GB2055882A - Bis-azo compounds and the preparations thereof - Google Patents

Abstract

Bis-azo compounds suitable for use in electrophotographic conductors have the formula: <IMAGE> in which R is an orthophenylene or paraphenylene group; A is a group <IMAGE> or a group <IMAGE> and R<1>, R<2> and R<3> are the same or are different and each is a hydrogen or halogen atom or an alkyl, alkoxy, nitro or dialkylamino group. The compounds may be prepared by reacting a tetrazonium compound of the formula. <IMAGE> (in which R has the meaning defined above and X is an anion), with a coupling compound of the formula: <IMAGE> (in which R<1>, R<2> and R<3> have the meanings defined above).

Description

SPECIFICATION Bis-azo compounds and the preparation thereof This invention relates to bis-azo compounds which are suitable for use in electrophotographic conductors and to the preparation of such bis-azo compounds.

Known photoconductors for use in electrophotography include inorganic photoconductors comprising an electroconductive support material and an inorganic photoconductive material such as selenium, cadmium sulphide or zinc oxide, which is coated onto the electroconductive support material.

Generally, in the art of electrophotography, a photoconductor is electrically charged, for example by corona charging in the dark, and is then imagewise exposed to light, thereby selectively dissipating the charge in the illuminated areas of the photoconductor while leaving behind a latent electrostatic image in the non-illuminated areas. This latent electrostatic image may then be developed to form a visible image by depositing thereon finely divided electroscopic marking particles (toner) which comprise a colouring material, such as dyestuff or pigment, and a polymeric binder material. The following basic characteristics are required for photoconductors for use in electrophotography: (1) The photoconductors must be electrically chargeable to a predetermined potential in the dark.

(2) The photoconductors must retain their charge sufficiently in the dark. In other words, the dark decay of the photoconductors must be smali.

(3) The charge on the photoconductors must be dissipated quickly under illumination. In other words, the light decay of the photoconductors must be high and accordingly their photosensitivity must be high.

Additionally, it is required that the photoconductors have high mechanical strength and be workable into the desired shape.

Conventional inorganic photoconductors have some advantages, but, at the same time, they have several drawbacks. For example, the selenium photoconductor which is now widely used, can satisfy the above-mentioned requirements (1), (2) and (3) to some extent. However, difficulties are encountered when producing the photoconductor and its production cost is high. More specifically, since its flexibility is poor, it is difficult to form it into various shapes. Furthermore, it is highly susceptible to heat and mechanical shocks, so that care must be taken when handling it. Cadmium sulphide and zinc oxide are generally used as dispersions in a binder resin.However, since they are poor in mechanical characteristics, such as smoothness, hardness, tensile strength and durability, they cannot be used repeatedly as they are, so that, for exam pie, a protective layer is required, which complicates the process of producing electrophotographic elements using these materials.

Recently, in order to eliminate the above-mentioned drawbacks of the inorganic photoconductors, a variety of organic electrophotographic photoconductors have been studied and developed and used in practice; for example, a photoconductor comprising a support material and a photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on (as described in U.S. Patent No.

3,484,237), which is formed on the support material; a photoconductor comprising a photosensitive layer containing poly-N-vinylcarbazole sensitized by pyrylium salt dyestuff (as described in Japanese Patent No. 48-25658); a photoconductor having a photosensitive layer consisting essentially of an organic pigment (as described in Japanese Laid-Open Patent Application No. 47-37543); and a photoconductor having a photosensitive layer which contains as a main component a eutectic crystal complex consisting of a dyestuff and a resin (as described in Japanese Laid-Open Patent Application No.

47-10735). These organic electrophotographic photoconductors have improved mechanical characteristics and working properties as compared with those of the inorganic photoconductors.

However, the organic photoconductors generally have a low photosensitivity and accordingly do not sufficiently satisfy the requirements for electrophotographic photoconductors. Furthermore, the characteristics of electrophotographic photoconductors depend significantly upon the materials used and the preparation methods employed; in particular upon the nature of the photoconductive materials, and therefore, photoconductive materials have been actively studied.

