among these, a methyl group is more preferable because the compound is stable.

  In the aromatic boronic acid compound represented by the general formula (1), BOL represents a boronic acid or a boronic acid ester.

The BOL, is not particularly limited, for _{example, ^{B (OH) 2, B (}} OMe) 2, B (O i Pr) 2, B (OBu) 2, B (OPh) 2 or the like group, The following groups can be mentioned.

  Of these BOLs, the group represented by (II) is more preferable in that the reaction selectivity is good.

  Although it does not specifically limit as an aromatic boronic acid compound represented by General formula (1), For example, the compound (1) -1-(1) -18 shown below can be mentioned.

  Although it does not specifically limit as an aromatic halogen compound or aromatic triflate compound in this invention, The aromatic compound which has a generally well-known halogen element or triflate group can be used. As the aromatic halogen compound or the aromatic triflate compound, the aromatic halogen compound or the aromatic triflate compound represented by the above general formula (2) is preferable in that the effect of the present invention is remarkable.

In the aromatic halogen compound or aromatic triflate compound represented by the general formula (2), Ar ³ is a heterocyclic aromatic group having 4 to 20 carbon atoms (this group is an alkyl group having 1 to 4 carbon atoms or fluorine). Which may be substituted with an atom). HAL represents a halogen element or a triflate group.

In Ar ³ , the alkyl group having 1 to 4 carbon atoms is not particularly limited, and examples thereof include a methyl group, an ethyl group, a normal propyl group, a normal butyl group, an isopropyl group, and a t-butyl group. It is done. Among these, a methyl group is more preferable because the compound is stable.

In Ar ³ , the heterocyclic aromatic group having 4 to 20 carbon atoms is not particularly limited, and examples thereof include a pyridyl group, a pyrimidyl group, a pyrazyl group, a quinolyl group, an isoquinolyl group, and a phenanthrolinyl group. Is mentioned. Among these, a pyridyl group, a pyrimidyl group, or a pyrazyl group is more preferable in terms of high purification efficiency of the by-product.

  HAL represents a halogen atom or a triflate group, and is not particularly limited, and examples thereof include a chlorine atom, a bromine atom, an iodine atom, and a triflate group. Among these, a bromine atom or a chlorine atom is preferable in that the reaction yield is good.

  Although it does not specifically limit as an aromatic halogen compound or aromatic triflate compound represented by General formula (2), For example, the compound (2) -1 to (2) -20 shown below is mentioned. it can.

  Although it does not specifically limit as a compound represented by General formula (3), For example, the compound (3) -1-(3) -18 shown below can be mentioned.

  The production method of the present invention includes a step of performing a coupling reaction by heating a mixture of the aromatic boronic acid compound and the aromatic halogen compound or aromatic triflate compound in the presence of a palladium catalyst and a reaction solvent.

  Although it does not specifically limit as a palladium catalyst which can be used for reaction, For example, salts, such as palladium chloride, palladium acetate, trifluoroacetate palladium, palladium nitrate, can be mentioned. Further, π-allyl palladium chloride dimer, palladium acetylacetonate, bis (dibenzylideneacetone) palladium, tris (dibenzylideneacetone) dipalladium, dichlorobis (triphenylphosphine) palladium, tetrakis (triphenylphosphine) palladium, tri (tert -Butyl) phosphine palladium, dichloro (1,1'-bis (diphenylphosphino) ferrocene) palladium and the like. Among them, a palladium complex having a tertiary phosphine such as dichlorobis (triphenylphosphine) palladium, tetrakis (triphenylphosphine) palladium, tri (tert-butyl) phosphinepalladium as a ligand is preferable in terms of a good yield. In terms of easy availability, tetrakis (triphenylphosphine) palladium, palladium acetate, or tri (tert-butyl) phosphinepalladium is more preferable. In addition, the palladium complex which has said tertiary phosphine as a ligand can also add a tertiary phosphine to a palladium salt or a complex compound, and can also prepare it in a reaction system.

