METHOD FOR PRODUCING OXONOL COMPOUND

Technical Field This invention relates to a method for producing an oxonol compound useful, for example, as a dye, a functional pigment and an information recording medium.

Background Art Oxonol compounds are one of the dyes useful for preventing irradiation of silver halide photosensitive materials, preventing halation of the same and for filter use (e.g., JP-A-10-251532) . Also, it has been found in recent years that they can be applied to a heat mode type information recording medium which uses high energy density laser beam and can perform writing (recording) and reading (refreshing) of information, and studies thereon have been carried out actively. JP-A-63-2O9995 discloses a CD-R type information recording medium in which a recording layer consisting of an oxonol compound is arranged on a base board. An oxonol dye in which ammonium is introduced in the form of a salt into the molecule is described therein. JP-A- 2000-52658 discloses an information recording medium in which a recording layer consisting of an oxonol dye whose acidic nucleus is a Meldrum' s acid structure (a 1,3- dioxolan-4, 6-dione derivative) is arranged on a base board. Various methods are known for the production of these oxonol compounds (e.g., Heterocyclic Compounds Cyanine Dyes and Related Compounds, edited by F.M. Hamer, John Wiley and Sons, 1964) . In addition, illustrative examples are disclosed also in JP-A-10-251532, JP-A-2000- 52658 and JP-A-2002-249674 on the method for producing oxonol compounds. On the other hand, in recent years, load of chemical production processes against environment is becoming a subject of discussion in recent years, and clean chemical reactions which do not use toxic solvents, reactants and the like to the utmost are in demand (e.g., Kagaku Frontier (Chemical Frontier) 4 "Green Chemistry", Kagaku Dojin, translated by GSC Network, November 30, 2001) .

Disclosure of the Invention JP-A-10-251532 discloses a production example in which the formed oxonol compound is precipitated as a salt with an organic base. However, according to the examinations carried out by the present inventors, it was revealed that application of this method is difficult when the acidic nucleus moiety of the oxonol compound has a Meldrum' s acid structure (a 1, 3-dioxolan-4, 6-dione derivative) , and the product of interest cannot be obtained with good yield and purity in many cases. JP-A- 2000-52658 discloses a production example in which an oxonol compound is purified by carrying out extraction with an organic solvent or silica gel column chromatography, but the operation is complex, in addition to a problem in view of waste. Thus, these conventional production methods can by no means be said advantageous methods, when operability, production cost, treating amount per one reaction, separation and purification of the product of interest and the like are taken into consideration. Accordingly, the object of the invention is to provide a method for producing an oxonol compound, which can be carried out economically and in an industrial scale. By taking the aforementioned situations into consideration, the present inventors have conducted intensive studies on the production method of oxonol compounds and, as a result, accomplished the invention by the following means. (1) A method for producing an oxonol compound represented by formula (1), the method comprising a step [1] and a step [2] , wherein the step [1] comprises: reacting an active methylene compound represented by formula (2) , an active methylene compound represented by formula (3) and a methine source compound under a basic condition, so as to obtain a reaction mixture; neutralizing the reaction mixture with an acid to effect precipitation of a free oxonol compound represented by formula (4) as a crystal; and isolating the free oxonol compound by a solid-liquid separation, and wherein the step [2] comprises: reacting the free oxonol compound represented by formula (4) with a compound represented by formula (5) to obtain the oxonol compound represented by formula (1) :

Formula (1)

wherein in formula (1), R1, R2, R3 and R4 each independently represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein R1 and R2 and R3 and R4 may be connected to form a ring, Li, L2 and L3 each independently represents a methine group which may have a substituent group, m is an integer of from 0 to 3, wherein two or more of -L2=L3~ may be the same or different when m is an integer of 2 or more, each of R5 and R6 is an alkyl group having from 4 to 12 carbon atoms, an aryl group having from 6 to 12 carbon atoms, a chlorine atom, a bromine atom, a hydroxyl group, an acyl group having from 7 to 12 carbon atoms, an aryloxy group having from 6 to 12 carbon atoms or an amido group having from 4 to 8 carbon atoms, and each of p and q is an integer of from 1 to 3, wherein two or more of R5 and R6 may be the same or different when each of p and q is an integer of 2 or more;

wherein in formula (2), R1 and R2 each independently represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein R1 and R2 may be connected to form a ring; Formula (3)

wherein in formula (3), R3 and R4 each independently represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein R3 and R4 may be connected to form a ring;

