Influence of temperature and pH on the stability of dimethoxy biphenyl monocarboxylate HCl solutions.

The accelerated stability of dimethoxy biphenyl monocarboxylate x HCl (DDB-S) was investigated in 6 mg/mL water solution in the pH ranging 2-10 and the temperature of 45-85 degrees C. The observed rate of degradation followed first-order kinetics. The energy of activation for DDB-S degradation was calculated to be 14.1 and 16.5 Kcal/mole at pH 5 and in distilled water, respectively. The degradation rate constant (K(25 degrees C)) obtained by trending line analysis of Arrhenius plots for DDB-S was 5.3 x 10(-6) h(-1). The times to degrade 10% (t10) and 50% (t50) at 25 degrees C were 829 and 5,416 days, respectively. DDB-S exhibited the fastest degradation at pH 10 and the slowest rate at pH 5. In addition, at 65 degrees C, degradation rate constants of DDB-S were 0.066, 0.059, 5.460, 32.171, and 1.41 x 10(6) h(-1) at pH 2, 5, 8, 10 and in distilled water, respectively. These observations indicated that the rate-pH profile of DDB-S showed general acid-base catalysis reaction in the range of pH 2-10.