FIELD OF THE INVENTION

The present invention relates to a novel coupler which is capable of releasing a development accelerator, to a photographic silver halide element containing the novel coupler in combination with an electron transfer-releasing coupler and to a method for processing such an element.

BACKGROUND OF THE INVENTION Couplers which release a development accelerator (DARCs) are known in the art. They are added to silver halide emulsions in order to achieve an increase in speed and/or contrast, brought about by the increased image development caused by the image- wise release of the development accelerator. Typically, these couplers release a hydrazine derivative, which is activated by oxidized colour developing agent and hydroxyl ions. For example US Patent Nos. 4,482,629, 4,618,572 and 4,820,616 all describe the use of DARCs that release hydrazine derivatives, including those in which the hydrazine derivative also bears a silver absorbable moiety.

It is also known in the art that a silver halide photographic element containing a combination of a DARC and a coupler that releases a specific type of electron transfer agent (ETARC) can lead to improved photographic imaging. US Patent No. 6,756,188 discloses the synergistic speed improvement when a DARC of the type that releases a hydrazine nucleator is used in combination with an ETARC. However this combination also resulted in a high level of undesirable dye density in the unexposed region of the photographic element (D _m i _n )-

PROBLEMTOBE SOLVED BYTHEINVENTION

The DARCs described in US Patent No. 6,756,188, when used in combination with ETARCs to provide synergistic speed improvement, also resulted in a high level of undesirable dye density in the unexposed region of the photographic element (D _m i _n ). It would therefore be desirable to provide a novel DARC that would maintain the synergistic speed improvement as described

therein, without the higli D _m ; _n penalty.

SUMMARY OF THE INVENTION

According to the present invention there is provided a photographic element comprising a support bearing at least one silver halide emulsion layer and associated therewith (a) at least one coupler capable of releasing a development accelerator on colour development and (b) at least one electron transfer agent- releasing coupler, the coupler capable of releasing a development accelerator having the formula (I):-

COUP-(T) _n -X

(I) wherein

COUP is a coupler moiety; T is a timing group and n is 0, 1 or 2; and

X is A-(L) ₁ . -(Y) _S -NPv ₁ NR ₂ -CO-CO-R ₃ ; wherein

A is a group capable of being adsorbed to the silver halide surface; L is a divalent linking group and r is 0, 1 or 2; Y is selected from the class consisting of an unsubstituted or substituted aryl or heterocyclic ring or ring system containing one or more O, N or S atoms and s is 0 or 1;

R ₁ and R ₂ are independently selected from the class consisting of hydrogen, an unsubstituted or substituted acyl or alkyl- or aryl-sulfonyl group; and R ₃ is selected from the class consisting of R, OR, NHR and NRR ¹ ; wherein R and R ¹ are independently selected from the class consisting of an unsubstituted or substituted alkyl, aryl or heterocyclic ring or ring system containing one or more O, N or S atoms; provided that (a) when s is 0, r is 0 and

(b) the log Kow of XH is at least 3.

In another embodiment of the invention there is provided a multicolour photographic element comprising a support bearing yellow, magenta and cyan image-dye-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, wherein the element is as herein described.

In a further embodiment there is provided a method of processing an image-wise exposed photographic element containing (a) a coupler capable of releasing a development accelerator as above defined and (b) an electron transfer agent-releasing coupler, wherein the element is processed in a colour developing solution containing a colour developer.

In another embodiment there is provided the novel coupler capable of releasing a development accelerator of formula (I), as above defined.

ADVANTAGEOUS EFFECT OF THE INVENTION

The elements comprising the novel DARCs of the present invention maintain the known synergistic speed improvement when combined with ETARCs, without however the high D _m i _n penalty.

DETAILED DESCRIPTION OF THE INVENTION

An important characteristic of the compounds for use in this invention is the finely tuned balance between their lipophilic and lipophobic nature. The lipophilicity of the hydrazine derivative (X) that is released from the compound of formula (I) during colour development is a key factor in governing whether the DARC can provide the required low D _m i _n , whilst retaining a synergistic speed improvement with the ETARC.

