JPH04279585A - Phenylenediamine-based compound and electrophotographic sensitizing material using the same compound - Google Patents

Abstract

PURPOSE:To obtain a new compound as an electron charge transporting material, having excellent weather resistance, light stability high sensitivity and repeating characteristics. CONSTITUTION:A compound shown by formula I (R<1> to R<4> are H, halogen, alkyl or alkoxy) such as a compound shown by formula II. The compound shown by formula I is obtained by reacting a compound shown by formula III with a secondary amine compound shown by formula IV (R<n> and R<m> are H, halogen alkyl or alkoxy) in the presence of copper or a basic substance in an organic solvent. The compound is useful as a photosensitive layer of electrophotographic sensitizing material.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phenylenediamine compound suitable as a charge transport material in an electrophotographic photoreceptor, and an electrophotographic photoreceptor using the same.

0002

BACKGROUND OF THE INVENTION In recent years, organic electrophotographic photoreceptors have been widely used as electrophotographic photoreceptors in image forming apparatuses such as copying machines, which are excellent in processability and economical efficiency and have a large degree of freedom in functional design. Further, when forming a copy image using an electrophotographic photoreceptor, the Carlson process is widely used. The Carlson process consists of a charging process in which an electrophotographic photoreceptor is uniformly charged by corona discharge, an exposure process in which an original image is exposed to the charged electrophotographic photoreceptor to form an electrostatic latent image corresponding to the original image, and a static A developing process in which an electrostatic latent image is developed with a developer containing toner to form a toner image, a transfer process in which the toner image is transferred to paper, etc., a fixing process in which the transferred toner image is fixed, and after the transfer process. , and a cleaning step of removing toner remaining on the electrophotographic photoreceptor. In this Carlson process, in order to form a high quality image, the electrophotographic photoreceptor is required to have excellent charging characteristics and photosensitivity characteristics, and to have a low residual potential after exposure.

Conventionally, inorganic photoconductors such as selenium and cadmium sulfide have been known as materials for electrophotographic photoreceptors.
These have the disadvantage of being toxic and having high production costs. Therefore, so-called organic electrophotographic photoreceptors using various organic substances in place of these inorganic substances have been proposed. Such an organic electrophotographic photoreceptor has a photosensitive layer composed of a charge-generating material that generates charges upon exposure to light, and a charge-transporting material that has a function of transporting the generated charges.

[0004] In order to satisfy various conditions desired for such an organic electrophotographic photoreceptor, it is necessary to appropriately select these charge generating materials and charge transporting materials. As charge transport materials, various organic compounds such as polyvinyl carbazole, oxadiazole compounds, pyrazoline compounds, and hydrazone compounds have been proposed and commercialized. Hydrazone compounds disclosed in JP-A-2-210451 are known.

[0005]

However, the charge transport materials described above have relatively low drift mobility, which indicates charge transport ability. Further, since the dependence of drift mobility on electric field strength is large, there is a problem that charge movement is small in a low electric field and residual potential is difficult to escape. Furthermore, there is also the problem that it is easily deteriorated by irradiation with ultraviolet rays.

[0006] In order to solve these problems, m-
As a phenylenediamine compound, N, N, N', N
'-Tetraphenyl-1,3-phenylenediamine has been proposed (see JP-A-1-142642). This m-phenylenediamine compound has good light resistance against ultraviolet rays and the like, and exhibits stable characteristics even when used in an actual copying machine. However, there is a problem in that when a copying machine malfunctions and exposure to light occurs for a long time or at high temperatures, irreversible damage may occur. Further, there was also a drawback that the sensitivity and repeatability were insufficient.

The object of the present invention is to provide a phenylenediamine compound which has high light resistance and excellent photostability and is suitable as a charge transport material, and an electrophotographic photoreceptor using the same which has high sensitivity and excellent repeatability. and to provide the following.