Formula (4)

wherein in formula (4), R1, R2, R3 and R4 each independently represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein R1 and R2 and R3 and R4 may be connected to form a ring, Li, L2 and L3 each independently represents a methine group which may have a substituent group, and m is an integer of from 0 to 3, wherein two or more of -L2=L3- may be the same or different when m is an integer of 2 or more; and Formula (5) xy

wherein in formula (5) , each of R5 and R6 is an alkyl group having from 4 to 12 carbon atoms, an aryl group having from 6 to 12 carbon atoms, a chlorine atom, a bromine atom, a hydroxyl group, an acyl group having from 7 to 12 carbon atoms, an aryloxy group having from 6 to 12 carbon atoms or an amido group having from 4 to 8 carbon atoms, each of p and q is an integer of from 1 to 3, wherein two or more of R5 and R6 may be the same or different when each of p and q is an integer of 2 or more, X represents an anion, and y is a number necessary for neutralizing electric charge. (2) The method for producing an oxonol compound as described in (1) above, wherein the acid for neutralizing the reaction mixture is a mineral acid. (3) The method for producing an oxonol compound as described in (1) or (2) above, wherein the acid for neutralizing the reaction mixture is a hydrohalogenic acid. (4) The method for producing an oxonol compound as described in any of (1) to (3) above, wherein a pH of a reaction mixture for precipitating the free oxonol compound represented by formula (4) as a crystal is within a range of from 2.0 to 7.0.

Best Mode For Carrying Out the Invention Details of each definition in the aforementioned general formulae are as follows . Firstly, the oxonol compound represented by the general formula (1) is described.

Formula (1)