It has now been found, in accordance with the present invention that certaih bis-azo compounds, as hereinafter defined, may be used as electrographic conductive materials.

According to the invention therefore there are provided, as new compounds, bis-azo compounds of the general formula:

in which R is an ortho-phenylene group

or a para-phenylene group

A is a group

or a group

and Rr, R2 and R3 are the same or are different and each is a hydrogen or halogen atom or an alkyl, alkoxy, nitro or dialkylamino group.

The bis-azo compounds of formula (I) are symmetrical, that is the substituents on the central o- phenylene nucleus are the same.

The bis-azo compounds of formula (I) may be prepared by the reaction of a tetrazonium salt of the formula:

(in which R has the meaning defined above and X is an anion), with a coupling compound of the formula:

(in which R', R2 and R3 have the meanings defined above).

The tetrazonium salt of formula IV can be prepared, for example, by reducing a 1,2-bis (nitrostyryl) benzene of the formula:

(in which R has the meaning defined above) to give a 1,2-bis (aminostyryl) benzene of the formula:

and then subjecting this latter to diazotization. More specifically the 1,2-bis) nitrostyryl) benzene of formula (VI) can be prepared by preparing the 1 ,2-bis-(nitros-yryl) benzene of formula (V) (forexample the compound of formula (V) in which R is a p-phenylene group can be prepared by the procedure described in German Offenlegungsschrift No. 1,108,219), and then reducing it with a reducing agent, for example an iron/hydrochloric-acid reducing system, in an organic solvent such as for example, N,N dimethylformamide.The reduction of the bis(nitrostyryl)benzene of formula (V) can be completed in from 30 minutes to 2 hours at a temperature of from 70 to 1 200C.

Diazotization of the 1 ,2-bis(aminostyryl) benzene of formula (V) is suitably conducted as follows.

The 1 ,2-bis(aminostyryl) benzene is added to a dilute inorganic acid, such as dilute hydrochloric acid or dilute sulphuric acid. To the mixture is then added an aqueous solution of sodium hyponitrite, while maintaining the temperature of the mixture in the range --100C to 1 OOC. The diazotization reaction terminates in 30 minutes to 3 hours. It is preferably that the diazonium compound of the 1,2 bis(aminostyryl) benzene be separated in the form of a tetrazonium salt by adding, for example, fluorboric acid to the reaction mixture, to precipitate the tetrazonium salt. The tetrazonium salt is then separated from the solution by filtration.

A bis-azo compound of formula (I) is obtained from the tetrazonium salt by reacting it with a coupling component of formula (V) or formula (VI), suitably in a molar ratio of coupling component to tetrazonium salt of from 1 to 10, preferably from 2 to 5. In practice, the coupling reaction is suitably accomplished by dissolving the tetrazonium salt and the coupling component in an organic solvent, such as N,N-dimethylformamide or dimethyl sulphoxide, and then adding dropwise to the solution an 'alkaline aqueous solution, such as an aqueous solution of sodium acetate, while maintaining the reaction mixture at a temperature between approximately -1 O0C and 1 OOC. The reaction terminates in 5 minutes to 30 minutes, whereby the bis-azo compound of formula (I) can be prepared.

The bis-azo compounds of formula (I) are useful as electrophotographic photoconductive materials, and thus, for example may be used to prepare electrophotographic conductors, as follows: (1) The bis-azo compound is ground into small particles with a diameter of from approximately 0.05 to 5 microns and the particles are then dispersed in a binder resin, such as a polyester, polyamide, polyurethane, polyketone, polycarbonate, polystyrene or polyvinyl toluene resin. The dispersion is coated onto an electroconductive support, whereby an electrophotographic photoconductor is prepared.

(2) To the bis-azo compound-containing layer prepared as described in (1), there is added an inorganic photoconductive material, for example cadmium sulphide or a cadmium sulphide selenium alloy; or an organic photoconductive material, for example poly-N-vinylcarbazole, polyvinyl pyrene or the like, is added thereto, whereby an electrophotographic photoconductor is prepared.

