# Patent

## Title
Process for preparing a pigment based on 4,4',7,7'-tetrachlorothioindigo

## Abstract

This is a division of application Ser. No. 454,092 filed 12/18/82 now U.S. Pat. No. 4,416,971.

## Background
1. Field of the Invention

This invention relates to novel xanthene compounds and to their use, e.g., as light-screening dyes in photographic products and processes.

2. Description of the Prior Art

It is well known that photographic film, and especially multicolor films, may and generally do vary from lot to lot, notwithstanding efforts to "repeat" previous films. Manufacturers of multicolor photographic films have developed a number of procedures to minimize the effects upon the final multicolor image of unavoidable variations in the manufacturing operations. These variations are reflected primarily in shifts in color balance as reflected in mismatching of the D log E curves of the individual red, green and blue exposures. Equipment used to coat multicolor films is highly precise but variations between intended coverage of silver halide and/or the dye image-forming materials do occur. Repeat batches of silver halide emulsions may, and usually do, vary in their photographic response. Individual layers may be dried to slightly different degrees. Films are stored for a period of time after coating to allow the films to "age", so that changes in sensitometry following coating have an opportunity to reach a plateau prior to sale. If the film is designed to be developed by a photofinisher or in a darkroom, processing of the exposed multicolor film is controlled within very narrow limits, typically within plus or minus a half degree of a prescribed temperature, in order to minimize sensitometric variations from film to film. Where the multicolor film is of the negative type, an opportunity to adjust the sensitometry occurs in printing the desired final positive image, during which operation the printing exposure may be appropriately color filtered.

The basic sources of sensitometric variations noted above exist also in multicolor diffusion transfer films, with the added complication that once the film is shipped, the sensitometric properties are essentially fixed. The opportunity for adjustment provided in darkroom processing, practically speaking, is unavailable for users of self-developing films. While professional and advanced amateur photographers may be skillful enough to utilize color correction filters to at least partially "rebalance" the color balance, ordinary users of the film would only be confused by such additional operations.

It is well known to use light-screening dyes in photographic elements. Such a dye may be incorporated as a filter dye in a light-sensitive emulsion layer(s) or in a layer coated over one or more light-sensitive emulsion layers or between two differently color-sensitized emulsion layers to modify the light record in the emulsion layer or to control the spectral composition of light falling on the underlying light-sensitive layer, or it may be incorporated as an anti-halation dye in a non-light-sensitive layer positioned on either side of a support carrying the light-sensitive layer(s).

The dyes employed for these purposes, in addition to having the requisite spectral absorption characteristics for their intented use, should be photochemically inert, that is, they should not have any adverse effect on the properties of the light-sensitive emulsion layer(s), and also, they should be capable of being decolorized or removed during photographic processing so as not to leave stain in the processed photographic element. In photographic processes where the dye is removed by being dissolved in a processing solution, it is usually preferred that the dye also decolorize in order to avoid contamination of the processing solution and to prevent staining from residual dye in the processed light-sensitive element.

Though various classes of dyes have been proposed for use in antihalation and color correction filter layers, the dyes heretofore employed have not been altogether satisfactory. Some of the dyes tend to reduce sensitivity, fog or exert other adverse effect on the light-sensitive material. However, the major drawback of previously employed dyes is their tendency to cause stain due to incomplete decolorization or reversal of some of the decolorized form to the original colored form. For example, some classes of dyes rely on the presence of a reagent, such as, a sulfite for "bleaching", i.e., decolorization and unless the dyes are removed from the light-sensitive material during or after processing, their color may reappear in time.

Among the classes of light-screening dyes used previously are the triarylmethane and xanthenes. For example, U.S. Pat. Nos. 1,879,537; 1,994,876; 2,350,090 and 3,005,711 disclose the use of fuchsone-type dyes in antihalation layers, and U.S. Pat. Nos. 3,406,069 and 3,615,548 are concerned with the metal chelates of fuchsone dyes as antihalation dyes. These and other types of triarylmethane dyes suffer from one or more of the drawbacks discussed above, and in particular, prior dyes of this type have been difficult to keep decolorized at the pH's normally encountered during processing subsequent to "bleaching" and in the final product. Xanthenes have been employed in antihalation layers that are removed during photographic processing. For example, U.S. Pat. Nos. 2,182,794; 2,203,767 and 2,203,768 disclose the use of rhodamine dyes in certain antihalation layers that are removed during processing in an acid bath or a plain water rinse bath depending upon the solubility characteristics of the particular layer.

U.S. Pat. Nos. 4,258,118 and 4,304,834 disclose certain 3,6-disubstituted xanthene compounds possessing a substituted phenyl moiety in the 9-position which moiety has the formula ##STR3## wherein X is ##STR4## and R' is alkyl and Y is an electron-withdrawing group. In these compounds, the X group undergoes an irreversible cleavage reaction in base to provide a moiety that adds to the central carbon atom to form a new ring-closed compound which is colorless. As disclosed and claimed in these patents, these compounds are useful as photographic light-screening dyes which offer advantages over prior light-screening dyes because of their ability to decolorize completely and irreversibly to a substantially inert product that remains colorless over a broad pH range.

Xanthenes of the structure ##STR5## wherein R is H or --COCH.sub.3 are disclosed in Beilstein's Handbuch der Organischen Chemie, Vol. 27, p. 534. These compounds are synthesized by condensing m-diethylaminophenol with saccharin at a temperature of 165.degree. C. to give the compound wherein R is H, which compound is then heated to boiling with acetic acid anhydride to yield the N-acylated derivative. As reported therein, solutions of the N-acetyl compound, unlike solutions of the N-unsubstituted compound (R=H), are not decolorized by boiling, and the acetyl group splits off only after prolonged boiling with alcoholic sodium hydroxide. Further to the N-unsubstituted compound, it has been found that this compound is colorless at an alkaline pH, faintly colored at neutrality and becomes more intensely colored as the pH is reduced.