[0008]

Means and Effects for Solving the Problems Generally, the cause of deterioration of photoreceptor characteristics due to photodeterioration is the formation of impurities in the photoreceptor that act as traps for the charge transport material. In the case of m-phenylenediamine compounds, a ring-closing reaction occurring between the central benzene ring and other phenyl groups can be considered as such a photodegradation reaction. This reaction is thought to occur more easily because the electron density of the phenylenediamine compound molecule is biased towards the central benzene ring. In particular, the 4, 5, and 6 positions of the central benzene ring have a molecular structure that is easily attacked by oxidizing substances such as oxygen during photoexcitation due to their steric configuration, and as electrons are extracted from these positions, a ring-closing reaction occurs. Conceivable. Therefore, we thought that it would be possible to suppress the reactivity of the phenylenediamine compound and improve its stability against light by substituting and protecting this part with a substituent, and as a result of various experiments, we found that
It has been found that by substituting this position with a predetermined substituent, the photostability of the electrophotographic photoreceptor can be effectively improved without impairing charge transport properties such as drift mobility.

[0009]The phenylenediamine compound of the present invention has the following general formula (1):

0010

[Chemical formula 3]

(wherein R1, R2, R3 and R
4 are the same or different, hydrogen atom, halogen atom,
It is characterized by being represented by an alkyl group or an alkoxy group). Further, the electrophotographic photoreceptor of the present invention for achieving the above object is characterized by having a photosensitive layer containing a phenylenediamine compound represented by the above general formula (1) on a conductive substrate. There is.

The phenylenediamine compound represented by the above general formula (1) has the 4, 5, and 6 positions of the central benzene ring protected with substituents, making it less susceptible to attack from oxidizing substances, etc. Ring closure reaction is suppressed and stability against light is improved. In addition, electrophotographic photoreceptors containing the phenylenediamine compound represented by the above general formula (1) are more susceptible to damage than conventional electrophotographic photoreceptors when exposed to light for long periods of time or exposed to light at high temperatures. It is less likely to overlap and has excellent photostability.

Furthermore, since the phenylenediamine compound represented by the above general formula (1) has excellent charge transport ability, by incorporating this phenylenediamine compound as a charge transport material into the photosensitive layer, the sensitivity and charge can be improved. An electrophotographic photoreceptor having excellent performance and high repeatability can be obtained. Examples of the halogen atoms include fluorine, chlorine, bromine, and iodine.

Examples of the alkyl group include lower alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group, and hexyl group. It will be done. Examples of the alkoxy group include lower alkoxy groups in which the alkyl moiety has 1 to 6 carbon atoms, such as methoxy group, ethoxy group, isopropoxy group, butoxy group, t-butoxy group, pentyloxy group, and hexyloxy group.

Specific examples of the phenylenediamine compound represented by the general formula (1) include those shown in the following formulas (2) to (7).

[0016]

[C4]

[0017]

[C5]

The phenylenediamine compound of the present invention is
It can be synthesized by various methods, for example, it can be obtained by the following reaction formula.

[0019]

[C6]

(In the formula, Rn and Rm are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group, or an alkoxy group.) This reaction formula shows that the two iodo groups represented by formula (a) are substituted. A phenyl ether compound and a secondary amine compound represented by formula (b) in which two phenyl groups are bonded are reacted in an organic solvent in the presence of copper or a basic substance to form formula (1'). The phenylenediamine compound of the present invention represented by:

The secondary amine compound (b) may be reacted in a molar amount at least twice that of the phenyl ether compound (a). Examples of the basic substance include NaOH, KCO3, NaCO3, etc.
Examples of the organic solvent include nitrobenzene, dichlorobenzene, n-methylpyrrolidone, and the like. Also,
This reaction is suitably carried out at about 190-220°C.

[0022] The above-mentioned phenylenediamine compound can also be obtained by the following reaction formula.

