BACKGROUND OF THE INVENTION Photographic bleaches are used to remove silver from photographic material carrying developed images during photographic processing so that only image dye remains in the photographic material. The bleaches typically comprise an oxidizing agent, for oxidizing metallic silver particles to silver (I) ions, and a halogenating agent, for converting the silver ions to silver halide, which is then soluble in the bleach solution and can be removed from the photographic material.

A bleach composition may also consist of other components for modifying pH, or for scavenging other metal ions that may be present and may also be combined with a fixing agent, such as ammonium thiosulphate, to form a bleach-fix composition.

The halogenating agent is typically a bromide, such as potassium bromide. The halogenating agent, and any other components are typically added to an aqueous solution of the oxidizing agent.

Conventionally, bleach baths have often been based on alkali metal ferricyanide as the oxidizing agent, because it gives fast and effective bleaching.

For the most part, this has been superceded in commercially used bleach or bleach-fix baths by iron (III) ions complexed with a suitable iron-complexing

agent, which is typically etShylenediamine tetraacetic acid/EDTA), 1, 3- propylenediamine tetraacetic acid (1,3 PDTA) or nitrilotriacetic acid (NTA).

A number of alternative, biodegradable ligands (or complexing agents) have been developed, such as alkyliminodiacetic acid derived ligands.

Methyliminodiacetic acid (MIDA), for example, does not have the same toxicity objections as the ferrocyanide bleach and even the EDTA and PDTA ligands.

MIDA can be made by reaction of hydrogen cyanide, formaldehyde and an alkylamine via a cyanohydrin intermediate and can be prepared such that the product can be used in preparing a bleach solution without further purification.

An alternative preparation for MIDA is described by Berchet (Organic Syntheses, Combined Volume 2,397) and utilised in US-A-4294914 (see Example 2) as a ligand in a photographic bleach solution by complexing with'iron (III), to which was added ammonium bromide as a rehalogenating agent in the bleach.

According to this method of preparing MIDA, methylamine is added to an aqueous solution of two equivalents of chloroacetic acid in the presence of a base.

In the preparation of commercial bleaches, it is necessary to remove the chloride by-product to prevent corrosion of equipment. The chloride is removed using barium chloride.

The two described methods of preparing MIDA are not ideal for use in the preparation of commercial rehalogenating bleach compositions because formaldehyde and hydrogen cyanide used in the cyanohydrin route described above are hazardous materials, which are preferably avoided, and because barium chloride, which is involved in the necessary removal of chloride from the reaction mixture in the chloroacetic acid route to prevent corrosion of equipment, is toxic.

PROBLEM TO BE SOLVED BY THE INVENTION It is desirable to improve the process for preparing biodegradable photographic bleach compositions comprising complexed iron (III) as the bleach by avoiding the use of hydrogen cyanide, formaldehyde and barium chloride. It is also desirable to prepare bleach compositions without the necessity to isolate intermediate ligands so that the bleach composition may be prepared in a one-pot reaction.

There is, therefore, a need for an improved process for preparing iron (III) bleach compositions and for preparing biodegradable ligands for use in such iron (III) bleach compositions, which processes avoid the use of toxic materials and at the same time provides a more efficient process.

SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a process for the preparation of a photographic bleach composition, the process comprising treating a solution of an iron complexing agent, which solution further comprises a silver precipitating or complexing moiety for precipitating or complexing silver ions, with an iron (III) source to form an iron (III) oxidising agent, characterized in that the. silver precipitating or complexing moiety is a by-product in the preparation of the iron complexing agent.

Generally, the silver precipitating or complexing moiety according the first aspect of the invention is preferably a halogenating agent. It is preferable that the halogenating agent is a bromide. It is also preferable that the iron complexing agent is an optionally substituted alkyliminodiacetic acid.

According to a second aspect of the invention, there is provided a process for the preparation of an optionally substituted alkyliminodiacetic acid iron

complexing agent comprising reacting an optionally substituted bromoacetic acid with an optionally substituted alkylamine in the presence of a base.