The present invention is concerned with a new class of xanthene compounds which find utility as photographic light-screening dyes, and like the xanthene compounds of the aforementioned U.S. Pat. Nos. 4,258,118 and 4,304,834, they also are free from the deficiencies associated with the dyes previously used for this purpose. The subject dyes are efficient absorbers of radiation within a predetermined range in the visible range of 400 to 700 nm, may be incorporated in gelatin or other processing composition-permeable colloidal binding agents and are decolorized at an alkaline pH to yield a colorless product. Because of their ability to decolorize completely and irreversibly in base without requiring an additional reagent, such as, a sulfite for the "bleaching" reaction and because the new colorless product produced upon irreversible cleavage remains colorless in aqueous solution from pH 14 to below neutrality, the cleavage product normally may be retained in the photographic light-sensitive element without the possibility of color reappearing in time. Besides being non-staining, the compounds usually are substantially inert with respect to the light-sensitive material and thus, may be positioned in a layer adjacent to a silver halide emulsion layer or directly incorporated into an emulsion layer without having any adverse effect on the properties of the emulsion. In addition to the foregoing advantages, the rate at which the subject dyes decolorize at a given pH can be readily adjusted to meet the requirements of a given photographic system.

It is therefore the primary object of the present invention to provide novel xanthene compounds.

It is another object of the present invention to provide xanthene compounds useful as light-screening dyes in photographic products and processes.

It is a further object of the present invention to provide photographic products and processes employing said compounds.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

This invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others and the products and compositions possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a diagrammatic, enlarged cross-sectional view of a diffusion tranfer film unit incorporating a xanthene dye of the present invention as a bleachable antihalation dye layer;

FIG. 2 is a diagrammatic, enlarged cross-sectional view of another diffusion transfer film unit incorporating a xanthene dye of the present invention as a color correction filter dye in the image-receiving layer; and

FIG. 3 is a graph based on the Hammett Equation where a change in the Hammett sigma value for the substituent X of the subject xanthene compounds is linearly correlated with the hydrolysis rate of the compounds in 0.25N potassium hydroxide solution.

Specifically, the compounds provided in accordance with the present invention may be represented by the formula ##STR6## wherein each R.sup.1 is the same and is selected from ##STR7## R.sup.2 is alkyl, R.sup.3 is an electron-withdrawing group positioned ortho, meta or para to said N atom, R.sup.4 is hydrogen, alkyl or an electron-withdrawing group positioned ortho, meta or para to said N atom; R.sup.5 is alkyl; X is hydrogen, an electron-withdrawing group or an electron-donating group; and A is an anion. By "electron-withdrawing group" is meant a group having a positive sigma value as defined by Hammett's Equation, and by "electron-donating group" is meant a group having a negative sigma value as defined by Hammett's Equation.

Typically said R.sup.2, R.sup.4 and R.sup.5 groups are alkyl groups containing 1 to 4 carbon atoms, e.g., methyl, ethyl, n-propyl, n-butyl, and s-butyl, and preferably are methyl.

Any electron-withdrawing group or any electron-donating group may be used for X, and any electron-withdrawing group may be used for R.sup.3 and R.sup.4. Typical electron-withdrawing groups that may be used for R.sup.3, R.sup.4 and X include ##STR8## Br and Cl. Typical electron-donating groups that may be used for X, when X is electron-donating rather than electron-withdrawing, include ##STR9## The sigma value for these and other groups have been reported in Lang's Handbook of Chemistry, John A. Dean, McGraw-Hill, New York, 1972, pp. 3-132 to 3-137.

The anion associated with the subject xanthene compounds, i.e., A in formula I above may be any of the simple anions, for example, tosylate, sulfate, nitrate, perchlorate, methane sulfonate, methane hydrogen disulfonate, m-benzene hydrogen disulfonate, acetate, oxalate, or halide, such as, chloride, bromide or iodide.

It should be understood that other resonance forms of the subject compounds are intended to be encompassed by Formula I.

As noted above, the subject compounds are initially colored, i.e., capable of absorbing visible radiation, and at an alkaline pH, are converted to a colorless product by undergoing an irreversible cleavage reaction with base, namely, a hydrolysis reaction. The colorless product formed is a new compound which is different from and non-reversible to the colored compound by a change in pH. In particular, it is the benzoylsulfonamido group substituted on the phenyl moiety that undergoes the irreversible cleavage reaction in alkaline solution that is complete within a predetermined time at a predetermined alkaline pH to give the new colorless compound, namely, the cyclic sulfonamide, as illustrated by the following wherein A is Cl.sup.- ##STR10##

It will be appreciated that the by-product formed upon hydrolysis of the benzoylsulfonamido group also is colorless. Because the said hydrolysis reaction proceeds at a faster rate at higher pH's, the subject compounds are particularly suitable for use in photographic processes wherein the pH is maintained above about 10 at least for the time necessary for decolorization to the corresponding ring-closed product.

As noted above, the rate at which the subject dyes decolorize at a given pH may be readily adjusted to meet the needs of a given photographic process. This is achieved by appropriate selection of the X group. Compared to X being H, the hydrolysis rate may be decreased by using an electron-donating group as X, and the hydrolysis rate may be increased by using an electron-withdrawing group as X. The particular rate required for decolorization in a given photographic system and the particular X group needed to provide the desired rate may be determined empirically.

Also as noted above, the cyclic sulfonamides formed as a result of said alkaline hydrolysis remain colorless to below neutrality. Since the final pH, i.e., the pH ultimately attained subsequent to processing may vary for different photographic systems, it will be appreciated that the combined electron-withdrawing effect of the R.sup.3 and R.sup.4 groups should be sufficient to provide a cyclic sulfonamide that remains colorless at a given final pH. For lower pH's of 4 to 5, the electron-withdrawing group(s) selected will have a greater negative sigma value than required for a pH of 6, for example. The particular groups needed to adjust the electron withdrawing effect to ensure that the cyclic sulfonamide cleavage product remains colorless at a particular pH below neutrality may be readily determined empirically for a given photographic system.

The xanthene dyes of the present invention may be prepared in a conventional manner using the procedures disclosed in the aforementioned U.S. Pat. Nos. 4,258,118  and 4,304,834. For example; the subject dyes may be synthesized

(a) by reacting a cyclic sulfonamide of the formula ##STR11## wherein R.sup.1 and R.sup.5 have the same meaning given above with a reducing agent to give the corresponding reduction product of the formula ##STR12## wherein R.sup.1 and R.sup.5 have the same meaning given above;

(b) reacting said reduction product with the appropriate benzoyl chloride, ##STR13## to give the leuco dye precursor of the formula ##STR14## wherein R.sup.1, R.sup.5 and X have the same meaning given above; and

(c) oxidizing said leuco dye precursor preferably using o-chloranil or p-chloranil as the oxidizing agent followed by isolating the dye from its chloranil complex with acid to yield the dye product.