(3) A layer of the bis-azo compound having a thickness of approximately 0.05 to 10 microns is formed on an electroconductive support and another photoconductive layer is formed on the bis-azo compound layer, whereby a layered type electrophotographic photoconductor is prepared.

In order that the invention may be well understood the following Examples are given by way of illustration only.

In the Examples reference wiil be made to the accompanying drawings in which: Figure 1 is the infrared spectrum of a tetrazonium fluoborate as obtained in Preparative Example 1, Figure 2 is the infrared spectrum of a compound according to the invention obtained in Example 1, Figure 3 is the infrared spectrum of a tetrazonium fluoborate obtained in Preparative Example 2, and Figure 4, is the infrared spectrum of a compound according to the invention obtained in Example 14.

Preparative '(Preparation of Tetrazonium Salt of 1,2-bisF4-aminostyryl)benzene) Fifteen grams of 1 ,2-bis(4-aminostyryl)benzene was added to dilute hydrochloric acid (prepared by dissolving 25 ml of concentrated hydrochloric acid in 700 ml of water), and the mixture was stirred and cooled to OOC. To the mixture, an aqueous solution of sodium hyponitrite (7.5 g of sodium pyponitrite in 25 ml of water) was added dropwise over a period of 40 minutes. The rate of addition of the sodium hyponitrite solution was so regulated that the temperature remained between 0 and 50C. Thereafter, the reaction mixture was stirred for 30 minutes, and 30 ml of 42 percent fluoboric acid was added thereto.Yellowish-red crystals separated out and were collected on a suction funnel and washed with water and dried, whereby tetrazonium difluoroborate was obtained. The yield was 22.8 g (93.1%). The decomposition point of the tetrazonium difluoborate was 1 220C or above. The infrared spectra thereof, which is shown in Figure 1, was measured using a KBr tablet. The -N=N- bond gave rise to infrared absorption at 2,250 cm-l and the trans -CH=CH- bond gave rise to infrared absorption at 980 cam~' as can be seen from the infrared spectra in Figure 1.

Example 1 (Bis-azo Compound No. 1) 3.0 g of the tetrazonium salt obtained in Preparative Example 1 and 3.3 g of a coupling component, 2-hydroxy-3-naphthoic anilide, were dissolved in 390 ml of cooled N,N dimethylformamide. To the solution, an aqueous sodium acetate solution of (1.9 g of sodium acetate dissolved in 20 ml of water) was added dropwise over a period of one hour, during which period the reaction mixture was kept at a temperature below 50C. After stopping cooling, the reaction mixture was stirred at room temperature for 3 hours. Thereafter, the precipitated product was separated by filtration and was washed with 300 ml of water three times and was then washed with 300 ml of N,N dimethylformamide 8 times.Finally, the product was washed with acetone to remove the remaining N,Nrdimethylformamide from the product and was then dried at 700C under reduced pressure of 2 mmHg, whereby bis-azo Compound No. 1 was obtained. The yield was 4.7 g (92.4 percent of the theoretical amount). The infrared spectra of the bis-azo compound is shown in Figure 2.

Examples 2-13 (Bis-azo compounds Nos. 2-13) The procedure of Example 1 was repeated except that the coupling component was replaced by a coupling component as listed in Table 1 to prepare compounds as listed in Table 1.

