Polymethine dye intermediate

Abstract

Claims

Patented Nov. 18, 1941 UNITED STATES PATENT OFFICE POLYMETHINE DYE INTERMEDIATE Robert H. Sprague, Rochester, N. Y., assignor to 'Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application January 7, 1941, Serial No. 373,463 18 Claims. This invention relates to polymethine'dye intermediates and to a process for preparing. them. It is known that merocyanine dyes containing the following grouping: monium quaternary salts containing a reactive methyl group to give complex polymethine dyes. Moreover, it is known that the aforesaid polymethine dye intermediates can be reacted with organic compounds containing a ketomethylene group to give still other complex polymethine dyes. I have now found that the condensation products of the aforesaid polymethine dye intermediates and malonic esters, can be hydrolyzed to giVe new polymethine dye intermediates containing the following grouping: These new polymethine dye intermediates, I have found, can be employed to prepare complex polymethine dyes of a kind heretofore unavailable. It is accordingly an object of my invention to provide new polymethine dye intermediates and a process for preparing the same. It is a further object to provide a, process for preparing complex polymethine dyes. A further object is toprovide complex polymethine dyes. Other objects will become apparent hereinafter. In accordance with my invention, I hydrolyze, in the presence of an acid, a condensation product of the following general formula: wherein L represents a methine group, it represents a positive integer of from one to two, 11 represents a positive integer of from one to three, R, R and R" each represent an alkyl group, such as methyl, ethyl, n-primarybutyl, p-ethoxyethyl and benzyl for example, R represents a member selected from the group consisting of alkyl and aryl groups, such as a methyl, an ethyl, a phenyl or a. naphthyl group for example, and Z represents the non-metallic atom-s necessary to complete a heterocyclic organic nucleus, for, example (when d represents one) a five-membered nucleus, such as an oxazole nucleus (e. g. 4-methyloxazole, 4- .phenyloxazole, benzoxazole or naphthoxazole), a thiazole nucleus (e. g. 4-methylthlazole, 4- phenylthiazole, benzothiazole or naphthothiazole) a selenazole nucleus (e. g. 4-methy1selenazole, 4-. phenylselenazole or benzoselenazole) a thiazoline nucleus, or a six-membered nucleus, such as a pyridine or a quinoline nucleus, and, when 01 represents two, a six-membered nucleus, such as a pyridine or a quinoline nucleus. Hydrochloric acid is advantageously employed in practicing my invention. Mineral acids are especially suitable for the practice of my invention, sulfuric, phosphoric and hydrobromic acids being further examples of acids which can be employed. Heat accelerates the hydrolysis. The following examples will serve to illustrate the manner of practicing my invention. ExAMrLE 1.5 (3 ethy 2 (3) benzothiazolylidene) -2-methyZ-4 (5) -thiazolone ethiodide 4.0 g. (1 mol.) of 2-dicarbethoxymethylene-3- ethyl -5-(3-ethyl -2(3) -benzothiazolylidene) 4- thiazolidone wereplaced in 50 cc. of 15% hydrochloric acid. The mixture was boiled, under reflux, for 30 minutes. Carbon dioxide was evolved and the mixture took on a pale yellow color. The undissolved solid which remained after the boiling was filtered off, using a sintered lass filter. The filtrate was concentrated nearly to dryness under reduced pressure. The yellow crystals which separated were dissolved in 20 cc. of absolute ethyl alcohol, an excess of sodium iodide dissolved in methyl alcohol was added, and the resulting mixture was chilled to 0 C. The crystals were filtered off, washed with acetone, then the Water and finally dried in the air. After recrystallization from methyl alcohol, the product was obtained, in 36% yield, as yellow crystals, melting tit-217 to 220 C. with decomposition. u The dicarbethoxymethylene compound used above .was prepared as follows: 13.2 g. (1 mol.) of 5.