[0023]

[C7]

(In the formula, Rp, Rq and Rr are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group) This reaction formula is expressed by the formula (c)
The compound represented by and the compound represented by formula (d) are mixed in an organic solvent such as nitrobenzene, dichlorobenzene, n-methylpyrrolidone, etc. in the presence of copper or a basic substance such as NaOH, KCO3, NaCO3, etc. The phenylenediamine compound of the present invention represented by the formula (1'') is obtained by reacting the compound in the reactor.

In contrast to the above compound (c), compound (d
) may be reacted in at least twice the molar amount. Further, this reaction is suitably carried out at about 190 to 220°C. The photosensitive layer in the present invention contains one or more phenylenediamine compounds represented by the general formula (1) above as a charge transport material. The photosensitive layer in the present invention includes a single-layer type in which a charge-generating material, a charge-transporting material, which is a compound represented by the general formula (1) and a binder resin, and a charge-generating layer and a charge-transporting layer are laminated. Although there is a laminated type, the photosensitive layer of the present invention can be applied to either type.

In order to obtain a single-layer type electrophotographic photoreceptor, a photosensitive layer containing a compound represented by the general formula (1) as a charge transporting material, a charge generating material, a binder resin, etc. is made electrically conductive. It may be formed on the base. In addition, in order to obtain a laminated electrophotographic photoreceptor, a charge generation layer containing a charge generation material is formed on a conductive substrate by means such as vapor deposition or coating, and a charge transport layer is formed on this charge generation layer. It is sufficient to form a charge transport layer containing a compound represented by the general formula (1) as a material and a binder resin. Further, contrary to the above, a charge transport layer similar to the above may be formed on a conductive substrate, and then a charge generation layer containing a charge generation material may be formed by means such as vapor deposition or coating. Furthermore, the charge generation layer may be formed by coating a charge generation material and a charge transport material dispersed in a binder resin.

As charge generating materials, conventionally used selenium, selenium-tellurium, selenium-arsenic, amorphous silicon, pyrylium salts, azo compounds, disazo compounds, phthalocyanine compounds, anthanthrone compounds, and perylene compounds are used. compounds, indigo-based compounds, triphenylmethane-based compounds, threne-based compounds, toluidine-based compounds, pyrazoline-based compounds, perylene-based compounds, quinacridone-based compounds, pyrrolopyrrole-based compounds, and the like. These charge generating materials can be used alone or in combination of two or more so that they have absorption wavelengths in desired regions.

The phenylenediamine compound represented by the general formula (1), which is a charge transporting material, can be used alone or in combination with other conventionally known charge transporting materials. Conventionally known charge transport materials include:
Various electron-withdrawing compounds and electron-donating compounds can be used. Examples of the electron-withdrawing compound include:
Diphenoquinone derivatives such as 2,6-dimethyl-2',6'-ditert-dibutyldiphenoquinone, malononitrile, thiopyran compounds, tetracyanoethylene, 2
, 4,8-trinitrothioxanthone, 3,4,5,7
Examples include -tetranitro-9-fluorenone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromomaleic anhydride, and the like.

Further, as the electron donating compound, 2,5
-Oxadiazole compounds such as di(4-methylaminophenyl), 1,3,4-oxadiazole, 9-(4
- styryl compounds such as (diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, pyrazoline compounds such as 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline, hydrazone compounds, triphenylamine compounds, indole compounds Examples include nitrogen-containing cyclic compounds such as compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds, and fused polycyclic compounds.

These charge transport materials may be used alone or in combination of two or more. In addition, when using a charge transport material with film-forming properties such as polyvinylcarbazole,
A binder resin is not necessarily required. Various resins can be used as the binder resin in the photosensitive layer, charge generation layer and charge transport layer. For example, styrene polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers,
Acrylic copolymer, styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane , thermoplastic resins such as polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, and other cross-linkable thermoplastic resins. Examples include curable resins and photocurable resins such as epoxy acrylate and urethane-acrylate. These binder resins can be used alone or in combination of two or more.