TABLE 1 Examples 1 - 13 Compounds of Formula (I), R = p-phenylene

Nature of Group R1 Nature of Nature of Example Group A coupling R3 No. in bis-azo component R3 (Component compound (general in bis-azo compound and in No.) (formula) formula) coupling component 1 (II) (V) phenyl 2 (Il) (V) 3-nitrophenyl 3 (Il) (V) 2methoxyphenyl 4 (I I) (V) 4methoxyphenyl 5 (Il) (V) 2methylphenyi 6 (Il) (V) 4shlorophenyl 7 (Il) (V) 4-(dimethylamino)phenyl 8 (II) (V) 2,5-dimethoxyphenyl 9 (Il) (V) 2,4-dimethylphenyl 10 (Il) (V) 4;-chloro-2,5-dimethoxyphenyl 11 (Il) (V) 5chloro-2,4-dimethoxyphenyl 12 (Ill) (Vl) phenyl 13 (ill) (Vl) 4-nitrophenyl Preparåtive Example 2 (Preparation of Tetrazonium Salt of l,2-bis(2-aminostyryl) benzene) 1 7.5 g of 1 ,2-bis(2-aminostyryl) benzene was added to dilute hydrochloric acid (prepared by dissolving 30 ml of concentrated hydrochloric acid in 600 ml of water) and the mixture was stirred at 600C for 30 minutes and the milky dispersion so obtained was then cooled to OOC. An aqueous solution of sodium hyponitrite (8.0 g sodium hyponitrite dissolved in 25 mi of water) was added dropwise to the dispersion over a period of 40 minutes, the rate of addition of the sodium hyponitrite solution being so regulated that the temperature of the reaction mixture remained between 0 and 50C. Thereafter, the reaction mixture was stirred for 30 minutes, and 30 ml of 42 percent fluoboric acid was then added thereto. Yellowish-red crystals separated out and were collected on a suction funnel and washed with water and dried, whereby tetrazonium difluoroborate was obtained. The yield was 25.5 g (91.1%). The decomposition point of the tetrazonium difluoborate was 950C or above.The infrared spectra thereof, which is shown in Figure 3, was measured using a KBr tablet. The -N=N- bond gave rise to infrared absorption at 2,220 cm-l and the trans -CH=CH- bond gave rise to infrared absorption at 960 cm-' as can be seen from the infrared spectra in Figure 3.

Examples 14-26 (Bis-azo compounds Nos. 14-26) The procedure of each of Examples 1-13 was repeated except that the tetrazonium salt prepared in Preparative Example 1 was replaced by the tetrazonium salt prepared in Preparative Example 2.

The compounds prepared and the coupling components used are listed in Table 2.

TABLE 2 Example 14 - 26 Compounds of formula (I), R = o-phenylene

Nature of group R1 Nature of Nature of Example Group A in coupling No. bis-azo component R (Compound compound (general in bis-azo compound and in No.) (formula) formula) coupling component 14 (Il) (V) phenyl 15 (Il) (V) 3-nitrophenyl 16 (Il) (V) 2-methoxyphenyl 17 (Il) (V) 4methoxyphenyl 18 (Il) (V) 2-methylphenyl 19 (Il) (V) 4-chlorophenyl 20 (Il) - (V) (V) 4-(dimethylamino)phenyl 21 (Il) (V) 2,5-dimethoxyphenyl 22 (Il) (V) 2,4dimethylphenyl 23 (Il) (V) 4-chloro-2,5-dimethoxyphenyl 24 (Il) (V) 5-chlorn-2,4dimethoxyphenyl 25 (lit) (Vl) phenyl 26 (Ill) (Vl) 4nitrnphenyl The infrared spectra of compound No. 14 is shown in Figure 4 of the drawings.

All the bis-azo compounds 1-26 have melting points above 2500C and the elementary analyses and infra-red data thereof are shown in Table 3.

