A spectrophotometric method for the determination of equilibrium constants of the reversible 1,4-benzodiazepine ring-opening reaction
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A general spectrophotometric method is proposed for the quantitative investigation of the hydrolysis of 1,4-benzodiazepines which, under the effect of nucleophilic hydration, undergo reversible cleavage of the 4,5-azomethine bond, followed by simultaneous simple acid-base reactions. The method is based on establishing the pH region of the solution in which, at the state of complete equilibration, three species dominate, as well as on using suitable isosbestic points and the differences in rates of simple protolysis and hydrolysis. The method is presented using flurazepam as an example, but it also can be applied to other compounds which hydrolyse by a similar mechanism.