Further, when forming the charge generation layer and the charge transport layer by coating means, a solvent is used to prepare the coating solution. Various organic solvents can be used as this solvent, including alcohols such as methanol, ethanol, isopropanol, and butanol, aliphatic hydrocarbons such as n-hexane, octane, and cyclohexane, and aromatic solvents such as benzene, toluene, and xylene. group hydrocarbons, halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene, ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, and ethyl acetate. , esters such as methyl acetate, dimethyl formaldehyde, dimethyl formamide, dimethyl sulfoxide, and the like. These solvents can be used alone or in combination of two or more.

Further, in order to improve the sensitivity of the charge generation layer, a known sensitizer such as terphenyl, halonaphthoquinones, acenaphthylene, etc. may be used together with the charge generation material. Furthermore, a surfactant, a leveling agent, etc. may be used to improve the dispersibility, dyeability, etc. of the charge transport material and charge generation material.

[0033] As the conductive substrate, various conductive materials can be used, such as aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, and indium. Examples include simple metals such as stainless steel and brass, plastic materials on which the above metals are vapor-deposited or laminated, and glass coated with aluminum iodide, tin oxide, indium oxide, etc.

The conductive substrate may be in the form of a sheet or a drum, as long as the substrate itself is conductive or the surface of the substrate is conductive. Further, the conductive substrate preferably has sufficient mechanical strength during use. In the laminated electrophotographic photoreceptor, the charge generation material and the binder resin constituting the charge generation layer can be used in various ratios, but based on 100 parts (parts by weight, the same applies hereinafter) of the binder resin. , the charge generating material is preferably used in an amount of 5 to 500 parts, particularly 10 to 250 parts. Further, the charge generation layer may have an appropriate thickness, but it is preferably formed to a thickness of about 0.01 to 5 μm, particularly about 0.1 to 3 μm.

The above general formula (1) constituting the charge transport layer
The phenylenediamine compound (charge transport material) represented by the formula and the binder resin can be used in various ratios as long as they do not inhibit charge transport and do not crystallize. In order to easily transport the charges generated in the generation layer, the phenylenediamine compound represented by the above general formula (1) is added at a ratio of 25 to 200 parts, particularly 50 to 150 parts, per 100 parts of the binder resin. It is preferable to use it in Further, the charge transport layer has a thickness of 2 to 100 μm,
In particular, it is preferably formed to have a thickness of about 5 to 30 μm.

In a single-layer type electrophotographic photoreceptor, the charge generating material is 2 to 20 parts, particularly 3 to 15 parts, based on 100 parts of the binder resin, and the charge generating material is 2 to 20 parts, particularly 3 to 15 parts, and a phenylenediamine type compound represented by the above general formula (1). 40 to 200 parts of the compound (charge transport material),
Particularly suitable is 50 to 150 parts. In addition, the thickness of the single-layer type photosensitive layer is 10 to 50 μm, especially 15 to 30 μm.
It is preferable that it is about m.

In a single-layer electrophotographic photoreceptor, there is a gap between the conductive substrate and the photosensitive layer, and in a laminated electrophotographic photoreceptor, there is a gap between the conductive substrate and the charge generation layer. A barrier layer may be formed between the conductive substrate and the charge transport layer, and between the charge generation layer and the charge transport layer, as long as it does not impede the characteristics of the electrophotographic photoreceptor. A protective layer may be formed on the surface of the photoreceptor.

When the charge generation layer and the charge transport layer are formed by coating, the charge generation material and the binder resin are mixed using a known method such as a roll mill, a ball mill, an attritor, a paint shaker, or an ultrasonic wave. A coating liquid may be prepared by dispersing and mixing using a disperser or the like, and this may be applied and dried by known means. Note that, as described above, the charge generation layer may be formed by vapor depositing the charge generation material.

[0039]

[Examples] The present invention will be explained in detail below with reference to Examples and Comparative Examples. Example 1 <Synthesis of phenylenediamine compound represented by the above formula (2)> 4.25 g of iodinated julorindine represented by the following formula (8), 3.36 g of N,N-diphenylamine
g and 0.02 g of copper powder were reacted in 80 ml of nitrobenzene by refluxing at a temperature of 200° C. for 12 hours,
It was isolated and purified by a conventional method to obtain a phenylenediamine compound represented by the formula (2) (hereinafter referred to as phenylenediamine compound 2).

