Bis-dithiobenzilnickel complexes for use in near-infrared absorbing materials and benzoin derivatives as intermediates therefor

Abstract: A benzoin compound is synthesized from phenylglyoxal and a substituted benzene, and the resulting benzoin compound is converted to a bis-thiobenzilnickel complex using phosphorus pentasulfide/nickel chloride. The resulting bis-thiobenzilnickel complex of Formula [1] and/or [2]: (wherein R₁ to R₅ are the same or different, and denote substituted or unsubstituted alkyl, cycloalkyl, alkoxy, aryl, aryloxy, halogen atom, or hydrogen atom, except for substituted or unsubstituted amino group and alkoxyalkoxy group. However, a case where all of R₁ to R₅ are hydrogen atoms is excepted.) contains two phenyl groups and two substituted phenyl groups and is useful as a near-infrared absorbing material in, for example, optical recording materials and molding compositions containing transparent resins.

Description: This invention relates to optical recording materials of which the recording layer comprises bis-dithiobenzilnickel complexes. Bis-dithiobenzilnickel complexes such as bis-dithiobenzilnickel, bis-(4-dimethylamino)-dithiobenzilnickel, and bis-(4-diethylamino)-dithiobenzilnickel have strong absorption in the near-infrared region of 700-1,300 nm, and thus are known to be used as near-infrared absorbing materials or organic materials for optical disks, as reported, for example, in Senryo To Yakuhin (Dyes and Chemicals), 35 5 (1990) [4-25], Japanese Patent Laid-open Publication 63-227597, and Japanese Patent Laid-open Publication 64-61432. EP-A-0 192 215 discloses a class of tetraphenyl dithiol complexes of Ni, Pd and Pt which are used in optical recording materials. EP-A-0 316 926 describes the use of dithiolene nickel (II) complexes in dye-donor elements for thermal dye transfer. An optical recording medium comprising a near-infrared absorbing material and a thermal recording material is disclosed in Japanese Patent Laid-open Publication 2-120082. However, these complexes show dark green colors. Since optical recording materials based on paper using these complexes are required to have high brightness, complexes of paler color have been in demand. Furthermore, since the maximum absorptions of these complexes differ between the solid state and solution, especially when coated on paper, the maximum absorptions are shifted from those of the solution. Therefore, when these complexes are applied to an optical recording material using a semiconductor laser (wavelength: 830 nm), it is necessary to use one which has a maximum absorption in the vicinity of 830 nm in the solid state. However, the known bis-dithiobenzilnickel complexes do not have suitable maximum absorptions near 830 nm, for example, bis-dithiobenzilnickel has its maximum absorption in 850-870 nm, bis-(4-dimethylamino)-dithiobenzilnickel has a maximum absorption in 1,060-1,070 nm, and bis-(4-diethylamino)-dithiobenzilnickel has a maximum absorption in 1,100-1,120 nm. The present invention provides an optical recording material which comprises, disposed on a substrate, a recording layer comprising a colour developer, a colour former which will react with the developer to develop a colour and which is selected from metal salts of organic acids, metal salts of inorganic acids and leuco dyes, and a bis-dithiobenzilnickel complex selected from: Bis-(4-ethyldithiobenzil)-nickel [22]; Bis-(4-n-propyldithiobenzil)-nickel [23]; Bis-(4-n-butyldithiobenzil)-nickel [25]; Bis-(2,5-dimethyldithiobenzil)-nickel [32]; Bis-(4-phenyldithiobenzil)-nickel [39]; and Bis-(4-phenoxydithiobenzil)-nickel [40]. In one aspect of the invention, the recording layer further comprises a sensitiser. The invention further provides a near-infrared absorbing resin pellet which comprises a transparent resin matrix and a compound which is a bis-dithiobenzilnickel complex of the following formula [1] or [2]: wherein R 1 to R 5 , which may be the same or different, each represent a substituted or unsubstituted alkyl, cycloalkyl, alkoxy, aryl or aryloxy group, or a halogen or hydrogen atom, provided that R 1 to R 5 are not all hydrogen, and that R 1 to R 5 do not represent an alkoxyalkoxy group. The resin pellet may comprise one complex of formula [1] or [2], or a mixture thereof. The bis-dithiobenzilnickel complexes of formula [1] and/or [2] include, for example Bis-(4-methyldithiobenzil)-nickel [21] Bis-(4-ethyldithiobenzil)-nickel [22] Bis-(4-n-propyldithiobenzil)-nickel [23] Bis-(4-iso-propyldithiobenzil)-nickel [24] Bis-(4-n-butyldithiobenzil)-nickel [25] Bis-(4-sec-butyldithiobenzil)-nickel [26] Bis-(4-tert-butyldithiobenzil)-nickel [27] Bis-(4-n-amyldithiobenzil)-nickel [28] Bis-(4-n-hexyldithiobenzil)-nickel [29] Bis-(4-n-heptyldithiobenzil)-nickel [30] Bis-(4-n-octyldithiobenzil)-nickel [31] Bis-(2,5-dimethyldithiobenzil)-nickel [32] Bis-(3,5-dimethyldithiobenzil)-nickel [33] Bis-(3,4-dimethyldithiobenzil)-nickel [34] Bis-(2,4,6-trimethyldithiobenzil)-nickel [35] Bis-(2,3,4,5-tetramethyldithiobenzil)-nickel [36] Bis-(4-methoxydithiobenzil)-nickel [37] Bis-(2,5-dimethoxydithiobenzil)-nickel [38] Bis-(4-phenyldithiobenzil)-nickel [39] Bis-(4-phenoxydithiobenzil)-nickel [40] Bis-(4-cyclohexyldithiobenzil)-nickel [41] Bis-(4-chlorodithiobenzil)-nickel [42] The bis-dithiobenzilnickel complexes can be synthesized by a method of G. N. Schrauzer, et al. in which the corresponding benzoin derivative is treated with phosphorus pentasulfide/nickel chloride [JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 87, (1965), 1483-1489]. Specifically, the benzoin derivative is dissolved in 1,4-dioxane, phosphorus pentasulfide is added, and reacted under reflux. The reaction mixture is filtered, aqueous nickel chloride solution is added to the filtrate, and refluxed again. The resulting precipitate is filtered and purified to yield bis-dithiobenzilnickel complex of Formula [1] and/or [2]. Since the substituent groups of the bis-dithiobenzilnickel complex are derived from that of benzoin derivative, the synthesis of benzoin derivative is important in the synthesis of the complex. The most general method of obtaining the benzoin derivative is the reaction called "benzoin condensation." For example, Japanese Patent Laid-open Publication 63-227597, Japanese Patent Laid-open Publication 3-148290, and the like describe examples in which a benzoin derivative is synthesized by the use of the benzoin condensation, and then a bis-dithiobenzilnickel complex is synthesized. The benzoin condensation is a method in which two molecules of benzaldehyde derivative are reacted in the presence of cyan ions. Therefore, this method is normally suitable for symmetrically introducing substituent groups into both aromatic rings of benzoin. 2X-Ph-CHO → X-Ph-C(=O)-CH(OH)-Ph-X However, the corresponding benzoin derivative for synthesizing the bis-dithiobenzilnickel complex of Formula [1] and/or [2] must have Substituent groups in only one of the two aromatic rings. Such a benzoin derivative is possible to be synthesized by using two types of benzaldehyde derivatives (benzaldehyde and a substituted benzaldehyde). However, in this method, a reaction between the same type of benzaldehyde derivative inevitably takes place, and thus has a problem in view of yield. In the present invention, the benzoin derivative is synthesized by a method using phenylglyoxal, in view of simplicity and yield of the reaction. Benzoin derivatives which are useful as intermediate in the syntheses of the bis-dithiobenzilnickel complexes of Formula [1] and/or [2] include the following compounds [3] to [20]: 4'-Ethylbenzoin [3] 4'-n-Propylbenzoin [4] 4'-iso-Propylbenzoin [5] 4'-n-Butylbenzoin [6] 4'-sec-Butylbenzoin [7] 4'-tert-Butylbenzoin [8] 4'-n-Amylbenzoin [9] 4'-n-Hexylbenzoin [10] 4'-n-Heptylbenzoin [11] 4'-n-Octylbenzoin [12] 2',5'-Dimethylbenzoin [13] 3',5'-Dimethylbenzoin [14] 3',4'-Dimethylbenzoin [15] 2',3',4',5'-Tetramethylbenzoin [16] 2',5'-Dimethoxybenzoin [17] 4'-Phenylbenzoin [18] 4'-Phenoxybenzoin [19] 4'-Cyclohexylbenzoin [20] The compounds [3] to [20] can be synthesized by a method in which phenylglyoxal and a substituted benzene derivative are reacted in the presence of a Lewis acid. Specifically, phenylglyoxal and the substituted benzene derivative are dissolved in a halogenated hydrocarbon solvent such as dichloromethane or dichloroethane, a Lewis acid such as boron trifluoride etherate or titanium tetrachloride is added, and reacted at room temperature. The reaction mixture is extracted with ethylacetate, the extract is neutralized, washed, dried, and then evaporated. Then, the reaction product is recrystallized to yield the compounds [3] to [20]. The bis-dithiobenzilnickel complex of formula [1] and or [2] was dissolved in a solvent, the solution was coated on paper, and the coated paper was measured for near-infrared absorption spectrum. The complex was found to have a strong absorption in the near-infrared region, and the maximum absorption was 810 to 900 nm. Bis-dithiobenzilnickel complexes are also known to have superior characteristics as quenchers of singlet oxygen, and are used as photo-discoloration prevention agents for cyanine dyes. The complex used in the present invention is a near-infrared absorbing agent in itself, but may be combined with cyanine dyes or the like to obtain a near-infrared absorbing material. That near-infrared absorbing material comprising the complex is then used in the optical recording material or the near-infrared absorbing resin pellet of the present invention. The optical recording material of the invention thus comprises, on a substrate, a recording layer comprising: a bis-dithiobenzilnickel complex [22] , [23] , [25] , [32] , [39] or [40] as specified above, optionally present in a near-infrared absorbing material as specified above, together with a color developer and a color former which will react with the color developer to develop a color and which is selected from metal salts of organic acids, metal salts of inorganic acids and leuco dyes. The color developer and the color former used here can be conventional compounds known in the field of pressure sensitive and thermal recording paper. The substrate