2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene and method for producing the same

Abstract

The present invention aims to provide a novel compound having a mesogenic skeleton that is highly soluble in organic solvents and useful as a monomer for curable resins. [Solution] The present invention is based on formula (1) This relates to 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene represented by TIFF2026045927000022.tif34105 [wherein R1 represents a hydrogen atom or an acetyl group, and R2 represents an alkyl group having 2 to 10 carbon atoms].

Description

[Technical Field]

[0001] This invention relates to a novel compound having a mesogenic skeleton. [Background technology]

[0002] Thermosetting resin compositions such as epoxy resins are widely used as insulating materials for various motors and inverters due to their high insulating performance, ease of molding, and heat resistance. With the recent miniaturization and weight reduction of devices, the thermal conductivity of insulating materials is increasingly important, and there is a demand for further improvements in the thermal conductivity of materials used in insulating materials.

[0003] As a resin cured product of a thermosetting resin composition having high thermal conductivity, a resin cured product of a thermosetting epoxy resin composition containing an epoxy resin monomer having a mesogenic skeleton and a curing agent for epoxy resins has been proposed (Patent Document 1). Mesogenic refers to a rigid part that exhibits liquid crystalline properties and is mainly composed of aromatic groups, and various epoxy resins having a mesogenic skeleton have been proposed to date.

[0004] In particular, cured resins of diexo compounds having a mesogenic skeleton with aromatic groups ester-bonded are known to exhibit high toughness and high thermal conductivity (Patent Documents 2 and 3). As precursors of such diexo compounds, for example, compounds in which two molecules of 4-hydroxybenzoic acid and one molecule of hydroquinone are ester-bonded are known. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2002 / 094905 [Patent Document 2] Japanese Patent Publication No. 2010-241797 [Patent Document 3] Japanese Patent Publication No. 2011-074366 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, such compounds have low solubility in organic solvents and are not very versatile. The object of the present invention is to provide a novel compound having a mesogenic skeleton that has high solubility in organic solvents and is useful as a monomer for curable resins. Another object of the present invention is to provide a method for producing a novel compound having a mesogenic skeleton. [Means for solving the problem]

[0007] In view of the above problems, the present inventors conducted diligent research and found that compounds with a specific structure having a mesogenic skeleton have high solubility in organic solvents, thus completing the present invention.

[0008] In other words, the present invention encompasses the following preferred embodiments. [1] Formula (1) TIFF2026045927000001.tif34105 [In the formula, R1 represents a hydrogen atom or an acetyl group, and R2 represents an alkyl group having 2 to 10 carbon atoms] 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene, represented as such. [2] R1 is an acetyl group, the 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene described in [1]. [3] R1 is a hydrogen atom, the 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene described in [1]. [4] R2 is a tert-butyl group, and is a 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene as described in any of [1] to [3]. [5] A monomer for curable resins, which is 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene as described in any of [1] to [4]. [6] Formula (2) TIFF2026045927000002.tif2669 [In the formula, X represents a chlorine atom, a bromine atom, or an iodine atom] A compound represented by the formula (1) and a compound of the formula (3) TIFF2026045927000003.tif3055[wherein, R2 represents an alkyl group having 2 to 10 carbon atoms] and 2,5-disubstituted hydroquinone represented by the formula (4) A process for producing 2,5-disubstituted-1,4-bis(4-substituted-benzoyloxy)benzene according to [2], which comprises reacting them. A process for producing 2,5-disubstituted-1,4-bis(4-substituted-benzoyloxy)benzene according to [3], which comprises a step of deacetylating 2,5-disubstituted-1,4-bis(4-substituted-benzoyloxy)benzene according to [2]. [Advantages of the Invention]

[0009] The compound represented by the formula (1) of the present invention has high solubility in organic solvents and can be used particularly as a monomer for thermosetting resins. [Brief Description of the Drawings]

[0010] [Figure 1] It is a diagram showing the solubility (mass %) at the time of temperature rise in methyl ethyl ketone for each of 2,5-di-tert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene obtained in Example 1, 2,5-di-tert-butyl-1,4-bis(4-hydroxy-benzoyloxy)benzene obtained in Example 2, and 1,4-bis(4-hydroxy-benzoyloxy)benzene obtained in Comparative Example 1. [Modes for Carrying Out the Invention]

[0011] One embodiment of the present invention is 2,5-disubstituted-1,4-bis(4-substituted-benzoyloxy)benzene represented by the formula (1). TIFF2026045927000004.tif41124[wherein, R1 represents a hydrogen atom or an acetyl group, and R2 represents an alkyl group having 2 to 10 carbon atoms.]