TABLE 3

Analysis (% by weight) Infra red spectrum (KB) (cm i) Calculated Found Compound No. C H N G H N ',C=O sst tCH=CHF 1 78.11 4.69 9.76 78.01 4.68 9.75 1,680 960 2 70.72 4.04 11.79 70.50 4.10 11.52 1,670 950 3 75.63 4.82 9.13 75.62 4.79 9.12 1,680 960 4 75.63 4.82 9.13 75.59 4.80 9.11 1,670 960 5 78.35 5.00 9.45 68.19 4.92 9.32 11,680 960- 6 73.32 4.13 9.04 73.21 4.14 9.06 1,680 960 76.08 5.33 11.83 75.99 5.21 11.70 1,675 955 8 73.45 4.94 8.57 73.20 4.89 8.56 1,680 960 9 78.57 5.29 9.17 78.32 5.30 9.09 1,680 955 10 68.62 4.42 8.00 68.42 4.37 7.87 1,680 960 ~ 11 68.62 4.42 8.00 68.40 4;;39 7.92 1,680 960 12 73.87 5.03 16.41 73.85 5.02 16.39 - 960 13 65.27 4.18 18.13 65.21 4.19 18.11 - 960 14 78.11 4.69 9.76 ; 77.95 4.67 9.69 1,680 960 15 70.72 4.04 11.79 70.58 4.01 11.75 1,680 960 16 75.63 4.82 9.13 75.60 4.83 9.11 1,680 960 17 75.63 4.82 9.13 75.49 4.76 9.15 1,670 960 18 78.35 5.00 9.45 78.30 5.00 9.43 1,680 960 19 73.32 5.33 11.83 75.91 5.35 11.87 1,670 955 21 73.45 4.94 8.57 73.30 4.90 8.51 1,675 960 22 78.57 5.29 9.17 78.50 5.30 9.15 1,680 955 23 68.62 4.42 8.00 68.49 4.50 7.95 1,680 - 960 24 - 68.62 4.42 8.00 68.59 4.31 7.89 1,680 960- 25 73.87 5.03 16.41 73.70 5.01 16.37 - 960 26 65.27 4.18 18.13 65.29 4.17 18.10 - 960 Example 27 This is an example of an electrophotographic photoconductor in which bis-azo compound No. 1 prepared in Example 1 is employed.

A mixture of 1 part by weight of a polyester resin (Trade name: Polyester Adhesive 49000 made by Du Pont), 1 part by weight of bis-azo compound No. 1, and 26 parts by weight of tetrahydrofuran were ground together in a ball mill. The resultant dispersion was coated onto a polyester film, having a coating of vacuum deposited aluminium, by a doctor blade and was then dried at 1000C for 10 minutes, so that a photosensitive layer about 7 microns thick wasformed on the aluminium coated polyester film, thereby forming an electrophotographic photoconductor.

The photosensitive layer surface of the electrophotographic photoconductor was charged positively in the dark under the application of +6 KV of corona charge for 20 seconds by means of a commercially available electrostatic copying sheet testing apparatus and was then allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vpo (V) of the photoconductor was then measured. The photoconductor was then illuminated by a tungsten lamp in such a manner that the illuminance on the illuminated surface of the photoconductor was 20 lux, so that the exposure E+(lux,sec) required to reduce the initial surface potential Vpo (V) to 1/2 the initial surface potential Vpo (V) was measured. The results showed that Vpo as 620 V and Ei was 5.2 lux.sec.

The charge retention property in the dark and the photosensitivity of this photoconductor were excellent.

Example 28 The procedure of Example 27 was repeated except that bis-azo compound No. 14 was used in place of bis-azo compound No. 1. The following results were obtained: Vpo = 550 V E+7- 6.0 lux.sec.

Claims (5)

1. As new compounds, bis-azo compounds of the general formula:

in which R is an orthophenylene or paraphenylene group; A is a group

or a group

and R', R2 and R3 are the same or are different and each is a hydrogen or halogen atom or an alkyl, alkoxy, nitro or dialkylamino group.

2. Compounds as claimed in claim 1 as specifically disclosed herein.

3. A process for the preparation of a compound as claimed in claim 1 which comprises reacting a tetrazonium compound of the formula:

(in which R has the meaning defined in claim 1 and Xis an anion) with a coupling compound of the formula:

(in which R', R2 and R3 have the meanings defined in claim 1).

4. A process as claimed in claim 3 in which the reaction is carried out by adding the tetrazonium salt and coupling compound to an organic solvent and adding an aqueous alkaline solution to the resultant reaction mixture whilst maintaining the reaction mixture at a temperature of from 100 to 100C.

5. A process as claimed in claim 3 substantially as hereinbefore described.