used here can be paper, synthetic paper, laminated paper, non-woven fabrics, plastic sheets, pigment-filled plastic films, filler-coated plastic films, metal foils, or combinations thereof. A bis-dithiobenzilnickel complex [22] , [23] , [25], [32], [39] and/or [40] as named above was mixed with a sensitizer, and coated with a thermal color developing material on paper to obtain an optical recording material. When the recording material was irradiated with a laser light, it was found to provide a print of a high image density and a sufficient contrast. Furthermore, the complexes provided improved brightness over conventional bis-dithiobenzilnickel complexes. The near-infrared absorbing resin pellet of the present invention preferably comprises a bis-dithiobenzilnickel complex [22] , [23] , [25] , [32] , [39] or [40] as defined above. The pellet may be moulded into a near-infrared absorbing resin moulded article. The near infrared absorbing resin pellet may be prepared by kneading a bis-dithobenzilnickel complex of formula [1] and/or [2] as defined above, and a transparent resin pellet, by an extruder. The pellet may then be molded by a molding machine to form a near-infrared absorbing resin moulded article. The transparent resin used here can be a substantially transparent resin with reduced absorption and scattering of visible light. Suitable resins include acrylic resins such as those of methacrylic esters, polystyrene, polyvinylchloride, polycarbonate, olefin resins, epoxy resins, and the like. Since the bis dithiobenzilnickel complex used in the present invention is higher in decomposition temperature than near-infrared absorbing dyes used in the prior art, it can be contained in resins which require higher temperatures for molding such as polycarbonate. The resins are used not only alone but also can be used as mixtures of two or more types. In a further aspect, the present invention provides a near-infrared process for producing a near-infrared absorbing resin molding, which process comprises dissolving, in a transparent resin monomer, a compound which is a bis-dithiobenzilnickel complex of formula [1] or [2] as defined above, or a mixture of the said compounds or a near-infrared absorbing material comprising the said compound or compounds; and polymerising the resulting mixture. For example, the bis-dithiobenzilnickel complex of formula [1] and/or [2] may be dissolved in a methylmethyacrylate monomer, and pre-polymerized using a polymerization initiator such as 2,2'-azobis-(isobutyronitrile), 2,2'-azobis-(2,4-dimethylvaleronitrile), or benzoylperoxide. The prepolymer is then poured into a mold for substantial polymerization to prepare the near-infrared absorbing resin molding. The resulting resin molding has a characteristic absorption in the wavelength region 800-950 nm. The molding is useful for near-infrared cutting filters, semiconductor light receiving element filters, protective glasses for semiconductor lasers, and the like. Furthermore, the molding can also be applied to heat rays absorbing glazing materials and green house materials. The complex of formula [1] or [2] can also be contained in hard coating agents and ultraviolet curing resins. The bis-dithiobenzilnickel complex of Formula [1] and/or [2] was dissolved in a hard coating agent, and the solution was applied to the surface of a substrate by coating or dipping, and heat cured to obtain a near-infrared absorbing material. Here, the hard coating agent is a sol obtained by dissolving polysiloxane, which is a hydrolyzed product or partial condensation product of mainly a three-functional or four-functional organoalkoxysilane monomer by and acid or base, in a solvent such as alcohols, benzene, toluene, acetone, methylethylketone, methylcellosolve, or the like, and mixing with a hardener and various additives. The substrate to which the hard coating agent is applied includes paper, tissue paper, synthetic paper, fibers, soft metals, natural or synthetic resins, or the like, in the form of films, sheets, boards, textiles, or any other specific shapes. The bis-dithiobenzilnickel complex of Formula [1] and/or [2] was dissolved in an ultraviolet curing resin such as (meth)acrylic resins or (meth)alkoxysilane, filled in a space provided between two transparent glass plates, irradiated with ultraviolet rays through transparent glass to cure the ultraviolet curing resin, obtaining a near-infrared absorbing glass composite. In the accompanying drawings: Fig.1 is transmission spectra of a near-infrared absorbing resin molding obtained in Example 2 and in Example 3. Reference Example 1 (4'-Ethylbenzoin [3]) Phenylglyoxal monohydrate (304 mg, 2mM) and ethylbenzene (0.49ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 2 hours. The reaction mixture was extracted with ethylacetate, the extract was washed with saturated sodium hydrogen carbonate solution and brine, dried with sodium sulfate anhydrous, and then concentrated to obtain a yellow-colored oil. The oil was crystallized from a petroleum ether/diethylether to obtain 357.1 mg (74.0% yield) of 4'-ethylbenzoin. The