Initial degradation mechanism of salicylic acid via electrochemical process

Highlights: • The hydroxylation of salicyclic acid was systematically investigated with DFT calculations. • Calculated standard reduction potential indicates that forming of salicyclic acid radical is lower than formation of ^.OH radical. • The degradation of Salicylic acid follows the ECE mechanism. • The attack of hydroxyl anion HO⁻ was more favourable on the position C3 and C5 with lower activation barriers. • The findings suggest the favorable formation of 2,3dHBA acid and 2,5dHBA as observed in experimental work. Salicylic acid is a common chemical used in the pharmaceutical industry. Much attention has been paid in recent years to the elimination of this contaminant from the water by electrochemical oxidation. However, there is still a debate about its intermediate products during the degradation process. The goal of this work was to provide further insight into the degradation of salicylic acid by the Density Functional Theory calculations. The detailed mechanism shall be investigated along with the most suitable intermediate products during the process. The results provide an explanation for the experimental observation of 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid over other derivatives.