[0012] In formula (1) of the present invention, R2 is an alkyl group having 2 to 10 carbon atoms, for example, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, cyclobutyl group, pentyl group, isopentyl group, sec-pentyl group, tert-pentyl group, neopentyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, cyclopentyl group, hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, neohexyl group, 2-methylpentyl group, 1,2-dimethylbutyl Examples include groups such as 2,3-dimethylbutyl group, 1-ethylbutyl group, cyclohexyl group, heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, neoheptyl group, cycloheptyl group, octyl group, isooctyl group, sec-octyl group, tert-octyl group, neoooctyl group, 2-ethylhexyl group, cyclooctyl group, nonyl group, isononyl group, sec-nonyl group, tert-nonyl group, neononyl group, cyclononyl group, decyl group, isodecyl group, sec-decyl group, tert-decyl group, neodecyl group, and cyclodecyl group.

[0013] As one embodiment of the 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene represented by formula (1) of the present invention, a compound represented by formula (1)-(A), in which R1 is an acetyl group, is preferably mentioned. TIFF2026045927000005.tif33116

[0014] Specific examples of compounds represented by formula (1)-(A) include (1)-(A)-1, in which R2 is a tert-butyl group; (1)-(A)-2, in which R2 is a tert-pentyl group; and (1)-(A)-3, in which R2 is an isopropyl group. TIFF2026045927000006.tif31109 TIFF2026045927000007.tif35109 TIFF2026045927000008.tif27106

[0015] As one embodiment of the 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene represented by formula (1) of the present invention, a compound represented by formula (1)-(B), in which R1 is a hydrogen atom, is preferably mentioned. TIFF2026045927000009.tif3099

[0016] Specific examples of compounds represented by formula (1)-(B) include (1)-(B)-1, where R2 is a tert-butyl group; (1)-(B)-2, where R2 is a tert-pentyl group; and (1)-(B)-3, where R2 is an isopropyl group. TIFF2026045927000010.tif30106 TIFF2026045927000011.tif33105 TIFF2026045927000012.tif27104

[0017] The present invention provides a method for producing the compound represented by formula (1)-(A), which includes, for example, a step of reacting the compound represented by formula (2) with a 2,5-substituted hydroquinone represented by formula (3). TIFF2026045927000013.tif30115 [In the formula, X represents a chlorine atom, a bromine atom, or an iodine atom.] TIFF2026045927000014.tif34131 [In the formula, R2 represents an alkyl group having 2 to 10 carbon atoms.]

[0018] The compound represented by formula (2) and the 2,5-substituted hydroquinone represented by formula (3) can be commercially available or manufactured by methods known to those skilled in the art.

[0019] As for the compound represented by formula (2), it is preferable that X is a chlorine atom, i.e., the compound represented by formula (2)-1. TIFF2026045927000015.tif30128

[0020] One method for producing the compound represented by formula (2)-1 is to react the compound represented by formula (4) with thionyl chloride. TIFF2026045927000016.tif33134

[0021] The step of reacting the compound represented by formula (2) with the 2,5-substituted hydroquinone represented by formula (3) is preferably carried out in the presence of a deoxidizing agent and / or a solvent.

[0022] As a deoxidizing agent, one or more selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium carbonate, pyridine, and triethylamine may be used.

[0023] The amount of deoxidizing agent used is not particularly limited, but is generally preferably 0.1 to 10 molar equivalents, and more preferably 0.6 to 3.0 molar equivalents, per molar equivalent of the compound represented by formula (2) which is the raw material.

[0024] As the reaction solvent, one or more selected from the group consisting of THF (tetrahydrofuran), DMF (N,N-dimethylformamide), DMA (N,N-dimethylacetamide), acetone, diethyl ether, chlorobenzene, hexane, heptane, octane, decane, nitrobenzene, carbon disulfide, nitromethane, dichloromethane, dichloroethane, chloroform, dioxane, benzene, toluene, xylene, mesitylene, carbon tetrachloride, nitromethane, acetonitrile, and diesel fuel may be used, with xylene being preferred due to its excellent reactivity.

[0025] The amount of reaction solvent used is not particularly limited, but is usually preferably 200 to 2000 parts by mass, and more preferably 400 to 1000 parts by mass, per 100 parts by mass of the compound represented by formula (2), which is the starting material.

