Basicity Possible Use as Indicators

Because of the striking color change between the bases (1) and monocations (4), it has been suggested that they could be useful indicators in acid-base titrations. A number of 2,4-disubstituted derivatives have been suggested for use over the pH range 5-9 (80MI2), and certain 3-aryl- 

In the formation of a benzimidazole the steps involving loss of a methyl ketone, which are essentially irreversible, control the course of the reaction. Examples of such ring-contraction reactions are the formation of 2-methyl-benzimidazole and acetone from 2,4-dimethylbenzodiazepine and its salts (07CB955 59JCS1132 65JCS3785) and of a mixture of acetone, acetophenone, 2-methyl-, and 2-phenyl-benzimidazoles from 2-methyl-4-phenyl-benzodiazepine (07CB955). The same ring contractions also ensue when aqueous solutions of benzodiazepines or their salts are kept at room temperature. It seems likely that in the case of solutions of the salts, some free base, present in equilibrium with the cation, may be the species in- 

3-Disubstituted benzodiazepines appear to be more readily hydrolyzed than 2,4-disubstituted analogs (67CB584). Hydrolysis involves attack at the 2- or 4-positions, and this is easier in the absence of a blocking substitutent. 

Hydrolysis of 3-acylbenzodiazepines in acidic conditions may lead to hydrolytic removal of the acyl group. Thus, treatment of 3-benzoyl-2,4-diphenylbenzodiazepine with aqueous hydrochloric acid provides 2,4-diphenylbenzenediazepinium chloride and benzoic acid some 2-phenyl-benzimidazole and dibenzoylmethane are also formed (71MI2). The 

Distillation of solid benzodiazepinium salts may also lead to the formation of a ketone and a benzimidazolium salt (65JCS3785). A number of benzodiazepinium salts contain water of crystallization, and this, or adsorbed water, can presumably participate in the reaction. In the absence of 

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