The rate of hydrolytic degradation of N-methyl-2,4-dithiophenobarbital by spectrophotometric and separation methods was studied. The rate constants, order of reaction, activation energy, and pKa values were calculated based on the measurements of absorbance in the UV range. The changes in the absorbance values over time for solutions of different pH were analysed. Based on the obtained results, it was found that the hydrolysis of N-methyl-2,4-dithiophenobarbital followed the kinetics of a pseudo-first order reaction. Plots illustrating dependences, log k, and pH indicate the catalytic effect of OH– ions on the occurring process. The results show that in an alkaline environment the pyrimidine ring undergoes cleavage in the 1–6 position, and gradual desulfurization. The obtained results were compared with data for phenobarbital, 2-thiophenobarbital, and 2,4-dithiophenobarbital. It can be concluded that the change of an oxygen atom to a sulfur atom in the ring of a barbituric acid derivative causes an easier decomposition of the compound. However, the insertion of a methyl group on the nitrogen atom increases the durability of the compound.
通过分光光度法和分离法研究了 N-甲基-2,4-二噻吩巴比妥的水解降解速率。根据紫外线范围内的吸光度测量值计算出了速率常数、反应顺序、活化能和 pKa 值。分析了不同 pH 值溶液的吸光度值随时间的变化。根据所得结果,发现 N-甲基-2,4-二硫苯巴比妥的水解遵循假一阶反应动力学。依存关系、对数 k 和 pH 值曲线图显示了 OH 离子对反应过程的催化作用。结果表明,在碱性环境中,嘧啶环在 1-6 位发生裂解,并逐渐脱硫。所得结果与苯巴比妥、2-噻吩巴比妥和 2,4-二噻吩巴比妥的数据进行了比较。可以得出的结论是,将巴比妥酸衍生物环中的氧原子改为硫原子会使化合物更容易分解。不过,在氮原子上插入一个甲基会增加化合物的耐久性。