The starting materials for use in step (a) may be synthesized by reacting sulfonefluorescein dichloride with indoline or with a substituted aniline, ##STR15## wherein R.sup.3 and R.sup.4 have the same meaning given above, to produce the corresponding 3,6-disubstituted sulfonefluorescein. Rather than replacing both chloro groups of the sulfonefluorescein dichloride in a single step, they may be replaced stepwise. Where the 3,6-substituents are derived from an aniline, the compound is reacted with an alkylating agent to substitute the N atoms of the 3,6-anilino substituents with alkyl. The 3,6-disubstituted compounds are then treated with phosphorus pentachloride or thionyl chloride to give the corresponding sulfonyl chlorides which are converted to the cyclic sulfonamides with ammonia.

The benzoyl chlorides, if not commercially available, may be derivatized with the desired X group to provide the acylating agent for use in step (b) above.

The following examples are given to further illustrate the present invention and are not intended to limit the scope thereof.

Preparation of the compound having the formula ##STR16##

(a) 10.0 g of the compound having the formula ##STR17## was dissolved in a solution of 60 ml of N-methylpyrrolidinone and 15 ml trifluoroacetic acid and then heated to 60.degree. C. under nitrogen. Zinc dust (5.0 g) was added all at once and the reaction mixture was stirred at 65.degree. C. for one-half hour. The light grey reaction mixture was poured into a solution of 500 ml methanol/40 ml conc. hydrochloric acid and stirred overnight. The solid was collected, washed well with methanol and dried in vacuo to yield 10.8 g of the intermediate having the formula ##STR18##

(b) 9.0 g of the intermediate prepared in step (a) was added to a suspension of 11.4 g of p-nitrobenzoyl chloride in 200 ml of pyridine at 5.degree. C. The reaction mixture was stirred at 5.degree. C. for one hour and then allowed to stir at room temperature. After 5 hours, TLC showed the reaction to be about 50% complete. Another 4.1 g of p-nitrobenzoyl chloride was added and the reaction mixture was stirred over the weekend. The reaction mixture was then poured into 1600 ml of water and the resulting precipitate was collected to give the dye precursor having the formula ##STR19##

(c) The dye precursor of step (b) was dissolved in 100 ml of a solution of 80% methyl ethyl ketone/20% methanol. To this solution was added 7.4 g of p-chloranil. After refluxing for 2 hours, TLC indicated that reaction was substantially complete. The solvent was evaporated and the solid was refluxed for 2 hours in 200 ml of toluene. The solid comprising the chloranil complex of the dye product was then dissolved in 300 ml of dichloromethane and 10 ml of methanol and saturated for 20 minutes with dry HCl. The solution was stirred for one hour and the solvents were evaporated to leave 19.5 g of blue solid. The title compound was isolated using high pressure liquid chromatography and 5-6% methanol/dichloromethane as the eluent.

Preparation of the compound having the formula ##STR20##

Step (a) was carried out in the same manner as described in Example 1 to give the intermediate having the formula ##STR21##

(b) The intermediate prepared in step (a) (0.78 g) was added to 20 ml of cold (5.degree. C.) pyridine. A partial solution occurred, then a solid formed. To the suspension was added 1.0 g of p-dimethylaminobenzoyl chloride, and the reaction mixture was allowed to stir at room temperature over the weekend. An additional 0.4 g of the benzoyl chloride was added, and the reaction mixture was stirred for 6 hours. The reaction mixture was then filtered and the filtrate was precipitated into 200 ml of water. The pale blue precipitatate was collected, air dried, washed with methanol and again air dried to give 1.3 g of the dye precursor having the formula ##STR22##

(c) The dye precursor prepared in step (b) (1.3 g) was dissolved in 25 ml of 20% methanol in methyl ethyl ketone. To complete solution, 20 ml of dichloromethane was added. To this solution was added 0.87 g of p-chloranil, and the mixture was refluxed for 1.5 hours. The reaction mixture was cooled and precipitated into methanol. The solid was refluxed with toluene to remove impurities and excess chloranil. The solid was then dissolved in dichloromethane, and dry HCl was bubbled into the solution for 10 minutes. After stirring for one hour, the solvent was removed by evaporation and the blue solid was chromatographed using high pressure liquid chromatography to give 0.17 g of the title compound.

Preparation of the compound having the formula ##STR23##

(a) 1.5 g of the compound having the formula ##STR24## wherein R.sub.1 has the same meaning given above was dissolved in 40 ml of acetic acid and heated to 60.degree. C. under nitrogen. A total of 0.75 g of zinc dust was added in three portions over one-half hour. The reaction was heated at 60.degree. C. for 2 hours, filtered and the filtrate was precipitated into 500 ml of water. The precipitate was collected and air dried to give 1.5 g of the following intermediate as a light pink solid ##STR25## wherein R.sub.1 has the same meaning given above.

(b) The intermediate prepared in step (a) (0.2 g) was dissolved in 20 ml of pyridine and cooled to 0.degree. to -5.degree. C. p-Chlorobenzoyl chloride (0.4 g) was added and the reaction mixture was stirred at 5.degree. C. for one hour then allowed to warm to room temperature. After stirring at room temperature for 4 hours, TLC showed some unreacted intermediate. An additional five drops of the benzoyl chloride was added and the reaction mixture was stirred for an additional hour. The reaction mixture was then poured into water and the precipitate was collected and air dried to give 0.6 g of the following dye precursor as a white solid ##STR26## wherein R.sub.1 has the same meaning given above.

(c) The dye precursor prepared in step (b) (0.6 g) was dissolved in 25 ml of dichloromethane and 0.28 g of p-chloranil was added. The reaction mixture was stirred at room temperature and TLC after 2 hours indicated that the reaction was about 50% complete. The mixture was allowed to stir over the weekend and then was saturated with dry HCl for one-half hour. The reaction mixture was poured into ether and a super-fine precipitate was separated by centrifuge and dried to give 0.43 g of solid. This solid was chromatographed on silica gel using 4-5% methanol/dichloromethane as eluent to give 0.32 g of the title compound.

Preparation of the compound having the formula ##STR27##

The title compound (0.285 g) was prepared in the same manner as described in Example 3 above except that benzoyl chloride was employed in step (b).

Preparation of the compounds of the formulae ##STR28## Example 5                Example 6 ______________________________________ ##STR29## ##STR30## ______________________________________

The title compounds were prepared in the same manner described in Example 3 above except that p-nitrobenzoyl chloride was employed in step (b).

