Self-catalyst degradation of amoxicillin in alkaline condition driven by superoxide radical

We studied the rate of amoxicillin (AMX) degradation in oxygen-contained (OCG) and oxygen-free (OFG) groups under alkaline conditions by comparing the molecular structure of AMX with penicillin (PG) and penicillin V potassium (PV) resulting from measuring the hydrolysis rate, performing quenching experiments, and analyzing the products of AMX. The pseudo first-order rate constants of AMX hydrolysis were 0.003 h−1 and 0.032 h−1 (pH = 9, 25 ℃) in OCG and OFG, respectively, with both dissolved oxygen and OH− radicals playing important roles in AMX hydrolysis in OCG. According to the quenching experiments, the signal intensity of O2− in OCG appeared after 3 h and increased consistently, which confirmed that the participation of dissolved oxygen in AMX degradation accelerates the reaction and O2− generate from the reaction between dissolved oxygen and the hydrolysis products of AMX. The phenol group was the key functional group involved in the O2− reaction when comparing the molecular structure differences between PG, PV, and AMX. In total, 30 degradation products of AMX were found by liquid-chromatography triple-quadrupole mass spectrometry. Five degradation pathways of AMX were suggested, which are similar to those of photodegradation. Among them, path 3, which involves phenol (phenol, p-carboxyphenol, etc.) reactions, contained reactions with both dissolved oxygen and OH−. Considering there were no extra reagents added to the reaction system, the degradation of AMX in OCG appeared to be a self-catalytic reaction.