Kinetics of hydrolysis of oxazolam in aqueous solution.
作者:MASARU IKEDA、TSUNEJI NAGAI
DOI:10.1248/cpb.32.1080
日期:——
The hydrolysis reaction of oxazolam, a representative of 1, 4-benzodiazepinooxazoles (BDOZ), was investigated kinetically. The reaction product was identified by thin layer chromatography (TLC) and infrared (IR) spectroscopy, and it was concluded that irreversible hydrolytic cleavage took place at the diazepinone nucleus. The rate constant was determined by ultraviolet (UV) spectroscopy. The reaction was a first-order process consisting of two parallel reactions with different reacting species of oxazolam, depending on the pH of the medium. The pH-rate profile obtained for the reaction suggested that the reaction was independent of hydrogen ion concentration in acidic media, while it was catalyzed by hydroxide ion in alkaline media. The nonlinear least-squares fit method was employed to determine the catalytic rate constants involved in the equation describing the pH-rate constant relationship. Activation energies as well as other thermodynamic parameters were obtained in media of pH 2.0 and 8.0, and the values confirmed that different chemical species of oxazolam were involved. The observed effect of buffer concentration indicated that general base catalysis was involved in the reaction of the ionized species of oxazolam. A mechanistic consideration indicated that the rate-determining step may be the nucleophilic attack of a water molecule or hydroxide ion at the 11b-position in the diazepinone nucleus.
研究了1,4-苯二氮卓噻唑(BDOZ)代表性化合物氧噻唑的水解反应动力学。通过薄层色谱(TLC)和红外光谱(IR)鉴定了反应产物,并得出结论:在二氮杂庚酮核发生了不可逆的水解裂解。通过紫外光谱(UV)确定了反应速率常数。该反应为一阶过程,由两种不同反应物种的平行反应组成,取决于介质的pH值。获得的pH-速率曲线表明,在酸性介质中,反应与氢离子浓度无关,而在碱性介质中则受到氢氧根离子的催化。采用非线性最小二乘拟合方法确定了描述pH-速率常数关系方程中涉及的催化速率常数。在pH为2.0和8.0的介质中获得了活化能和其他热力学参数,数值确认了不同化学物种的氧噻唑参与了反应。观察到的缓冲浓度效应表明,反应中涉及了离子化氧噻唑物种的一般碱催化。机理考量表明,速率决定步骤可能是水分子或氢氧根离子在二氮杂庚酮核的11b位点的亲核攻击。