Preparation of the compound having the formula ##STR31##

(a) 0.4 g of the compound having the formula ##STR32## wherein R.sub.2 has the same meaning given above was added to a cooled solution (5.degree. C.) of 0.21 g of p-methoxybenzoyl chloride in 20 ml of dry pyridine. The reaction mixture was stirred in an ice bath for one hour and then kept at about -5.degree. C. for 5 ours. The reaction mixture was precipitated into 400 ml of water and the purple solid was collected, air dried, and chromatographed on a medium pressure column of silica gel using 2% methanol/dichloromethane as eluent to give the intermediate having the formula ##STR33##

(b) The intermediate prepared in step (a) (0.5 g) was dissolved in 10 ml of dimethyl sulfoxide and 0.04 g of 60% sodium hydride was added along with 0.5 ml of methyl iodide. The reaction mixture was heated to 50.degree.-60.degree. C. for 2 hours and allowed to stir overnight at room temperature. An additional 0.04 g of 60% sodium hydride was added along with one ml of methyl iodide and heated at 50.degree. C. for 7 hours with an additional one ml of methyl iodide being added after 3 hours. After taking a sample for TLC, the reaction was left again overnight with additional methyl iodide. The reaction mixture was then poured into water and the precipitate was collected and air dried to give 0.46 g of material. This material was chromatographed on a medium pressure silica gel column using 5% methanol/dichloromethane as eluent to give 0.27 g of the title compound.

The following intermediates also were prepared by reduction of the corresponding cyclic sulfonamides as described in the above Examples. ##STR34## It will be appreciated that these intermediates may be reacted with a benzoyl chloride to provide the dye precursor followed by oxidation and isolating the dye product using the procedures described above.

As noted previously, the dyes of the present invention have the ability to decolorize completely and irreversibly in base by undergoing an irreversible cleavage reaction within a predetermined time at a predetermined pH to give a new colorless compound which remains colorless at the pH's normally encountered during processing subsequent to "bleaching" so that the new compound may be retained in a photographic film unit, e.g., a developed photosensitive element without the possibility of color reappearing in time. Typically, dyes may be selected for use as antihalation dyes, e.g., in a non-light-sensitive layer positioned intermediate a photosensitive silver halide emulsion layer and the support. Also, dyes may be selected for use as color correction filter dyes where absorption of light within a particular wavelength range during exposure is desirable for achieving appropriate color balance.

Illustrative film units in which the dyes of the present invention may be advantageously used as antihalation dyes are described, for example, in British Patent No. 1,482,156. These film units comprise, in the order in which incident light passes therethrough, an additive multicolor screen, a photosensitive silver halide emulsion layer, an antihalation layer in which the selected compound may be disposed, and preferably, an image-receiving layer. As described therein, exposure of the silver halide layer is accomplished through the screen which possesses optical filter elements selectively transmitting predetermined portions of incident radiation, e.g., red, green and blue light, to the underlying photosensitive silver halide layer. Upon photographic processing with an aqueous alkaline processing composition, soluble silver complex is transferred by diffusion and deposited in a superposed image-receiving layer as a function of the degree of exposure of silver halide behind each filter element. The silver image thus formed may then serve to modulate the quantity of light passing through the filter elements in the reverse direction during projection through a transparent support.

In a preferred embodiment, the image-receiving layer is intermediate the photosensitive silver halide emulsion layer and the additive multicolor screen and remains in position as part of an integral film unit prior to, during and after formation of the image. The antihalation dye is disposed in a processing composition permeable layer adjacent to the photosensitive layer on the side opposite the screen and serves to prevent the reflection or back-scattering of incident light which has passed through the photosensitive layer.

As noted above, the dyes of the present invention also are useful as color correction filter dyes in photographic film units comprising multilayered, multicolor photosensitive elements employing a blue-, a green- and a red-sensitive silver halide layer, and particularly in integral negative-positive diffusion transfer film units wherein the image-receiving layer carrying the color transfer image is not separated from the developed photosensitive layers after processing but both components are retained together as a permanent laminate. Included as part of the laminate is a layer of light-reflecting material, preferably titanium dioxide, positioned between the image-carrying layer and the developed photosensitive layer(s). The light-reflecting layer separating the image-carrying and photosensitive components provides a white background for the transfer image and masks the developed photosensitive layer(s). In addition to these layers, the laminate usually includes dimensionally stable outer layers or supports, at least one of which is transparent so that the resulting transfer image may be viewed by reflection against the background provided by the light-reflecting layer.

Illustrative of patents describing such film units are U.S. Pat. No. 2,983,606 issued Mar. 9, 1961 to Howard G. Rogers, U.S. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land, U.S. Pat. Nos. 3,594,164 and 3,594,165 issued July 20, 1971 to Howard G. Rogers, and U.S. Pat. No. 3,647,437 issued Mar. 7, 1972 to Edwin H. Land. U.S. Pat. No. 4,329,411 issued May 11, 1982 to Edwin H. Land discloses multicolor diffusion transfer film units, wherein a layer of a dye, preferably a dye bleachable by the processing composition, is so positioned that photoexposure is effected therethrough, whereby said dye layer is effective as a color correction filter. For convenience, the disclosure of this patent is specifically incorporated herein.

Whether used as antihalation dyes, color correction filter dyes or in other conventional photographic light-screening applications, the dyes of the present invention when disposed in a processing composition-permeable layer are completely and irreversibly decolorized by contacting with an aqueous alkaline processing composition for the time necessary for converting the colored dye compound to the new colorless ring-closed compound. The time required for decolorization, i.e., for conversion of the colored compound to the colorless product via said irreversible cleavage reaction may be measured at any given alkaline pH, and for a selected decolorization time, the pH of the processing composition contacted with and remaining in contact with the colored filter dye should be at least as high as that predetermined to give the selected decolorization time.

The dyes of the present invention may be incorporated into the appropriate layer of the photographic film unit using any of the techniques known in the art. For instance, the selected compound can be dissolved in the appropriate solvent and then dispersed, in the presence of a wetting agent if desired, in a coating solution containing a hydrophilic colloid binder, e.g., gelatin, and the resulting coating solution applied as the desired layer, for example, coated on a transparent support to provide an antihalation layer, or coated over the outermost photosensitive layer of a multilayered, multicolor photosensitive element to provide a color correction filter layer through which photoexposure is made. The concentration of compound in the layer will vary depending upon the product in which the filter layer is to be used and may be readily determined empirically to provide the optical density necessary for the specific use. It will be appreciated that the dyes of the present invention may be used in combination with each other and also may be used in combination with other classes of dyes previously employed in antihalation, color correction and other filter layers.