- (3-ethyle2(3) -benzothiazolylidene) -2 methylmercapto-4(5)-thiazolone ethiodide, 8.0 g. of diethyl malonate and 2.5 g. (1 mol.) of triethylamine were placed in 50 cc. of absolute ethyl alcohol. The mixture was boiled, under reflux, for 30 minutes. The yellow crystals which separated slowly from the boiling mixture were filtered off (after chilling the mixture), washed with methyl alcohol and'dried in the air. Yield 9.8 g..(87%). After several crystallizations from acetone'('71 cc. per gram of crystals), the crystals melted at. 172.to 174 C. EXAMPLE; 2.--5 [(3 ethyl 2(3) benzoxazolylidene) ethylide'ne] -2 methyl 4(5) thiazolo'ne ethz'odz'de I, 2.3 g. (1 mol.) of 2dicarbethoxymethylene-3 ethyl .5 [(3 ethyl 2(3) benzoxazolyliden'e) ;-:ethylidenel -4-thiazolidone and 25-cc.'o-f 18% hydrochloric acid were mixed together. The mix- .tur'ezwasboiled, under reflux, for 15 minutes. the product was obtained, in 30% yield, as minute brown needles, with abright reflex, and melting at 226 to 227 C. with decomposition. I The dicarbethoxymethylene compound used above was prepared as follows: 47.4 g. (1 mol.) of '5-'['(3 ethyl-2 (3) benzoxazolylidene) ethylid'ene] 2 methylmercapto 4(5) thiazolone ethiodide, 32 g. (1 mold-100% excess) of diethylmalonate and 10.1 g. (1 mol.) of triethylamine were placed in 150 cc. of absolute ethyl alcohol.- The mixture was boiled, under reflux, for 15 minutes. The resulting orange mixture was chilled to C., the solid product filtered off, washed with methyl alcohol and dried in the air. After recrystallization from acetone (14 cc. per gramof solid), the product was obtained, in 30% yield, as bright orange needles, melting with decomposition at 4.42gA1-mol.) of 2-dicarbethoxymethylene-3- ethyl 7 (3 ethyl 2(3) benzothiazolylidene) ethylidene]+4-thiazolidone were, placed in 50 cc. oi,15%vv hydrochloric acid. The mixture .was boiled, under reflux, for 15. minutes. The resulting orange .solution was concentrated under diminished-pressure and'chilled to 0 C. The crystals which 'separated were collected on a fil'ter, washed with acetone and dried in the air. i The product was dissolved in a small amount of methyl-alcohol and treated with an excess of-sodium' i'odide dissolved in methyl alcohol. -The product which separated was filtered off and recrystallized from methyl alcohol (35 cc. per gram "of product). It was obtained, in 53% yield, as dark red crystals, melting at 199 -to 201*!C. with decomposition. I f The dicarbethoxymethylene compound used aboveitwas' prepared as :follows: 24.5 g. (l molsy'o'f 5-= [(3 ethyl 2(3) benzothiazolylidene) ethlylidene] -2-methylmercapto-,4 (5) -thiazolone ethiodide, 16 g. (1 mol.+100% excess) of diethylmalohate and 5 g.(1 mol.) of trie'thylamine were .placed in 100 cc. of absolute ethyl alcohol. The mixture was boiled, under reflux, for 45'minutes. Th resulting orange mixture was chilled to 0 C., was ob'tainedfin 32% yield, as red crystals, melting at.185 to "187 C. with decomposition. In-a similar manner, 2-dicarbmethoxy-methylene-3- ethyl 5 (3 ethyl 2(3) benzothiazolylidene) ethylidene] -4-thiazo1idone, was obtained as red crystals, melting at 218 to 219 C. with decompositionm g v v 7 EXAMPLE 4 .-5 (3 ethyl -'2(3) -benzothiazolylidene) -2 methyl 4(5) thiazolone n mopyl chloride 24.5 g. (-1 mol.) of Z-dicarbethoxymethylene 5 (3-ethyl-2(3) -benzothiazolylidene) -3-'npropyl-4-thiazolidone were placed in 500 cc. of 15% hydroch'loricjacid.- The mixture was boiled, under reflux, for 2 hours. Carbon dioxide was evolved. The resulting mixture was filtered, using a'sinter'ed glass filter, to remove some solid matter. The filtrate was "evaporated to dryness under reduced pressure. Thev orange crystals thus obtained were stirred with cc.'of acetone. 'The acetone mixture was chilled to 0 C. and the crystals filtered off and dried in the air. 15.2 g. of "crystals meltingat 146 to 148 C. with de-. compositionwere thus obtained. p The dicarbethoxymethylene compound used above was prepared as follows: 130 g. (1 mol.) ;' of 5- [3-ethyl-Z(3) -benzothiazolylidene-Ii-(n-propyl) ]-rhodanine and 144 g. (1 mo1.