In the general formula (1), R1, R , R3 and R4 each independently represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group. As the alkyl group, alkyl groups having from 1 to 20 carbon atoms (e.g., methyl, ethyl, n-propyl, n-butyl, isopropyl, isobutyl, tert-butyl, cyclopropyl and cyclohexyl) can be exemplified, which may have the following substituent groups (alkyl groups are excluded) . Substituent groups including the following substituent groups (to be called "substituent groups W") and the aforementioned substituent groups are called "substituent groups V" hereinafter. Examples of the substituent groups include an alkoxy group having from 1 to 8 carbon atoms (e.g., methoxy, ethoxy) , an aryl group having from 6 to 20 carbon atoms (e.g., phenyl, 1-naphthyl), an aryloxy group having from 6 to 20 carbon atoms (e.g., phenoxy, 1-naphthoxy) , a heterocyclic group (e.g., pyridyl, pyrimidyl, pyridazyl, benzoimidazolyl, benzothiazolyl, benzooxazolyl, 2- pyrrolidinon-1-yl, 2-piperidon-l-yl, succinimido, maleimido, phthalimido) , a halogen atom (e.g., fluorine, chlorine) , carboxyl group, an alkoxycarbonyl group having from 2 to 20 carbon atoms (e.g., ethoxycarbonyl, t- butoxycarbonyl) , a cyano group, an acyl group having from 2 to 10 carbon atoms (e.g., acetyl, pivaloyl) , a carbamoyl group having from 1 to 10 carbon atoms (e.g., carbamoyl, methylcarbamoyl) , an amino group, a substituted amino group having from 1 to 20 carbon atoms (e.g., dimethylamino, bis (methylsulfonylethyl) amino) , a sulfo group, a hydroxyl group, a nitro group, a sulfonamido group having from 1 to 10 carbon atoms (e.g., methanesulfonylamino) , an ureido group having from 1 to 10 carbon atoms (e.g., ureido, methylureido) , a sulfonyl group having from 1 to 10 carbon atoms (e.g., methanesulfonyl, benzenesulfonyl) , a sulfinyl group having from 1 to 10 carbon atoms (e.g., methanesulfinyl) , a sulfamoyl group having from 0 to 10 carbon atoms (e.g., sulfamoyl) and the like. The carboxyl group and sulfo group may be in the form of a salt. The aforementioned substituent groups may be further substituted with a possible substituent group. When R1, R2, R3 and R4 represent an aryl group, aryl groups having from 6 to 20 carbon atoms (e.g., phenyl, naphthyl) can be exemplified, and said aryl groups may have the aforementioned substituent groups V. When R1, R2, R3 and R4 represent a heterocyclic group, it is a 5- or 6-membered saturated or unsaturated heterocyclic group constituted from carbon atom, nitrogen atom or sulfur atom, and its examples include pyridyl, pyrimidyl, pyridazyl, piperidyl, triazyl, imidazolyl, triazolyl, furyl, thienyl, thiazolyl, oxazolyl and isoxazolyl, or benzo ring-condensed products thereof (e.g., quinolyl, benzoimidazolyl, benzooxazolyl) . In addition, these may have the aforementioned substituent groups V. Preferred as R1, R2, R3 and R4 are a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms (including an aralkyl group having from 7 to 10 carbon atoms) , an aryl group having from 6 to 12 carbon atoms or a heterocyclic group having from 4 to 10 carbon atoms. Also, when R1 and R2 and R3 and R4 respectively represent an alkyl group, they may be mutually connected to form a ring structure, illustratively a carbon ring (e.g., cyclopropane, cyclopentane, cyclohexane, adamantane, cyclooctane) or a heterocyclic ring (e.g., Piperidine) . • A preferred ring structure is a carbon ring having from 3 to 10 carbon atoms or a heterocyclic ring having from 2 to 10 carbon atoms, of which a carbon ring having from 3 to 10 carbon atoms is more preferable. Li, L2 and L3 each independently represents a methine group which may have a substituent group. Preferred as Li, L2 and L3 are unsubstituted methine group, a methine group substituted with an alkyl having from 1 to 5 carbon atoms, a methine group substituted with an aryl having from 6 to 10 carbon atoms, a methine group substituted with an aralkyl having from 7 to 10 carbon atoms, a methine group substituted with a saturate or unsaturated hetero ring and a methine group substituted with a halogen. The reference sign m is an integer of from 0 to 3. Preferably, it is 1, 2 or 3. In addition, two or more of -L2=L3- may be the same or different from one another when m is an integer of 2 or more. Each of R5 and R6 is an alkyl group having from 4 to 12 carbon atoms (e.g., butyl, hexyl, benzyl), an aryl group having from 6 to 12 carbon atoms (e.g., phenyl, naphthyl), a chlorine atom, a bromine atom, a hydroxyl group, an acyl group having from 7 to 12 carbon atoms (e.g., benzoyl), an aryloxy group having from 6 to 12 carbon atoms (e.g., phenoxy) or an amido group having from 4 to 8 carbon atoms. These groups may have the aforementioned substituent groups V or substituent groups W. Particularly preferred as the R5 and R6 are an aryl group having from 6 to 12 carbon atoms, a hydroxyl group, an acyl group having from 7 to 12 carbon atoms and a chlorine atom. The reference signs p and q are each independently an integer of from 1 to 3. Two or more of R5 and R6 may be the same or different from one another when each of p and q is an integer of 2 or more. The oxonol compound represented by the general formula (1) may have one or two or more asymmetric carbons in some cases depending on the kinds of R1, R2, R3, R4, R5 and R6, and all of the optional isomers or diastereomers based on the asymmetric carbon (s) are included within the scope of the invention. In addition to the pure form of isomers, their optional mixtures, racemic bodies and the like are also included within the scope of the invention. The oxonol compound represented by the general formula (1) contains two or more double bonds, and optional geometrical isomers based on the double bond(s) are also included within the scope of the invention. In addition, the oxonol compound represented by the general formula (1) may exist in some cases as a hydrate or a solvate, and these are also included within the scope of the invention. Kind of the solvent which forms the solvate is not particularly limited, but for example, methanol, acetone, isopropyl alcohol, dimethyl sulfoxide and the like solvents can be cited. Next, the active methylene compound represented by the general formula (2) is described.

