GB1571531A - Process for the preparation of 2-equivalent colour couplers - Google Patents

Description

(54) PROCESS FOR THE PREPARATION OF 2-EQUWALENT COLOUR COUPLERS (71) We, AGFA-GEVAERT AKTIEN GESELLSCHAFT, a body corporate organised under the laws of Germany, of 509 Leverkusen, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process for the preparation of 2-equivalent colour couplers.

To produce coloured photographic images, ir is known to develop the exposed silver halide of a light-sensitive silver halide emulsion layer with an aromatic developer substance containing primary amino groups in the presence of colour couplers. The couplers react with the oxidised colour developer to form an image dye in accordance with the silver image present.

For subtractive three-colour photography, a light sensitive multi-layered photographic material is generally used, which contains a red-sensitised, a green sensitised and a bluesensitive silver halide emulsion layer, in which a cyan, a magenta and a yellow dye image, respectively, are formed by colour development with the aid of suitable colour couplers.

The couplers used for forming the cyan dyes are generally phenols or naphthols, the couplers for the formation of the magenta dyes are usually pyrazolones and the couplers for forming the yellow dye are usually compounds containing a methylene group with carbonyl groups adjacent thereto. The dyes formed by the coupling reaction are azomethines, indamines or indophenols, depending on the composition of the coupler and of the developer.

Conventional yellow couplers and magenta couplers contain an active methylene group.

Conventional cyan couplers contain as their active group what is normally referred to as a methine group but which in view of the ketoenol-tautomerism peculiar to this class of compounds may equally be regarded as a methylene group. The active methylene or methine groups of conventional colour couplers react with the oxidised colour developer in the colour development process, and require four equivalents of developable silver halide for this reaction. These couplers are therefore known as 4-equivalent couplers. Other couplers are known which contain a methylene group in which one hydrogen atom is substituted by a group which is split off in the coupling reaction. These couplers only require two equivalents of developable silver halide to form the dye and are therefore known as 2equivalent couplers. The following are examples of the known groups which are split off in the coupling reaction: halogen, alkoxy or aroxy, thioether groups or saturated or unsaturated heterocyclic rings in most cases containing keto groups and attached to the coupling position by a ring nitrogen atom.

The advantage of the 2-equivalent couplers compared with 4-equivalent couplers is that they require only about half the quantity of silver halide to form a given quantity of dye.

Apart from the saving in silver thereby obtained, the emulsion layer can therefore be cast more thinly, and this has an advantageous effect on the resolution and sharpness of the photographic material.

2-Equivalent yellow couplers which have proved to be satisfactory in practice include compounds in which the removable group in the coupling position is linked through oxygen or nitrogen to the carbon atom of the activated methylene group of the acyl acetamide yellow coupler molecule.

Couplers of this type have hitherto been prepared by a two-stage reaction from the corresponding 4-equivalent couplers. In the first stage, the 4-equivalent coupler is reacted with a halogenating agent to produce the u- halogen acyl acetamide coupler and, in the second stage, the halogen atom situated in the coupling position of the resulting a-halo gen acyl acetamide yellow coupler is replaced ~by~the corresponding oxygen-containing or nitrogen-containing group by a substitution reaction.

The preparation of halogen acyl acetamide yellow couplers has been described in Ger man Offenlegungsschrift Nos. 2,263,587 and Z057,941 and in U.S. Patent No. 2,728,658.

After careful purification, the a-halogen compounds obtained must be reacted to form the corresponding 2-equivalent couplers as described in Offenlegungsschriften Nos.

2,318,807; 2,163,812; 2,329,587; 2,057,941 and 2,291,807 and in U.S. Patent Specification No. 3,644,498.

In these methods of preparation, phenols or heterocyclic compounds are reacted with the a-halogen couplers of a basic condensing agent to form the 2-equivalent couplers which con tain the required removable group linked through oxygen or nitrogen in the coupling position.

These methods are generally accompanied by undesirable side reactions, depending on the nature of the base and the reaction temperature employed, higher reaction temperatures gener ally favouring the formation of by-products.