+100%) of methyl-p-t'oluenesulfonate were heated together in an' foil "bath at to C. for one hour. The reddish brown'vi'scous mass was then cooled and washed, by decantation, several times with 200 cc."portions of absolute diethyl ether. The residue'wasplaced in a one liter flask with 124 g. (l. mol'.+100% excess) of diethyl-malonate, 3&6 g. (*1 mol.) of ,tri'ethylamine and 200 cc. of absolute ethyl alcohol. The mixture was boiled, under reflux, for one hour. solution was chilled to 0C. and stirred to promote crystallization. The crystals were filtered ofi, washed. with methyl alcohol and sucked nearly dry on the filter. The sticky orange crystals were purified by crystallization from methyl alcohol, (50 cc. per gram of crystals) and obtained, in 19% yield, as bright orange crystals, melting at 182 to 184 C. with decomposition. ".In a manner similar to that illustrated in the above examples 5-(3=ethyl-2 (3) -benzoselenazolylidene)-2-methy1-J4(5) -thiazolone .pheniodide; 5 ('1 ethyl 1, 4-dihydroquinolylidine) ethylidenel 2 -methyl -"4(5) -thiazolone ethiodide; 5- (3methyl-2(3) -thiazolinylidene) ethylidene] -2- methyl 4(5 -thiazolone ethiodide and 5 -'[(3- My new intermediates can be "condensed, to The resulting orange EXAMPLE 5.-2- [3- (3-ethyl-2 (3) -benzothz'azolylidenemropenyll 5-[3-ethyl-2(3) -benzoxazolylz'dene) ethylz'dene] -4 5) -thiazolone ethiodide 0.66 g. (1 mol.) of 5-[(3-ethyl-2(3)-benzoxazolylidene) ethylidene] 2 methyl-4 (5) -thiazolone ethiodide and 0.7 g. (1 mol.) of 2-(,B-acetanilidovinyl) benzothiazole ethiodide were placed in 15 cc. of pyridine. The mixture was boiled, under reflux, for 5 minutes. The resulting green mixture was chilled to C., diluted with 100 cc. of diethyl ether and stirred. A sticky green solid separated. The ether was decanted and the residue was stirred with cc. of cold acetone until crystalline. The acetone mixture was chilled to 0 C., the dye filtered off, washed with acetone and water and finally dried in the air. After recrystalization from methyl alcohol (200 cc. per gram of dye), the dye was obtained, in 54% yield, as green crystals melting with decomposition at 271 to 273 C. In a similar manner, 5[ (3-ethyl-2(3) -benzoa:- azolylidene) ethylidenel-2[(3-ethyl-2(3) -benzoxazolylidene) propenyl] -4 (5) -thiazolone ethiodide was obtained, in yield, as minute green crystals, melting with decomposition at 218 to 220 C. Also in a similar manner, 5-[(3-ethyl- 2(3) vbenzothiarolylidene) ethylidene] 2 [(3 ethyl 2(3) -bnzothiazolylidene) propenyll -4 (5) thiazolone ethiodide was obtained, in 38% yield as minute greenish-bronze crystals, melting with decomposition at 273 to 274 C. EXAMPLE 6.-5 (3 ethyl 2(3) benzothiazolylidene) 2 [5 (ethyl 2(3) benzothiazolylidene) 1,3 pentadienyl] 4(5) thiazolone ethiodide 2.16 g. (1 mol.) of 5-(3-ethyl-2(3) -benzothiazolylidene) -2-methyl4 (5) -thiazolone ethiodide and 2.4 g.'(1 mol.) of 2-(4-acetanilido 1,3-butadienyl) -benzothiazole ethiodide were placed in 15 cc. of pyridine. The mixture was boiled, under reflux, for 5 minutes. The resulting blue mixture was chilled to 0 C. The dark blue dye which separated was filtered 01f, washed with water, then with acetone and finally dried in the air. After recrystallization from methyl alcohol (1250 cc. per gram of dye), the dye was obtained, in 50% yield, as green crystals, having a golden reflex and melting with decomposition at 239 to 241 C. In a similar manner, 5(3-ethy1-2(3)-benzothiazolylidene) 2- 3-ethyl-2 (3) -benzothiazolylidene)propenyl]-4(5)-thiazolone ethiodide was obtained, in 46% yield, as minute green crystals, melting with decomposition at 287 to 288 C. My new intermediates can be condensed, to give polymethine dyes, with dialkylamino-benzaldehydes, dialkylaminocinnamic aldehydes and pyrrole aldehydes. The condensations are advantageously effected, in the presence of a waterbinding