The partition coefficient of a compound provides a means of gauging its lipophilicity but this is not a convenient property to measure. The lipophilic/lipophobic nature of a compound can, however, be estimated by calculation of its partition coefficient between octanol and water. In order to maximize the photographic effect, the partitioning into water cannot be too high.

Since it can be difficult to measure Io gP values above 3, a model can be used to compute an estimate of logP that defines the limits of the invention.

In some instances (i.e. in US Patent No. 6,319,660) ClogP was used as a predictor of logP and the model used therein utilizes the software program by W. Meylan from Syracuse Research Corporation, 6225 Running Ridge Road, North Syracuse, NY, 13212. The compound whose logP is desired is entered into the program called KowWin, 32-bit Version 1.66, written in year 2000. The computed logP is then called log Kow. A literature article that describes the program is W. M. Meylan and P.H. Howard, 'Atom/fragment contribution method for estimating octanol-water partition coefficients', J. Pharm. Sci. 84: 83-92, 1995.

Thus log Kow using the KowWin program can be used to define the values of log Kow for any class of compound which exhibits the desired effect. The terms 'ballast' or 'ballasted' as generally applied in the photographic art are often applied only loosely and without quantification to imply a restriction of movement. The activity of the compounds for use in the invention is therefore best defined in terms of the calculated log Kow values of XH.

According to the invention the log Kow of XH is at least 3, but normally less than 10, generally from 3.5 to 8, preferably from 4 to 6. It has been found that compounds with a log Kow below 3 do not provide both a synergistic speed increase with an electron transfer-releasing coupler and a satisfactorily low

Y in X of formula (I) is selected from an unsubstituted or substituted aryl ring or ring system, such as, for example, a phenyl or naphthyl group, or an unsubstituted or substituted heterocyclic ring or ring system, such as, for example, a pyridine, pyrrole, furan, thiophene, thiazole, imidazole, or a benzo derivative of any of these. However Y is preferably a phenyl group, optionally substituted, for example, with from 1 to 4 substituents selected from halogen, hydroxy, cyano, and an unsubstituted or substituted alkyl, aryl, heterocyclyl, alkoxy, acyloxy, aryloxy, carbonamido, sulfonamide, ureido, thioureido, semicarbazido, thiosemicarbazido, urethane, quaternary ammonium, alkyl- or aryl-thio, alkyl- or aryl-sulfonyl, alkyl- or aryl-sulfinyl, carboxyl, alkoxy- or aryloxy-carbonyl, carbamoyl, sulfamoyl, phosphonamido, diacylamino, imido or

acylurea group, a group containing a selenium or a tellurium atom, and a group having a tertiary sulfonium structure.

More preferably Y is an unsubstituted phenyl group or a phenyl group substituted, for example, with an alkylthio or alkylsulfonamido group or in particular with an alkyl or alkoxy group, especially in a position ortho or para to the hydrazino group, or with, for example, a trifluoromethyl group, especially in a position meta to the hydrazino group.

Ri and R ₂ are independently hydrogen or an unsubstituted or substituted acyl group, such as, for example a trifluoroacetyl group, or an unsubstituted or substituted alkyl- or aryl-sulfonyl group, but preferably R ₁ and R ₂ are each a hydrogen atom.

R ₃ is selected from the class consisting of R, OR, NEIR and NRR ¹ ; wherein R and R ¹ are independently selected from an unsubstituted or substituted alkyl, aryl or heterocyclic ring or ring system containing one or more O, N or S atoms and is preferably the group OR or NHR, wherein R is an unsubstituted or substituted alkyl group.

The group A capable of being adsorbed to the silver halide surface defines a group well known in the photographic field For example, A can be selected from the class consisting of unsubstituted or substituted purines, triazoles, benzotriazoles, tetrazoles, indazoles, imidazoles, benzimidazoles, thioureas, mercaptotetrazoles, mercaptoimidazoles, mercaptothiazoles, mercaptooxazoles, mercaptotriazoles, thioethers, thiadiazoles, aminothiadiazoles, mercapto- thiadiazoles and mercaptopurines.

