Pyrazolo [1,5A]benzimidazole photographic colour couplers

Abstract: A photographic non-diffusible magenta dye-forming colour coupler which is a 2-alkoxypyrazolo[1,5-a]-benzimidazole, for example a dye of the formula: wherein R¹ to R⁴ are each hydrogen or a substituent, R⁵ is an alkyl or substituted alkyl group, and X is hydrogen or a coupling-off group, and wherein at least one of R¹ to R⁵ or X contain a ballast group capable of rendering the coupler non-diffusible in photographic layers.

Description: This invention realates to 4-H-pyrazolo-[1,5-a]benzimidazole magenta colour couplers. 4-H-Pyrazolo-[1,5-a]benzimidazole magenta colour couplers have the basic ring structure: German Patent 1 070 030 describes pyrazolo[1,5-a]benzimidazole couplers which form magenta dye on coupling. Specifically the 2-octadecyl and 2-phenyl derivatives are prepared. It also describes couplers containing 2-carboxy groups while German Specification 1 099 349A describes corresponding 2-sulpho derivatives, both of which being useful to prepare Fischer type dispersions. 2-Anilino derivatives described in Japanese Specification 51/26541 and German specification 2 156 111A are said to be more active than their 2-alkyl analogues. Pre-formed dyes containing the 4-H-pyrazolo-[1,5-a]benzimidazole nucleus for use in instant photographic film units are described in the prior art containing groups in the coupling position which would not be displaced by oxidised colour developer, for example Dye 7 of British Specification 1 546 103: and Dye 5 in British specification 2 128 349A: The present invention provides new 4-H-pyrazolo[1,5-a]benzimidazole couplers which form dyes with improved hue characteristics. US Patent 4 774 172 describes couplers of the formula: wherein, inter alia, R1 is hydrogen or a substituent and Za and Zb are each: -CH=, =C(R 2 )- or -N=. Claim 2 lists 5 structures which represent different combinations of Za and Zb. Later general description lists examples of R 1 including alkoxy. No specific compound containing a 4-H-pyrazolobenzimidazole having an alkoxy group in the 2-position is described. According to the present invention there are provided photographic non-diffusible colour couplers which are 2-alkoxy-4-H-pyrazolo[1,5-a]benzimidazoles. A preferred class of the present couplers has the general formula: wherein R 1 to R 4 are each hydrogen or a substituent, R 5 is an alkyl or substituted alkyl group, and X is hydrogen or a coupling-off group, and wherein at least one of R 1 to R 5 or X contain a ballast group capable of rendering the coupler non-diffusible in photographic layers. The dyes formed from the present couplers have superior spectral properties compared to their 2-alkyl and 2-aryl analogues, in that the image dyes formed therefrom have a λ max of desirably shorter wavelength and a narrower half bandwidth. R 1 to R 4 may be any substituent which is not incompatible with the intended use of the coupler. Examples of groups which R 1 to R 4 may represent are H, R [where R is alkyl (including cycloalkyl), substituted alkyl, aryl or substituted aryl], halogen (eg Cl, Br or F), CF 3 , NO 2 , CN, OH, O-R, SO 2 R, SO 2 NR 2 , CONR 2 , COOH, COOR, NHSO 2 R, NRSO 2 , NHCOR, NRCOR, NH 2 , NHR, NR 2 , and SR. The preferred groups are H, R, NHCOR and NHSO 2 R. Examples of groups which R 5 may represent are alkyl, especially alkyl of 1-20 carbon atoms, having a straight or branched chain which is optionally substituted with any of the substituents listed above for R 1 to R 4 . Specific examples of such groups include methyl, ethyl, iso-propyl, tert-butyl, s-C 5 H 11 , n-C 12 H 25 , cyclohexyl, benzyl, CH 2 CH 2 -aryl, CH 2 CH 2 OH and CH 2 COOR. Examples of coupling-off groups X are: H, halogen (eg Cl or Br), SR, S-heterocycle (eg phenylmercaptotetrazole) OR, OSO 2 R, OCOR, N-containing heterocycles attached to the coupling position by the N atom (eg pyrazole, imidazole and triazole). Specific examples of couplers of the present invention are listed in the following table. Examples