| Abstract: | The ring-opening addition reaction of phthaloylasparic anhydride (I) with o-phenylenediamine (II) in a solution is affected by the polarity of the solvent used. At the molar ratio of 1:1, I and II undergo a β-oriented ring-opening reaction in polar solvents, such as DMF, DMAC, and DMSO; while in weaker polar solvents, such as dioxane and tetrahydrofuran, α-orientation predominates. By heating in a solvent mixture of DMF and xylene, the ring-opening products undergo condensation, and are converted into two isomers. One is methanol soluble 3-phthalimido-3-(2)benzimidazolylpropanoic acid (V) resulting from the α-oriented ring-opening reaction, the other is the sparingly soluble (in DMF) 2-phthalimido-3-(2)benzimidazolylpropanoic acid (VI) resulting from the β-oriented ring-opening reaction. The soluble V can be precipitated as cotton-like crystals from methanol and chloroform. When treated with acetic anhydride, V and VI are converted to other isomers, namely 3-phthalimidobenzimidazopyrrolone (VII) and 2-phthalimidobenzimidazopyrrolone (VIII). The isomers were identified by spectral analysis. |