product (benzoin compound) was identified by 1 H-NMR. Basically, the production was confirmed by checking the peaks of the functional groups derived from phenylglyoxal and that from the substituted benzene, and the peak of α-hydrogen of the produced α-hydroxyketone (in the vicinity of δ = 5.90). For 4'-ethylbenzoin, since peaks resulting from the aromatic ring of phenylglyoxal are noted at δ = 7.39, 7.91), peaks from the aromatic ring of ethylbenzene at δ = 7.12, 7.24, peaks from ethyl of ethylbenzene at δ = 1.18, 2.58, and a peak from α-hydrogen of the α-hydroxyketone at δ = 5.93, 4'-ethylbenzoin is identified. Also by IR spectrum, a peak of hydroxyl group of α-hydroxyketone is noted at 3417 cm -1 , and a peak of ketone is noted at 1676 cm -1 , indicating the structure of 4'-ethylbenzoin. Melting point: 120-121°C. NMR (CDCl 3 , δ): 1.18 (3H, t, J=7.5), 2.58 (2H, m), 4.50 (1H, broad d, J=3.0), 5.93 (lH, d, J=3.0), 7.12 (2H, d, J=7.5), 7.24 (2H, d, J=7.5), 7.39 (2H, tt, J=7.5, 1.5), 7.39 (1H, tt, J=7.5, 1.5), 7.91 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3417, 1676. Reference Example 2 (4'-n-Propylbenzoin [4]) Phenylglyoxal monohydrate (304 mg, 2mM) and n-propylbenzene (0.56ml, 4mM) were dissolved in dichloroethane (6ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 2 hours. Using the same procedure as in Reference Example 1, 4'-n-propylbenzoin was obtained as crystal (369.9 mg, 71.9% yield). Melting point: 111-112°C. NMR (CDCl 3 , δ): 4.52 (1H, d, J=5.0), 5.93 (1H, d, J=5.0), 7.12 (2H, d, J=7.5), 7.23 (2H, d, J=7.5), 7.37 (2H, tt, J=7.5, 1.5), 7.50 (1H, tt, J=7.5, 1.5), 7.91 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3416, 1675. Reference Example 3 (4'-iso-Propylbenzoin [5]) Phenylglyoxal monohydrate (304mg, 2mM) and cumene (0.56ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 4 hours. Using the same procedure as in Reference Example 1, 4'-iso-propylbenzoin was obtained as crystal (300.6 mg, 59.6% yield). Melting point: 116-117°C. NMR (CDCl 3 , δ): 1.18 (3H, s), 1.20 (3H, s), 2.80 (1H, m), 5.93 (1H, s), 7.17 (2H, d, J=8.5), 7.25 (2H, d, J=8.5), 7.40 (2H, tt, J=7.0, 1.5), 7.52 (1H, tt, J=7.0, 1.5), 7.93 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3415, 1678. Reference Example 4 (4'-n-Butylbenzoin [6]) Phenylglyoxal monohydrate (304mg, 2mM) and n-butylbenzene (0.62ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 1 hour. Using the same procedure as in Reference Example 1, 4'-n-butylbenzoin was obtained as crystal (362.7 mg, 67.2% yield). Melting point: 75-77°C. NMR (CDCl 3 , δ): 0.86-0.94 (3H, m), 1.22-1.38 (2H, m), 1.48-1.62 (2H, m), 2.52-2.64 (2H, m), 5.92 (1H, s), 7.13 (2H, d, J=8.0), 7.23 (2H, d, J=8.0), 7.39 (2H, tt, J=7.0, 1.5), 7.52 (1H, tt, J=7.0, 1.5), 7.92 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3419, 1677. Reference Example 5 (4'-sec-Butylbenzoin [7]) Phenylglyoxal monohydrate (304mg, 2mM) and sec-butylbenzene (0.62ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 2.5 hours. Using the same procedure as in Reference Example 1, 4'-sec-butylbenzoin was obtained as crystal (200.6 mg, 37.3% yield). Melting point: 77-78°C. NMR (CDCl 3 , δ): 0.76 (3H, t, J=7.5), 1.17 (3H, m), 1.53 (1H, m), 2.54 (1H, m), 5.93 (1H, s), 7.13 (2H, d, J=8.0), 7.24 (2H, d, J=8.0), 7.40 (2H, tt, J=7.0, 1.5), 7.52 (1H, tt, J=7.0, 1.5), 7.93 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3416, 1676. Reference Example 6 (4'-tert-Butylbenzoin [8]) Phenylglyoxal monohydrate (304mg, 2mM) and tert-butylbenzene (0.62ml, 4mM) were dissolved in dichloroethane (2ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 2.5 hours. Using the same procedure as in Reference Example 1, 4'-tert-butylbenzoin was obtained as crystal (216.9 mg, 40.5% yield). Melting point: 114-115°C. NMR (CDCl 3 , δ): 1.26 (9H, s), 5.94 (1H, s), 7.25 (2H, s), 7.25 (2H, dt, J=7.5, 1.5), 7.34 (2H, dt, J=7.5, 1.5), 7.40 (2H, tt, J=7.5, 1.5), 7.52 (1H, tt, J=7.5, 1.5), 7.94 (2H, dt, J=7.5, 1.5). IR (ν, cm- 1 ): 3413, 1676. Reference Example 7 (4'-n-Amylbenzoin [9]) Phenylglyoxal monohydrate (304mg, 2mM) and n-amylbenzene (0.69ml, 4mM) were dissolved in dichloroethane (3ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 2 hours. Using the same procedure as in Reference Example 1, 297.1 mg (52.6% yield) of 4'-n-amylbenzoin was obtained as crystal (297.1 mg, 52.6% yield). Melting point: 83-84°C. NMR (CDCl 3 , δ): 0.88 (3H, t, J=6.5), 1.20-1.35 (4H, m), 1.48-1.62 (2H, m), 2.53 (2H, dd, J=8.0, 7.5), 5.92 (1H, s), 7.13 (2H, d, J=8.0), 7.23 (2H, d, J=8.0), 7.38 (2H, tt, J=7.5, 1.5), 7.51 (1H, tt, J=7.5, 1.5), 7.92 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3417, 1676. Reference Example 8 (4'-n-Hexylbenzoin [10]) Phenylglyoxal monohydrate (304mg, 2mM) and n-hexylbenzene (0.76ml, 4mM) were dissolved in dichloroethane (3ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 1 hour. Using the same procedure as in Reference Example 1, 4'-n-hexylbenzoin was obtained as crystal (352.8 mg, 59.4% yield). Melting point: 87-88°C. NMR (CDCl 3 , δ): 0.85 (3H, t, J=7.0), 1.20-1.32 (6H, m), 1.48-1.64 (2H, m), 2.53 (2H, t, J=7.5), 4.50 (1H, d, J=5.0), 5.92 (1H, d, J=5.0), 7.12 (2H, d, J=8.0), 7.23 (2H, d, J=8.0), 7.40 (2H, tt, J=7.5, 1.5), 7.52 (1H, tt, J=7.5, 1.5), 7.92 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3414, 1678. Reference Example 9 (4'-n-Heptylbenzoin [11]) Phenylglyoxal monohydrate (304mg, 2mM) and n-heptylbenzene (0.82ml, 4mM) were dissolved in dichloroethane (3ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 1 hour. Using the same procedure as in Reference Example 1, 4'-n-heptylbenzoin was obtained as crystal (386.7 mg, 61.5% yield). Melting point: 82-83°C. NMR (CDCl 3 , δ): 0.86 (3H, t, J=7.0), 1.18-1.32 (8H, m), 1.48-1.60 (2H, m), 2.54 (2H, dd, J=8.0, 7.5), 5.92 (1H, s), 7.13 (2H, d, J=8.0), 7.23 (2H, d, J=8.0), 7.39 (2H, tt, J=7.5, 1.5), 7.52 (1H, tt, J=7.5, 1.5), 7.92 (2H, dt, J=7.5). IR (ν, cm -1 ): 3416, 1677. Reference Example 10 (4'-n-Octylbenzoin [12]) Phenylglyoxal monohydrate (608mg, 4mM) and n-octylbenzene (1.77ml, 8mM) were dissolved in dichloroethane (8ml), titanium tetrachloride (0.66ml, 6mM) was added, and reacted at room temperature for 30 minutes. Using the same procedure as in Reference Example 1, 4'-n-octylbenzoin was obtained as crystal (810.0 mg, 62.6% yield). Melting point: 88-89°C. NMR (CDCl 3 , δ): 0.86 (3H, t, J=7.5), 1.20-1.32 (10H, m), 1.48-1.60 (2H, m), 2.54 (2H, dd, J=8.0, 7.5), 5.92 (1H, s), 7.12 (2H, d, J=8.0), 7.23 (2H, d, J=8.0), 7.38 (2H, tt, J=7.5, 1.5), 7.52 (1H, tt, J=7.5, 1.5), 7.92 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3414, 1679. Reference Example 11 (2',5'-Dimethylbenzoin [13]) Phenylglyoxal monohydrate (500mg, 3.29mM) and p-xylene (0.59ml, 4.79mM) were dissolved in dichloroethane (5ml), titanium tetrachloride (0.9ml, 8.2mM) was added, and reacted at room temperature for 30 minutes. Using the same procedure as in Reference Example 1, 2',5'-dimethylbenzoin was obtained as crystal (584.7 mg, 73.9% yield). Melting point: 91-93°C. NMR (CDCl 3 , δ): 2.18 (3H, s), 2.49 (3H, s), 4.54 (1H, broad s), 6.01 (1H, s), 6.82 (1H, broad s), 6.98 (1H, broad d, J=8.0), 7.09 (1H, d, J=8.0), 7.36 (2H, tt, J=7.5, 1.5), 7.49 (1H, tt, J=7.5, 1.5), 7.81 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3472, 1671. Reference Example 12 (3',5'-Dimethylbenzoin [14]) Phenylglyoxal monohydrate (304mg, 2mM) and m-xylene (0.49ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 30 minutes. Using the same procedure as in Reference Example 1, 3',5'-dimethylbenzoin was obtained as a light-yellow oil (363.2 mg, 75.3% yield). NMR (CDCl 3 , δ): 2.25 (3H, s), 2.50 (3H, s), 4.34 (1H, s), 6.01 (1H, s), 6.90 (2H, s), 7.02 (1H, s), 7.36 (2H, tt, J=7.5, 1.5), 7.49 (1H, tt, J=7.0, 1.5), 7.82 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3456, 1682. Reference Example 13 (3',4'-Dimethylbenzoin [15]) Phenylglyoxal monohydrate (304mg, 2mM) and o-xylene (0.49ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 20 minutes. Using the same procedure as in Reference Example 1, 3',4'-dimethylbenzoin was obtained as crystal (258.7 mg, 54.0% yield). Melting point: 127-129°C. NMR (CDCl 3 , δ): 2.19 (3H, s), 2.20 (3H, s), 4.47 (1H, d, J=6.2), 5.89 (1H, d, J=6.2), 7.08-7.09 (3H, m), 7.39 (2H, tt, J=7.0, 1.5), 7.51 (1H, tt, J=7.0, 1.5), 7.93 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3456, 1673. Reference Example 14 (2',3',4',5'-Tetramethylbenzoin [16]) Phenylglyoxal monohydrate (304mg, 2mM) and 1,2,3,4-tetramethylbenzene (0.60ml, 4mM) were dissolved in dichloroethane (5ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 10 minutes. Using the same procedure as Reference Example 1, 2',3',4',5'-tetramethylbenzoin was obtained (378.2 mg, 70.7% yield). Melting point: 99-101°C. NMR (CDCl 3 , δ): 2.12 (3H, s), 2.13 (3H, s), 2.22 (3H, s), 2.44 (3H, s), 4.31 (1H, broad s), 6.07 (1H, s), 6.64 (1H, s), 7.35 (2H, tt, J=7.0, 1.5), 7.48 (1H, tt, J=7.0, 1.5), 7.83 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3468, 1665. Reference Example 15 (2',5'-Dimethoxybenzoin [17]) Phenylglyoxal monohydrate (152mg, 1mM) and p-dimethoxybenzene (0.21ml, 1.5mM) were dissolved in dichloroethane (2ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 4 hours. Using the same procedure as in Reference Example 1, 2',5'-dimethoxylbenzoin was obtained as an oil (219.4 mg, 79.2% yield). NMR (CDCl 3 , δ): 3.69 (3H, s), 3.82 (3H, s), 4.53 (1H, broad s), 6.23 (1H, s), 6.77 (1H, d, J=8.5), 6.82 (1H, d, J=8.5), 7.36 (2H, tt, J=7.5, 1.5), 7.50 (1H, tt, J=7.5, 1.5), 7.94 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3456, 1683. Reference Example 16 (4'-Phenylbenzoin [18]) Phenylglyoxal monohydrate (200mg, 1.31mM) and diphenyl (405mg, 2.62mM) were dissolved in dichloroethane (5ml), titanium tetrachloride (0.15ml, 1.31mM) was added, and reacted at room temperature for 20 minutes. Using the same procedure as in Reference Example 1, 4'-phenylbenzoin was obtained as crystal (136.0 mg, 35.5% yield). Melting point: 150-151°C. NMR (CDCl 3 , δ): 6.01 (1H, s), 7.33 (2H, tt, J=7.0, 1.5), 7.38-7.46 (5H, m), 7.51-7.57 (5H, s), 7.96 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3426, 1679. Reference Example 17 (4'-Phenoxybenzoin [19]) Phenylglyoxal