In the general formula (2) , R1 and R2 are as defined in the aforementioned general formula (1) , and their illustrative examples and preferred ranges are also the same. In addition, R1 and R2 may be connected to form a ring. Preferred range in that case is also the same as described in the aforementioned general formula (1) . Next, the active methylene compound represented by the general formula (3) is described. Formula (3)

In the general formula (3) , R3 and R4 are as defined in the aforementioned general formula (1), and their illustrative examples and preferred ranges are also the same. In addition, R3 and R4 may be connected to form a ring. Preferred range in that case is also the same as described in the aforementioned general formula (1) . Among those described in the above, a case in which the active methylene compound represented by the general formula (2) and the active methylene compound represented by the general formula (3) are the same compound is more desirable. Next, the free oxonol compound represented by the general formula (4) is described.

Formula (4)

In the general formula (4), R1, R2, R3, R4, Li, L2 and L3 are as defined in the aforementioned general formula (1), and their illustrative examples and preferred ranges are also the same. In addition, R1 and R2 and R3 and R4 may be connected to form rings . Preferred ranges in that case are also the same as described in the aforementioned general formula (1) . Next, the compound represented by the general formula (5) is described.

Formula (5) Xy

In the general formula (5) , R5 and R6 and p and q are as defined in the aforementioned general formula (1), and their illustrative examples and preferred ranges are also the same. X represents an anion. Examples of the anion include a halide ion (e.g., chloride ion, bromide ion) , sulfate ion, hydrogensulfate ion, phosphate ion, nitrate ion, an alkyl sulfonate anion (e.g., methanesulfonate anion, trifluoromethanesulfonate anion), an aryl sulfonate anion (e.g., p-toluenesulfonate anion) and a carboxylate anion (e.g., acetate anion, oxalate anion) , of which a halide ion, an alkyl sulfonate anion, an aryl sulfonate anion or a carboxylate anion is preferable, and a halide ion, an alkyl sulfonate anion or an aryl sulfonate anion is more preferable. Most preferred X is a halide ion, more illustratively chloride ion or bromide ion. The reference sign y is a number necessary for neutralizing electric charge. For example, y is 2 when X is a monovalent anion such as a halide ion, and y is 1 when X is divalent sulfate ion. Preferred illustrative examples of the oxonol compound represented by the general formula (1) are shown bellow, though the invention is- not limited thereto. In this connection, tautomers are present in the oxonol compound represented by the general formula (1), but it should be understood that each of the chemical structural formulae described in this specification is one of these tautomers described for the sake of convenience. It is needless to say that all of the tautomers are included within the scope of the invention.