  The tertiary phosphine is not particularly limited, and examples thereof include triphenylphosphine, trimethylphosphine, tributylphosphine, tri (tert-butyl) phosphine, tricyclohexylphosphine, tert-butyldiphenylphosphine, and 9,9-dimethyl. -4,5-bis (diphenylphosphino) xanthene, 2- (diphenylphosphino) -2 '-(N, N-dimethylamino) biphenyl, 2- (di-tert-butylphosphino) biphenyl, 2- ( Dicyclohexylphosphino) biphenyl, bis (diphenylphosphino) methane, 1,2-bis (diphenylphosphino) ethane, 1,3-bis (diphenylphosphino) propane, 1,4-bis (diphenylphosphino) butane, 1,1'-bis (diphenyl Sufino) ferrocene, tri (2-furyl) phosphine, tri (o-tolyl) phosphine, tris (2,5-xylyl) phosphine, (±) -2,2′-bis (diphenylphosphino) -1,1 ′ -Binaphthyl, 2-dicyclohexylphosphino-2 ', 4', 6'-triisopropylbiphenyl and the like can be exemplified. Of these, 2-dicyclohexylphosphino-2 ', 4', 6'-triisopropylbiphenyl is preferable in terms of easy handling and good yield.

  When adding a tertiary phosphine to a palladium salt or complex compound, the addition amount of the tertiary phosphine should be 0.1 to 10 times mol per mol of the palladium salt or complex compound (in terms of palladium atom). It is more preferable that it is 0.3-5 times mole in terms of a good yield.

  For the coupling reaction of the present invention, a base can be further added and used. The base that can be used is not particularly limited. For example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, cesium carbonate, potassium acetate, sodium acetate, potassium phosphate, phosphoric acid Examples thereof include sodium, sodium fluoride, potassium fluoride, cesium fluoride and the like. Among these, potassium carbonate, potassium phosphate, or sodium hydroxide is preferable in terms of a good yield.

  The coupling reaction of the present invention is carried out in a reaction solvent. The reaction solvent is preferably an organic solvent and is not particularly limited. Examples thereof include dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, toluene, benzene, diethyl ether, 1,4-dioxane, ethanol, butanol, and xylene. These may be used in appropriate combination. Among these, tetrahydrofuran, 1,4-dioxane, or a toluene-butanol mixed solvent is preferable in terms of a good yield.

The production method of the present invention includes a step of obtaining the product precipitated in the coupling reaction step by filtration, and the reaction solvent is added to the mixture for the operation from the start of heating in the coupling reaction step until the filtration is completed. In the production method of the present invention, the filtration method is not particularly limited as long as it is a publicly known method, for example, filter paper, filter cloth, glass. A method using a filter can be exemplified.

  In the present invention, the solvent different from the reaction solvent is not particularly limited, but is not particularly limited as long as it is other than those actually used as the reaction solvent from the examples of the reaction solvent described above. In general, a poor solvent inferior in solubility of the target product is preferred over the reaction solvent. In the present invention, a solvent different from the reaction solvent is inferior in solubility of the target product in comparison with the reaction solvent. A poor solvent is preferred, and water is more preferred.

  EXAMPLES Hereinafter, although an Example and a reference example are given and this invention is demonstrated in detail, this invention is limited to these and is not interpreted.

  Example 1

  Under a nitrogen atmosphere, 20 mL of Schlenk was added to 2- {5- (9-phenanthryl) -3- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl} -4, 1.00 g (1.64 mmol) of 6-diphenyl-1,3,5-triazine (compound (1) -4), 3.70 mg (0.02 mmol) of palladium (II) acetate, and 15.-Xhos of 15. After adding 6 mg (0.03 mmol), 8.2 mL of tetrahydrofuran and 0.23 mL of 3-bromo-2,6-dibromopyridine (compound (2) -3) were added dropwise. Then, it stirred for 10 minutes and heated to 65 degreeC. After the reaction solution changed from a gray suspension to a black transparent solution, 2.45 mL of 2.0 M potassium phosphate aqueous solution was added dropwise. After 4 hours, the heating was stopped and the mixture was cooled to room temperature. Thereafter, filtration is performed as it is, and the desired 2- {3- (2,6-dimethylpyridin-3-yl) -5- (9-phenanthryl) phenyl} -4,6-diphenyl-1,3,5- 0.87 g (yield 90%) of triazine (Compound A-1) was obtained. Thereafter, the purity of the impurities was measured by liquid chromatography (HPLC). The content of Compound (3) -4 as an impurity was 0.006 LC area%.