monohydrate (200mg, 1.31mM) and diphenylether (0.4ml, 2.62mM) were dissolved in dichloroethane (3ml), titanium tetrachloride (0.07ml, 0.66mM) was added, and reacted at room temperature for 1 hour. Using the same procedure as in Reference Example 1, 4'-phenoxybenzoin was obtained as crystal (331.2 mg, 80.7% yield). Melting point: 100-102°C. NMR (CDCl 3 , δ): 5.94 (1H, s), 6.92 (2H, dd, J=7.5, 1.0), 6.97 (2H, dd, J=7.5, 1.0), 7.10 (1H, ddd, J=7.5, 6.5, 1.0), 7.27 (2H, t, J=6.5), 7.29 (2H, d, J=6.5), 7.31 (2H, tt, J=7.5, 1.5), 7.40 (1H, tt, J=7.0, 1.5), 7.92 (2H, dt, J=7.0, 1.5). IR (ν, cm -1 ): 3422, 1674. Reference Example 18 (4'-Cyclohexylbenzoin [20]) Phenylglyoxal monohydrate (304mg, 2mM) and phenylcyclohexyl (0.67ml, 4mM) were dissolved in dichloroethane (4ml), titanium tetrachloride (0.33ml, 3mM) was added, and reacted at room temperature for 1.5 hours. Using the same procedure as in Reference Example 1, 4'-cyclohexylbenzoin was obtained as crystal (441.8 mg, 75.2% yield). Melting point: 139-140°C. NMR (CDCl 3 , δ): 1.14-1.44 (5H, m), 1.66-1.68 (6H, m), 4.48 (1H, d, J=6.0), 5.93 (1H, d, J=6.0), 7.13 (2H, dd, J=7.0, 1.5), 7.24 (2H, dd, J=7.0, 1.5), 7.40 (2H, tt, J=7.5, 1.5), 7.52 (1H, tt, J=7.5, 1.5), 7.93 (2H, dt, J=7.5, 1.5). IR (ν, cm -1 ): 3414, 1677. Reference Examples 19-36 Each of the benzoin compounds (1 equivalent) synthesized in Reference Examples 1-18 was dissolved in 1,4-dioxane, phosphorus pentasulfide (3 equivalents) was added, and reacted for 2 hours under reflux. The reaction mixture was filtered, the filtrate was mixed with an aqueous solution of nickel chloride hexahydrate (0.5 equivalent), and refluxed further for 2 hours. The resulting reaction precipitate was filtered, which was extracted with methylene chloride and purified to give an objective bis-dithiobenzilnickel complex. Reference Examples 37-40 Using 4'-methylbenzoin, 2',4',6'-trimethylbenzoin, 4'-methoxybenzoin, and 4'-chlorobenzoin as materials, each was reacted by the same method as shown in Reference Examples 19-36 to give a corresponding bis-dithiobenzilnickel complex. The complexes obtained in Reference Examples 19-40 were identified by IR spectrum and X-ray microanalysis. Further, the resulting complex was dissolved in methylene chloride, dropped onto Whatman filter paper, dried, and measured for near-infrared absorption spectrum by means of the Nippon Bunko UNIDEC-590 Near-Infrared Recording Spectrophotometer. Bis-(4-methyldithiobenzil)-nickel [21] Yield: 12.2% IR (ν, cm -1 ): 1356, 1140, 884, 755, 695 X-ray microanalysis: S/Ni = 4.09 Maximum absorptions: 840-850 nm Bis-(4-ethyldithiobenzil)-nickel [22] Yield: 13.4% IR (ν, cm -1 ): 2950, 2864, 1358, 1140, 883, 755, 695 X-ray microanalysis: S/Ni = 4.38 Maximum absorptions: 825-835 nm Bis-(4-n-propyldithiobenzil)-nickel [23] Yield: 6.7% IR (ν, cm -1 ): 2954, 2859, 1357, 1140, 883, 754, 692 X-ray microanalysis: S/Ni = 4.39 Maximum absorptions: 825-835 nm Bis-(4-iso-propyldithiobenzil)-nickel [24] Yield: 11.4% IR (ν, cm -1 ): 2956, 2864, 1359, 1142, 884, 756, 693 X-ray microanalysis: S/Ni = 4.12 Maximum absorptions: 860-880 nm Bis-(4-n-butyldithiobenzil)-nickel [25] Yield: 28.5% IR (ν, cm -1 ): 2951, 2856, 1359, 1141, 884, 753, 694 X-ray microanalysis: S/Ni = 4.39 Maximum absorptions: 830-845 nm Bis-(4-sec-butyldithiobenzil)-nickel [26] Yield: 5.9% IR (ν, cm -1 ): 2958, 2864, 1358, 1140, 883, 754, 693 X-ray microanalysis: S/Ni = 4.39 Maximum absorptions: 870-880 nm Bis-(4-tert-butyldithiobenzil)-nickel [27] Yield: 5.1% IR (ν, cm -1 ): 2957, 2862, 1356, 1141, 884, 755, 693 X-ray microanalysis: S/Ni = 4.24 Maximum absorptions: 870-880 nm Bis-(4-n-amyldithiobenzil)-nickel [28] Yield: 13.8% IR (ν, cm -1 ): 2922, 2855, 1359, 1141, 884, 754, 694 X-ray microanalysis: S/Ni = 4.18 Maximum absorptions: 875-885 nm Bis-(4-n-hexyldithiobenzil)-nickel [29] Yield: 13.5% IR (ν, cm -1 ): 2920, 2851, 1358, 1140, 883, 752, 692 X-ray microanalysis: S/Ni = 4.09 Maximum absorptions: 875-885 nm Bis-(4-n-heptyldithiobenzil)-nickel [30] Yield: 12.1% IR (ν, cm -1 ): 2921, 2852, 1360, 1142, 885, 753, 694 X-ray microanalysis: S/Ni = 4.35 Maximum absorptions: 870-880 nm Bis-(4-n-octyldithiobenzil)-nickel [31] Yield: 11.4% IR (ν, cm -1 ): 2922, 2851, 1359, 1141, 884, 751, 692 X-ray microanalysis: S/Ni = 4.27 Maximum absorptions: 850-860 nm Bis-(2,5-dimethyldithiobenzil)-nickel [32] Yield: 14.3% IR (ν, cm -1 ): 1363, 1147, 1114, 856, 754, 692 X-ray microanalysis: S/Ni = 4.06 Maximum absorptions: 825-835 nm Bis-(3,5-dimethyldithiobenzil)-nickel [33] Yield: 3.3% IR (ν, cm -1 ): 1357, 1142, 1029, 867, 757, 686 X-ray microanalysis: S/Ni = 4.03 Maximum absorptions: 850-860 nm Bis-(3,4-dimethyldithiobenzil)-nickel [34] Yield: 13.5% IR (ν, cm -1 ): 1343, 1140, 1021, 860, 751, 695 X-ray microanalysis: S/Ni = 4.07 Maximum absorptions: 880-890 nm Bis-(2,4,6-trimethyldithiobenzil)-nickel [35] Yield: 3.2% IR (ν, cm -1 ): 1345, 870, 754, 695 X-ray microanalysis: S/Ni = 4.16 Maximum absorptions: 870-880 nm Bis-(2,3,4,5-tetramethyldithiobenzil)-nickel [36] Yield: 11.2% IR (ν, cm -1 ): 2866, 1362, 1190, 880, 759, 694 X-ray microanalysis: S/Ni = 4.02 Maximum absorptions: 850-860 nm Bis-(4-methoxydithiobenzil)-nickel [37] Yield: 1.1% IR (ν, cm -1 ): 1360, 1220, 752, 693 X-ray microanalysis: S/Ni = 4.36 Maximum absorptions: 850-860 nm Bis-(2,5-dimethoxydithiobenzil)-nickel [38] Yield: 18.6% IR (ν, cm -1 ): 2929, 1361, 1221, 1113, 939, 760, 696 X-ray microanalysis: S/Ni = 4.26 Maximum absorptions: 870-880 nm Bis-(4-phenyldithiobenzil)-nickel [39] Yield: 5.7% IR (ν, cm -1 ): 1177, 1357, 1138, 879, 757, 693 X-ray microanalysis: S/Ni = 4.49 Maximum absorptions: 830-840 nm Bis-(4-phenoxydithiobenzil)-nickel [40] Yield: 22.1% IR (ν, cm -1 ): 1486, 1358, 1236, 1137, 868, 750, 692 X-ray microanalysis: S/Ni = 4.28 Maximum absorptions: 835-845 nm Bis-(4-cyclohexyldithiobenzil)-nickel [41] Yield: 17.6% IR (ν, cm -1 ): 2919, 2848, 1357, 1140, 885, 754, 693 X-ray microanalysis: S/Ni = 4.42 Maximum absorptions: 845-855 nm Bis-(4-chlorodithiobenzil)-nickel [42] Yield: 5.6% IR (ν, cm -1 ): 1357, 1140, 1093, 884, 755, 695 X-ray microanalysis: S/Ni = 3.96 Maximum absorptions: 865-875 nm Example 1 An electron donating colorless dye dispersion (solution A), an electron accepting acid dispersion (solution B), and a light absorbing sensitiser dispersion (solution C) containing bis-(4-ethyldithiobenzil)-nickel of the following compositions were individually wet milled by a sand grinder. Then, 7.3 parts of the solution A, 30 parts of the solution B, 20 parts of the solution C, 25 parts of 25% aqueous silica dispersion, and 10% aqueous PVA solution were mixed to obtain a coating color. The coating color was coated to a coverage of 5 g/m 2 on fine paper with a substance of 60 g/m 2 using a Meyer bar, and dried to give an optical recording material. Solution A: Electron donating colorless dye dispersion ODB 2.0 parts 10% Aqueous PVA solution 3.4 Water 1.9 * ODB: 3-diethylamino-6-methyl-7-anilinofluorane Solution B: Electron accepting acid dispersion Bisphenol A 6.0 parts 10% Aqueous PVA solution 15.0 Water 9.0 Solution C: Light absorbing sensitizer dispersion 49 Parts of p-benzylbiphenyl (PBB) was mixed with 1 part of bis-(4-ethyldithiobenzil)-nickel, and melted by heating to 100-150°C. The mixture was milled by a sand grinder to obtain a light absorbing sensitizer. Light absorbing sensitizer 4.0 parts 10% Aqueous PVA solution 10.0 Water 6.0 The thus prepared optical recording material was irradiated with laser light by a device comprising a semiconductor laser head combined with a focusing lens to obtain a print. The optical recording material was measured for reflectance by the Toyo Seiki TYPE-D Hunter Reflectometer, and showed a reflectance of 73.01%. [Comparative Example 1] Dithiobenzilnickel complexes, which are known in the prior art were individually dissolved in methylene chloride, dropped onto a Whatman filter paper, dried, and measured for near-infrared absorption spectrum as in the above Example 19-41. Bis-(dithiobenzil)-nickel Maximum absorptions: 850-890 nm Bis-4,4'-dimethyldithiobenzil)-nickel Maximum absorptions: 875-890 nm Bis-(4-dimethylaminodithiobenzil)-nickel Maximum absorptions: 1060-1070 nm Bis-(4-diethylaminodithiobenzil)-nickel Maximum absorptions: 1100-1120 nm [Comparative Example 2] Using bis-(dithiobenzil)-nickel, an optical recording material was prepared by the same method as used in Example 41. The optical recording material had a reflectance of 71.88%. Example 2 Bis-(4-ethyldithiobenzil)-nickel (0.05 parts) and polystyrene pellet (tradename: Estyrene (Nippon Steel Chemical) 99.95 parts) were mixed, and extruded by an extruder to produce a pellet containing bis-dithiobenzilnickel complex. The resulting pellet was molded by a molding machine to obtain a 2.0 mm thick resin plate. Example 3 Bis-(4-ethyldithiobenzil)-nickel (0.05 parts) and polycarbonate pellet (tradename: Toughlon (Idemitsu Petrochemical) 99.95 parts) were mixed, and extruded by an extruder to produce a pellet containing bis-dithiobenzilnickel complex. The resulting pellet was molded by a molding machine to obtain a 2.0 mm thick resin plate. Example 4 Bis-(4-ethyldithiobenzil)-nickel (0.02 parts) was dissolved in methylmethacrylate monomer (99.98 parts). This solution was mixed with 2,2'-azobis-isobutyronitrile (1 part) and treated at 70°C for 1 hour. The resulting syrup was poured into a mold comprising two glass plates by a conventional method known in the prior art, treated at 70°C for 3 hours, followed by treatment at 100°C for 1 hour, cooled, and released from the mold to obtain a 2.6 mm thick resin plate. Example 5 Bis-(4-n-propyldithiobenzil)-nickel (0.01 part) was dissolved in a silicone hard coating agent (tradename: Si-801A (Daihachi Kagaku) (200 parts)) to prepare a near-infrared absorbing hard coating composition. The composition was coated on a polyester film (tradename: AK Clear Film (Kimoto)) using a Meyer bar, air-dried, and heated in an oven at 150°C for 2 minutes to obtain a near-infrared absorbing film. Example 6 Bis-(4-ethyldithiobenzil)-nickel (0.01 part) was dissolved in an ultraviolet curing resin (tradename: UVEKOL-S20 (UCB) (200 parts)) to prepare a near-infrared absorbing intermediate