US2336463A - Cyanine dye containing a tetrahydrobenzothiazole nucleus - Google Patents

Description

Patented Bee. 14, 1943 LINETED STATES PATENT QFFICE CYANINE DYE CONTAINING A TETRAHY- DROBENZOTHIAZOLE NUCLEUS Jersey No Drawing. Application November 9, 1939, Serial No. 303,618

4 Claims.

This invention relates to cyanine dyes containing a tetrahydrobenzothiazole nucleus and to a process for preparing such dyes.

Cyanine dyes contain at least two auxochromic nitrogen atoms, the one ternary and the other quaternary, the one nitrogen atom lying in one heterocyclic nucleus and the other lying in another heterocyclic nucleus, the two nitrogen atoms being connected by a conjugated carbon chain. A number of cyanine dyes containing benzothiazole nuclei as one or both of the aforesaid heterocyclic nuclei are known.

We have now found that it is possible to prepare cyanine dyes in which one or both of the aforesaid auxochromic nitrogen atoms lie in a 4,5,6,7-tetrahydrobenzothiazole nucleus. We have further found that these new cyanine dyes sensitize photographic emulsions strongly and cleanly, i. e. without producing excessive fog.

It is, accordingly, an object of our invention to provide new cyanine dyes. A further object is to provide a method for preparing such dyes. A further object is to provide photographic emulsions sensitized with such dyes. Other objects will appear hereinafter.

As starting material for the preparation of our new dyes, we employ .2-alkyl-4,5,6,'7-tetrahydrobenzothiazoles, particularly 2-methyl-4,5,6,7- tetrahydrobenzothiazole. We first convert these tetrahydrobenzothiazole bases to quaternary salts by reacting the bases with esters, such as alkyl halides, alkyl sulfates .or alkyl-p-toluenesulfonates, for example.

To prepare pseudocyanine dyes from such quaternary salts, we react the quaternary salts with 2-halogenoquinoline quaternary salts, in the presence of an acid-binding a ent, such, for example, as sodium ethylate, sodium carbonate, pyridine or a strong tertiary organic base (e. g. trimethylamine, triethylamine and N-methylpioeridine). Strong organic bases are those which have a dissociation constant substantially greater than that of p ridine. We have found it advantageous to employ strong tertiary organic bases.

Instead of 2-halogenoquinoline quaternary salts, we can employ 2-alkylmercaptoor 2-arylmercaptoquinoline quaternary salts to condense with the quaternary salts of 2-alkyltetrahydrobenzothiazoles, in the presence of an acid-binding agent. Z-alkylmercaptoand 2-arylmercaptoquinoline quaternary salts are described in United States Patent 2,117,986, dated May 1'7, 1938.

Using Z-halogenopyridine or Z-halogenopyridine quaternary salts instead of 2-halogenoquinoline quaternary salts, We can prepare pyridopseudocyanine dyes containing a tetrahydrobenzothiazole nucleus.

Using Z-alkylmercaptoor 2-arylmercaptobenzothiazole quaternary salts instead of Z-halogenoquinoline quaternary salts, we can prepare simple cyanine dyes other than pseudocyanine dyes.

To prepare symmetrical carbocyanine dyes from 2 alkyl 4,5,6}? tetrahydrobenzothiazole quaternary salts, we react the quaternary salts with esters of orthoacids, e. g. ethyl orthoiormate, ethyl orthoacetate, ethyl orthopropionate and ethyl orthobenzoate, in the presence of pyridine.

To prepare unsymmetrical carbocyanine dyes from 2 alkyl 4,5,6,7 tetrahydrobenzothiazole quaternary salts, we react the quaternary salts with cyclammonium quaternary salts containing a p-arylaminovinyl group in the alpha or gamma position, i. e. in one of the so-called reactive positions, in the presence of an acid binding agent, e. g. pyridine.

