Low-temperature route to 1,2-benzoylenebenzimidazole ladder structure

Low-temperature catalytic conversion of N-(o-aminophenyl)phthalamic acid (I ) was studied as a model reaction for the synthesis of ladder poly(aroylene benzimidazole)s. The treatment of I with acetic anhydride/pyridine or trifl uoroacetic anhydride resulted in the selective and quantitative cyclodehydr ation to yield either imide or isoimide structures respectively. The imidiz ation was accompanied by acylation of the ortho amino group to form lateral acetamide or trifluoroacetamide substitutes. Thermodynamically unstable N- (o-trifluoroacetamidophenyl)phthalisoimide (III) underwent secondary cycliz ation to yield ladder 1,2-benzoylenebenzimidazole (V) between 130 and 150 d egrees C. The;conversion of this reaction did not exceed 35% because it com peted with the thermal isomerization of III to the stable N-(o-trifluoroace tamido-phenyl)phthalimide (IV). The cyclization of N-(o-trifluoroacetamidop henyl)phthalisoimide (III) was found to be possible even at room temperatur e. The formation of 30-35% of the ladder 1,2-benzoylene-benzimidazole (V) w as observed after III was dissolved in DMF and stored at room temperature f or 4-10 h. This also was accompanied by the catalytic isoimide-to-imide iso merization. The obtained data may be useful for the further development of novel low-temperature approaches to the synthesis of ladder poly(aroylenebe nzimidazole)s. Synthesis of aromatic polyimides and polyisoimides with late ral alkylamide or trifluoroalkylamide from available aromatic dianhydrides and tetraamines may also be of practical interest.