agent, such as acetic anhydride. Some of these dyes are of use as filter dyes in photographic silver halide emulsions, inasmuch as they arebleached by the usual photographic developers, such as Eastman Kodak Co.s D-76. The following examples will serve to illustrate these dyes. EXAMPLE 7.2 (p dimethylaminostyryl) 5 [(3 ethyl 2(3) benzowazolylidene) ethyl- 1.0 g. (1 mol.) of 5-[(3-ethyl-2(3) -benzoxazolylidene) ethylidene] 2-methyl-4-(5) -thiazolone ethiodide and 0.33 w. (1 mol.) of p-dimethylamino-benzaldehyde were placed in 15 cc. of acetic anhydride. ,The mixture was boiled, under reflux, for one hour. The dye separated from the hot mixture. The mixture was chilled to 0 C., the, dye filtered off, washed with acetone and dried in the air. After recrystallization from methyl alcohol (320 cc. per gram of dye), the dye was obtained, in 38% yield, as felted green crystals, melting with decomposition at 260 to 262 C. The dye gave a blue solution. in in ethyl alcohol and was bleached by Eastman Kodak's D-76 developer to a pale yellow. In a similar manner, 2-(p-dimethylaminostyryl) 5 (3 ethyl 2,(3) benzothiazolylidene) -4 5) -thiazolo-ne ethiodide was obtained, in 64% yield, as minute dark green crystals, melting with decomposition at 281 to 282 C. The dye gave a blue solution in methyl alcohol and was bleached by Eastman Kodaks D-76 developer. Also in a similar manner, 2-[4(p-dimethylaminophenyl) 1,3 butadienyl] 5 (3 ethyl 2(3) benzothiazolylidene) 4(5) thiazolone ethiodide was obtained, in 61% yield, as bright green crystals, melting with decomposition at 262 to 264 C. The dye gave a blue solution in methyl alcohol and was bleached by Eastman Kodaks D-76 developer. Also in a similar manner, 5-(3-ethyl-2(3)- benzothiazolylidene) 2 [,6 (1 heptyl 2,5 dimethyl 3 pyrryl) vinyl] 4(5) thiazolone n-propyl chloride was obtained from l-heptyl- 2,5-dimethyl-3-pyrrole aldehyde, in 25% yield, as green crystals melting with decomposition at tion .in methyl alcohol and was bleached by Eastman Kodaks D-76 developer. My new intermediates can also be condensed with diarylformamidines to give more complex intermediates which, in turn, can be employed: to prepare polymethine dyes. The following examples will serve to illustrate the formationof these new intermediates. EXAMPLE s. 2-ce-ecetamzidommgz) --[.(3-emy1- v emylidene1-4(5.)'- 2 (3) -benzothiazolylidene) thiazone ethiodide COCH; 2.2 g. (1 mol.) of .5-[(3-ethyl-2-.(3) -benzothiazolylidene) ethylidene] -2-meth:yl-4 (5) -thiazolone ethiodide and 0.94 g. (1 mol.) of diphenylformamidine were placed in cc. of acetic anhydride. The resulting mixture was boiled, under reflux, for 10 minutes. The intermediate separated from the boiling reaction mixture. The mixture was chilled, the intermediate filtered off, washed with acetone and dried in the air. The dark blue crystals thus obtained, in 69% yield, melted at 260 to 262 C. with decomposition. In a similar manner, Z-(fl-acetanilidovinyb- 5- (3-ethyl-2(3) benz'othiazolylidene) -4(5) -thia- 'zolone ethiodide was obtained, in 60% yield,;as dull blue crystals, melting at 285 to 288 C. with decomposition. The following examples illustrate the formation of polymethine dyes from the above intermediates. EXAMPLE 9.3-ethyZ-5- (3-ethyZ-2 (a) -benzothiazolylidene) e' thy'lidene] 2- (3-e thyl-4-oxo-2- thiono-5 thiazolidylidene) ethylid'ene] -4- thiazolidone 1.5 g. (1 mol.) of 2-(B-acetanilidovinyl) -5- [(3 ethyl 2(3) benzothiazolylidene) ethyli dene]-4(5) thiazoloneethiodide, 0.4 g. (1 mol.) of B-ethylrhodanine and 0.25 g. (1 mol.) of triethylamine were placedin cc. of .acetic anhydride. The mixture was'boiled, under reflux, for one minute. Green crystals of dye separated from the boiling mixture. These were filtered ofi and recrystallized several timesffrom glacial acetic acid (600 cc per gram of dye). The dye was obtained, in 15% yield, as minute green crystals, melting with decomposition at 291 to 293 C. 1 In a similar manner, '3-ethyl-5-(3-ethyl-2 (3) v as green