To prepare dicarbocyanine dyes from Z-allzyl- 4,5,6,7-tetrahydrobenzothiazcle quaternary salts, we react the quaternary salts with cyclammonium quaternary salts containing an w-arylaminobutadienyl group in the alpha or gamma position, in the presence of an acid-binding agent, e. g. triethylamine dissolved in ethyl or isopropyl alcohol.

The following examples will serve to demonstrate the manner of obtaining our new dyes.

These examples, however, are not intended to limit our invention:

EXAMPLE 1 1 ',3-diethyl -,5,6,7-tetmhydrothia-2 -cyanine iodide CzH5 I ing the mixture. Boiling was continued for about 20 minutes. At the end of this time, the reaction mixture was cooled and chilled to C. The dye separated from the chilled reaction mixture. The dye was filtered ozi, washed with acetone, then with water and finally with acetone, and then allowed to dry in the air. A yield of 84% of dye was thus obtained. The crude dye was recrystallized from methyl alcohol (25 cc. per gram of dye) and a 65% yield of pure dye was obtained. The pure dye was obtained in the form of reddish-orange crystals which melted at 279 to 280 C. with decomposition.

EXAMPLE 2 3,3-diethyl4,5,6,7,4',5',6,7'-0ctahydr0thiacarbocyanine iodide 3.09 g. (2 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazole ethiodide and 2.2 g. (3 mol.) of ethylorthoformate were mixed together in cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 2 hours. At the end of this time, the reaction mixture was cooled and diethyl ether was added to the reaction mixture to precipitate the dye. The precipitated dye was filtered off, washed with water and then with acetone, and finally allowed to dry in the air. The yield of crude dye was 12%. The crude dye was recrystallized from acetone (110 cc. per gram of dye) and an 8% yield of pure dye was obtained in the form of greenishbronze crystals melting at 216 to 217 C. with decomposition.

EXAMPLE 3 3,3-diethyl-9-meth1 Z-4,5,6,7,4,5,6,7'metalwdrothzacarbocyanine iodide 3.09 g. (2 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazole ethiodide and 2. g. (3 mol.) of ethyl orthoacetate were mixed together in 10 cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 2%; hours. The reaction mixture was then cooled and diluted with 150 cc. of diethyl ether to precipitate the dye. The ethereal layer wa then decanted. The sticky residue was stirred with another 159 cc. portion of diethyl ether and again the ethereal layer was decanted. The sticky residue was dissolved in cc. of acetone and the resulting solution was diluted with diethyl ether to precipitate the dye. The precipitated dye was filtered ofi and washed with acetone and allowed to dry in the air. The yield of crude dye was 10%. After recrystallization from acetone (160 cc. per gram of dye) a yield of 6% of pure dye was obtained. The dye was obtained in the form of dull dark green crystals, melting at 246 to 248 C. with decomposition.

EXAMPLE 4 3,3',9-triethyZ-4,5,6,7,4',5',6',7-0ctahydrothiacarbocyanine iodide 7.06 g. (2 mol.) of 2-n1ethyl-4,5,6,7-tetrahydrobenzothiazole etho-p-toluenesulfonate and 5.28 g. (3 mol.) of ethyl orthopropionate were mixed together in 10 cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 4 hours. At the end of this time, the hot reaction mixture was treated with a hot solution of potassium iodide (5 g.) dissolved in water (50 cc.). The resulting mixture was chilled to 0 C. when the dye separated out. It was filtered off, washed with water and finally stirred with boiling acetone (25 00.). The acetone suspension was chilled to 0 C. and the dye filtered off and washed with cold acetone and allowed to dry in the air. The yield of crude dye was 16% and after two recrystallizations from acetone cc. per gram of dye), a yield of pure dye of 7% was obtained. The dye was obtained in th form of dark green crystals.