In a third aspect of the invention, there is provided the use of an optionally substituted bromoacetic acid in the preparation of an alkyliminodiacetic acid complexing agent for use in a rehalogenating photographic bleach.

ADVANTAGEOUS EFFECT OF THE INVENTION The preparation of an iron complexing agent, such as optionally substituted alkyliminodiacetic acid, for use in a photographic bleach composition in such a way that as a by-product of that preparation a silver precipitating or complexing moiety, especially a halogenating agent (such as a bromide) is provided, enables the preparation of the iron complexing agent and subsequently the photographic bleach composition to be carried out in a one-pot synthesis without the necessity of adding a silver precipitating or complexing moiety, for example a bromide, or other rehalogenating agent, to the bleach solution to provide precipitation or complexing of silver ions, by for example rehalogenation.

Furthermore, where the iron complexing agent is a substituted alkyliminodiacetic acid, the process of preparing that agent whereby a bromide is a by-product of the reaction enables the product mixture to be used in preparing a bleach solution without purification, and avoids the use of undesirable components such as barium chloride, hydrogen cyanide and formaldehyde.

DETAILED DESCRIPTION OF THE INVENTION In the general sense, the present invention is concerned with a process for preparing a bleach solution by treating a solution of an iron complexing agent with an iron (HI) source to form an iron (III) oxidising agent, where the, solution of the iron complexing agent comprises, as a by-product in its preparation, a silver ion precipitating or complexing moiety, which when it precipitates or complexes silver

ions to form a silver compound or complex, is soluble in the fix solution to be used so that the silver can be washed form the photographic material.

The by-product from the reaction in which the iron complexing agent is formed could be a thiosulphate, for example, whereby a bleach-fix solution would be formed on treatment with an iron (III) source. In this embodiment, the thiosulphate would be a silver complexing moiety which would be capable of forming a complex with silver and the silver complex formed would be soluble in the bleach-fix solution and would then be washed from the photographic material.

The by-product as a silver precipitating or complexing moiety according to the invention could be any silver ion precipitating or complexing moiety, such as halides or phosphates, for example, but is preferably a halide.

The embodiments of the invention described herein with reference to a halide as the silver precipitating or comlexing moiety may alternatively be applied to any silver precipitating or complexing moiety, in a more general sense.

More particularly, therefore, the invention provides a process of preparing a photographic bleach composition where a solution of an iron complexing agent and a halogenating agent is treated with an iron (III) source to form an oxidizing agent as a complex between iron (III) and the iron complexing agent. The halogenating agent, which is suitable for rehalogenating silver ions (for example, those oxidized from silver by the oxidizing agent) is a by-product of the reaction in which the iron complexing agent is formed.

Preferably, the iron complexing agent intermediate used for forming the iron (III) oxidizing agent is not isolated prior to use in the process for preparing the photographic bleach composition. For example, the product mixture in the iron complexing agent preparation may be used without significant work up procedures or without undertaking a purification procedure.

This enables the photographic bleach composition to be prepared in a simple and efficient manner, for example, in a"one-pot"synthesis whereby the reaction to prepare the iron complexing agent is carried out, then the product mixture treated with a source of iron (III) to produce a rehalogenating bleach solution comprising an iron (III) oxidizing agent and a halogenating agent without the necessity of adding further halogenating agent to the bleach solution.

The invention is particularly applicable to commercial bleach solutions where it is normally necessary to ensure any chloride ions are absent or minimise to prevent corrosion of equipment. Such a commercial bleach solution would be required, for example, for use in commercial photographic mini-labs.

The source of iron (III) for use in the present invention may be any suitable iron (III) source that allows iron (III) to complex with the iron complexing agent in aqueous solution. Examples of iron (III) sources according to the invention include iron (III) nitrate, sulfate and acetate, preferably as hexahydrate salts.