FIG. 1 of the accompanying drawing, which illustrates one embodiment of the present invention, is an enlarged cross-sectional view of an integral diffusion transfer film unit comprising a transparent film base or support 1 carrying on one surface, in order, additive multicolor screen 3 comprising a plurality of primary red color filter elements, a plurality of primary green color filter elements and a plurality of blue color filter elements arranged in a geometrically repetitive distribution in side-by-side relationship in substantially a single plane, photoinsensitive layer 5 carrying silver precipitating nuclei, photosensitive layer 7 containing silver halide crystals and antihalation layer 9 containing one or more light-screening dyes of the present invention.

As discussed in aforementioned British Pat. No. 1,482,156, the degree of light absorption of the antihalation layer in such film units can vary over a relatively wide range, but usually, the antihalation layer possesses a transmission density range from about 0.4 to 1.4. Preferably, the transmission density is greater than 0.6 so that in the event a plurality of film units is employed in a stacked relationship during photoexposure, the antihalation layer will have sufficient density, i.e., light-absorbing capacity, to also prevent exposure of underlying film units.

In determining the appropriate light-absorbing capacity for cyan, magenta and yellow for color correction purposes, "color compensating" filters as conventionally used in front of the camera lens may be employed in the usual manner as a convenient method of approximating the type and quantity of filtration which it would be desirable to provide. A layer containing the appropriate color correction dye(s) in a corresponding density may then be provided as a layer through which photoexposure is to be made.

Multicolor diffusion transfer images may be obtained using a variety of arrangements of the image-receiving layer and the silver halide emulsions. Thus, these layers may be carried by a common support brought into superposition after photoexposure. A particularly advantageous film structure is shown in U.S. Pat. No. 3,415,644 wherein the requisite layers are in superposed relationship prior to and during photoexposure, and these layers are maintained in superposed relationship as a permanent laminate after processing and image formation. Such film units typically contain an outer transparent layer or support through which photoexposure is effected and the final multicolor image viewed, and another outer layer or support carrying at least the photosensitive layers, the latter support being opaque. While these supports or sheet-like elements may simply be held in superposed relationship, e.g., by a binding tape around the edges, these elements may be laminated together prior to photoexposure. This prelamination provides a number of benefits, both during manufacture and in photoexposure. Following exposure, the elements are delaminated by the distribution of a fluid processing composition which, upon solidification, bonds the elements together to form the desired permanent laminate. Procedures for forming such prelaminated film units wherein the two elements are temporarily laminated together prior to exposure are described, for example, in U.S. Pat. No. 3,625,231 to Albert J. Bachelder and Frederick J. Binda, and U.S. Pat. No. 3,652,282 to Edwin H. Land, both issued Mar. 28, 1972 and in U.S. Pat. No. 3,793,023 issued to Edwin H. Land on Feb. 19, 1974.

Further description of this embodiment of the present invention may be facilitated by reference to FIG. 2 of the accompanying drawing which illustrates a diffusion transfer film unit adapted to provide integral negative-positive reflection prints and employing dye developers as the image dyes.

FIG. 2 illustrates a diffusion transfer film unit comprising a photosensitive element or component 2, a rupturable container 30, and an image-receiving element or component 4. The photosensitive element 2 comprises an opaque support 10 carrying, in turn, a cyan dye developer layer 12, a red-sensitive silver halide emulsion layer 14, an interlayer 16, a magenta dye developer layer 18, a green-sensitive silver halide emulsion layer 20, an interlayer 22, a yellow dye developer layer 24, a blue-sensitive silver halide emulsion layer 26, and an auxiliary layer 28. The positive or image-receiving element 4 comprises a transparent support 40 carrying, in turn, a polymeric acid layer 42, a timing layer 44 and an image-receiving layer 46 having dispersed therein a bleachable, light-screening dye of this invention as a color correction filter dye. The two elements are held in superposed, registered relationship, e.g., by a binding tape (not shown), so that photoexposure of the silver halide emulsion layers is effected through image-receiving layer 46 containing the bleachable dye. The rupturable container 30 contains a processing composition and is so positioned that, upon rupture the processing composition is distributed between the superposed elements 2 and 4. By including in the processing composition a light-reflecting pigment, preferably titanium dioxide, a light-reflecting layer may be provided against which the transfer image formed in the image-receiving layer 46 may be viewed. The developed photosensitive layers are masked from view by the light-reflecting layer and remain with the receiving layer 46 as part of a permanent laminate. The rupturable container 30 is of the type shown in U.S. Pat. No. 2,543,181 and is positioned adjacent the leading edge of the film unit.

In the processing of the film unit, the film unit is advanced relative to and between a pair of pressure-applying members which apply compressive pressure to the rupturable container 30 to eject its liquid contents between the photosensitive and image-receiving components 2 and 4 and then distribute the mass of liquid between the sheets toward the trailing ends thereof to form a layer of substantially uniform, predetermined thickness at least co-extensive with the image area. In order to insure sufficient processing liquid to form a layer of the required area and thickness between the sheets, excess processing liquid may be provided in container 30 and trapping means (not shown) provided for collecting and retaining excess processing liquid overrun. Details of the various layers of this and of the film unit of FIG. 1 may be found in the herein cited patents and applications and need not be recited here.

Processing of film units of the type described in FIG. 2 is initiated by distributing the processing composition between predetermined layers of the film unit. In exposed and developed areas, the dye developer will be immobilized as a function of development. In unexposed and undeveloped areas, the dye developer is unreacted and diffusible, and this provides an imagewise distribution of unoxidized dye developer, diffusible in the processing composition, as a function of the point-to-point degree of exposure of the silver halide layer. The desired transfer image is obtained by the diffusion transfer to the image-receiving layer of at least part of this imagewise distribution of unoxidized dye developer. In the illustrated embodiment, the pH of the photographic system is controlled and reduced by the neutralization of alkali after a predetermined interval, in accordance with the teachings of the above noted U.S. Pat. No. 3,615,644, to reduce the alkalinity to a pH at which the unoxidized dye developer is substantially insoluble and non-diffusible. As will be readily recognized, the details of such processes form no part of the present invention but are well known; the previously noted U.S. patents may be referred to for more specific discussion of such processes.