A one-stage method of preparing 2-equivalent yellow couplers has been described in Ger man Offenlegungsschrift No. 2,545,756, according to which a 4-equivalent acyl aceta mide yellow coupler compound can be con verted in a single stage process to a 2-equiva lent acyl acetamide yellow coupler compound which contains, in the coupling position, a group attached through oxygen or nitrogen which can be split off by chromogenic develop ment. In this reaction, a compound contain ing an NH or OH group is introduced into the acyl acetamide yellow coupler molecule in the position through the nitrogen or oxy gen atom of the NH or OH group in the presence of a halogen or a halogen producing agent by means of a basic condensing agent in a substantially aprotic solvent. Hydrogen halide is split off and the desired 2-equivalent yellow coupler is obtained in a single stage reaction, the removable group being provided by the compound which contains the NH or OH group.

The magenta couplers which are prefer ably used are pyrazolones-5 and pyrazolo benzimidazoles which are substituted in the position and the 3-position with substituents which are very conventional in the chemistry of colour couplers. These magenta couplers may also be used as 2-equivalent or 4-equiva lent couplers.

Various processes have been described for the synthesis of 2-equivalent magenta couplers.

The introduction of releasable groups having the structure S(O) from sulphenyl chlorides and 4-equivalent magenta couplers, followed by oxidation, has been described in German Offenlegungsschrift No. 2,532,225. The reaction of 4-amino pyrazolones-5 with acid chlorides having the structure Hal-(CO)-B has been described in German Offenlegungsschrift No. 2,528,845. 2-Equivalent magenta couplers obtained from 4-amino-pyrazolones-5 and sulpho chlorides having the structure Cl-SO2-Y, which couplers contain a sulphonamide group as removable group, are described in German Offenlegungsschrift No.

2,526,111. Other 2-equivalent magenta couplers have been described in German Offenlegungsschrift No. 2,417,945. They contain releasable groups having the structure represented by the formula O-CO-( CO )nOR (n = 0 or 1) and they are obtained by the reaction of 4-hydroxy-5-pyrazolones with acid chlorides. Reference may also be made to German Offenlegungsschrift Nos. 2,424,467; 2,444,422 and 2,501,260.

2-Equivalent cyan couplers have been disclosed, for example, in German Offenlegungsschrift Nos. 2,163,811 and 2,504,844.

2-Equivalent couplers are frequently prepared by reaction of the corresponding chlorinated parent compounds with the organic compound providing the labile group in dipolar aprotic solvents in the presence of a base. This reaction has been described for yellow couplers in the following specifications: U.S. Patent No. 2,728,658 and German Offenlegungsschrift Nos. 2,057,941; 2,261,361; 2,433,812; 2,219,917 and 2,163,812.

These processes have, however, the disadvantage that solvents such as acetonitrile, dimethyl formamide (DMF) and hexamethyl phosphoric acid triamide (HMPA) are generally used in them. The use of these solvents is inadvisable on economical grounds and some of these solvents are toxicologically very suspect. A teratogenic effect has been described for DMF while HMPA has been found to be carcinogenic, at least in animal experiments.

Magenta couplers containing a piperidine releasable group have been described in German Offenlegungsschrift No. 2,424,467. These couplers are obtained by a complicated method of hydrogenating the corresponding pyridinium salt. In the process according to German Offenlengungsschrift No. 2,501,260, the releasable group must be built into the coupler before pyrazolone ring closure.

It is an object of the present invention to provide a process for the preparation of 2equivalent colour couplers containing, in the coupling position, a group which can be split off in the colour coupling reaction, these couplers starting from 2-equivalent colour couplers containing halogen in the coupling position, the desired products being substantially free from by-products and obtained in higher yield than in the known processes.

The present invention relates to a process for the preparation of photographic 2-equivalent colour couplers containing, in the coupling position, an organic group X attached through a nitrogen, oxygen or sulphur atom thereof, which group X is liberated by reaction with the oxidation product of the colour developer, characterised in that a 2-equivalent colour coupler which is substituted with a halogen atom in the coupling position is reacted with a compound represented by the following formula

in which X represents the residue, obtained by re moval of an acidic hydrogen atom, of an NH-acidic heterocyclic compound, of a phenol or of a mercaptan, the silicon atom being directly attached to a nitrogen, oxygen or sulphur atom of the group X.

The starting materials used are therefore known 2-equivalent colour couplers which contain a halogen atom, e.g. chlorine or bromine, in the coupling position, and they are reacted with "trimethyl silylated releasable groups" of the formula above. The reaction may be represented by the following equation:

in which Cp represents the residue of a conventional 4-equivalent colour coupler obtained by re moval of a hydrogen atom from the coupling position of a 4-equivalent coupler, Hal represents a halogen atom such as chlorine or bromine, and X represents a group suitable as a releasable group, obtained by the removal of an active hydrogen atom from a corresponding organic compound X-H, in particular an NH-acidic heterocyclic compound, phenol or mercaptan.

