Theoretical study of hydroxyl radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE)

Abstract

We have characterized the various pathways for OH radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE) and found an oxidative pathway that leads to complete degradation under the prerequisite that OH radicals are present in excess. A simple polarizable continuum model is used to predict the behavior in an aqueous medium and the behavior is unchanged compared to that in the gas phase. The computational study has also revealed some of the fundamental aspects of hydrogen transfer from asymmetric ethers; the ˙OH assisted hydrogen abstraction has a barrier when the reaction takes place at a distance from the heteroatom, that is, at the tert-butyl group, whereas hydrogen abstraction from the methyl group proceeds without a barrier. The addition of ˙OH to (CH₃)₃COCH₂˙ also proceeds without a barrier, and so does hydrogen abstraction from the resulting adduct ((CH₃)₃COCH₂OH) to form (CH₃)₃COCH(OH)˙. However, a barrier is yet again found in the hydrogen abstraction from the latter to form (CH₃)₃COCHO and yet again in the formation of the formyl radical (CH₃)₃COCO˙ by hydrogen abstraction. The latter is the last step before the final stage of complete oxidation of MTBE to form CO₂.