Multicolor images may be obtained by providing the requisite number of differentially exposable silver halide emulsions, and said silver halide emulsions are most commonly provided as individual layers coated in superposed relationship. Film units intended to provide multicolor images comprise two or more selectively sensitized silver halide layers each having associated therewith an appropriate image dye-providing material providing an image dye having spectral absorption characteristics substantially complementary to the light by which the associated silver halide is exposed. The most commonly employed negative components for forming multicolor images are of the "tripack" structure and contain blue-, green-, and red-sensitive silver halide layers each having associated therewith in the same or in a contiguous layer a yellow, a magenta and a cyan image dye-providing material respectively. Interlayers or spacer layers may, if desired, be provided between the respective silver halide layers and associated image dye-providing materials or between other layers. Integral multicolor photosensitive elements of this general type are disclosed in U.S. Pat. No. 3,345,163 issued October 3, 1967 to Edwin H. Land and Howard G. Rogers as well as in the previously noted U.S. patents, e.g., in FIG. 9 of the aforementioned U.S. Pat. No. 2,983,606.

A number of modifications to the structures described in connection with FIG. 2 will readily suggest themselves to one skilled in the art. Thus, for example, the multicolor multilayer negative may be replaced by a screen-type negative as illustrated in U.S. Pat. No. 2,968,554 issued Jan. 17, 1961 to Edwin H. Land and in the aforementioned U.S. Pat. No. 2,983,606 particularly with respect to FIG. 3 thereof.

The image dye-providing materials which may be employed in such processes generally may be characterized as either (1) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible in an imagewise pattern as a function of development; or (2) initially insoluble or non-diffusible in the processing composition but which are selectively rendered diffusible or provide a diffusible product in an imagewise pattern as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers. The requisite differential in mobility or solubility may, for example, be obtained by a chemical action such as a redox reaction or a coupling reaction.

As examples of initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of those disclosed, for example, in U.S. Pat. Nos. 2,968,554; 2,983,606; 3,087,817; 3,185,567; 3,230,082; 3,345,163; and 3,443,943. As examples of initially non-diffusible materials and their use in color transfer systems, mention may be made of the materials and systems disclosed in U.S. Pat. Nos. 3,185,567; 3,719,489; 3,443,939; 3,443,940; 3,227,550; 3,227,552; and 4,076,529. Many types of image dye-providing substances and film units useful therewith also are discussed in the aforementioned U.S. Pat. No. 3,647,437 to which reference may be made.

It is also to be understood that "direct positive" silver halide emulsions may also be used, depending upon the particular image dye-providing substances employed and whether a positive or negative color transfer image is desired.

A preferred opacification system to be contained in the processing composition to effect processing outside of a camera is that described in the above-mentioned U.S. Pat. No. 3,647,437, and comprises a dispersion of an inorganic light-reflecting pigment which also contains at least one light-absorbing agent, i.e., optical filter agent, at a pH above the pKa of the optical filter agent in a concentration effective when the processing composition is applied, to provide a layer exhibiting optical transmission density> than about 6.0 density units with respect to incident radiation actinic to the photosensitive silver halide and optical reflection density < than about 1.0 density units with respect to incident visible radiation.

In lieu of having the light-reflecting pigment in the processing composition, the light-reflecting pigment used to mask the photosensitive strata and to provide the background for viewing the color transfer image formed in the receiving layer may be present initially in whole or in part as a preformed layer in the film unit. As an example of such a preformed layer, mention may be made of that disclosed in U.S. Pat. No. 3,615,421 issued Oct. 26, 1971 and in U.S. Pat. No. 3,620,724 issued Nov. 16, 1971, both in the name of Edwin H. Land. The reflecting agent may be generated in situ as is disclosed in U.S. Pat. Nos. 3,647,434 and 3,647,435, both issued Mar. 7, 1972 to Edwin H. Land.

The dye developers (or other image dye-providing substances) are preferably selected for their ability to provide colors that are useful in carrying out subtractive color photography, that is, the previously mentioned cyan, magenta and yellow. They may be incorporated in the respective silver halide emulsion or, in the preferred embodiment, in a separate layer behind the respective silver halide emulsion. Thus, a dye developer may, for example, be in a coating or layer behind the respective silver halide emulsion and such a layer of dye developer may be applied by use of a coating solution containing the respective dye developer distributed, in a concentration calculated to give the desired coverage of dye developer per unit area, in a film-forming natural, or synthetic, polymer, for example, gelatin, polyvinyl alcohol, and the like, adapted to be permeated by the processing composition.

Dye developers, as noted above, are compounds which contain the chromophoric system of a dye and also a silver halide developing function. By "a silver halide developing function" is meant a grouping adapted to develop exposed silver halide. A preferred silver halide development function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and ortho- and para-amino substituted hydroxyphenyl groups. In general, the development function includes a benzenoid developing function, that is, an aromatic developing group which forms quinonoid or quinone substances when oxidized.

The image-receiving layer may comprise one of the materials known in the art, such as polyvinyl alcohol, gelatin, etc. It may contain agents adapted to mordant or otherwise fix the transferred image dye(s). Preferred materials comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4-vinylpyridine, as disclosed in U.S. Pat. No. 3,148,061 and graft copolymers containing 4-vinylpyridine as disclosed in U.S. Pat. No. 3,756,814.

In the various color diffusion transfer systems which have previously been described and which employ an aqueous alkaline processing fluid, it is well known to employ an acid-reacting reagent in a layer of the film unit to lower the environmental pH following substantial dye transfer in order to increase the image stability and/or to adjust the pH from the first pH at which the image dyes are diffusible to a second (lower) pH at which they are not. For example, the previously mentioned U.S. Pat. No. 3,415,644 discloses systems wherein the desired pH reduction may be effected by providing a polymeric acid layer adjacent the dyeable stratum. These polymeric acids may be polymers which contain acid groups, e.g., carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals or with organic bases; or potentially acid-yielding groups such as anhydrides or lactones. Preferably the acid polymer contains free carboxyl groups. Alternatively, the acid-reacting reagent may be in a layer adjacent to the silver halide most distant from the image-receiving layer, as disclosed in U.S. Pat. No. 3,573,043 issued Mar. 30, 1971 to Edwin H. Land. Another system for providing an acid-reacting reagent is disclosed in U.S. Pat. No. 3,576,625 issued Apr. 27, 1971 to Edwin H. Land.