[0040]

[Chemical formula 8]

The yield of this phenylenediamine compound 2 was 58%, and the melting point was 171-173°C. Further, when the compound 2 was subjected to elemental analysis, the following results were obtained. Elemental analysis value: Calculated value (%) C as C36H33N3
85.17 H6.55 N8.28 Actual value (%)
C85.06 H6.51 N8.30 Example 2 <Synthesis of phenylenediamine compound represented by the above formula (3)> 3.84 g of the compound represented by the following formula (9)
, m-iodotoluene 4.36g and copper powder 0.02g
g in 80 ml of nitrobenzene at a temperature of 20°C for 12 hours to react, isolate, and purify by a conventional method to obtain a phenylenediamine compound represented by the formula (3) (hereinafter referred to as phenylenediamine). A system compound 3) was obtained.

[0042]

[Chemical formula 9]

The yield of this phenylenediamine compound 3 was 62%, and the melting point was 169-172°C. Further, when the compound 3 was subjected to elemental analysis, the following results were obtained. Elemental analysis value: Calculated value (%) C as C40H41N3
85.22 H7.33 N7.46 Actual value (%)
C85.12 H7.40 N7.40 Example 3 <Synthesis of phenylenediamine compound represented by the above formula (4)> In place of the compound represented by the above formula (9),
A phenylenediamine compound represented by the formula (4) (hereinafter referred to as phenylenediamine compound 4) was prepared in the same manner as in Example 2 above, except that 3.84 g of the compound represented by the following formula (10) was used. ) was obtained.

[0044]

[Chemical formula 10]

The yield of this phenylenediamine compound 4 was 62%, and the melting point was 168-172°C. Further, when the compound 4 was subjected to elemental analysis, the following results were obtained. Elemental analysis value: Calculated value (%) C as C40H41N3
85.22 H7.33 N7.46 Actual value (%)
C85.15 H7.32 N7.41 Example 4 <Synthesis of phenylenediamine compound represented by the above formula (5)> In place of the compound represented by the above formula (9),
Using 3.87 g of the compound represented by the following formula (11), m
-m-iodoanisole instead of iodotoluene4.
A phenylenediamine compound represented by the formula (5) (hereinafter referred to as phenylenediamine compound 5) was obtained in the same manner as in Example 2 except that 36 g was used.

[0046]

[Chemical formula 11]

The yield of this phenylenediamine compound 5 was 60%, and the melting point was 162-164°C. Further, when the compound 5 was subjected to elemental analysis, the following results were obtained. Elemental analysis value: Calculated value as C40H41N3 O4 (
%) C76.53 H6.58 N6.69 O
10.20 Actual value (%) C76.49 H6.53 N6.6
7 O10.23 Examples 5 to 8 and Comparative Example 1 (Laminated electrophotographic photoreceptor)
Compound 2 represented by the following formula (12) as a charge generating material
Polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd.)
BH-5'') and 120 parts of tetrahydrofuran were dispersed for 2 hours in a paint shaker using zirconia beads (2 mm diameter). The resulting dispersion was coated onto an aluminum sheet using a wire bar and heated at 100°C.
The mixture was dried for 1 hour to obtain a charge generation layer of 0.3 μm.

[0048]

[Chemical formula 12]

On this charge generation layer, 1 part of a charge transport material and 1 part of poly(4,4'-cyclohexylidene diphenyl) polycarbonate ("Z-200" manufactured by Mitsubishi Gas Chemical Co., Ltd.) were dissolved in 9 parts of toluene. The solution was applied using a wire bar and dried at 100° C. for 1 hour to obtain a charge transport layer of 20 μm. The charge transport materials used in Examples 5 to 8 and Comparative Example 1 are shown in Table 1. Compounds 2 to 5, which are charge transport materials shown in Table 1, mean phenylenediamine compounds 2 to 5 obtained in Examples 1 to 4, respectively, and comparative compounds are N, N, N', N'- Tetrakis(3-methylphenyl)-1,3-diaminobenzene.