Next, conditions of the production method of the invention is described in detail. The production method of the invention is started from the reaction of an active methylene compound represented by the general formula (2), an active methylene compound represented by the general formula (3) and a methine source compound (a compound to be used for introducing methine group into a methine pigment) , and this can be carried out with reference to, for example, specifications of JP-B-39-22062, JP-B-43-3504, JP-B-52- 38056, JP-B-54-38129, JP-B-55-10059, JP-B-58-35544, JP-A- 49-99620, JP-A-52-92716, JP-A-59-16834, JP-A-63-316853, JP-A-64-4082, JP-A-10-251532, JP-A-2000-52658, JP-A-2002- 249674, British Patent No. 1133986, US Patent No. 3247127, US Patent No. 4042397, US Patent No. 4181225, US Patent No. 5213956, US Patent No. 5260179 and the like. As the methine source compound, those which are described in the aforementioned patent references are used, and illustrative examples of the methine source compound include l-phenylamino-5-phenylimino-l, 3-pentadiene hydrochloride (may be a free form) and l-phenylamino-5- phenylimino- 3-methyl-l, 3-pentadiene hydrochloride (may be a free form) , as well as the pyridinium compounds described, for example, in JP-A-10-251532. These are optionally selected in response to the structure of the oxonol compound of interest. The total of mole numbers of the active methylene compound represented by the general formula (2) and mole numbers of the active methylene compound represented by the general formula (3) is within the range of from 1.8 to 5.0 moles based on the methine source compound, but their use in large excess does not so much exert influence on the improvement of formation ratio/formation rate of the product of interest. On the contrary, use of the active methylene compounds in too excess amounts becomes the cause of increased amount of waste, cost up, crystallization inhibition and the like and rather becomes a hindrance in the case of an industrial scale production. When the active methylene compound represented by the general formula (2) and the active methylene compound represented by the general formula (3) are the same, amount of the active methylene compound to be used is preferably from 1.9 to 4.0 moles, preferably from 1.9 to 3.0 moles, further preferably from 2.0 to 2.5 moles, based on the methine source compound. In addition, when the active methylene compound represented by the general formula (2) and the active methylene compound represented by the general formula (3) are different from each other, it is possible to synthesize a compound having asymmetric structure, by firstly reacting from 0.9 to 1.2 moles of the active methylene compound represented by the general formula (2) based on the methine source compound, and subsequently reacting from 0.9 to 1.2 moles of the active methylene compound represented by the general formula (3) based on the methine source compound. Regarding the solvent to be used in the reaction of the active methylene compound(s) with the methine source compound, there is no particular limitation, with the proviso that it does not cause a problem on the process operation, does not hinder progress of the reaction and does not exert a bad influence upon the reaction by degrading under the reaction conditions of the invention, and its examples include methanol, ethanol, 2-propanol and the like alcohol solvents, N-methylpyrrolidone, sulfolane, dimethyl sulfoxide, N,N- dimethylimidazolidinone, N,N-dimethylformamide, N,N- dimethylacetamide and the like aprotic polar solvents, 1, 2-dimethoxyethane, tetrahydrofuran and the like ether solvents, ethyl acetate, n-butyl acetate and the like ester solvents, dichloromethane, 1, 2-dichloroethane and the like chlorine system hydrocarbons and the like. Among them, it is desirable to use an alcohol solvent, an aprotic polar solvent or an ester solvent, and it is more desirable to use methanol, ethanol, 2-propanol, N- methylpyrrolidone, N,N' -dimethylimidazolidinone, N,N- dimethylformamide, N,N-dimethylacetamide or ethyl acetate. Most desirable solvent is methanol, 2-propanol, N-methylpyrrolidone, N,N-dimethylacetamide or ethyl acetate, or a joint use system of 2 or 3 solvents selected from them. It is desirable to use a base in the reaction of the active methylene compounds and the methine source compound. Examples of the base include tertiary organic bases (triethylamine, tri-n-propylamine, tri-n-butylamine, N,N- diisopropylethylamine, N-methylpiperidine, N- methylmorpholine, 1, 8-diazabicyclo [5.4.0] -7-undecene, 1, 5-diazabicyclo [4.3.0] -5-nonene, 1, 4- diazabicyclo [2.2.2]octane and the like), pyridines (pyridine, 2-methylpyridine, 2,6-lutidine and the like), alkali metal alkoxides (sodium methoxide, sodium ethoxide, sodium t-butoxide and the like) , alkali metal hydroxides (sodium hydroxide, potassium hydroxide and the like) , alkaline earth metal hydroxides (magnesium hydroxide and the lie) , sodium acetate, potassium carbonate, sodium carbonate and the like. Preferred among them is a tertiary organic base, more preferably triethylamine, tri-n-butylamine or N,N- diisopropylethylamine, further preferably triethylamine. Amount of the base to be used is preferably from 2 to 12 equivalents, more preferably from 4 to 8 