A method for production of dibenzoxazolyl thiophenes

Abstract: There is disclosed a method of producing a thiophene-2,5-dicarboxylic acid diester represented by the formula wherein R' represents an alkyl of 1-8 carbons, a phenyl, a substituted phenyl or benzyl, which comprises: halogenating a tetrahydrothiophene-2,5-dicarboxylic acid diester represented by the formula wherein R' is the same as before, with a halogenating agent selected from the group consisting of halogens and sulfuryl halides in an amount of 2-4 moles per mole of the tetrahydrothiophene-2,5-dicarboxylic acid diester; and then dehydrohalogenating the resultant halogenated tetrahydrothiophene-2,5-dicarboxylic acid diester in the presence of an alcohol, a base, a metal or a metal ion. There is also disclosed a method of producing tetrahydrothiophene-2,5-dicarboxylic acid diester and dibenzoxazolyl thiophenes. Some of the thiophene-2,5-dicarboxylic acid diesters and tetrahydrothiophene-2,5-dicarboxylic acid diesters are novel.

Description: This invention relates to a method of producing dibenzoxazolyl thiophenes. Dibenzoxazolyl thiophenes are useful as fluorescent brightening agents for synthetic resins. Such compounds have been heretofore produced by the reaction of thiophene-2,5-dicarboxylic acid with aminophenols as described in Japanese Patent Laid-open No. 56-92278, or by the reaction of thiophene-2,5-dicarboxylic acid dichloride with aminophenols as described in French Patent No. 1,550,280. The thiophene-2,5-dicarboxylic acid is obtained by hydrolysis of thiophene-2,5-dicarboxylic acid diesters, and the dichloride is obtained by chlorination of thiophene-2,5-dicarboxylic acid. No method has been known which provides a dibenzoxazolyl thiophene in a single step using a thiophene-2,5-dicarboxylic acid diester. It is, therefore, an object of the invention to provide a novel and industrially advantageous method of producing in a single step a dibenzoxazolyl thiophene using a thiophene-2,5-dicarboxylic acid diester as a starting material. In accordance with the invention, there is provided a method of producing a dibenzoxazolyl thiophene represented by the formula wherein R''' represents hydrogen, alkyl of 1-8 carbons, cycloalkyl, phenyl, monoalkylated phenyl, polyalkylated phenyl, halogenated phenyl, alkoxyphenyl or benzyl, which comprises: reacting a thiophene-2,5-dicarboxylic acid diester represented by the formula wherein R' represents alkyl of 1-8 carbons, phenyl, monoalkylated phenyl, polyalkylated phenyl, halogenated phenyl, alkoxyphenyl or benzyl, with an aminophenol represented by the formula wherein R''' is the same as before, in the presence of an acid catalyst. As an example of mono- or polyalkylated phenyls tolyl, ethylphenyl or xylyl can be mentioned. Examples of halogenated phenyls are chlorophenyl bromophenyl or dichlorophenyl. As suitable alkoxyphenyls methoxyphenyl or ethoxyphenyl can be mentioned. The thiophene-2,5-dicarboxylic acid diester usable includes compounds such as thiophene-2,5-dicarboxylic acid dimethyl ester, thiophene-2,5-dicarboxylic acid diethyl ester, thiophene-2,5-dicarboxylic acid di-n-propyl ester, thiophene-2,5-dicarboxylic acid diisopropyl ester, thiophene-2,5-dicarboxylic acid di-n-butyl ester, thiophene-2,5-dicarboxylic acid di-sec-butyl ester, thiophene-2,5-dicarboxylic acid diisobutyl ester, thiophene-2,5-dicarboxylic acid di-tert-butyl ester, thiophene-2,5-dicarboxylic acid diisoamyl ester, thlophene-2,5-dicarboxylic acid di-sec-amyl ester, thiophene-2,5-dicarboxylic acid di-tert-amyl ester, thiophene-2,5-dicarboxylic acid di-n-octyl ester, thiophene-2,5-dicarboxylic acid diphenyl ester, thiophene-2,5-dicarboxylic acid di-m-tolyl ester or thiophene-2,5-dicarboxylic acid dibenzyl ester. Among these diesters are preferred in particular diisoproyl, diisobutyl, di-sec-butyl, di-tert-butyl, diisoamyl, di-sec-amyl, di-tert-amyl or diphenyl esters since the reaction proceeds very rapidly to provide the desired dibenzoxazolyl thiophene derivatives. The aminophenol used includes, for instance, 2-aminophenol, 4-methyl-2-aminophenol, 4-ethyl-2-aminophenol, 4-n-propyl-2-aminophenol, 4-isopropyl-2-aminopilenol, 4-n-butyl-2-aminophenol, 4-isobutyl-2-aminophenol, 4-sec-butyl-2-aminophenol, 4-tert-butyl-2-aminophenol, 4-n-octyl-2-aminophenol, 4-cyclohexyl-2-aminophenol, 4-phenyl-2-aminophenol and 4-benzyl-2-aminophenol The aminophenol is used usually in an amount of 1.8-3.0 moles, preferably of 2.0-2.6 moles, per mole of thiophene-2,5-dicarboxylic acid diester used. The acid catalyst used in the invention includes, for example, boric acid, phosphoric acid, polyphosphoric acid, zinc chloride, ferric chloride and sulfuric acid, among which boric acid is most preferred. The amount of the acid catalyst is usually in the range of 0.05-0.50 moles per mole of thiophene dicarboxylic acid diester. It is desired that the reaction is carried out under an inert gas atmosphere such as nitrogen to prevent coloration of the dibenzoxazolyl thiophene produced. It is also desired that the reaction is carried out while alcohol and water produced are removed from the reaction mixture by distillation so that the reaction proceeds smoothly. Accordingly, the reaction is carried out preferably at temperatures of 150-300°C, most preferably of 180-270°C so that the alcohol and water produced during the reaction are removed from the reaction mixture in a moment, thereby to provide the dibenzoxazolyl thiophene in high yields. The reaction may be effected either in the presence or in the absence of a solvent. When a solvent is used, it is so selected as permits the adoption of reaction temperature as above mentioned. Therefore, there may be used, as a solvent, for example, such a halogenated aromatic hydrocarbon as dichlorobenzenes or trichlorobenzenes, polyhydric alcohols such as ethylene glycol, glycerine, N,N-dimethylformamide, dimethylsulfoxide or diphenyl ether, depending upon the reaction temperature adopted. There may be obtained by the method, for instance, 2,5-bis(2-benzoxazolyl)thiophene, 2,5-bis[5-methylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-ethylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-n-propylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-isopropylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-n-butylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-sec-butylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-isobutylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-tert-butylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-n-octylbenzoxazolyl-(2')]thiophene, 2,5-bis[5-phenylbenzoxazolyl-(2')]thiophene or 2,5-bis[5-benzylbenzoxazolyl-(2')]thiophene. Now the invention will be described more specifically with reference to examples. The synthesis of the starting materials used in these examples is disclosed in EP-A-0 387 725. Synthesis of Dibenzoxazolyl Thiophenes EXAMPLE 1 In a 2 liter capacity four necked flask provided with a stirrer, a thermometer and a cooling tube were placed 284 g (1.0 mole) of thiophene-2,5-dicarboxylic acid di-tert-butyl ester, 330 g (2.0 mole) of 4-tert-butyl-2-aminophenol, 11.2 g of boric acid and 520 g of 1,2,4-trichlorobenzene under a nitrogen atmosphere, and the mixture was stirred at a temperature of 210-220°C over a period of four hours, while tert-butyl alcohol and water produced were removed by distillation. After the reaction, the reaction mixture was cooled to 60-65°C, and there were added there to 600 g of methanol, followed by stirring over a period of another one hour at a refluxing temperature. Thereafter, the reaction mixture was cooled to room temperature, filtered and dried, to provide 404.8 g of 2,5-bis[5-tert-butylbenzoxazolyl-(2')]thiophene as yellow crystals in an yield of 94.1 %. Mp. 201-202°C. EXAMPLES 2-22 The reaction was carried out in the same manner as in the Example 1 using the thiophene-2,5-dicarboxylic acid diesters, aminophenols, acid catalysts and solvents as shown in the Table 1. The results are shown in the Table 1, in which the compounds (A), (B) and (C) represent the compounds below, respectively.