EXAMPLE 5 3,3'-diethyZ-4',5',6',7-tetrahydro-oxathidcarbocyam'ne iodide 353' g. (1.1 mol.) of 2-methyl-4,5,6,7-tetrahy drobenzothiazole etho-p-toluenesulfonate and 3.95 g. (1 mol.) of 2-(B-acetanilid0vinyl) -bcnzcxazole ethiodide were mixed together in 15 cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 10 minutes. The reaction mixture was then cooled and diluted with cc. of diethyl ether. lhe ethereal layer was decanted and the residue was stirred with 50 cc. of hot acetone. The resulting acetone suspension was chilled to 0 C. and the dye was filtered oil and washed with cold acetone. The dye was allowed to dry in the air. The yield of crude dye was 45% and after two recrystallizations from methyl alcohol (45 cc. per gram of dye), a 26% yield of pure dye was obtained. The pure dye was obtained in the form of dark purple crystals having a blue reflex melting 247 to 248 C. with decomposition.

EXAMPLE 6 4.42 g. (1.3 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazole metho-p-toluenesulfonate and 4.5 g. (1 mol.) of 2-( s-acetanilidovinyl)-benzothiazole ethiodide were mixed together in 15 cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 10 minutes. The reaction mixture was then chilled and the crystalline dye which separated was filtered off, washed with acetone and allowed to dry in the air. The yield of crude dye was 62% and after recrystallization from methyl alcohol (75 cc. per gram of dye), a yield of pure dye of 42% was obtained. The pure dye was in the form of dark green needles having a blue reflex and melting at 273 to 274 C. with decomposition.

EXAMPLE 7 Neocarbocyanine perchlorate from Z-mdthyl- 4,5,6,7-tetrahyclrobenzothiazole 7.06 g. (3 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazole etho-p-toluenesulfonate and 4.44 g. (1 mol.) of ethyl orthoformate were mixed together in 10 cc. of dry pyridine. The resulting mixture was gently boiled, under reflux, for about 4 hours. The hot reaction mixture was then treated with a hot solution of potassium iodide (5 g.) in water (50 cc.) and the resulting mixture was chilled at C. The dye which separated was filtered oh and washed with water. The dye was then stirred with 25 cc. of hot acetone. The resulting suspension was chilled to 0 C. and the dye filtered oif and washed with cool acetone. The yield of crude dye-iodide was 32%, and after two recrystallizations from 95% ethyl alcohol (25 cc. per gram of dye) a yield of pure dye of 18% was obtained. The pure dye-iodide was dissolved in hot methyl alcohol (20 cc.) and to the hot solution was added a hot solution of sodium perchlorate (1 g. in 2.0 cc. of water). The resulting solution was chilled to 0 C. and the dyeperchlorate was filtered 01f. It was recrystallized from 95% ethyl alcohol ('70 00. per gram of dye) and obtained as shiny green crystals, melting at 244 to 246 C. with decomposition.

2-alkyl-4,5,6,7-tetrahydrobenzothiazoles can be prepared as described by Smith and Sapiro in Transactions of the Royal Society of South Africa, vol. 18, pages 229-235, 1929.

Quaternary salts of 2-alkyl-4,5,6,7-tetrahydrobenzothiazoles can be prepared as illustrated in the following examples:

EXAMPLE 8 Z-methyl-4,5,6,7-tetrahydrobenzothiaeole ethiodide 1.53 g. of 2-methyl-4,5,6,7-tetrahydrobenzothiazole and 2.0 g. of ethyl iodide were heated together, under reflux, for about 24 hours. The

solid reaction product consists essentially of the quaternary salt and can be used without further purification.

EXAMPLE 9 2-methyl-4,5,6,7-tetrahydrobenzothiazo le 10 etho-p-toluenesulfonate 3.06 g. of 2-methyl-4,5,6,7-tetrahydrobenzothiazole and 4.0 g. of ethyl-p-toluenesulfonate were heated together at 100 C. for four days. The solid reaction product consists essentially of the quaternary salt and can be used without further purification. The metho-p-toluenesulfonate can be similarly formed by using methyl instead of ethyl-p-to1uenesulfonate.