Preferred silver adsorbing groups A are selected from the following:-

N-N N-N

^S^SH ^\ _S ^--NH

The divalent linking group (L) may be selected from alkylene, -CO-, -CO-O-, -0-C0-, -CONR -, -NR'CO- -NR'CONR'-, -SO ₂ NR ⁵ - -NR ⁵ SO ₂ - -O- -0(CHs) _n - -NR'SO ₂ (CH ₂ ) _n - -NR'CO(CH ₂ ) _n - -NR ⁵ SO ₂ (C ₆ H ₄ )CONH- -NR'CO(CH ₂ ) _n O-CO- or a combination of these when r is 2, for example, -0(CH ₂ V-O-, -0(CH ₂ V-O-CO-, -NR'CO(CH ₂ ) _n CONR'-, wherein R ⁵ is hydrogen or an unsubstituted or substituted alkyl, aryl or heterocyclyl ring or ring system containing one or more O, N or S atoms and n is an integer from 1-5.

The timing group T, when present, can be any group which can be used to control the speed of release of a photographically useful group (PUG). Two timing groups may be used in circumstances where staged release is required. Exemplary timing groups include those shown below, wherein PUG is included to show the point of attachment:-

wherein R ₄ is an unsubstituted or substituted alkyl group, preferably having from 1 to 6 carbon atoms, and R5 is selected from the class consisting of hydrogen and a nitro, NHSO ₂ R ⁵ or NHCOR ⁵ group, wherein R ⁵ is hydrogen or an unsubstituted or substituted alkyl, aryl or heterocyclyl ring or ring

system containing one or more O, N or S atoms, but R ₅ is preferably hydrogen, nitro OrNHSO ₂ R', wherein R' is an alkyl group having from 1 to 6 carbon atoms. The ETARC may be, for example, any ETARC such as described in US patent No. 6,756,188, the disclosure of which is incorporated herein by reference. In particular the electron transfer releasing agent preferably has the formula (II) wherein

CAR" is a carrier moiety which is capable of releasing -(W)p -ETA on reaction with oxidised developing agent;

W is a divalent linking group and p is 0,1 or 2; and ETA is a releasable l-aryl-3-pyrazolidinone electron transfer agent having a Clog P of at least 2.20 and the total sum of the Hammett σ (para) values of the substituents on the 1-aryl ring is 0.51 or less, the ETA being bonded to W or CAR" through the N in the 2-position or the O attached to the 3-position of the pyrazolidinone ring.

The ETA is released from -(W) _p - and becomes an active electron transfer agent capable of accelerating development under processing conditions used to obtain the desired dye image. On reaction with oxidized developing agent during processing, the CAR" moiety releases the -(W) _P -ETA fragment which is capable of releasing an electron transfer agent.

The electron transfer agent participates in the color development process to increase the rate of silver halide reduction and color developer oxidation, resulting in enhanced detection of exposed silver halide grains and the consequent improved image dye density. If the ETA is too mobile, it can diffuse into other layers from where it was originally released and cause increased development in those layers, resulting in wrong- way interimage and a decrease in color saturation and purity.

The preferred ETA utilized in the invention has a Clog P greater than or equal to 2.20, which reduces mobility. However, in some instances the

ETA may not be mobile enough to interact efficiently with the developed silver and developer and hence it is preferred that the Clog P of the ETA fragment be no

more than 5.0, or more preferably, no more than 4.0 or most preferably, 3.40 or less. Moreover, if the ETA contains substituents with a sum total of Hamrnett σ (para) values of greater than 0.51, then the reduction potential of the ETA fragment becomes too low to interact effectively with silver development and/or developer oxidation.

The electron transfer agent pyrazolidinones that have been found to be useful in providing development increases are derived from compounds generally of the type described in U.S. Patent Nos. 4,209,580; 4,463,081; 4,471,045 and 4,481,287 and in published Japanese Patent Application Serial No. 62-123172. Such compounds comprise a 3-pyrazolidinone structure having an unsubstituted or a substituted aryl group in the 1 -position. Preferably these compounds have one or more alkyl groups in the 4- or 5-positions of the pyrazolidinone ring.