of comparative couplers having 2-alkyl groups are listed in Table II below, The present couplers may be prepared by methods in themselves known as exemplified in the preparative Examples 3-6 below. The dye-forming couplers of this invention can be used in the ways and for the purposes that dye-forming couplers have been previously used in the photographic art. Typically, the couplers are associated with a silver halide emulsion layer coated on a support to form a photographic element. As used herein, the term "associated with" signifies that the coupler is incorporated in the silver halide emulsion layer or in a layer adjacent thereto where, during processing, it is capable of reacting with silver halide development products. The photographic elements can be single colour elements or multicolour elements. In a multicolour element, the magenta dye-forming couplers of this invention would usually be associated with a green-sensitive emulsion, although they could be associated with an emulsion sensitised to a different region of the spectrum, or with a panchromatically sensitised, orthochromatically sensitised or unsensitised emulsion. Multicolour elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. A typical multicolour photographic element comprises a support bearing yellow, magenta and cyan dye image-forming units comprising at least one blue-, green- or red-sensitive silver halide emulsion layer having associated therewith at least one yellow, magenta or cyan dye-forming coupler respectively, at least one of the magenta dye-forming couplers being a coupler of this invention. The element can contain additional layers, such as filter and barrier layers. In the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure, December 1978, Item 17643, published by Industrial Opportunities Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hants P010 7DD, U.K. This publication will be identified hereafter as "Research Disclosure". The silver halide emulsion employed in the elements of this invention can be either negative-working or positive-working. Suitable emulsions and their preparation are described in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of elements of this invention are described in Research Disclosure Section IX and the publications cited therein. In addition to the couplers of this invention, the elements of the invention can include additional couplers as described in Research Disclosure Section VII, paragraphs D, E, F and G and the publications cited therein. The couplers of this invention and any additional couplers can be incorporated in the elements and emulsions as described in Research Disclosures of Section VII, paragraph C and the publications cited therein. The photographic elements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilisers (see Research Disclosure Section VI), antistain agents and image dye stabiliser (see Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (see Research Disclosure Section VIII), hardeners (see Research Disclosure Section XI), plasticisers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI). The photographic elements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein. Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed to form a visible dye image as described in Research Disclosure Section XIX. Processing to form a visible dye image includes the step of contacting the element with a colour developing agent to reduce developable silver halide and oxidise the colour developing agent. Oxidised colour developing agent in turn reacts with the coupler to yield a dye. Preferred colour developing agents are p-phenylene diamines. Especially preferred are 4-amino-3-methyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-β-(methanesulphonamido)ethylaniline sulphate hydrate, 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulphate, 4-amino-3-β-(methanesulphonamido)ethyl-N,N-diethylaniline hydrochloride and 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulphonate. With negative-working silver halide emulsions this processing step leads to a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniform fogging of the element to render unexposed silver halide developable. Alternatively, a direct positive emulsion can be employed to obtain a positive image. Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying. The following Examples are given for a better understanding of the invention. EXAMPLE 1 Comparison of Dye Hues from Alkoxy Pyrazolobenzimidazole Couplers with Dye Hues from Alkyl Pyrazolobenzimidazole Couplers in Ethyl Acetate Solution. The data in this table shows that alkoxy pyrazolobenzimidazole (PBI) couplers afford dyes that are hypsochromic in dye hue to those produced by analogous or very similar alkyl PBI couplers. This is an advantage as the alkyl PBIs are too bathochromic in a conventional colour negative format and the new couplers would therefore lead to better colour reproduction. The couplers are arranged in groups for comparison eg. in the first group (of two) coupler (1) of the invention is compared to comparison coupler (C1). A second advantage is the narrower half-band width (HBW) shown by the couplers of the invention, which also leads to improved colour reproduction. The two colour developers used have the following formulae: Coupler CD4 CD2 λmax/nm HBW/nm λmax/nm HBW/nm (1) (Invention) 535 80 530 81 (C1) (Comparison) 546 87 540 86 (4) (Invention) 534 82 530 82 (C2) (Comparison) 546 85 540 85 (C3) (Comparison) 549 84 545 86 (6) (Invention) 539 87 532 84 (C4) (Comparison) 549 91 545 88 (9) (Invention) 545 83 539 87 (C5) (Comparison) 557 83 553 84 EXAMPLE 2 Comparison of Dye Hues from Alkoxy Pyrazolobenzimidazole Couplers with Dye Hues from Alkyl Pyrazolobenzimidazole Couplers in Photographic Coatings. The couplers were incorporated into a photographic silver bromoiodide emulsion and coated in the following format:- Gel supercoat gelatin 1.5 gm -2 Emulsion Layer Silver bromoidide 1.6 gm 2 Coupler 1.4 mmolm 2 Gelatin 2.42 gm -2 Bis(vinylsulphonyl)methane (hardener) 0.06 gm -2 Support Cellulose acetate The couplers dispersion used contained 6% w/w gelatin, 8.8% coupler and coupler solvents in the ratio coupler:triphenyl phosphate:2-(2-butoxyethoxy)ethyl acetate 1:0.5:1.5. On fogging and processing through a standard C-41 process, the dye hues were measured. The table below shows photographic hue data for a selection of couplers of the invention compared to some related alkyl analogues. The same trends in dye hue are seen in this coated format as are seen in solution (Example 1). Coupler CD4 λmax/nm HBW/nm (2) (Invention) 544.5 100 (C1) (Comparison) 558.0 - (3) (Invention) 546.5 107 (C6) (Comparison) 560.0 - (9) (Invention) 558.0 115 (10) (Invention) 555.5 113 (C7) (Comparison) 560.0 122 (C8) (Comparison) 582.0 106 EXAMPLE 3 Preparation of 2-Dodecyloxy-4-H-pyrazolo[1,5-a]benzimidazole (Coupler 1) (a) O-Dodecyl-2-ethoxycarbonylacetimidate hydrochloride. Ethyl cyanoacetate (84.8g, 0.75 mole) and dodecyl alcohol (140g, 0.75 mole) were dissolved in diethyl ether (120ml). The stirred solution was saturated with HCl gas over a period of 1.5 hrs whilst being cooled in an ice bath. A further quantity of ether was added (300ml), and the clear solution was stirred in an ice/salt bath for 1.5 hrs to precipitate the product. The mixture was stood in a cool room at 4/C overnight, the crystalline solid filtered off, washed with a little ether, and dried under vacuum at 20/C,(yield = 30.27g.). The mass spectrum and elemental analysis results were consistent with the product being O-dodecyl-2-dodecyloxycarbonylacetimidate hydrochloride. The filtrate was placed in the fridge overnight, and this precipitated a further quantity of crystals. These were filtered off, washed with ether, and dried under vacuum at 20/C. Analysis was consistent with the desired product, O-Dodecyl-2-ethoxycarbonylacetimidate hydrochloride. The yield was 100.87g, 40%. Analysis; calculated for C 14 H 34 ClNO 3 Calc: C 60.8%, H 10.2%, Cl 10.6%, N 4.2% Found: C 60.3%, H 10.1%, Cl 