To sensitize photographic silver halide emulsions with our new dyes, we disperse the dyes in the emulsions. Our invention is particularly directed to the customarily employed gelatinosilver-halide emulsions, such a the gelatinosilver-bromide, bromiodide, chloride and chlorobromide for example. The methods of incorporating dyes in emulsions are simple and well known to those skilled in the art. In practicing our invention, it is convenient to add the dyes from solutions in appropriate solvents. Methanol has proven satisfactory as a solvent for our new dyes. The dyes are advantageously incorporated in the finished, washed emulsions and should be uniformly distributed throughout tosecure best results.

The concentration of our new dyes in the emulsions can vary widely, e. g. from about 5 to about 100 mg. per liter of flowable emulsion. The concentration of the dye will vary according to the type of light-sensitive material in the emulsion and according to the efiects desired. The suitable and most economical concentration for any given emulsion will be apparent to those skilled in the art, upon making the ordinary tests and observations customarily used in the art of emulsion-making. To prepare a gelatino-silverhalide emulsion sensitized with one of our new dyes, the following procedure is satisfactory: A quantity of the dye is dissolved in methyl alcohol, and a volume of the solution (which may be diluted with water) containing from 5 to 100 mg. of dye is slowly added to about 1000 cc. of a gelatin-o-silver-halide emulsion with stirring. Stirring is continued until the dye is uniformly dispersed. With the more powerful of our new sensitizing dues, 10 to 20 mg. of dye per 1000 cc. of emulsion sufiice to produce the maximum sensitizing effect with the ordinary gelatino-silyer-halide emulsions. The above statements are only illustrative and not to be understood as limiting our invention in any sense, as it will be apparent that our dyes can be incorporated by other methods in many of the photographic emulsions customarily employed in the art, such, for instance, as by bathing the plate or film upon which the emulsion is coated, in a solution of the dye in an appropriate solvent, although such a method is ordinarily not to be preferred. The claims are intended to cover any combination of these new dyes with a photo-graphic silver halide emulsion whereby the dyes exert a sensitizing effect on the emulsion.

The following table contains data which show the sensitizing range of our new dyes on photographic silver halide emulsions:

Table Sensitivity Maximum Emulsion Dye (mg. per liter of emulsion) extends sensitivity M'u ll [it Gelatino-silver-bromiodide (about 40 g. of silver halide 1,3-cliethyl-4,5,6,7-tetrahydrothia-2-cyanine iodide. 10 mg. 575 540 per liter of emulsion).

Do 3, 3-d1ethyl-4, 5, 6, 7, 4, 5 ,6, 7-octahydrothiacarbooyanine 645 610 iodide. 10 m Do 3,3-diethyl-9-methyl 4,5.6,7,4,5,6,7-octahydrothiacarbo- 615 580 cyanine iodide. 10 mg. D 3,3,9-triethyl-4,5,6,7,4,5,6,7-0ctahydrothiacarbocyanine 615 580 iodide. 10 mg. Do 3,3 diethyl 4,5,6,7 tctrahydro oxathiacarbocyanine '35 560 iodide. mg. Do 3-ethyl-3-methyl4',5,6,7-tetrahydrothiacarbocyanine 640 600 iodide. 10 mg. Do Neothiazolooarbocyanine perchlorate from 2-methyl-4,5, 725 680 6,7-tetrahydrobenzothiazole. mg.

Photographic elements comprising our new dyes can be prepared in the usual manner by coating the emulsions on a. suitable support (e. g. glass, cellulose derivative film, resin film or photographic paper) to suitable thickness and drying the coated emulsion.

What We claim as our invention and desire to be secured. by Letters Patent of the United States l. A dye selected from the group characterized by the following general formula:

wherein R and R represent alkyl groups, R" represents a substituent selected from the group consisting of hydrogen and alkyl groups and X represents an acid radical.

2. 3,3'-diethy1-4,5,6,7,4',5,6','7'-- octahydrothiacarbocyanine iodide.

3. 3,3 diethy1-9-methy1-4,5,6,'7,4',5,6',7-octahydrothiacarbocyanine iodide.

4. 3,3',9- triethyl -4,5,6,7,4=',5',6',7' octahydrothiacarbocyanine iodide.

LESLIE G, S. BROOKER. FRANK L. WHITE.