Preferred electron transfer agents suitable for use in this invention are represented by structural formulae Ha and lib:

Ha Hb

(**denotes point of attachment to CAR'-CW^-) wherein R ² and R ³ each independently represents hydrogen, a substituted or unsubstituted alkyl group having from 1 to 12 carbon atoms, CH ₂ OR ⁷ or CH ₂ OC(O)R ⁷ , wherein R ⁷ is a substituted or unsubstituted alkyl, aryl or a heteroatom-containing group, CH ₂ SR ⁷ , or CH ₂ N(R ^7a )(R ^7b ), wherein R ^7a or R ⁷¹³ each independently represents hydrogen or a substituted or unsubstituted alkyl or aryl group.

When R ² and R ³ are alkyl, CH ₂ OR ⁷ or CH ₂ OC(O)R ⁷ groups and R ⁷ is a substituted or unsubstituted alkyl or aryl group, it is preferred that R ² and R ³ comprise from 3 to 8 carbon atoms. When R ⁷ is a substituted alkyl group, suitable

substituents may be, for example, a phenyl group, a group such as -O-(CH ₂ ) ₂ S(CH ₂ ) ₂ SCH ₃ or a benzotriazole group. When R ⁷ is a heteroatom- containing group, it is preferred that R and R comprise from 4 to 12 carbon atoms. R ⁷ may contain, for example, an imidazole, triazole or tetrazole group or a benzo derivative thereof, morpholino, or a sulfide or ether linkage.

R ⁴ and R ⁵ each independently represents hydrogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms or a substituted or unsubstituted aryl group having from 6 to 10 carbon atoms. Preferably R ⁴ and R ⁵ each represents hydrogen. It is also possible that R ³ and R ⁴ may be joined by the necessary atoms to together form a 5- or 6-membered carboxylic or heterocyclic ring system.

R ⁶ , which may be present in the ortho, meta or para positions of the aromatic ring, is any substituent which does not interfere with the required Clog P or the functionality of the ETA and meets the requirement that the sum total of all of the Hammett σ (para) coefficients is 0.51 or less. Hammett σ (para) values are as described in Substituent Constants for Correlation Analysis in Chemistry and Biology, C. Hansen and AJ. Leo, Wiley & Co., New York, 1979.

In one embodiment R ⁶ independently represents hydrogen, halogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkylthio group having from 1 to 8 carbon atoms, amido (-NHCO-), sulfonamido (-NHSO ₂ -) or a heteroatom-containing group or ring. Preferably R ⁶ is hydrogen, halogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms or a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms, m is 0 to 5. Specific R ₆ substituents that are not part of this invention are nitro, cyano, sulfonyl and sulfamoyl (-SO ₂ N<). When m is greater than 1, the R ⁶ substituents can be the same or different or can be taken together to form a carbocyclic or heterocyclic ring.

Especially preferred ETARCs, suitable for use in this invention are presented in Table I below, with R ⁴ and R ⁵ being hydrogen:

TABLE I

As used herein and throughout the specification unless where specifically stated otherwise, the term "alkyl" refers to a saturated or unsaturated, straight or branched chain alkyl group including alkenyl and aralkyl, and includes cyclic groups, including cycloalkenyl, having 3-8 carbon atoms and the term "aryl" includes fused aryl.

Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term "group" is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent's unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous or sulfur. The substituent may be, for example, halogen, such as

chlorine, bromine or fluorine; nitro; hydroxyl; cyano; caxboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, røc-butoxy, hexyloxy,

2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy and 2-dodecyl- oxyethoxy; aryl such as phenyl, 4-t-butyl-ρhenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyraniido, tetra- decanamido, alpha-(2,4-di-t-pentylphenoxy)acetamido, alpha-(2,4-di-£-pentyl- phenoxy)butyramido, alpha-(3-pentadecylρhenoxy)hexanamido, alpha- (4-hydroxy-3 -t-butylphenoxy)tetradecanamido, 2-oxopyrrolidin- 1 -yl, 2-oxo- 5-tetradecylpyrrolin-l-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-l-oxazolidinyl, 3-dodecyl-2,5-dioxo-l-imidazolyl and N-acetyl-N-dodecylaniino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxy- carbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, j^-dodecylphenylcarbonylammO _j /'-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-N'-ethylureido, N-phenylureido, N,N-di- phenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-^-pentylphenyl)-N'-ethylureido and t-butylcarbonamido; sulfonamido, such as methylsulfonarnido, benzenesulfonamido, p-toluylsulfonamido, /7-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-diρropyl- sulfamoylamino and hexadecylsulfonamido; sulfamoyl, such as N-methyl- sulfamoyl, N-ethylsulfamoyl, N,N-diproρylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di- /-ρentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl and N-dodecylsulfamoyl; carbamoyl, such as N-niethylcarbamoyl, N,N-dibutyl- carbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]- carbamoyl, N-methyl-N-tetradecylcarbamoyl and NjN-di-octylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl^-dodecyloxy-

phenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl and dodecyl- oxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyl- oxysulfonyL 2-etliylliexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxy- sulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy and hexadecylsulfonyloxy; sulfmyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl and^-toluylsulfϊnyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-£-pentylphenoxy)- ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio and/?-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, ^-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy and cyclohexylcarbonyloxy; amino, such as phenylanilino, 2-chloroanilino, diethylamino and dodecylamino; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzyl-hydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3- to 7- membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of O, N and S, such as 2-furyl,

2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl, quaternary ammonium, such as triethylammonium, and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.

Representative substituents on ballast groups include alkyl, aryl, alkoxy, aryloxy, alkylthio, hydroxy, halogen, alkoxycarbonyl, aryloxycarbonyl, carboxy, acyl, acyloxy, amino, anilino, carbonamido, carbamoyl, alkylsulfonyl, arylsulfonyl, sulfonamido and sulfamoyl groups wherein the substituents typically contain 1 to 42 carbon atoms. Such substituents can also be further substituted.

The coupler moiety COUP from which the developing accelerator moiety is released can be in the present invention any moiety of known couplers wherein COUP is bonded to the released moiety in the coupling-off position.

The coupler moieties capable by reaction with oxidised developing agent of releasing a photographically useful group are particularly well known in development accelerator technology. Typically, the coupler moiety (COUP) from which the development accelerator moiety is released includes a coupler moiety employed in conventional colour-forming photographic processes which yield coloured products based on reaction of couplers with oxidised colour developing agents. The coupler moiety can yield colourless products, or coloured products that can be washed out to remove any retained colour on reaction with oxidised colour developing agents.

The COUP can be unballasted or ballasted with an oil-soluble or lipophilic group. The coupler moiety can be a magenta, yellow, cyan or universal coupler.

Magenta couplers are described in such representative patents and publications as: US Patent Nos. 2,311,082, 2,343,703, 2,369,489, 2,600,788, 2,908,573, 3,062,653, 3,152,896, 3,519,429, and "Farbkuppler-eine Literaturiibersicht," published in Agfa Mitteilungen, Band III, pp. 126-156 (1961).

Preferably such couplers are pyrazolones, pyrazolotriazoles or pyrazolo- benzimidazoles.

Cyan couplers are described in such representative patents and publications as: US Patent Nos. 2,367,531, 2,423,730, 2,474.293, 2,772,162, 2,895,826, 3,002,836, 3,034,892, 3,041,236, 4,333,999, 4,883,746 and

"Farbkuppler-eine Literaturϋbersicht," published in Agfa Mitteilungen, Band HI, pp. 156-175 (1961). Preferably such couplers are phenols and naphthols.

Yellow couplers are described in such representative patents and publications as: US Patent Nos. 2,298,443, 2,407,210, 2,875,057, 3,048,194, 3,265,506, 3,447,928, 4,022,620, 4,443,536, and "Farbkuppler-eine Literatur- ϋbersicht," published in Agfa Mitteilungen, Band III, pp. r!2-126 (1961). Such couplers are typically open chain ketomethylene compounds.

Couplers that form colourless products upon reaction with oxidised colour developing agent are described in such representative patents as: British Patent No. 861,138; US Patent Nos. 3,632,345, 3,928,041, 3,958,993 and 3,961,959. Sometimes coloured products are foπned which are removed from the photographic material by dissolution in the developer medium. Typically such couplers are cyclic carbonyl containing compounds that form colourless products on reaction with an oxidised colour developing agent.

According to the present invention, the DARC coupler gives a dye on reaction with oxidised colour developing agent at the coupling-off position, the thus released moiety forming a development accelerator.

