5 - Who Replaced The Preparation Of Thiophene And Its Derivatives Research

Bithiophene based photoelectric material showed excellent performance, and attracted a widespread attention, such as photosensitive dye, electroluminescent materials and polymer cell. Compared with the structures of benzene and biphenyl, thiophene/bithiophene structural units can broaden spectra absorption band, and have higher electron transmitting capacity, therefore photoelectric materials based on thiophene/bithiophene units have a broad prospect. Although there had some literatures on thiophene/bithiophene based reactions, the study is not systematic. Herein, bithiophene5-site electrophilic substitution reactions and derivatization reaction were investigated in detail. The main research contents are as follows:1. Nitration and derivatization reaction. Acetic anhydride was added to the concentrated nitric acid, it is benifit to generate activity nitronium under this system. There are two-position isomer of2,2’-bithiophene nitrification product, namely,5-nitro-2,2’-bithiophene and4-nitro-2,2’-bithiophene, while the proportion of5-site and4-site nitrification product is2.7:1, which demonstrates higher reactivity at bithiophene5-site.2,2’-Bithiophene5-site nitrification product is purified, followed by reducing with Pd/C, hydrazine hydrate, and then occurred knoevenagel condensation reaction with4-N,N-diethylamine-benzaldehyde, finally, the bithiophene derivatives is obtained with total yield of22%.2. Formylation and derivatization reaction. A Vilsmeier reaction mechanism analysis is proposed, the higher concentration Vilsmeier reagent is considered useful method for facilitating the reaction. These reaction conditons were optimized. The research results show that the optimum condition for formylation reaction of bithiophene is that, the molar ratio of Vilsmeier reagent to2,2’-bithophene is5:1, Vilsmeier reagent should be prepared under lower temperature at50℃for5h, and2,2’-bithiophene-5-formaldehyde is obtained, with the conversion of97%, and selectivity of100%, and yield of83%. In the presence of acetic ammonium, and condensation reaction with methyl cyanoacetate occurred, and bithiophene derivatives with5-site ethylenic substitute is prepared with yield of77%. 3. Halogenation. The reactions of the bromination and iodination of bithiophene have been studied seperately in this thesis. Acetic acid as the catalyst and in dark conditions, using chloroform as solvent, the reaction between bithiophene and NBS, is carried out for three hours, the conversion can reach76%, selectivity of5-site is69%. The present method shows shorter reaction time than literature.