Irradiation of ultrasound to 5-methylbenzotriazole in aqueous phase: Degradation kinetics and mechanisms

Ultrasonic irradiation (640 kHz) leads to the effective degradation of 5-methyl-benzotriazole (5-MBT) in O-2 saturated aqueous solution. Up to 97% of 5-MBT is eliminated within 2 hours of treatment. Upon extended treatment of 6 hours, UV absorbance of the n -> pi* and pi -> pi* transitions associated with aromatic and conjugated systems are completely removed, indicating complete destruction of the aromatic system in 5-MBT. The decomposition of 5-MBT follows pseudo-first order kinetics and the observed decomposition rate dropped significantly in the presence of tertiary butyl alcohol. Detailed product studies were performed employing a negative mode ESI LC-MS. Twenty eight intermediate products were detected during ultrasonic mediated degradation of 5-MBT. Reaction pathways are proposed based on the structures of products assigned to observed 28 masses from LC-MS and commonly accepted degradation pathways observed by thermal and hydroxyl radical mediated pathways often associated with ultrasonic treatment. (C) 2016 Elsevier B.V. All rights reserved.