The coverage of a DARC(s) in the photographic material is from 0.1 μmol/m ² to 25 μmol/m ² , preferably 0.3 μmol/ m ² to 15 μmol/m ² , most preferably 0.5 μmol/m ² to 10 μmol/m ² and the coverage of an ETARC(s) is from 6 μmol/m ² to 1000 μmol/m ² , preferably 15 μmol/ m ² to 250 μmol/m ² , most preferably 20 μmol/m ² to 140 μmol/m ² .

Thus the ETARC(s) is present in a ratio of 5% to 60% of total coupler (image coupler + ETARC) on a molar basis, preferably 10% to 50% of total coupler, most preferably 20% to 40 % of total coupler, (the amount of DARC(s) being very small in comparison). The photographic material of the present invention will normally also contain one or more conventional image-dye forming couplers in addition to the DARC(s) and the ETARC(s).

The DARC(s) and ETARC(s) of the present invention and, when present, the conventional coupler compound(s) can be incorporated in silver halide emulsions and the emulsions can be coated on a support to form a photographic recording material. Alternatively, one or more DARCs and ETARCs and conventional couplers can be incorporated in photographic layers

adjacent to the silver halide emulsion where, during development, the DARC(s) and ETARC(s) and coupler(s) will be in reactive association with the oxidised colour developing agent.

The photographic elements can be single colour elements or multicolour elements. 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. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.

A typical multicolour photographic element comprises a support bearing a cyan dye image-forming unit comprised of a least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye- forming coupler, a magenta dye image-forming unit comprising at least one green sensitive silver halide emulsion layer having associated therewith at least one magenta dye- forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers and subbing 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 Item 36544, September 1994, published by Kenneth Mason Publications, Emsworth, Hants POlO 7DQ, United Kingdom which will be identified hereafter by the term "Research Disclosure".

The contents of the Research Disclosure, including the patents and publications referenced therein, are incorporated herein by reference, and the Sections hereafter referred to are Sections of the Research Disclosure.

The silver halide emulsions employed in the elements of this invention can be either negative-working or positive-working. Suitable emulsions and their preparation, as well as methods of chemical and spectral sensitisation,

are described in Sections I through IV. Colour materials and development modifiers are described in Sections V and XXI. Vehicles are described in Section IX and various additives such as brighteners, antifoggants, stabilisers, light-absorbing and scattering materials, hardeners, coating aids, plasticisers, lubricants and matting agents are described, for example, in Sections V, VI, VIII, X, XI, XII and XVI. Manufacturing methods are described in Sections XIV and XV, other layers and supports in Sections XIII and XVII, processing methods and agents in Sections XIX and XX and exposure alternatives in Section XVIII. 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-phenylenediamines. Especially preferred are 4-amino-3-metliyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-β-(methanesulfonamido)ethylanili ne sulfate hydrate, 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylamline sulfate, 4-amino- 3-β- (methane-sulfonamido)ethyl-N,N-diethylaniline hydrochloride and 4-atnino- N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfate.

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. Examples of suitable DARCS within the scope of formula (I) are as follows, wherein the log Kow of XH is included under each formula in parenthesis but the invention is in no way to be construed as limited thereto:-.

CYAN DARC COUPLERS

IC1 IC2 (3.74) (5.71)

IC3 (3.70)

IC4 (5.42)

IC5 (4.08)

IC6 IC7 (5.73)- (5.62)

IC8 IC9 (6.21) (5.37)

IC10 (5.62)

IC11 (5.54)

IC12 (3.95)

IC13 IC14 (6.93) (3.26)

YELLOW DARC COUPLERS

IY1 (5.37)

IY2 (6.92)

IY3 (5.90)

IY4 (4.07)

IY5 (5.07)

IY6 (7.45)

IY7 (4.70)

IY8 (5.08)

IY9

10 (4.19)

MAGENTA DARC COUPLERS

IM1

(6.69)

IM2 (7.61)

IM3 (7.99)

IM4 (4.57)

IM5 (3.48)

(3.90)

UNIVERSAL DARC COUPLERS

IU1 IU2 (5.71) (6.21)

IU3 (5.54)

IU5 (4.07)

Tlie invention is described herein with reference to the following examples which are not however to be construed as limiting the scope thereof.