equivalents, based on the methine source compound. The reaction temperature is generally within the range of from 0 to 6O0C, but is preferably from 5 to 45°C, more preferably from 10 to 400C. The reaction time varies depending on the charging amount and reaction temperature, but is generally within the range of from 0.5 to 8 hours, more preferably from 1 to 6 hours. Though an inert atmosphere is not particularly necessary in this step, the reaction may be carried out in a stream of argon or nitrogen. Post-treatment of the reaction mixture after the reaction of the active methylene compounds and the methine source compound is firstly carried out by neutralizing the reaction mixture with an acid. Examples of the acid to be used in the neutralization include sulfuric acid, phosphoric acid, nitric acid, a hydrohalogenic acid, perchloric acid and the like mineral acids, or methanesulfonic acid, p-toluenesulfonic acid, acetic acid, trichloroacetic acid, oxalic acid, succinic acid, tartaric acid and the like organic acids, of which sulfuric acid, a hydrohalogenic acid and the like mineral acids are preferred, and a hydrohalogenic acid is more preferred. As the hydrohalogenic acid, hydrochloric acid, hydrobromic acid and hydroiodic acid can be exemplified, and among them, the use of hydrochloric acid or hydrobromic acid is more desirable, and the use of hydrochloric acid further desirable. By carrying out neutralization with an acid, the free oxonol compound represented by the general formula (4) is precipitated as crystals. The pH for effecting precipitation of the free oxonol compound represented by the general formula (4) as crystals varied depending on the structure of intended product, but is generally within the range of from 2.0 to 7.0. The crystals are not easily precipitated when the pH is higher than 7.0,' and when the pH is lower than 2.0 on the contrary, it leads to the degradation of acidic nucleus moiety connected to the methine chain, increase of strongly acidic waste liquid and the like, so that these cases are not desirable. The thus precipitated free oxonol compound represented by the general formula (4) can be easily isolated by a usual solid-liquid separation. This is an industrially superior advantage, because the extraction with an organic solvent, purification by a silica gel column chromatography and the like, as the methods described in JP-A-2000-52658 and the like, are not necessary. Next, the method for obtaining the oxonol compound represented by the general formula (1) by allowing the free oxonol compound represented by the general formula (4) to react with the compound represented by the general formula (5) is described. Molar ratio of the free oxonol compound represented by the general formula (4) to be used in the reaction is within the range of from 2.0 to 3.0 moles, preferably from 2.1 to 2.5 moles, based on the compound represented by the general formula (5) . The use of the free oxonol compound represented by the general formula (4) in an excess amount than this does not lead to the improvement of yield of the oxonol compound represented by the general formula (1) . On the contrary, when using amount of the free oxonol compound represented by the general formula (4) is smaller than the above range, the compound represented by the general formula (5) partially remains which is not desirable. Examples of the solvent to be used in the reaction of the free oxonol compound represented by the general formula (4) with the compound represented by the general formula (5) include methanol, ethanol, 2-propanol and the like alcohol solvents, N-methylpyrrolidone, sulfolane, dimethyl sulfoxide, N,N-dimethylimidazolidinone, N,N- dimethylformamide, N,N-dimethylacetamide and the like aprotic polar solvents, 1,2-dimethoxyethane, tetrahydrofuran and the like ether solvents, and the like. Among them, it is desirable to use an alcohol solvent or an aprotic polar solvent, and it is more desirable to use an alcohol solvent. Most desirable solvent is methanol, ethanol, 1-propanol, 2-propanol, or a joint use system of 2 or 3 solvents selected from them. The reaction temperature is generally within the range of from 20 to 100°C, but a temperature of as high as possible is desirable for the improvement of reaction efficiency. For example, the desirable reaction condition when methanol is used as the solvent is a refluxing condition. The reaction time varies depending on the charging amount and reaction temperature, but is generally within the range of from 0.5 to 6 hours, more preferably from 1 to 5 hours. Though an inert atmosphere is not particularly necessary in this step, the reaction may be carried out in a stream of argon or nitrogen. Since the oxonol compound represented by the general formula (1) formed by the reaction of the free oxonol compound represented by the general formula (4) with the compound represented by the general formula (5) has excellent crystallizing property, it precipitates as crystals when the reaction mixture is cooled or a bad solvent is added, so that it can be easily isolated by carrying out a usual solid-liquid separation. The oxonol compound represented by the general formula (1) obtained in the above manner has such a high purity that it is not necessary in general to carry out further purification.