Preferably, iron (III) nitrate is utilised. One advantage of using iron (III) nitrate is that it provides an anti-corrosive effect.

The halogenating agent can be any material that facilitates the halogenation of silver or silver ions to silver halide. Examples of suitable halogenating agents include alkali metal halides, preferably chlorides, bromides or iodides, preferably sodium bromide or potassium bromide. In any case the preferred halogenating agent is a brominating agent, because in the photographic processing of colour negative film, the fix solution is less effective if silver iodides are formed and it is more difficult to form silver chlorides during the rehaloginating bleaching step unless a particularly strong bleach is utilised. The halogenating agent is typically formed by loss of a bromine anion from one of the starting materials in the preparation of the iron complexing agent, e. g. from bromoacetic acid in the formation of an alkyliminodiacetic acid, which may be picked up by a counter-ion available in the reaction mixture, which may be, for example, potassium from potassium hydroxide if used as a base.

The iron complexing agent (or ligand) according to the present invention may be any compound capable of forming a complex with iron (III) so as to be <BR> <BR> <BR> <BR> capable of oxidizing silver to silver (I). The complexing agent may be mono-, di-<BR> or tri-dentate, for example, and there may be required one or more-complexing agents to form an effective complex with iron (III).

Preferably, the complexing agent is an optionally substituted alkyliminodiacetic acid. The complexing agent (or ligand) should be soluble in the bleach solution. The alkyliminodiacetic acid may have a straight chain or branched alkyl group, which may be substituted or unsubstituted. Preferably, the alkyl group is a substituted or unsubstituted Cl-Cl2 straight chain or branched alkyl group, more preferably a substituted or unsubstituted Cl-C6 straight chain or branched alkyl group, still more preferably a substituted or unsubstituted methyl, ethyl, (iso) propyl or butyl group and most preferably a methyl or ethyl group. The alkyliminodiacetic may also be substituted on the a-carbon of one or both of the acetic acid groups, for example with a hydroxy group, a fluorine or a methyl group.

Suitable substituents on the alkyl group of the alkyliminodiacetic acid may include, for example, a carboxylic acid group (i. e. C02H), hydroxy, methylamido, sulphonate or methylsulphonamido, at any point on the alkyl chain. For example, the alkyl group may be a propanoic acid group (e. g.-CH2-CH2-C02H). As another example, for a Cl2 alkyl group, the substituent may be a solubilizing group such as a carboxylic acid group or sulphonate.

Preferred optionally substituted alkyliminodiacetic acid include methyliminodiacetic acid (MIDA), ethyliminodiacetic acid (EIDA), propyliminodiacetic acid (PIDA) and butyliminodiacetic acid (BIDA), most preferably MIDA or EIDA.

The optionally substituted alkyliminodiacetic acid, as the complexing agent, is prepared, according to the invention, by treating an optionally substituted bromoacetic acid with optionally substituted alkylamine in the presence of a base. <BR> <BR> <BR> <P> The base may be, for example, any strong base having a pKb of less than one, may<BR> The base may be, for example, any strong base having a pKb of less than one, may be an organic or inorganic base, but is preferably an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. In order to achieve the stoichiometry of the desired alkyliminodiacetic acid, it is necessary to employ 2 moles of bromoacetic acid per mole of the alkylamine. However, excess alkylamine not directly involved in the reaction can be used. Preferably, at least 4 molar equivalents of base are utilized.

The reaction of the alkylamine with bromoacetic acid in the presence of a base is exothermic. The reaction temperature should be controlled so as to minimise the formation of glycolic acid as a by-product. Where the base is a strong base such as potassium hydroxide, it is preferable that the temperature should be kept below 50°C, more preferably below 30°C, during addition of the base to bromoacetic acid solution. The temperature of the reaction during and following addition of the alkylamine should be maintained at or below 50°C, preferably at or below 30°C, to minimise the formation of side products.