EXAMPLE 1

Preparation of PARC (IC2)

All the compounds prepared had infra-red, mass and NMR spectra which were in accord with pure samples of the desired products

The synthetic pathway to DARC (IC2) is described in some detail below. It illustrates the general method by which other examples may be prepared.

(1) (2) (3)

C ₁₆ H ₃₃ NH ₂

IC2

Preparation of Intermediate (2)

4-Nitrophenylhydrazine (1) (100. Og, 0.653 mol) was dissolved in a mixture of dry tetrahydrofuran (THF) (600ml) and dry N,N-dimethylacetamide (120ml). N,N-dimethylaniline (79.1g, 0.653 mol) was added and the dark solution stirred under nitrogen. The flask was immersed in an ice/acetone bath and ethyl oxalyl chloride (89.2g, 0.653 mol) in dry THF (100ml) was added dropwise over 45 min. with stirring. The reaction was left to stand overnight and the volume of solvent reduced under vacuum. The residue was slowly added to a stirred mixture of ice/water (3.5 1) and concentrated hydrochloric acid (10ml). An orange/brown solid was filtered and washed with copious amounts of water. The product was dried in the vacuum desiccator over the weekend. Yield = 153.Og (93%).

Preparation of Intermediate (3)

A 500ml hydrogenation vessel was charged with 0.5g of Pd/C (5%, Aldrich), THF (250ml) and Intermediate (2) (6.Og, 0.24 mol). The reaction mixture was placed under 32 atmospheres pressure of hydrogen overnight with stirring. The reaction mixture was filtered and the solvent removed on the rotary evaporator. The yield of product was assumed to be 90% and was taken directly on to the next stage without further purification.

Preparation of Intermediate (4)

A preparation of this compound is given in DE Offenlegungscrift 2247496.

Preparation of Intermediate (5)

A preparation of this compound is given in Journal of Heterocyclic Chemistry (1978), 15(6), 981-5, entitled 4,5-Dihydro-5-thioxo-lH-tetrazole- 1-alkanoic and alkanesulfonic acids and their amide derivatives by Berges, David A.; Chan, George W.; Polansky, Theodore J.; Taggart, John J.; Dunn, George L.

Preparation of Intermediate (6)

Intermediate (4) (84.Og, 0.13 mol) and mercaptotetrazole (5) (24.4g, 0.14 mol) were dissolved in dimethylformamide (1200 ml) with stirring. The mixture was heated to 9OC and potassium carbonate (40.Og, 0.28ml) added in small portions. The mixture was maintained at 9OC for 5 h. and left at room temperature overnight. The reaction mixture was poured into a mixture of iced water (2.5 1) with concentrated hydrochloric acid (80ml) and allowed to stir. A brown gum was obtained and this was extracted into ethyl acetate (4 x 200ml). The combined extracts were washed with dilute hydrochloric acid, then brine and dried over magnesium sulfate. The solvent was removed on the rotary evaporator. The residue was stirred overnight with diethyl ether (250ml) and the pale pink solid product filtered and dried under vacuum. Yield = 76.Og (90%)

Preparation of Intermediate (7)

To a solution of intermediate (6) (42.94g, 0.06 mol) and intermediate (3) (13.4g, 0.06 mol) in dry THF (150ml) a solution of N,N'-dicyclo- hexylcarbodiimide (12.4g, 0.06 mol) in dry THF (100ml) was added dropwise with stirring. The mixture was allowed to stir for 2 days. The mixture was filtered and the solvent removed under vacuum. A 5g sample of the crude product was purified by recrystallization from methanol. Recovery of purified material gave a yield= 1.7g (34%).

Preparation of DARC (IC2)

A solution of intermediate (7) (2.0g, 0.00235 mol) in 25ml dry

THF and hexadecylamine (1.4g, 0.006 mol) was heated under nitrogen at lOOC. The mixture was allowed to reflux overnight. The mixture was allowed to cool. The reaction mixture was poured into a mixture of ice/water (1 1) and concentrated hydrochloric acid (0.1ml). The product was filtered, washed with water and air- dried. The material was extracted with diethyl ether and then boiling ethyl acetate, filtered and dried. Yield = 0.7g (29%)

EXAMPLE 2 Single Layer Film

Cyan development accelerator-releasing couplers of the present invention (and control compounds) were incorporated as solid particle dispersions in photographic coatings on a transparent cellulose acetate support (with Gel U-coat and removable carbon antihalation backing), according to the coating diagram shown in TABLE 2 below.