crystals melting at 157 to 159 C. with decomposition. The dye gave a bluish red solubenzothziazolylidene) -2-;[ (3-ethyl-i4-oxo -2- thio- -no-'5 thliazolidylidene)gethfylidene] 4 thiazloli- .done was obtained from 2-(',8-acetanilidovinyl)- .5- (.3-ethyl-2 (3) benzothiazolylidene) -4 (5) -thiazolone ethiodide, .in 67% yield, as bronze crystals, melting above 300 C. My new intermediates can also be condensed, with ,B-alkoxy-acrolein acetals, in'glacial acetic acid, to give more complex intermediates, as shown in the following example. EXAMPLE 10.2-(4-ethOmy L3-butadienyZ)'-5-(3- ethyl-2 (3) -benzothiazolylidene) -4(5) thiazolone ethiodid 16.7 g. (1 mol.) of 5-(3-ethyl2(3) -benzothia- .zolylidene') -2-methyl-4(5) -thiazolone ethiodide and 13.6 g. (1 mol.) of fl-ethoxyacrolein'acetal were placed in 100 cc. of glacialacetic acid and heated, with stirring, on the steam bath. Coppery crystals separated from the hot mixture. The mixture was chilled to 0 C., the intermediate filtered ofi, washed with acetone and dried in the air. It melted at 237 to 240 C. with decomposition. Yield From intermediates such as the above, poly- .methine' dyes can be obtained by condensation EXAMPLE. l1. 5- (3-ethyZ -2( 3.) benzothiazolylidene) 2 5(1 ethyl-2 (1 -quinolylidene)1,3 pentadienyl] -4(5) -thiazolone ethiodide 1.71,,g. (1 mol.) of 2-(4-ethoxy-1,3-butadienyl)- 5- (3-ethyl-2 (3) -loenzothiazolylidene) -4 (5)-thiazolone ethiodide and 1.0 g. (1. mol.) of quinaldine ethiodide :were :placed in 25 cc. of acetic anhydride containing 0.3 5 g. (1 mol.) of'triethylamine. The mixture was boiled, under reflux, for one minute. The dye separated from the boiling solution. The reaction mixture was chilled, the dye filtered off, washed with acetone, then with water and dried in the air. After recrystallization from methyl alcohol (640 cc. per gram. of dye), the dye was obtained, in 33% yield, as minute coppery crystals, melting at 240 to 242 C. with decomposition. In a similar manner, the corresponding 4(1)- quinolylidene dye was obtained, in 33% yield, as minute coppery crystals,melting with decomposition at 231 to 233 C. In a similar manner, 3-ethylrhodam'ne was The same intermediate was also condensed, in acetic anhydride, with 1-eth'y1-2,5-dimethyl pyrrole to give -(3-ethyl-2-(3)-benzothiazolylidene) -2- [4-(1-ethyl-2,5-dimethyl- 3 -pyrryl) -1,3- butadienyll-4(5)-thiazolone ethiodide. in 30% yield, as green crystals melting with decomposition at 247 to 249 C. The dye gave a blue methyl alcoholic solution and was bleached by Eastman Kodaks D-76 developer. The polymethine dyes obtainable from my intermediates are not of any particular use as sensitizers for photographic silver halide emulsions, showing, at best, only a weak sensitizing action. The dyes, especially those which .are bleached by the ordinary developers, are of use as filter dyes. What I claim as my invention and desire to be secured by Letters Patent of the United States is: 1. A polymethine dye intermediate of the folthe following general formula: wherein R represents an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, X represents an acid radical, and Z represents the non-metallic atoms necessary to complete a heterocyclic organic nucleus. 3. A polymethine dye intermediate of the folwherein R represents an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, X represents an acid radical, and Z represents the non-metallic atoms necessary to complete a heterocyclic organic nucleus. 4. A polymethine dye intermediate of the following general formula: wherein R represents an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, X represents an acid radical, and Z represents the non-metallic atoms necessary to complete a benzothiazole nucleus. 5 A polymethine dye intermediate of the following general formula: wherein R represents an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, X represents an acid radical, and Z represents the non-metallic atoms necessary to complete a benzothiazole nucleus. 