A spectral and polarographic study of the acid--base and complexing behaviour of bromazepam

Protolytic equlibria of bromazepam

The protolytic equilibria of bromazepam, an ampholyte sparingly soluble in water, in homogeneous and heterogeneous systems were studied in the pH range 0?14 at 25?C and at ionic strength of 0.1 mol/dm3 (NaCl). On the basis of 13C-NMR spectra, the protonation site was predicted ? in acidic media the pyridine nitrogen of bormazepam is protonated. The acidity constants of bromazepam were determined spectrophotometrically (pKa1 2.83 and pKa2 11.60) and potentiometrically (pKa1 2.99). In the heterogeneous system the following equilibrium constants were determined: Ks0 =[HA]?(pKs0 3.44), Ks1 =[H2A+]/[H3O+](pKs1 0.61), and Ks2 =[A-][H3O+](pKs2 15.04).

Acidic hydrolysis of bromazepam studied by high performance liquid chromatography. Isolation and identification of its degradation products

A kinetic study on the acidic hydrolysis of bromazepam was carried out in 0.01 M hydrochloric acid solution at 25 and 95 degrees C. A reversed-phase HPLC method was developed and validated for the determination of bromazepam and its degradation products. Bromazepam degraded by a consecutive reaction with a reversible first step. Two degradation products were isolated and identified by infrared, 1H and 13C nuclear magnetic resonance and mass spectroscopy. Spectroscopic data indicated that N-(4-bromo-2-(2-pyridylcarbonyl)phenyl)-2-aminoacetamide was the intermediate degradation product of this acid hydrolysis, whereas 2-amino-5-bromophenyl-2-pyridylmethanone was the final one. Therefore, the mechanism of this acid-catalysed hydrolysis involved initial cleavage of the 4,5-azomethine bond, followed by slow breakage of the 1,2-amide bond. Statistical evaluation of the HPLC method revealed its good linearity and reproducibility. Detection limits were 3.8 x 10(-7) M for bromazepam, 6.25 x 10(-7) M for the intermediate and 8.16 x 10(-7) M for the benzophenone derivative.

Kinetics of the acid hydrolysis of diazepam, bromazepam, and flunitrazepam in aqueous and micellar systems

A kinetic study of the acid hydrolysis of aqueous diazepam, bromazepam, and flunitrazepam was carried out at 25 degrees C using a spectrophotometric method. For diazepam and flunitrazepam, the experimental pseudo first-order rate constant decreased as the acid concentration was increased. The contrary behavior was found in the case of bromazepam. A kinetic scheme that includes the hydrolysis reaction of both protonated and nonprotonated species of the drug can account for these results. Also, the kinetics of the acid hydrolysis of the same drugs in the presence of micellar aggregates [nonionic polyoxyethylene-23-dodecanol (Brij 35); cationic cetyl trymethyl ammonium bromide (CTAB); and anionic sodium decyl (SdeS), dodecyl (SDS), and tetradecyl (STS) sulfate] was studied at 25 degrees C. Negligible effects were observed in the cases of nonionic and cationic micelles. Anionic micelles produced an inhibitory effect in the reaction velocity. This effect increased as the hydrophobic nature of the surfactant increased. All these facts are interpreted quantitatively by means of a pseudophase model.

Analysis of the 1,4-benzodiazepines by methods based on hydrolysis

The analytical applications of the hydrolysis of 1,4-benzodiazepines to the corresponding benzophenone derivatives are reviewed according to the analytical methods used for their final determination. The scope and limitations of the individual methods for the hydrolysis products are discussed: Colour reactions, photometry, fluorimetry, thin-layer chromatography, gas chromatography and high-performance liquid chromatography. Published data on the kinetic parameters and mechanisms are summarized in an attempt to explain the problems involved in exploiting this reaction for analytical applications.