The method is equally suitable for the preparation of 2-equivalent yellow couplers, 2equivalent magenta couplers and 2-equivalent cyan couplers.

Particularly suitable releasable groups X are the residues of heterocyclic compounds containing a 5- or 6-membered nitrogen-containing ring which may also be part of a condensed ring system, in particular a substituted or unsubstituted imadazole, imidazolone, imidazoline dione, quinazolone, benzotriazinone, pur- ine or phthalimide ring. This 5- or 6membered nitrogen-containing ring must, at least in its tautomeric form, contain a labile hydrogen atom attached to one of its nitrogen atoms. Other possible releasable groups include aroxy groups and aliphatic, aromatic and heterocyclic thioether groups. The latter are generally distinguished by their development inhibiting action. The corresponding 2-equivalent couplers are known as DIR couplers.

Examples of suitable releasable groups X have been described in German Offenlegungsschrift Nos. 2,318,807; 2,329,587 and 2,433,812.

The "trimethyl silylated releasable groups may be obtained in known manner from the organic compounds X-H providing the releasable groups by reacting these compounds with a suitable trimethyl silylating agent such as trimethyl chlorosilane, trimethyl silyl acetamide or hexamethyl disilazane in inert organic solvents. Information on this method of silylation may be found in the following publications: 1) Birkhofer und Ritter Angew. Chemie, 77 (1965), pages 414--426 2) Birkhofer/Richter/Ritter Them. Ber. 93 (1960), pages 2804-2809 The following are examples of suitable trimethyl silylated releasable groups:

Kp 0,2 mm 11W120 C

Kp 0,2 mm 1100 C Kp 0,2 mm 1250 C

Kp 0,2 mm 1500 C

CH3 5.

CH3 Scamp. 1671700 C CH3 CH3

Kp 0,2 mm 1700 C Kp 0,2 mm 110"C The solvents used for the reaction according to the invention may be inert organic solvents which are incapable of being silylated and do not decompose the "silylated releasable group" by hydrolysis. Preferred solvents include, for example, benzene, toluene, dioxane, aliphatic hydrocarbons and chlorinated hydrocarbons. In some cases, solvent may be completely dispensed with. In that case, the silylated releasable group" and the halogenated coupler compound are simply added together. The reaction temperatures used may be, for example, from 0 to 200 C, more preferably from 50 to 1500 C.

It is found to be particularly advantageous in the method of preparation according to the invention that the reaction equilibrium can be substantially shifted in the direction of the desired 2-equivalent coupler by removal of the trimethyl halogen silane by distillation. The trimethyl halogen silane can be recovered and used again for trimethyl silylation of suitable organic compounds X-H. Owing to the mild reaction conditions, the 2-equivalent couplers prepared by the method according to the invention are distinguished by greater purity (less by-products) and frequently also by higher yields. Isolation of the 2-equivalent couplers is generally achieved by evaporation of the inert organic solvent.

In some cases, it is not even necessary to isolate the silylated releasable group, and the organic compound X-H and the silylating agent may simply be mixed with the halogenated coupler compound. Any "silylated releasable group" formed as intermediate product reacts to form the 2-equivalent coupler with reformation of trimethyl halogen silane which can again react with the organic compound. In some cases, much less than the stoichiometric quantity of silylating agent is required.

Example of Preparation 1 12 g of 2 - hexadecyloxy - 5 - monomethylsulphamyl - a - chloro - a - pivaloylacetanilide were disolved in 200 ml of distilled toluene, and 4.5 g of 1 - trimethylsilylimidazole were added. The reaction mixture was heated to boiling and trimethyl chlorosilane was distilled off in addition to toluene. After about 3 hours, the solvent was evaporated off under vacuum and the residue recrystallised from acetonitrile.

C H N S calc. (%) 64 8.74 9.06 5.17 found (%) 63.9 8.70 9.04 5.20 Example of Preparation 2 6.19 g of 2 - (w - 3 - pentadecylphenoxy propoxy) - 3 - chloro - 6 - trifluoromethylpyrazolobenzimidazole were dissolved in 200 ml of anhydrous toluene, and 2.5 g of 1 - trimethylsilyl - 2 - methylimidazole were added.