Examples The following describes the invention further in detail with reference to examples, but the invention is not limited thereto. Example 1 Synthesis of compound A-3 The compound A-3 was synthesized by the following reaction scheme.

Intermedia 1

Intermedia 2

1-1. Synthesis of intermediate 1

Concentrated sulfuric acid (1 ml) was added to a

mixture of acetic anhydride (44 g) and malonic acid (50

g) , and cyclohexanone (40 g) was subsequently added

dropwise thereto at 30°C. The reaction mixture was

stirred at 4O0C for 5 hours and then poured into a mixed

medium consisting of 2-propanol (80 ml) and water (170

ml) at 20°C, and the mixture was neutralized to pH 3 with

a sodium hydroxide aqueous solution. The reaction

mixture was stirred at 20°C for 1 hour, and then the

precipitated crystals were filtered, washed with a mixed

solution consisting of 2-propanol/water (volume ratio

1/2) and then dried to obtain 40.5 g of the intermediate

1 as grayish white crystals. Yield 54%.

1-2. Synthesis of intermediate 2

Triethylamine (72 ml) added dropwise to a mixture

consisting of l-phenylamino-5-phenylimino-l, 3-pentadiene hydrochloride (40 g) , the intermediate 1 (60 g) and 2- propanol (256 ml) at room temperature. The reaction mixture was stirred at 3O0C for 3 hours and then cooled to 2O0C or less, and the reaction mixture was neutralized to pH 4 by adding dilute hydrochloric acid. After stirring at 20°C for 2.5 hours (a seed crystal may be added as occasion demands), the thus precipitated crystals were filtered, washed with warm water of 35°C and the dried to obtain 59 g of the intermediate 2 as a purplish red crystalline powder, m. p. 233°C (decomposition) 1-3. Synthesis of A-3 The intermediate 2 (58 g) and bipyridinium compound 1 (32 g) were suspended in methanol (500 ml) , and the reaction mixture was heated under reflux for 3 hours. Water (200 ml) was added dropwise thereto while keeping the temperature at 600C or more, and the reaction mixture was stirred at 60 to 7O0C for 2 hours. After cooling to 300C or less and subsequent stirring for 2 hours, the thus precipitated crystals were filtered, washed with a mixed medium consisting of methanol/water and then dried to obtain 52 g of the A-3 as dark green crystalline powder. Yield 78% as l-phenylamino-5-phenylimino-l, 3-pentadiene hydrochloride basis, m. p. 235°C (decomposition) Example 2 Synthesis of compound A-4 The compound A-4 was by the following reaction scheme.

Intermediate 1 Intermediate 4

Bipyridinium Compound 1 2-1. Synthesis of intermediate 4 At room temperature, triethylamine (60 ml) was added dropwise to a mixture consisting of the intermediate 3 (1- (benzothiazol-2-yl) -4-phenylpyridinium chloride, 40 g) , the intermediate 1 (50 g) and 2-propanol (200 ml) . The reaction mixture was stirred at 300C for 3 hours and then cooled to 20°C or less, and the reaction mixture was neutralized to pH 3 by adding dilute hydrochloric acid. After stirring at 25°C for 2 hours (a seed crystal may be added as occasion demands), the thus precipitated crystals were filtered, washed with warm water of 40°C and the dried to obtain 60 g.of the intermediate 4 as a deep blue crystalline powder, m. p. 248°C 1-3. Synthesis of A-4 The intermediate 4 (35 g) and bipyridinium compound 1 (17 g) were suspended in methanol (220 ml), and the reaction mixture was heated under reflux for 2 hours. Water (100 ml) was added dropwise thereto while keeping the temperature at 60°C or more, and the reaction mixture was stirred at 60 to 70°C for 1 hour. After cooling to 30°C or less and subsequent stirring for 2 hours, the thus precipitated crystals were filtered, washed with a mixed medium consisting of methanol/water and then dried to obtain 29 g of the A-4 as brilliant green crystalline powder. Yield 74% as intermediate 3 basis, m. p. 248°C (decomposition) Example 3 Synthesis of compound A-2 When compared with the compound A-3, the compound A- 2 is different in terms of the structure of the 1,3- dioxolan-4, 6-dione moiety of both termini of the molecule. The 1, 3-dioxolan-4, 6-dione moiety was synthesized by the following reaction scheme and method.

