Stability of cefoselis sulfate in aqueous solutions

The influence of pH on the stability of cefoselis sulfate was investigated in the pH range 0.44–13.00. The degradation of cefoselis sulfate in aqueous solutions was a pseudo-first order reaction. General acid–base hydrolysis of cefoselis sulfate was observed in phosphate and acetate buffers. In solutions of hydrochloric acid, sodium hydroxide and borate buffer, kobs = kpH because only specific acid–base catalysis occurred. Specific acid–base catalysis of cefoselis sulfate involved such reactions as the hydrolysis of protonated cefoselis sulfate molecules (k1), hydrolysis of cefoselis sulfate zwitter ions (k2) and hydrolysis of cefoselis sulfate monoanions (k3) under the influence of water. The total reaction rate was equal to the sum of partial reactions: kpH = k1·F1 + k2·F2 + k3·F3 where: k1, k2 and k3 were the catalytic rate constants calculated as the mean values of kpH at pH 1.89–3.10, 4.01–6.16 and at pH above 11.24. F1, F2 and F3 were the molar concentration fractions of the cefoselis sulfate.