Claims: A method of producing a dibenzoxazolyl thiophene represented by the formula wherein R''' represents hydrogen, alkyl of 1-8 carbons, cycloalkyl, phenyl, monoalkylated phenyl, polyalkylated phenyl, halogenated phenyl, alkoxyphenyl or benzyl, which comprises: reacting a thiophene-2,5-dicarboxylic acid diester represented by the formula wherein R' represents alkyl of 1-8 carbons, phenyl, monoalkylated phenyl, polyalkylated phenyl, halogenated phenyl, alkoxyphenyl or benzyl, with an aminophenol represented by the formula wherein R''' is the same as before, in the presence of an acid catalyst. The method as claimed in claim 1 wherein R' is a branched alkyl of 3-5 carbons or a phenyl. The method as claimed in claim 2 wherein the branched alkyl is isopropyl, isobutyl, sec-butyl, tert-butyl, isoamyl, sec-amyl or tert-amyl. The method as claimed in claim 1 wherein R''' is hydrogen or tert-butyl. The method as claimed in claim 1 wherein the acid catalyst is boric acid, phosphoric acid, polyphosphoric acid, zinc chloride, ferric chloride or sulfuric acid. The method as claimed in claim 1 wherein the acid catalyst is used in an amount of 0.05-0.5 moles per mole of the thiophene-2,5-dicarboxylic acid diester. The method as claimed in claim 1 wherein the reaction is carried out at temperatures of 150-300°C.

Inventors: GODA HIROSHI, KIMURA NARIO, KIMURA SATOSHI, TERAMOTO MASAKI, YOSHIKAWA NAOHIRO, GODA, HIROSHI, KIMURA, NARIO, KIMURA, SATOSHI, TERAMOTO, MASAKI, YOSHIKAWA, NAOHIRO, GODA, HIROSHI, C/O SUMITOMO SEIKA CHEM. CO., LTD., KIMURA, NARIO, C/O SUMITOMO SEIKA CHEM. CO., LTD., KIMURA, SATOSHI, C/O SUMITOMO SEIKA CHEM. CO., LTD, Teramoto, Masaki, c/o Sumitomo Seika Chem Co.,Ltd., Yoshikawa, Naohiro, c/o Sumitomo Seika Chem Co Ltd
Applicants: SUMITOMO SEIKA CHEMICALS, SUMITOMO SEIKA CHEMICALS CO., LTD.
Application year: 1990
Main classification: C07D413
IPC codes: C07D333, C07D413