The Arrhenius Experiment: An Analysis Of Acidic Hydrolysis

For Acidic hydrolysis, SAC was found to be well susceptible to acid hydrolysis with 0.05 M HCl at 40 ˚C for 30 min caused about 8% reduction in the peak area of SAC (Fig.4a). While this mild condition didn’t affect VAL. While, nearly 27% was the reduction in SAC’s peak area when subjected to alkaline hydrolysis. This considerable decline in the peak area of SAC when subjected to 0.01 M NaOH at 40°C for 30 min revealed degradation products peaks appeared at 3.339 and 9.482 minutes (Fig.4b) and they were well resolved from VAL and SAC peaks. On the other hand, the peak area of VAL remains nearly the same under this mild condition. Both VAL and SAC were found to be stable under neutral condition when heated at 90 °C for 30 min and their peak areas
This was done for the estimation of its degradation rate constant (K) and half-life at room temperature at different conditions which is very essential for the estimation of the stability of the drug on shelf. When the degradation processes were induced and observed using the proposed HPLC method, a regular decrease in the drug concentration with increasing time intervals was noticed.
For each temperature and strength of HCl, NaOH and H2O2 stated in the experimental part, the logarithm of intact drug remaining percent was plotted against the corresponding time in minutes as shown in Figures 5 and 6, respectively, also the regression equations were computed.
For all the investigated degradation conditions, it was found that the degradation followed pseudo-first order kinetics. The pseudo-first order rate constants (K) were calculated at each temperature and at each reagent strength from the slopes of the regression lines (Slope= -K/2.303) [28], as shown in Tables 3 and 4. The corresponding t1/2 values were also calculated where (t1/2 = 0.693/K)[28]. Moreover, practically K25 and t1/2 at room temperature in 0.1M HCl, 0.01M NaOH or 15% H2O2 were estimated, Tables 3 and
7. However, for a more accurate result, it was calculated by compensation in the corresponding equation (2, 3 or 4) followed by the calculation of t1/2. There is no great difference between t1/2 values obtained by extrapolation and compensation in equation but these values were far from the practically calculated values at room temperature, Tables 3 and 4. As a result, the values of t1/2 obtained from the Arrhenius equations or plots are used to estimate the stability of SAC. These t1/2 values at room temperature of SAC at acidic, alkaline and oxidative stated conditions were found to be 20.50, 2.76 and 51.58 hours, respectively. These values are very important in measuring the stability of drug at room