Mechanistic considerations for the degradation of methyl tert-butyl ether (MTBE) by sonolysis: Effect of argon vs. oxygen saturated solutions

The ultrasonic degradation mechanism of methyl tert-butyl ether (MTBE) in aqueous solution is complex because of the competition between hydroxyl radical attack, pyrolysis, and hydrolysis reactions. A detailed investigation of degradation pathways using sonolysis has been performed using reaction byproducts identification. The observed bi-product distributions are rationalized in terms of hydroxyl radical (OH) mediated processes and pyrolysis. The role of oxygen mediated and pyrolytic pathways were assessed using O2 and Ar saturated solutions. Chemical destruction by sonolysis is often rationalized using hydroxyl radical chemistry. Pyrolysis is unique to this advanced oxidation process, and is important in the case of MTBE because it transfers into the cavitating bubbles. While α-hydrogen abstraction by OH and low temperature pyrolysis was important, it was also shown that β-hydrogen abstraction leads, in some cases, to the same reaction byproducts, which emphasized the importance of α-hydrogen abstraction. High temperature pyrolysis resulted in minor degradation reactions based on the formation of reaction by-products.