The reaction mixture was then heated to boiling and trimethylchlorosilane was distilled off in addition to toluene. After about 3 hours, the solvent was evaporated off under vacuum and the residue recrystallised from acetonitrile.

C H N calc. 68.5 7.52 16.5 found 68.3 7.40 10.5 WHAT WE CLAIM IS: 1. A process for the preparation of a photographic 2-equivalent colour coupler containing, in the coupling position, a releasable organic group X attached through a nitrogen, oxygen or sulphur atom, which group X is liberated by reaction with the oxidation product of the colour developer, in which a 2-equivalent colour coupler which is substituted with a halogen atom in the coupling position is reacted with a compound represented by the following formula

in which X represents the residue, obtained by removal of an acidic hydrogen atom, of an NH-acidic heterocyclic compound, a phenol or a mercaptan, the silicon atom being directly attached to a nitrogen, oxygen or sulphur atom of the group X.

2. A process as claimed in claim 1 in which the group X is the residue of a heterocyclic compound containing a 5- or 6-membered nitrogen containing ring which may be part of a condensed ring system.

3. A process as claimed in claim 1 or claim 2 in which the trimethyl silylated releasable group is a compound of any of the formulae 1 to 9 as herein defined.

4. A process as claimed in any of claims 1 to 3 in which X represents the residue obtained after removal of an acidic hydrogen atom from a substituted or unsubstituted imidazole, imidazolone, imidazoline done, quinazolone, benzotriazinone, purine or phthalimide ring.

5. A process as claimed in any of claims 1 to 4 in which the reaction is carried out in the presence of an inert organic solvent which is incapable of being silylated and does not decompose the silylated releasable group by hydrolysis.

6. A process as claimed in claim 5 in which the solvent is benzene, toluene, dioxane, an aliphatic hydrocarbon or a chlorinated hydrocarbon.

7. A process as claimed in any of claims 1 to 6 in which the reaction is carried out at a temperature of from 0 to 2000 C.

8. A process as claimed in claim 7 in which the reaction is carried out at a temperature of from 50 to 1500 C.

9. A process as claimed in claim 1 substantially as herein described with reference to either of the Examples.

10. A photographic 2-equivalent colour coupler which has been prepared by a process as claimed in any of claims 1 to 9.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. The reaction mixture was then heated to boiling and trimethylchlorosilane was distilled off in addition to toluene. After about 3 hours, the solvent was evaporated off under vacuum and the residue recrystallised from acetonitrile. C H N calc. 68.5 7.52 16.5 found 68.3 7.40 10.5 WHAT WE CLAIM IS:

1. A process for the preparation of a photographic 2-equivalent colour coupler containing, in the coupling position, a releasable organic group X attached through a nitrogen, oxygen or sulphur atom, which group X is liberated by reaction with the oxidation product of the colour developer, in which a 2-equivalent colour coupler which is substituted with a halogen atom in the coupling position is reacted with a compound represented by the following formula

in which X represents the residue, obtained by removal of an acidic hydrogen atom, of an NH-acidic heterocyclic compound, a phenol or a mercaptan, the silicon atom being directly attached to a nitrogen, oxygen or sulphur atom of the group X.

2. A process as claimed in claim 1 in which the group X is the residue of a heterocyclic compound containing a 5- or 6-membered nitrogen containing ring which may be part of a condensed ring system.

3. A process as claimed in claim 1 or claim 2 in which the trimethyl silylated releasable group is a compound of any of the formulae 1 to 9 as herein defined.

4. A process as claimed in any of claims 1 to 3 in which X represents the residue obtained after removal of an acidic hydrogen atom from a substituted or unsubstituted imidazole, imidazolone, imidazoline done, quinazolone, benzotriazinone, purine or phthalimide ring.

5. A process as claimed in any of claims 1 to 4 in which the reaction is carried out in the presence of an inert organic solvent which is incapable of being silylated and does not decompose the silylated releasable group by hydrolysis.

6. A process as claimed in claim 5 in which the solvent is benzene, toluene, dioxane, an aliphatic hydrocarbon or a chlorinated hydrocarbon.

7. A process as claimed in any of claims 1 to 6 in which the reaction is carried out at a temperature of from 0 to 2000 C.

8. A process as claimed in claim 7 in which the reaction is carried out at a temperature of from 50 to 1500 C.

9. A process as claimed in claim 1 substantially as herein described with reference to either of the Examples.

10. A photographic 2-equivalent colour coupler which has been prepared by a process as claimed in any of claims 1 to 9.