[0026] The compound represented by formula (2) is preferably reacted in an amount of 1.5 to 2.5 molar equivalents per molar equivalent of the 2,5-substituted hydroquinone represented by formula (3), and more preferably in an amount of 1.8 to 2.2 molar equivalents. If the amount of the compound represented by formula (2) is less than 1.5 molar equivalents per molar equivalent of the 2,5-substituted hydroquinone represented by formula (3), the reaction tends not to proceed sufficiently. If the amount of the compound represented by formula (2) exceeds 2.5 molar equivalents per molar equivalent of the 2,5-substituted hydroquinone represented by formula (3), there is a tendency for a lot of raw materials to be wasted and by-products to be generated.

[0027] The reaction temperature is not particularly limited as it varies depending on the raw materials and solvent, but the reaction usually takes place between 30 and 100°C.

[0028] The reaction time is not particularly limited as it varies depending on the raw materials and solvent, but it is usually between 0.5 and 20 hours.

[0029] By further deacetylating the compound represented by formula (1)-(A) of the present invention, the compound represented by formula (1)-(B) of the present invention can be obtained.

[0030] Deacetylation is carried out by reacting a deacetylating agent with formula (1)-(A).

[0031] As the deacetylating agent, one or more selected from the group consisting of methylamine, diethylamine, triethylamine, potassium carbonate, sodium hydroxide, potassium hydroxide, and ammonia may be used, and diethylamine is preferably used because it is excellent in suppressing overreactions.

[0032] For example, one or more solvents selected from the group consisting of THF (tetrahydrofuran), DMF (N,N-dimethylformamide), DMA (N,N-dimethylacetamide), methanol, ethanol, isopropanol, acetone, diethyl ether, chlorobenzene, hexane, heptane, octane, decane, nitrobenzene, carbon disulfide, nitromethane, dichloromethane, dichloroethane, chloroform, dioxane, benzene, toluene, xylene, mesitylene, carbon tetrachloride, nitromethane, acetonitrile, and diesel fuel may be used as solvents for deacetylation, with THF being preferred due to its excellent reactivity.

[0033] The temperature for deacetylation is not particularly limited as it varies depending on the starting materials and solvent, but the reaction usually takes place between 0 and 40°C.

[0034] The deacetylation time is not particularly limited as it varies depending on the raw materials and solvent, but it is usually between 1 and 24 hours.

[0035] Deacetylation is terminated by neutralization with an acid such as hydrochloric acid.

[0036] The compound obtained after the reaction of the compound represented by formula (2) with the 2,5-substituted hydroquinone represented by formula (3), or after deacetylation, can be further purified to improve its purity. Purification can be carried out through general purification operations such as filtration, washing, concentration, extraction, distillation, and column chromatography, and the compound can be purified to the desired purity as appropriate.

[0037] The compound represented by formula (1) obtained in this way is highly soluble in organic solvents and can be used in various solution reactions.

[0038] The compound represented by formula (1) is particularly preferred as a monomer for curable resins. For example, a polyhydroxypolyether resin can be obtained by reacting the compound represented by formula (1)-(B) with a diexopy compound in the presence of a reaction solvent and a reaction catalyst, and further a curable resin can be obtained by using a crosslinking agent such as an amino resin or isocyanate. Alternatively, for example, a diexopy compound can be obtained by reacting the compound represented by formula (1)-(B) with epichlorohydrin.

[0039] As the reaction solvent, aprotic organic solvents such as methyl ethyl ketone, dioxane, tetrahydrofuran, acetophenone, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, sulfolane, propylene glycol monomethyl ether, and cyclohexanone can be suitably used. Using a reaction solvent can reduce the initial viscosity and improve the reactivity of the monomer.

[0040] Conventional polymerization catalysts can be used as the reaction catalyst, and alkali metal hydroxides, tertiary amine compounds, quaternary ammonium compounds, tertiary phosphine compounds, and quaternary phosphonium compounds and imidazole compounds are preferably used.

[0041] The present invention will be described in more detail below with reference to examples. [Examples]

[0042] Each compound was analyzed using the following method.

[0043] < 1 H-NMR spectrum> Dissolve 10 mg of the sample in deuterated dimethyl sulfoxide (DMSO-d6) and use a Bruker Biospin AV400M (Bruker) to analyze the solution. 1 The 1H-NMR spectrum was measured.

[0044] <FT-IRスペクトル> The FT-IR spectrum was measured using Spectrum One (PerkinElmer).

[0045] <Mass Spectrum (MS)> MS spectra were measured using a Waters 2690 / 2996 Alliance-TQ Detector.

