Synthesis And Characterization Of Thiophene-2,5-dicarboxylic Acid And Its Derivatives

Thiophene-2,5-dicarboxyl acid is an important chemical raw materials, which can be widely used in medicine, pesticide, catalysis and light-emitting materials and other fields.At present, thiophene-2,5-dicarboxyl acid is mainly prepared by the reaction of 1,6-adipic acid with thionyl chloride and the pollution is very serious. Seeking a low-cost,environmental friendly synthetic route, which is suitable for industrialized production, has become the key point of the research. In this paper, the synthesis process of thiophene-2,5-dicarboxyl acid and its derivatives were investigated and then metal complexes of thiophene-dicarboxyl acid were synthesized by reactions of sodium thiophene dicarboxylate with metal chlorides and obtained following results:The 5-(ethoxycarbonyl)thiophene-2-carboxylic acid was synthesized via the reaction of diethyl-2,2’-thiodiacetate with poly glyoxal. The performance of poly glyoxal prepared by different methods was evaluated. The results showed that the dissolving capacity,depolymerization ability and water content of poly glyoxal have an important influence on the reaction. The thiophene-2,5-dicarboxyl acid(H2L)was obtained by further hydrolysis of the 5-(ethoxycarbonyl)thiophene-2-carboxylic acid.The 3,4-diphenylthiophene-2,5-dicarboxylic acid was synthesized by reaction of diethyl-2,2’-thiodiacetate with benzyl at 40℃ for 72 h in yield of 88%, when the molar ratio of 2,2’-thiodiacetate, benzil and sodium was 1.2:1:3.6. The effects of feeding method and the reaction temperature on the reaction were researched.The metal salts of thiophene-2,5-dicarboxylic acid and 3,4-diphenylthiophene-2,5-dicarboxylic acid were prepared by the reactions of the sodium salts with metal chloride. The apparent structure of the complexes was confirmed by elemental analysis to be NiL·2H2O, La2L3·6H2O(L: thiophene-2,5-dicarboxylic acid), MD·2H2O(M=Mg, Ca,Ni, Cu, Zn, D: 3,4-diphenylthiophene- 2,5-dicarboxylic acid) and La2D3·6H2O. Based on FT-IR spectra analysis, in NiL and La2L3, the carboxyl of the ligand linked with Ni, La ion in bidentate chelating form. While in MD(M=Mg,Ca,Ni,Cu,Zn) and La2D3, the carboxyl of the ligand linked with Mg, Ca, La ion in chelating manner and with Ni, Cu, Zn in monodentate mode, respectively. The different coordination states of carbonyl of acid with different metals were also confirmed by the XPS analysis of MD·2H2O(M=Mg,Ca,Ni,Cu,Zn) and La2D3·6H2O. The fluorescence of ZnD and NiD salts was enhanced, whilefluorescence of the other salts was abated and the La2L3, NiL and CuD have a fluorescence quenching phenomenon. Based on the analysis of XRD, ZnD, NiD and CaD have layered structure, while CuD and MgD have a micro crystal powder and La2D3 was amorphous due to the complex chelating of carbonyl to La. The layered fiber structure of generated in situ ZnD was further confirmed by SEM.The composites of ZnO-ZnD with different ratios were prepared by reactions of ZnO with different proportions of H2 D in ethanol. Compared with ZnO, the strength of fluorescence of ZnO-ZnD was improved. XRD analysis showed that the particle sizes of ZnO were increased as the increase of ZnD content.