10.0%, N 4.1% (b) 3-Dodecyloxy-1-(2-nitrophenyl)pyrazol-5-one. 2-Nitrophenylhydrazine (16.1g, 105 mmole) was stirred in tertiary butyl alcohol (150mls), and O-dodecyl-2-ethoxy- carbonylacetimidate hydrochloride (35.0g, 105 mmole) added with stirring. After 1.5 hr at room temperature, the formation of the intermediate hydrazone was complete. The reaction mixture was brought to reflux temperature, a solution of sodium hydroxide in water (140ml, 0.2g/ml) was added, and heating was continued for a further 10 min. The solution was allowed to cool and was drowned in dilute (5%) hydrochloric acid (21). The crude product was extracted into ethyl acetate, and the extracts were combined, dried with magnesium sulphate, and concentrated by rotary evaporation. The product was purified by column chromatography on silica gel, using an ethyl acetate/60-80/C petrol mixture (1:2) as eluant. The solid was further purified by recrystallisation from ethyl acetate:60- 80/C petrol (1:9) to give the product, 3-dodecyloxy-1-(2-nitrophenyl)-pyrazol-5-one, as a brown solid. The yield was 8.0g, 20%. Analysis; Calculated for C 21 H 31 N 3 O 4 Calc: C 64.8%, H 8.0%, N 10.8% Found: C6 5.2%, H 8.3%, N 10.5% (c) 2-Dodecyloxy-4-H-pyrazolo[1,5-a]benzimidazole. 3-Dodecyloxy-1-(o-nitrophenyl)pyrazol-5-one (8.0g, 20.54 mmole) was dissolved in acetic acid (200ml), and 10% palladium on charcoal (0.8g) in acetic acid (10ml) added. The reaction mixture was hydrogenated under pressure for a period of 1.5 hrs. The catalyst was filtered from the mixture to leave a solution of the 3-alkoxy-1-(o-aminophenyl)pyrazol-5-one in acetic acid. Cyclisation to (1) was effected by heating the acetic acid solution under reflux for fifteen minutes. The solution was allowed to cool, and the solvent was removed by rotary evaporation to give the crude product as a dark orange solid. Recrystallisation, once from acetonitrile, and three times from an ethyl acetate/60-80°C petroleum ether mixture (1:2), gave pure 2-dodecyloxy-4-H-pyrazolo-[1,5-a]benzimidazole. The yield was 3.97, 57%. Analysis; Calculated for C 21 H 31 N 3 O Calc: C 73.9%, H 9.2%, N 12.3% Found: C 73.7%, H 9.2%, N 12.2% EXAMPLE 4 Preparation of N-(2-Ethoxypyrazolo-4H-benzimidazol-6-yl)pentadecylamide (Coupler 6) (a) Preparation of 4-Hydrazino-3-nitrophenylpentadecanamide. 4-Fluoro-3-nitrophenylpentadecanamide (67.8g, 0.172 mole) was dissolved in dimethyl sulphoxide (11), and hydrazine monohydrate (20.67g, 0.413 moles) was added in a dropwise fashion whilst keeping the temperature below 40/C. The reaction mixture was stirred for 1.5 hr at room temperature, and was then drowned in an ice/brine mixture (101). The red solid obtained was filtered off and dried at room temperature. The product was used in this crude form without any further purification. The yield was 68.14g, 97%. (b) N-[3-Nitro-4-(3-Ethoxy-5-pyrazolon-1-yl)phenyl]pentadecanamide. N-[3-nitro-4-(3-Ethoxy-5-pyrazolon-1-yl)phenyl]pentadecanamide was prepared by the method in (3c) from 4-hydrazino-3-nitro- phenylpentadecanamide (4a) and O-ethyl 2-ethoxycarbonyl- acetimidate hydrochloride (prepared from ethyl cyanoacetate and ethanol as in method (3a) ). The yield was 49%. Analysis; Calculated for C 27 H 42 N 4 O 4 Calc: C 64.5%, H 8.4%, N 11.2% Found: C 63.1%, H 8.4%, N 10.8% (c) N-(2-Ethoxypyrazolo-4H-benzimidazol-6-yl)pentadecylamide N-(2-Ethoxypyrazolo-4H-benzimidazol-6-yl)pentadecylamide (6), was prepared from (4b) by the method indicated in (3c). The yield was 33%. Analysis; Calculated for C 27 H 42 N 4 O 2 Calc: C 71.3%, H 9.3%, N 12.3% Found: C 71.4%, H 9.3%, N 12.1% EXAMPLE 5 Preparation of 2-Ethoxy-4-H-pyrazolo[1,5-a]benzimidazole, (Coupler 4) (a) 3-Ethoxy-1-(2-nitrophenyl)pyrazol-5-one. Finely ground ortho-nitrophenylhydrazine (2.0g, 13.1 mmole) and ethyl-/,/-diethoxyacrylate (2.46g, 13.1 mmole) were heated together on a steam bath for 45 minutes. Sodium metal (0.30g, 13.1 mg-atom) was dissolved in absolute ethanol (5ml), and the resultant solution added to the reaction mixture. Heating was continued