Intermediate 5

Concentrated sulfuric acid (1 ml) was added to a mixture of acetic anhydride (25.6 g) and malonic acid (18.7 g) , and ethyl levulinate (28.9 g) was subsequently added dropwise thereto at 3O0C or less. The reaction mixture was stirred at 35°C for 2 hours, and then ethyl acetate (150 ml) and 10% brine (100 ml) were added thereto to fractionate the organic layer. The organic layer was washed with 10% brine (100 ml) and concentrated, and the residue was crystallized from ethanol/water (volume ratio 1/3, crystallization temperature 50C) , filtered, washed and dried to obtain 27.7 g of the intermediate 5 as colorless crystals. Yield 63%. Thereafter, the compound A-2 was synthesized in accordance with the method described in Example 1, using the intermediate 5 instead of the intermediate 1, and the product of interest was obtained as a dark green crystalline powder. Example 4 Synthesis of compound A-5 The intended compound A-5 was obtained as a dark green crystalline powder by carrying out its synthesis in accordance with the method of Example 1 using 1- phenylamino-5-phenylimino-3-methyl-l, 3-pentadiene hydrochloride instead of l-phenylamino-5-phenylimino-l, 3- pentadiene hydrochloride. Example 5 Synthesis of compound A-I The intended compound A-I was obtained as a dark green crystalline powder by carrying out its synthesis in accordance with the method of Example 1 using 2-methyl-2- propyl-1, 3-dioxolan-4, 6-dione instead of the intermediate 1. 2-Methyl-2-propyl-l, 3-dioxolan-4, β-dione was synthesized by the following method. Concentrated sulfuric acid (2 ml) was added to a mixture of acetic anhydride (68.7 g) and malonic acid (50 g) , and 2-pentanone (41.4 g) was subsequently added dropwise thereto at a temperature of 1O0C or less. The reaction mixture was stirred at 20°C for 2 hours, and then toluene (200 ml) and 10% brine (70 ml) were added thereto. The organic layer was fractionated and concentrated, and the residue was crystallized from 2- propanol/water (volume ratio 1/3, crystallization temperature 5°C) , filtered using a mixed solution consisting of 2-propanol/water (volume ratio 1/3), washed and then dried to obtain 57.9 g of 2-methyl-2-propyl-l, 3- dioxolan-4, 6-dione. Yield 70%. Example 6 Synthesis of compound A-9 Compounds up to the intermediate 4 were synthesized by the method described in Example 2. The intended compound A-9 was obtained as a brilliant green crystalline powder by using the bipyridinium compound 2 shown below instated of the bipyridinium compound 1

Bipyridinium Compound 2

Example 7 Synthesis of compound A-Il The compound A-Il was synthesized by the following reaction scheme.

Intermediate 5 Intermediate 1

Intermediate 6

At room temperature, triethylamine (36 ml ) was added dropwise to a mixture consisting of l-phenylamino-5- phenylimino-1 , 3-pentadiene hydrochloride ( 40 g) , the intermediate 1 ( 28 g) and 2-propanol ( 240 ml ) . The reaction mixture was stirred at 30°C for 2 hours , the intermediate 5 ( 36 g) was added thereto, and then triethylamine ( 36 ml ) was subsequently added dropwise thereto. The reaction mixture was stirred at 35°C for 3 hours and then cooled to 20°C or less, and the reaction mixture was neutralized to pH 4 by adding dilute hydrochloric acid. The crystals precipitated after 2.5 hours of stirring at 15°C were filtered, washed with warm water of 35°C and then dried to obtain 50 g of the intermediate 6 as a purplish red crystalline powder. Thereafter, the compound A-Il was obtained as a dark green crystalline powder by carrying out its synthesis in accordance with the method described in Example 1. Yield 66% as l-phenylamino-5-phenylimino-l, 3-pentadiene hydrochloride basis. From the examples described in the foregoing, it can be understood that the production method of the invention is convenient in terms of operation, shows good productivity and economically advantageous too. Accordingly, superiority and usability of the production method of the invention are obvious.

Industrial Applicability By the method of the invention, an oxonol compound useful, for example, as a dye, a functional pigment and an information recording medium can be produced efficiently, safely and stably. The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.