| Abstract
| - Methyl group oxidation, SN2-type hydrolysis, and SN1-typehydrolysis are suggested as natural transformationmechanisms of MTBE. This study reports for the first timeMTBE isotopic fractionation during acid hydrolysis andfor oxidation by permanganate. In acid hydrolysis, MTBEisotopic enrichment factors were εC = −4.9‰ ± 0.6‰ forcarbon and εH = −55‰ ± 7‰ for hydrogen. Position-specific values were εC,reactiveposition = −24.3‰ ± 2.3‰ andεH,reactiveposition = −73‰ ± 9‰, giving kinetic isotopeeffects KIEC = 1.025 ± 0.003 and KIEH = 1.08 ± 0.01consistent with an SN1-type hydrolysis involving the tert-butyl group. The characteristic slope of Δδ2Hbulk/Δδ13Cbulk ≈εbulk,H/ εbulk,C = 11.1 ± 1.3 suggests it may identify SN1-type hydrolysis also in settings where the pathway is notwell constrained. Oxidation by permanganate wasfound to involve specifically the methyl group of MTBE,similar to aerobic biodegradation. Large hydrogen enrichmentfactors of εH = −109‰ ± 9‰ and εH,reactiveposition =−342‰ ± 16‰ indicate both large primary and largesecondary hydrogen isotope effects. Significantly smallervalues reported previously for aerobic biodegradation suggestthat intrinsic fractionation is often masked by additional non-fractionating steps. For conservative estimates ofbiodegradation at field sites, the largest ε values reportedshould, therefore, be used.
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