6.'A polymethinedye intermediate of the following general formula: COOR' wherein L represents a methine group, d represents a positive integer of from one to two, n represents a positive integer of from one to three, R, R and R each represent an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, and Z represents the non-metallic atoms necessary to complete a heterocyclic organic nucleus. 11. A process for preparing a polymethine dye intermediate comprising hydrolyzing, in the presence of hydrochloric acid, a condensation product of the following general formula: s 000R" wherein L represents a methine group, d represents a positive integer of from one to two, 71 represents a positive integer of from one to three, R, R and R" each represent an alkyl group, R represents a member selected from the group consisting of alkyl and aryl groups, and Z represents the non-metallic atoms necessary to complete a heterocyclic organic nucleus. 12. A process for preparing a polymethine dye intermediate comprising hydrolyzing, in the presence of hydrochloric acid, a condensation product of the following general formula: ,2. OC NR I RNC=C 0:0 s COOR" wherein R, R and R each represent an alkyl group, R" represents a member selected from the group consisting of alkyl and aryl groups and COOR Z represents the non-metallic atoms necessaryto complete a heterocyclic organic nucleus 13. A process for preparing a polymethine dye intermediate comprising hydrolyzlng, in the presence of hydrochloric acid, a condensation product of the following general formula: ' 's 000R" whereinR, R and R each represent analkyl group, R'" represents a member selected from the group consisting of alkyl and aryl groups, and Z represents the non-metallic atoms necessar to complete a heterocyclic nucleus. 14. A process for preparing a polymethine dye intermediatecomprising hydrolyzing, in the presence of hydrochloride acid, a condensation prodnot of the following general formula: product of the followinggeneral formula: s coon" wherein R, R and R" each. represent n alkyl group, R' represents a member selected from the group consisting of alkyl and aryl groups and Z represents the non met'allic atoms necessary to complete a, heterocyclic nucleus. 16. A. process: for preparing a polymethine dye intermediate comprising hydrolyzing, in the presence of hydrochloric acid, a condensationv product of the following general formula: z 0 (J NR c 00 R Rl T-d=CH-CH=C\ I v s 000R" wherein R, R and R each represent an alkyl group, R"" represents a member selected from the group consisting of alkyl and aryl groups, and Z represents the. non-metallic atoms necessary to complete a b'enzoxazo-le nucleus. V 17. A process for preparing a polymethine dye intermediate comprising hydrolyz'ing, in the presence of hydrochloric acid, a condensation product of the following general formula: ,zg 0c-'N-n" COOR s ooon" wherein R, R and R each represent an alkyl group, R' represents a member selected from the group consisting of alkyl and aryl groups, and Z represents the non-metallic atoms necessary to complete a benzothiazole nucleus. ROBERT H. YSPRAGUE.

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Cited By (7)

    Publication numberPublication dateAssigneeTitle
    US-2438782-AMarch 30, 1948Ilford LtdCyanine dyestuffs
    US-2493748-AJanuary 10, 1950Eastman Kodak CoMerocyanine dyes
    US-2500112-AMarch 07, 1950Gen Aniline & Film CorpPhotographic silver-halide emulsions containing trinuclear cyanine dyes
    US-2611695-ASeptember 23, 1952Gen Aniline & Film CorpPhotographic emulsions containing unsymmetrical tetranuclear cyanine dyes
    US-2728766-ADecember 27, 1955Eastman Kodak CoTrinuclear merocyanine dyes containing a chain alkoxyl group
    US-3152905-AOctober 13, 1964Minnesota Mining & MfgSensitizing methine dyes and intermediates, process for preparing same and photographic element containing these dyes
    US-4371734-AFebruary 01, 1983Basf AktiengesellschaftPreparation of thiazole derivatives