Examples 9 to 12 and Comparative Example 2 (single-layer electrophotographic photoreceptor) Compound 1 represented by the above formula (12) as a charge generating material
and 60 parts of tetrahydrofuran were dispersed for 2 hours in a paint shaker using zirconia beads (2 mm diameter). To the obtained dispersion, 50 parts of a tetrahydrofuran solution of poly(4,4'-cyclohexylidene diphenyl) carbonate ("Z-200" manufactured by Mitsubishi Gas Chemical Co., Ltd.) with a solid content of 20% by weight and 10 parts of a charge transport material were added. was added, and dispersion was continued for an additional hour. The obtained dispersion was coated on an alumite-treated aluminum tube, and 10
It was dried at 0° C. for 1 hour to obtain a 20 μm photosensitive layer. The charge transport materials used at this time are shown in Table 2. Compounds 2 to 5 and comparative compounds shown in Table 2 are the same as those shown in Table 1.

(Evaluation test) Surface potential SP (V) of the electrophotographic photoreceptors obtained in Examples 5 to 12 and Comparative Examples 1 and 2,
Half-reduction exposure amount E1/2 (lux・sec), residual potential V
L (V) and the surface potential SP (V) after light irradiation were measured using an evaluation tester ("EPA8100" manufactured by Kawaguchi Electric Co., Ltd.).

The measurement conditions are as follows. Light intensity: 50 lux Exposure intensity: 1/15 seconds Surface potential: The inflow current value was adjusted so as to be around (±)700V. Light source: Tungsten lamp Static elimination: 200 lux Residual potential measurement: Measurement was started 0.2 seconds after the start of exposure.

Measurement of surface potential after light irradiation: Adjust the inflow current value to around (±)700V, and set the light intensity to 1.
The surface potential of the electrophotographic photoreceptor was measured after 20 minutes of light irradiation at 000 lux ("National Highlight FL, 15W" manufactured by Matsushita Electric Industrial Co., Ltd.). Example 5~
Table 1 shows the test results of Examples 9 to 12 and Comparative Example 2 (single-layer electrophotographic photoreceptor).

[0054]

[Table 1]

[0055]

[Table 2]

From these test results, it was found that electrophotographic photoreceptors (Examples 5 to 1) using the compound for charge transport materials of the present invention
All of 2) show good values, although there is almost no difference from the conventional electrophotographic photoreceptors (Comparative Examples 1 and 2) in surface potential, half-reduction exposure, and residual potential. Furthermore, in terms of stability against light, it is significantly superior to conventional electrophotographic photoreceptors. Therefore, the electrophotographic photoreceptor using the phenylenediamine compound of the present invention as a charge transport material maintains good sensitivity, has excellent repeatability, has significantly improved light resistance, and has excellent photostability. I understand that.

[0057]

[Effects of the Invention] As described above, the phenylenediamine compound of the present invention has a phenyl group attached to each nitrogen atom attached to the central benzene ring, so the reactive site is protected and is not easily attacked by oxidizing substances. Since the ring-closing reaction is suppressed, it has excellent photostability and can be suitably used as a charge transport material. Further, by using this phenylenediamine compound as a charge transport material, an electrophotographic photoreceptor having excellent photostability, high sensitivity, and excellent repeatability can be obtained.

Claims (2)

[Claims] Claim 1: Represented by the following general formula (1): [Formula 1] (wherein R1, R2, R3 and R4 are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group) A phenylene diamine compound. 2. An electrophotographic photoreceptor comprising, on a conductive substrate, a photosensitive layer containing a phenylenediamine compound represented by the following general formula (1). [Formula 2] (wherein R1, R2, R3 and R4 are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group)