Kinetics of Hydrolysis of N-Methyl-2,4-dithiophenobarbital

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.