[0046] <Ultra-high-performance liquid chromatography (UPLC)> Equipment: Waters UPLC H-Class System Column model number: ACQUITY UPLC HSS C18 1.8μm 2.1×50mm Liquid volume: 0.5 mL / min Solvent ratio: H2O (pH 2.3) / CH3OH = 80 / 20 (1 min) → 7 min → 10 / 90 → 1 min → 5 / 95 (19 min), gradient analysis. Wavelength: 229nm Column temperature: 40℃ The purity of 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene was calculated from the area percentage of the ULC chart.

[0047] [Example 1] [Synthesis of 2,5-ditert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene] In a 1 L four-necked flask equipped with a stirrer and temperature sensor, 108.1 g (0.60 mol) of 4-acetoxybenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 367.5 g of xylene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.48 g of DMF (N,N-dimethylformamide) were charged. Under a nitrogen stream, 83.0 g (0.66 mol) of thionyl chloride was added dropwise while stirring at room temperature. Subsequently, the temperature was raised to 60°C and the mixture was stirred for 2 hours. After stirring, the reaction mixture was cooled to room temperature, the pressure was reduced to 10 hPa, and then the temperature was gradually raised to 70°C. By distillation, the xylene was removed to obtain 126.1 g of a concentrate containing 4-acetoxybenzoic acid chloride (compound of formula (2)-1).

[0048] The obtained concentrate was transferred to a 2 L four-necked flask equipped with a stirrer and a temperature sensor. Then, 1081.0 g of xylene was added again. While stirring at room temperature under a nitrogen stream, 66.7 g (0.30 mol) of 2,5-tert-butylhydroquinone (manufactured by Seiko Chemical Co., Ltd.) was added. Subsequently, 63.7 g (0.63 mol) of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise. Subsequently, the mixture was stirred and heated to 60 °C and reacted for 11 hours. After the reaction, it was cooled to room temperature and solid-liquid separation was carried out by filter filtration, and it was washed with 324.8 g of methanol and 323.9 g of ion-exchanged water. After washing, it was dried under reduced pressure at 10 hPa and 70 °C to obtain 103.1 g of a crude product of 2,5-tert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene (the compound of formula (1)-(A)-1).

[0049] 102.2 g of the obtained crude product and 767.9 g of methanol (manufactured by Fujifilm Wako Pure Chemical Corporation) were charged into a 2 L four-necked flask equipped with a stirrer and a temperature sensor. While stirring at 60 °C for 1 hour under a nitrogen stream, suspension washing was carried out. After cooling to room temperature, the suspension was subjected to solid-liquid separation by filter filtration, then washed with 306.9 g of ion-exchanged water, and the obtained solid was dried under reduced pressure at 10 hPa and 70 °C to obtain 97.9 g of 2,5-di-tert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene (yield 59.7%, purity 96.2%).

[0050] Regarding the obtained compound 1 1H-NMR spectrum, FT-IR spectrum and mass spectrum were measured. 1 1H-NMR spectrum, FT-IR spectrum and mass spectrum are shown below. 1 1H-NMR (400 MHz, DMSO-d6): δ 8.23 (d, 4H, H c , J = 7.8 Hz), 7.43 (d, 4H, H d , J = 7.8 Hz), 7.21 (s, 2H, H b ), 2.34 (s, 6H, H e ), 1.29 (s, 18H, H a ) TIFF2026045927000017.tif34116FT-IR:2968cm -1 (ν-CH), 1767cm -1 (ν-C=O), 1732cm -1 (ν-C=O), 1605cm -1 (ν-C=C), 1504cm -1 (ν-C=C) MS:m / z=564[M+NH4] +

[0051] [Example 2] [Synthesis of 2,5-ditert-butyl-1,4-bis(4-hydroxybenzoyloxy)benzene] In a 500 mL four-necked flask equipped with a stirrer and a temperature sensor, 54.7 g (0.10 mol) of the compound 2,5-ditert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene obtained in Example 1 and 328.4 g of tetrahydrofuran (THF, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added. Subsequently, 29.2 g (0.40 mol) of diethylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise under a nitrogen stream at room temperature, and the mixture was stirred for 15 hours. After stirring, the reaction mixture was neutralized with 1N hydrochloric acid, and 164.4 g of deionized water was added to precipitate a solid. The solid-liquid was separated by filter filtration, washed with 171.2 g of deionized water, and dried under reduced pressure at 10 hPa and 70°C to obtain 31.6 g of crude product of 2,5-tert-butyl-1,4-bis(4-hydroxybenzoyloxy)benzene (compound of formula (1)-(B)-1).