An inert interlayer or spacer layer may be and is preferably disposed between the polymeric acid layer and the dyeable stratum in order to control or "time" the pH reduction so that it is not premature and interferes with the development process. Suitable spacer or "timing" layers for this purpose are described with particularity in U.S. Pat. Nos. 3,362,819; 3,419,389; 3,421,893; 3,455,686; and 3,575,701.

While the acid layer and associated spacer layer are preferably contained in the positive component employed in systems wherein the dyeable stratum and photosensitive strata are contained on separate supports, e.g., between the support for the receiving element and the dyeable stratum; or associated with the dyeable stratum in those integral film units, e.g., on the side of the dyeable stratum opposed from the negative components, they may, if desired, be associated with the photosensitive strata, as is disclosed, for example, in U.S. Pat. Nos. 3,362,821 and 3,573,043. In film units such as those described in the aforementioned U.S. Pat. Nos. 3,594,164 and 3,594,165, they also may be contained on the spreader sheet employed to facilitate application of the processing fluid.

As is now well known and illustrated, for example, in the previously cited patents, the liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example sodium hydroxide, potassium hydroxide, and the like, and preferably possessing a pH in excess of 12, and most preferably includes a viscosity-increasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. Typical film-forming materials include cellulosic polymers, for example, hydroxyethyl cellulose, sodium carboxymethyl cellulose and carboxymethyl hydroxyethyl cellulose and oxime polymers, for example, polydiacetone acrylamide oxime. Other film-forming materials or thickening agents whose ability to increase viscosity is substantially unaffected if left in solution for a long period of time also are capable of utilization. The film-forming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity in excess of 100 cps, at a temperature of approximately 24.degree. C. and preferably in the order of 100,000 cps to 200,000 cps at that temperature.

In particularly useful embodiments, the transparent polymeric support contains a small quantity of a pigment, e.g., carbon black, to prevent fog formation due to light-piping by internal reflection within the transparent support, and subsequent exiting from the support surface carrying the photographic layers, of actinic light incident upon an edge thereof; such elements are described in Belgian Patent No. 777,407. The transparent support advantageously may include an ultraviolet light absorber.

For purposes of illustrating the invention, a polyoxyethylene polymer layer containing the compound of Example 1 was overcoated on an image-receiving layer containing a 2:1 mixture of a graft copolymer comprising 4-vinyl pyridine (4VP) and vinyl benzyl trimethyl ammonium chloride (TMQ) grafted onto hydroxyethyl cellulose (HEC) at a ratio HEC/4VP/TMQ of 2.2/2.2/1 and gelatin which was carried on a transparent 4 mil polyethylene terephthalate film base.

When several drops of aqueous IN KOH were applied to said overcoat layer, the compound of Example 1 decolorized.

The half-life for each of the compounds A to D set out below was measured in a conventional manner spectrophotometrically at 22.degree. C. using aqueous 0.25N KOH containing 30% acetonitrile as the solvent. By "half-life" is meant the time required for one-half of the compound to undergo alkaline hydrolysis according to the equation ##STR35## The results obtained are set forth in the Table wherein Y represents the substituent ortho to said benzoylsulfonamido group. __________________________________________________________________________ ##STR36##                          Compound A ##STR37##   Compound B ##STR38##                                              Compound C ##STR39##                                              Compound D Y Group of Cpd No. X    k'(sec..sup.-1) t1/2(Sec.) ##STR40## ##STR41## .sigma..rho. __________________________________________________________________________ A                OCH.sub.3 .024        28.9 .289      -.53 -.32 B                H    .083        8.3  1.0       0    0 C                Cl   .21         3.30 .39       .40  +.30 D                NO.sub.2 2.27        0.30 27.3      1.43 +.78 __________________________________________________________________________

FIG. 3 represents the Hammett Plot for the data given in the Table and is based on the equation Log k'.sub.x /k'.sub.h =.sigma.. As can be seen from reference to the data in the Table and from reference to the Hammett Plot, the hydrolysis rate increases as X becomes more electron-withdrawing. In terms of half-life expressed as T1/2, the preferred compounds of the present invention decolorize in about 30 seconds or less as measured in said 0.25N KOH solution, i.e., one-half of the colored compound undergoes alkaline hydrolysis in about 30 seconds or less.

In utilizing the dyes of the present invention, it will be appreciated that various solvents may be employed for dispersing the dyes in the appropriate layer of the photographic product and that useful solvents may be readily selected for a given compound. Also, it will be understood that where the anion may possibly have an adverse effect on the photosensitive material, the dye will be positioned other than in the silver halide emulsion layer(s), and depending upon the mobility of the dye in a given matrix or binder, it may be desirable to employ an immobilizing group or a group that will mordant to the matrix to prevent migration of the dye, particularly, where the photographic product is subjected to conditions of high temperature and high humidity prior to use.

Also, it will be appreciated that in utilizing the subject dyes to correct color balance, for example, in multicolor diffusion transfer photographic film units that a photosensitive element may be exposed to a suitable multicolor step-wedge and diffusion transfer processed with a given processing composition and image-receiving element. The blue, green and red D log E curves of the resulting multicolor transfer image (sample image) are then prepared. Examination of these D log E curves will indicate to one skilled in color photographic sensitometry the manner and extent to which the individual D log E curves depart from the desired curve shape. From this examination, one may determine by routine analysis and experimentation how much filtration would be required of what wavelength range or ranges to obtain a more desirable color balance. The photosensitive element of another film unit, having the identical photosensitive element, image-receiving element and processing composition as used in obtaining the sample image, is then given the same exposure through a conventional color correction filter(s) of the color and density estimated to be necessary to provide the desired changes in the D log E curves of the sample image. The blue, green and red D log E curves of the resulting test multicolor transfer image are then prepared and compared with the sample. While more than one "test" may be required to determine the color filtration most effective to give the desired D log E curve shape changes, such tests may be performed rapidly and easily. When the appropriate color filtration has been determined, a layer containing a color correction dye or dyes absorbing light in appropriate wavelength range(s) is coated on a transparent support at a coverage calculated to provide the requisite density. This "test" color correction dye layer is placed in the exposure path and the previous exposure test repeated. Analysis of the D log E curves of the resulting multicolor transfer image will indicate what changes, if any, should be made in the spectral absorption range and density prior to incorporating a corresponding color correction dye layer into the diffusion transfer film unit.