As mentioned above, in a preferred embodiment of the present invention, the product mixture formed in the preparation of the iron (III) complexing agent is utilised directlyin the preparation of the bleach composition. Addition of an iron (III) source, such as iron (III) nitrate, yields a rehalogenating bleach composition comprising an iron (III) oxidizing agent and a halogenating agent, without the necessity to add a halogenating agent.

Typically the preparation of the bleach composition involves adding an iron (III) source to a well-stirred iron (III) complexing agent solution. Optionally, a calcium ion scavenger, such as Dequest m 2000 (50% amino tris (methylene phosphonic acid) solution), available from Monsanto, may be added to the bleach

composition. Glacial acetic acid may also be added. The pH may be adjusted as desired, for example by addition of potassium hydroxide or acetic acid.

There may also be added to the bleach composition one or more additional iron (III) complexing agents, such as EDTA, 1, 3-PDTA and a second complexing agent according to the invention.

There may be a wide variation in the proportion of iron (III) ions present in the composition to iron (III) complexing agent. For example, where an alkyliminodiacetic acid is the complexing agent, there may be a ratio of alkyliminodiacetic acid to iron (III) ions of from 1 : 1. 5 to 15 : 1, preferably 1: 2 to 5: 1, more preferably 1 : 2 to 1 : 4 and most preferably about 1 : 3. The proportion of iron (III) ions to (one or more) iron (III) complexing agent may be adjusted as desired.

In a most preferred embodiment of the present invention, a bleach composition is prepared by treating an aqueous solution of bromoacetic acid with methylamine in the presence of an alkali metal hydroxide as base, under controlled temperature conditions as described above; to the completed reaction mixture adding a second iron (III) complexing agent, preferably 1,3-PDTA and adding iron (III) nitrate without adding any additional bromide. The second complexing agent is preferably the minor component, present in a ratio of MIDA to 1,3-PDTA of, for example, 5: 1 to 40 : 1, preferably 10: 1 to 30 : 1, most preferably 10 : 1 to 20: 1.

The invention will now be further illustrated without limitation by the following specific examples.

EXAMPLES Example 1 Preparation of AzllDA 279 g (2 mol) bromoacetic acid was placed in 150 ml water in a 2 L flask provided with a mechanical stirrer, separating funnel and thermometer. The flask was cooled in ice water and a cold solution of 224 g (4 mol) potassium hydroxide in 500 ml water was added, with stirring, from the separating funnel at such a rate as to maintain the temperature at 30°C or below. Following addition of the alkali solution, the cooling bath was removed and an aqueous solution containing 31g (1 mol) was slowly added to the reaction mixture. The resulting reaction is exothermic and the temperature of the reaction mixture was maintained below 50°C by controlling the rate of addition of the methylamne solution and by occasional immersion of the flask in ice water. Following addition of the methylamine, the reaction mixture was allowed to stand for 2 hours to allow completion of the reaction to form methyliminodiacetic acid (MIDA).

Preparation ofrehalogenating bleach composition To this mixture was added 1 L demineralised water and 19 g glacial acetic acid. 35g DequestTM 2000 (50% amino tds (methylene phosphonic acid)) was added to the mixture. 225 g 42% iron (III) nitrate solution was then added with vigorous stirring. The pH of the solution was adjusted to 4.64 with 10% potassium hydroxide solution. The total volume was made up to 2.5 L to give a biodegradable rehalogenating bleach without the addition of bromide.

Example 2 MIDA was prepared as per Example 1, and used in the form of the product mixture.

Preparation of rehalogenating bleach compostion To the MIDA solution was added 1 L demineralised water, 20 ml glacial acetic acid and 12 g 1,3-PDTA. This was followed by 36.5 ml DequestTM 2000.

To this was added 237 g 42% iron (III) nitrate solution with vigorous stirring. The pH of the solution was adjusted to 4.64 with 10% potassium hydroxide solution.

The total volume was made up to 2.5 L to give a biodegradable rehalogenating bleach without the addition of bromide.

The present invention has been described in. detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.