[0052] In a 500 mL four-necked flask equipped with a stirrer and temperature sensor, 30.3 g of the crude product obtained, 91.0 g of methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 91.1 g of deionized water were charged. The mixture was stirred under a nitrogen stream at 60°C for 1 hour, and the suspension was washed. After cooling to room temperature, the suspension was separated into solid and liquid by filter filtration, washed with 91.0 g of deionized water, and the resulting solid was dried under reduced pressure at 10 hPa and 70°C to obtain 29.5 g of 2,5-ditert-butyl-1,4-bis(4-hydroxybenzoyloxy)benzene (yield 66.0%, purity 96.9%).

[0053] Regarding the obtained compounds 1 1H-NMR spectra, FT-IR spectra, and mass spectra were measured. 1 The H-NMR spectrum, FT-IR spectrum, and mass spectrum are shown below. 1 H-NMR(400MHz,DMSO-d6):δ10.60(br,2H,H e ), 8.01-8.04(d,4H,H c ,J=8.8Hz),7.08(s,2H,H b ), 6.95-6.99(d,4H,H d ,J=8.8Hz),1.28(s,18H,H a ) TIFF2026045927000018.tif42136FT-IR:3302cm -1 (ν-OH), 2968cm -1 (ν-CH), 1689cm -1 (ν-C=O), 1605cm -1 (ν-C=C), 1588cm -1 (ν-C=C), 1588cm -1 (ν-C=C) MS:m / z = 461[MH] -

[0054] [Comparative Example 1] [Synthesis of 1,4-bis(4-hydroxybenzoyloxy)benzene] In a 500 mL four-necked flask equipped with a stirrer, temperature sensor, and Dean-Stark apparatus, 40.0 g (0.363 mol) of hydroquinone (HQ, manufactured by Tokyo Chemical Industry Co., Ltd.), 100.4 g (0.726 mol) of 4-hydroxybenzoic acid (POB, manufactured by Ueno Pharmaceutical Co., Ltd.), 4.0 g of p-toluenesulfonic acid monohydrate (PTS·H2O), and 352.0 g of mesitylene were added. The mixture was heated under a nitrogen stream, increased in temperature, and refluxed to 160-164°C for 7 hours. After separating the solid and liquid from the reaction mixture by filter filtration, the solid was washed with 260.0 g of methanol to obtain the crude product. In a 500 mL four-necked flask equipped with a stirrer and temperature sensor, the obtained crude product and 440.0 g of DMF were charged and heated to 80°C while stirring to dissolve the crude product. After hot filtration using a filter, the mixture was cooled to 5°C while stirring to precipitate crystals. After solid-liquid separation by filter filtration, the mixture was washed with 100.0 g of cyclohexanone and the crystals were recovered. The obtained crystals and 520.0 g of cyclohexanone were placed in a 1 L four-necked flask equipped with a stirrer and temperature sensor, and the mixture was heated to 150°C while stirring. The mixture was kept in a suspension state at 150°C for 2 hours. The suspension was cooled to 40°C, solid-liquid separation was performed by filter filtration, and the mixture was washed with 80.0 g of methanol and the crystals were recovered. The target product was obtained by vacuum drying at 30 hPa and 75°C (yield 71.0%, purity 99.7%).

[0055] The solubility of 2,5-ditert-butyl-1,4-bis(4-acetoxy-benzoyloxy)benzene (compound of formula (1)-(A)-1) obtained in Example 1, 2,5-ditert-butyl-1,4-bis(4-hydroxy-benzoyloxy)benzene (compound of formula (1)-(B)-1) obtained in Example 2, and 1,4-bis(4-hydroxy-benzoyloxy)benzene obtained in Comparative Example 1 in methyl ethyl ketone at increasing temperatures was measured. The results are shown in Figure 1.

[0056] The 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene represented by formula (1) of the present invention was found to have higher solubility compared to the comparative compound.

Claims

1. Formula (1) [In the formula, R １ R represents a hydrogen atom or an acetyl group. ２ [This indicates an alkyl group having 2 to 10 carbon atoms.] 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene, represented as such.

2. R １ The 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 1, wherein is an acetyl group.

3. R １ The 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 1, wherein is a hydrogen atom.

4. R ２ The 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 1, wherein is a tert-butyl group.

5. A monomer for curable resins, as described in claim 1: 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene.

6. Formula (2) [In the formula, X represents a chlorine atom, a bromine atom, or an iodine atom.] The compound represented by formula (3) [In the formula, R ２ [This indicates an alkyl group having 2 to 10 carbon atoms.] 2,5-substituted hydroquinone represented by and A method for producing 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 2, comprising the step of reacting the following:

7. A method for producing 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 3, comprising the step of deacetylating the 2,5-substituted-1,4-bis(4-substituted-benzoyloxy)benzene according to claim 2.

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