TABLE 2 Structure of Photographic Element

Gel Supercoat Gelatin 1.000 g/m ²

Bis(vinylsulfonyl)methane (hardener) 0.166 g/m ²

Red-sensitised silver bromoiodide 0.807 g/m ²

(96.3% silver bromide, 3.7 % silver iodide)

Image Coupler 0.269mmol/m ²

Emulsion Layer DARC 0.008mmol/m ²

ETARC-I 0.187mmol/m ²

Gelatin 2.420 g/m ²

Support Cellulose acetate (with Gel U-coat and removable carbon antihalation backing)

Solid particle dispersions of the DARCs were prepared by milling with zirconium beads (1.0-1.25 mm) in water with a blend of commercially available surfactants according to the following formulation:-

DARC 0.40Og

10% Dapral GE202 (Akzo Nobel Chemicals) 0.800g

47% Dowfax 2Al (Dow Chemicals) 0.043g

10% Luviskol K30 (B ASF) 0.40Og Water 18.357g

After milling for 7 days, the milling media were removed using a suitably fine sieve and the resultant dispersion diluted 1:1 with water to give 40.Og of a 1% DARC ball-milled dispersion of average particle size < 250nm (Z- Average mean, Malvern ZetaSizer).

Aqueous dispersions of the image coupler and ETARC-I were prepared by methods known in the art. The cyan dye- forming coupler dispersion contained 8% by wt. of gelatin, 6% by wt. of image coupler and a 1 : 1 :2 weight ratio of coupler to di-n-butyl sebacate coupler solvent to ethyl acetate auxiliary solvent. The auxiliary solvent was included to aid in dispersion preparation and was removed by evaporation. The cyan ETARC dispersion contained 6% by wt of gelatin, 2% by wt of ETARC-I and a 1:2:3 weight ratio of coupler to di-ethyl lauramide coupler solvent to 2-(2-butoxyethoxy)ethyl acetate auxiliary solvent. The auxiliary solvent was included to aid in dispersion preparation and was removed by washing the dispersion for 6 h at 4C and pH 6.0.

The single layer photographic coatings prepared in this way were slit and chopped into 30cm x 35mm test strips. After hardening the strips were exposed (0.01 sec) through a 0-4.0 neutral density step wedge (0.2 ND step increments) and Daylight V and Wratten 9 and 1.0 ND filters and then processed through a standard KODAK FLEXICOLOR™ (C-41) process as described in the

British Journal of Photography Annual (1988) 196 -198 using the following steps and process times:

Developer 2.5 min.

Bleach 4.0 min. Wash 2.0 min.

Fix 4.0 min.

Wash 2.0 min.

The processed images were read with red light to determine the D _tn i _n and HKIT speed (the exposure point minus the same point for the corresponding image coupler-only coating as computed as follows: the exposure required to produce a specified firm density (Ds) in the toe of a sensitometric DlogE curve of 0.2 x gradient (γ) at that density above D _mh , (i.e. Ds = 0.2γ +

The image coupler, ETARC-I and comparative DARCS are shown below; wherein the log Kow of XH for the comparative DARCS and the Clog P of the ETA of the ETARC is included under each formula in parenthesis:-

Image Coupler • ETARC-I (2.90)

C1 C2

(-1.29) (0.80)

C3 (2.67)

TABLE 3

As seen in TABLE 3, the comparative DARC, Cl, known in the art, exhibited good synergistic speed increase in combination with ETARC-I but suffered from very high D _m i _n - The comparative compounds Cl and C3, having the novel DARC structure but with the log Kow of their corresponding XH less than 3, did not provide any synergistic speed gain with ETARC-I although they showed much lower D _m i _n .

DARCs of the present invention ICl and IC2 with the log Kow of their corresponding XH greater than 3 showed both a synergistic speed advantage in combination with ETARC-I and a superior D _mln when compared with the D _m j _n of CIfET ARC-I combination.

The patents and publications referred to herein are incorporated by reference in their entirety. The 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 claims of the invention.