for a further 20 min. The volume of the reaction mixture was increased to 600ml by the addition of water, and the pH was adjusted to 4 by the addition of acetic acid. The aqueous mixture was extracted with ethyl acetate, and the crude product was purified by column chromatography on silica gel, using an ethyl acetate/60-80/C petrol mixture (1:2) as eluant. The solid was further purified by recrystallisation from an ethyl acetate/petrol mixture. The yield of pure 3-ethoxy-1-(2-nitrophenyl)- pyrazol-5-one was 1.63g, 50%. Analysis; Calculated for C 11 H 11 N 3 O 4 Calc: C 53.0%, H 4.5%, N 16.9% Found: C 53.1%, H 4.4%, N 17.0% (b) 2-Ethoxy-4-H-pyrazolo[1,5-a]benzimidazole 2-Ethoxy-4-H-pyrazolo[1,5-a]benzimidazole was prepared by the same route as described in (3c). The yield was 25%. Analysis; Calculated for C 11 H 11 N 3 O Calc: C 65.7%, H 5.5%, N 20.9% Found: C 65.5%, H 5.5%, N 20.8% EXAMPLE 6 Preparation of 3-(2-Dodecyloxy-4-H-pyrazolo[1,5-a]benzimidazol-3-ylthio)propionic acid. (Coupler 3) Coupler (1) (3.91g, 11.45 mmole) and 3-mercaptopropionic acid (1.22g, 11.45 mmole) were stirred in dimethylformamide (60ml), and a solution of bromine (2.93g, 18.3 mmole) in dimethyl formamide (10ml) was added dropwise until about a quarter of the bromine solution remained. The reaction mixture was then stirred at room temperature for two hours. The remaining bromine solution was then added in a dropwise manner, and the mixture was allowed to stir for a further thirty minutes. The solution was drowned in dilute hydrochloric acid (600ml), and the crude product was extracted into ethyl acetate. The extracts were combined, dried with magnesium sulphate, and concentrated by rotary evaporation to give a brown oil. The crude product was purified by column chromatography on silica gel, using an ethyl acetate/60-80/C petrol mixture (1:1) as eluant. The product was further purified by recrystallisation from an ethyl acetate/petrol mixture, to give pure 3-(2-dodecyloxy-4-H-pyrazolo[1,5-a]benzimidazol-3-ylthio)-propionic acid. The yield was 3.77g, 74%. Analysis; Calculated for C 24 H 35 N 303 S Calc: C 64.7%, H 7.9%, N 9.4%, S 7.2% Found: C 64.8%, H 7.9%, N 9.3%, S 6.8%

Claims: A photographic non-diffusible magenta dye-forming colour coupler which is a 2-alkoxy-4-H-pyrazolo[1,5-a]benzimidazole. A coupler as claimed in claim 1 which has the general formula: wherein R 1 to R 4 are each hydrogen or a substituent, R 5 is an alkyl or substituted alkyl group, and X is hydrogen or a coupling-off group, and wherein at least one of R 1 to R 5 or X contain a ballast group capable of rendering the coupler non-diffusible in photographic layers. A coupler as claimed in claim 2 in which R 1 to R 4 are, independently, H, R, halogen, CF 3 , NO 2 , CN, OH, O-R, SO 2 R, SO 2 NR 2 , CONR 2 , COOH, COOR, NHSO 2 R, NRSO 2 , NHCOR, NRCOR, NH 2 , NHR, NR 2 or SR where R is alkyl (including cycloalkyl), substituted alkyl, aryl or substituted aryl. A coupler as claimed in claim 2 or 3 in which R 5 is alkyl, preferably alkyl of 1-20 carbon atoms, having a straight or branched chain which is optionally substituted with any of the substituents R 1 to R 4 as defined in claim 2 or 3. A photographic material comprising a support, a silver halide emulsion layer and, associated therewith, a coupler as claimed in any of claims 1 - 4. A multicolour photographic material comprising a support bearing yellow, magenta and cyan dye image-forming units comprising at least one blue-, green- or red-sensitive silver halide emulsion layer having associated therewith at least one yellow, magenta and cyan dye-forming coupler respectively, at least one of the magenta dye-forming couplers being a coupler according to any of claims 1 - 4.

Inventors: CRAWLEY MICHAEL WILLIAM, GIBSON ANDREW WILLIAM, CRAWLEY, MICHAEL WILLIAM, GIBSON, ANDREW WILLIAM, CRAWLEY, MICHAEL WILLIAM, C/O KODAK LIMITED, GIBSON, ANDREW WILLIAM, C/O KODAK LIMITED
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1991
Main classification: G03C7
IPC codes: G03C7, C07D487