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

The accelerated stability of dimethoxy biphenyl monocarboxylate . HCl (DDB- S) was investigated in 6 mg/mL water solution in the pH ranging 2-10 and th e temperature of 45-85 degreesC. The observed rate of degradation followed first-order kinetics. The energy of activation for DDB-S degradation was ca lculated to be 14.1 and 16.5 Kcal/mole at pH 5 and in distilled water, resp ectively. The degradation rate constant (K-25 degreesC) Obtained by trendin g line analysis of Arrhenius plots for DDB-S was 5.3 x 10(-6)h(-1). The tim es to degrade 10% (t(10)) and 50% (t(50)) at 25 degreesC were 829 and 5,416 days, respectively. DDB-S exhibited the fastest degradation at pH 10 and t he slowest rate at PH 5. In addition, at 65 degreesC, degradation rate cons tants 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 in dicated that the rate-pH profile of DDB-S showed general acid-base catalysi s reaction in the range of pH 2-10.