layer solution for glass composite, the intermediate layer solution was injected between two glass plates incorporated in a 1.5 mm thick spacer, cured by irradiating with a 400-W mercury lamp to obtain a glass composite. The complexes used in the present invention, for example, bis-(4-ethyldithiobenzil)-nickel, bis-(4-n-propyldithiobenzil)-nickel, and bis-(3,5-dimethyldithiobenzil)-nickel have maximum absorptions in the vicinity of 830 nm in a paper-coated state, and are thus superior as sensing materials to the semiconductor laser (830 nm) over conventionally used materials. Furthermore, the complexes are also superior in brightness to materials used conventionally, and are thus very promising for use as near-infrared absorbents or near-infrared absorbing materials for optical recording materials. Furthermore, the complexes of the present invention are used in near-infrared absorbing resin moldings by containing in a transparent resin, near-infrared absorbing materials provided with a near-infrared absorbing hard coating layer by containing in a hard coating agent, or in near-infrared absorbing glass composites by containing in an ultraviolet curing resin. These near-infrared absorbing materials have characteristic absorptions in 800-950 nm, and can thus be applied, in addition to optical recording media, to near-infrared cutting filters, light receiving element filters, protective eyeglasses for semiconductor lasers, goggles, heat rays shielding eyeglasses, sunglasses, heat rays shielding films, agricultural films, green house materials, optical disks, and the like.

Claims: An optical recording material which comprises, disposed on a substrate, a recording layer comprising a colour developer, a colour former which will react with the developer to develop a colour and which is selected from metal salts of organic acids, metal salts of inorganic acids and leuco dyes, and a bis-dithiobenzilnickel complex selected from: Bis-(4-ethyldithiobenzil)-nickel; Bis-(4-n-propyldithiobenzil)-nickel; Bis-(4-n-butyldithiobenzil)-nickel; Bis-(2,5-dimethyldithiobenzil)-nickel; Bis-(4-phenyldithiobenzil)-nickel; and Bis-(4-phenoxydithiobenzil)-nickel. An optical recording material according to claim 1, wherein the recording layer further comprises a sensitizer. A near-infrared absorbing resin pellet which comprises a transparent resin matrix and a compound which is a bis-dithiobenzilnickel complex of the following formula (1) or formula (2): wherein R 1 to R 5 , which may be the same or different, each represent a substituted or unsubstituted alkyl, cycloalkyl, alkoxy, aryl or aryloxy group, or a halogen or hydrogen atom, provided that not all of R 1 to R 5 are hydrogen and that R 1 to R 5 do not represent an alkoxyalkoxy group; or a mixture of such compounds. A near-infrared absorbing resin pellet according to claim 3, wherein in the formulae (1) and (2) each of R 3 represents phenoxy and each of R 1 , R 2 , R 4 and R 5 represents a hydrogen atom. A near-infrared absorbing resin pellet according to claim 3, wherein the bis-dithiobenzilnickel complex is selected from Bis-(4-ethyldithiobenzil)-nickel; Bis-(4-n-propyldithiobenzil)-nickel; Bis-(4-n-butyldithiobenzil)-nickel; Bis-(2,5-dimethyldithiobenzil)-nickel; Bis-(-phenyldithiobenzil)-nickel; and Bis-(4-phenoxydithiobenzil)-nickel. A near-infrared absorbing resin pellet according to claim 3, 4 or 5 wherein the transparent resin comprises an acrylic resin, polystyrene, polyvinylchloride, polycarbonate, an olefin resin, an epoxy resin or a mixture thereof. A near-infrared absorbing molded article obtainable by molding a near-infrared absorbing resin pellet as defined in any one of claims 3 to 6. A process for producing a near-infrared absorbing moulding which process comprises dissolving, in a transparent resin monomer, a compound which is a bis-dithiobenzilnickel complex of the following formula (1) or formula (2) : wherein R 1 to R 5 , which may be the same or different, each represent a substituted or unsubstituted alkyl, cycloalkyl, alkoxy, aryl or aryloxy group, or a halogen or hydrogen atom, provided that not all of R 1 to R 5 are hydrogen and that R 1 to R 5 do not represent an alkoxyalkoxy group; or a mixture of such compounds; or a near-infrared absorbing material comprising such a compound or compounds, and polymerising the resulting mixture. A process according to claim 8 which further comprises forming the moulding into a moulded article. A process according to claim 8 or 9 wherein the bis-dithiobenzilnickel complex is selected from: Bis-(4-ethyldithiobenzil)-nickel; Bis-(4-n-propyldithiobenzil)-nickel; Bis-(4-n-butyldithiobenzil)-nickel; Bis-(2,5-dimethyldithiobenzil)-nickel; Bis-(-phenyldithiobenzil)-nickel; and Bis-(4-phenoxydithiobenzil)-nickel.

Inventors: SATAKE TOSHIMI, TAKANO TOSHIYUKI, SATAKE, TOSHIMI, TAKANO, TOSHIYUKI, SATAKE, TOSHIMI, NEW PRODUCTS RES. LAB., Takano, Toshiyuki, c/o New Products Res. Lab.
Applicants: JUJO PAPER CO LTD, NIPPON PAPER INDUSTRIES CO., LTD.
Application year: 1993
Main classification: C07C325
IPC codes: C07C321, C07C45, G11B7, C07C49, C07C325