  Example 2

  Instead of compound (1) -4, 2- {5- (9-anthracenyl) -3- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl}- The same operation as in Example 1 was carried out except that 4,6-diphenyl-1,3,5-triazine (compound (1) -5) was used. As a result, the desired 2- {5- (9-anthracenyl) -3- (2,6-dimethylpyridin-3-yl) phenyl} -4,6-diphenyl-1,3,5-triazine (Compound A -2) 0.80 g (yield 83%). The content of Compound (3) -5 as an impurity was 0.007 LC area%.

  Example 3

  The same operation as in Example 1 was carried out except that 4-bromo-2-methylpyridine (compound (2) -4) was used instead of compound (2) -3. As a result, the desired 2- {3- (3-methylpyridin-4-yl) -5- (9-phenanthryl) phenyl} -4,6-diphenyl-1,3,5-triazine (Compound A-4) ) Was obtained 0.79 g (yield 83%). The content of Compound (3) -4 as an impurity was 0.008 LC area%.

Reference example 1
In Example 1, the same operation as in Example 1 was carried out except that 12.5 mL of water was added immediately after the completion of the heating operation for 4 hours. 0.92 g (yield 95%) of the target compound A-1 was obtained. The content of the impurity (3) -4 was 0.019 LC area%.

Reference example 2
Compound A-1 after filtration obtained in Comparative Example 1 was recrystallized with 8 mL of toluene. After recrystallization, the mixture was filtered using toluene and methanol to obtain 0.76 g (yield 78%) of the target compound A-1. The content of the impurity (3) -4 after filtration was 0.012 LC area%.

  By using the production method of the present invention, it is possible to satisfy market demands that require extremely high material purity for compounds and materials for use in electronic products such as organic EL. By providing such a high-purity material, it is possible to reduce the risk of occurrence of defects such as a decrease in light emission performance and an increase in performance deterioration rate that may be caused by unintentional impurity contamination in organic EL elements and the like. It is possible to provide products with long life and excellent durability.

Claims (8)

The following general formula (1)

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
BOL represents a boronic acid group or a boronic acid ester group. )
A mixture of an aromatic boronic acid compound, an aromatic halogen compound or an aromatic triflate compound, a palladium catalyst, and a reaction solvent represented by the following: A method for producing a coupling reaction product including a step of obtaining by filtration, wherein a solvent different from the reaction solvent is additionally added to the mixture for the operation from the start of heating to the end of filtration of the reaction solution A method for producing a coupling reaction product, which is carried out without any further steps. An aromatic halogen compound or an aromatic triflate compound is represented by the following general formula (2)

(Where
Ar ³ represents a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
HAL represents a halogen element or a triflate group. )
A coupling reaction product represented by the following general formula (4):

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
Ar ³ represents a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom). )
And a by-product produced as a by-product in the coupling reaction is represented by the following general formula (3):

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH. )
The production method according to claim 1, wherein the compound is represented by the formula: It is a manufacturing method of Claim 1 or 2, Comprising: After completion | finish of filtration, the acquired product is wash | cleaned with a solvent, The manufacturing method characterized by the above-mentioned. It is a manufacturing method as described in any one of Claims 1 thru | or 3, Comprising: After completion | finish of filtration, the acquired product is wash | cleaned with the same solvent as the said reaction solvent, The manufacturing method characterized by the above-mentioned. The production method according to any one of claims 1 to 4, wherein in the general formulas (1), (3), and (4), both Ar ² are phenyl groups. In the general formulas (2) and (4), Ar ³ is a pyridyl group, a pyrimidyl group, or a pyrazyl group (these groups may be substituted with an alkyl group having 1 to 4 carbon atoms). The manufacturing method as described in any one of thru | or 5. In the general formulas (1) and (4), Ar ¹ is a phenanthroyl group or an anthracenyl group (these groups may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom). The manufacturing method as described in any one of thru | or 6. General formula (3)

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH. )
The compound represented by the general formula (4) is characterized by containing less than 0.01% by weight.

(Where
Ar ¹ is an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom), or a heterocyclic aromatic group having 4 to 20 carbon atoms. Represents a group (which may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
Ar ² each independently represents an aromatic hydrocarbon group having 6 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom).
X represents a nitrogen atom or CH.
Ar ³ represents a heterocyclic aromatic group having 4 to 20 carbon atoms (this group may be substituted with an alkyl group having 1 to 4 carbon atoms or a fluorine atom). )
A compound represented by