It will be recognized that effecting photoexposure through a layer containing the subject dye(s) is effective to "filter", i.e., decrease the exposure given to the silver halide layer(s) exposable by light absorbed by said color correction dye(s) and that one or more dyes of the present invention may be used in conjunction with other filter dyes for effecting changes in one, two or all three of the individual red, green and blue H and D curves to achieve the desired color balance. Though the subject dyes find particular utility in diffusion transfer and other photographic film units where it is desired to bleach the dye(s) during processing subsequent to photoexposure through the dye layer(s), the subject dyes also may be employed in diffusion transfer and other film units where the dye is so positioned as not to contribute dye density to the transfer or final image. Where the filter dye layer through which photoexposure has been made is not part of the transfer image, or where the final image is masked from view as in certain integral negative-positive reflection print structures, the "unbleached" filter dye should be non-diffusible to the image-receiving layer containing the transfer image. The requisite non-diffusion character may be provided by the use of a suitable mordant, by the use of long chain "ballast" or "anchor" substituents and/or other art known techniques.

The choice of location of the color correction dye(s) will depend in large part upon what stage of the manufacturing process the determination is made to incorporate such a color correction dye. As will be readily apparent, provision of the color correction dye(s) in a separate layer has the advantage of permitting modification after the components have fully "matured" and also permits different modification of portions of the same lot of the positive component.

The supports for the various layers may be any of the types known in the art to be useful. In the preferred embodiments wherein an integral negative-positive reflection print is obtained, the supports should be dimensionally stable and may be polyethylene terephthalate or other polymeric film base, as disclosed in the cross-referenced patents.

It will be recognized that the transfer image formed following exposure and processing of film units of the type illustrated in FIG. 2 will be a geometrically reversed image of the subject. Accordingly, to provide geometrically non-reversed transfer images, exposure of such film units should be accomplished through an image reversing optical system, such as in a camera possessing an image reversing optical system utilizing mirror optics, e.g., as described in U.S. Pat. No. 3,447,437 issued June 3, 1969 to Douglas B. Tiffany.

Where the expression "positive image" has been used, this expression should not be interpreted in a restrictive sense since it is used primarily for purposes of illustration, in that it defines the image produced on the image-carrying layer as being reversed, in the positive-negative sense, with respect to the image in the photosensitive emulsion layers. As an example of an alternative meaning for "positive image", assume that the photosensitive element is exposed to actinic light through a negative transparency. In this case, the latent image in the photosensitive emulsion layers will be positive and the dye image produced on the image-carrying layer will be negative. The expression "positive image" is intended to cover such an image produced on the image-carrying layer, as well as transfer images obtained by use of direct positive silver halide emulsions to provide a "positive" image of the photographed subject.

While the usefulness of the subject xanthene dyes has been illustrated as applied to integral diffusion transfer film units where the transfer image is retained with the developed photosensitive element as part of a permanent laminate, it will be understood that the xanthene dyes of this invention also may be used to provide antihalo, color correction or other light filtering layer(s) in diffusion transer film units where the transfer image, either in silver or in dye, is separated from the developed photosensitive layer(s) subsequent to processing. Though the image dye-providing materials are preferably dye developers, it will be appreciated that other types of image dyes and dye intermediates may be employed to provide the dye transfer image.

Besides their usefulness in diffusion transfer photographic products and processes, the xanthene dyes of the present invention also may be used in filter layers of conventional photographic materials, for example, in antihalation or color correction layers in conventional negatives, and may be disposed in the appropriate layer(s) in an amount sufficient to provide the desired filtering effect. The selection and incorporation of the xanthene dye for the desired filtering effect may be accomplished in a known manner using conventional techniques and is well within the skill of the art. For example, for color correction purposes, the dye(s) selected may absorb light within a specific wavelength range, e.g., blue, green or red light, or within a combination of several wavelength ranges and will be disposed in a layer through which photoexposure is made. Indeed, it may be desirable in a given instance to filter light of two different wavelength ranges in a ratio such that one silver halide emulsion receives more exposure filtration than does another. As in the diffusion transfer film units, the dye(s) selected for color correction are advantageously applied after the photosensitive element has aged to "maturity", i.e., the sensitometry of the photosensitive element as manufactured is no longer changing significantly with time. Where the subject dyes are employed for antihalation purposes, they may be incorporated, for example, in a layer on one or both sides of a support carrying the photosensitive layer(s) and where they are employed as optical filter agents, they will be so positioned as to prevent post-exposure fogging during processing in ambient light without, of course, interfering with imagewise exposure of the photosensitive layer(s) or with viewing of the final image.

Since certain changes may be made in the hereinafter defined subject matter without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description and examples be interpreted as illustrative and not in a limiting sense.

## Claims

1. A compound having the formula ##STR42## wherein each R.sup.1 is the same and is selected from ##STR43## R.sup.2 is alkyl, R.sup.3 is an electron-withdrawing group positioned ortho, meta or para to said N atom, R.sup.4 is hydrogen, alkyl or an electron-withdrawing group positioned ortho, meta or para to said N atom; R.sup.5 is alkyl; X is an electron-withdrawing group or an electron-donating group; and A is an anion, said compound at an alkaline pH undergoing a hydrolysis reaction to give a colorless compound of the formula ##STR44##

2. A compound as defined in claim 1 wherein X is an electron-withdrawing group.

3. A compound as defined in claim 1 wherein X is an electron-donating group.

4. A compound as defined in claim 1 wherein R.sup.1 is ##STR45##

5. A compound as defined in claim 1 wherein R.sup.1 ##STR46##

6. A compound as defined in claim 4 wherein R.sup.5 is methyl.

7. A compound as defined in claim 6 wherein X is nitro.

8. A compound as defined in claim 6 wherein X is N,N-dimethylamino.

9. A compound as defined in claim 5 wherein R.sup.2 is methyl and R.sup.5 is methyl.

10. A compound as defined in claim 9 wherein ##STR47## positioned para to said N atom, and R.sub.4 is hydrogen.

11. A compound as defined in claim 10 wherein X is chloro.

12. A compound as defined in claim 10 wherein X is nitro.

13. A compound as defined in claim 9 wherein R.sup.3 is para-chloro and R.sup.4 is meta-carbomethoxy.

14. A compound as defined in claim 13 wherein X is methoxy.