title: A mechanistic change results in 100 times faster CH functionalization for ethane versus methane by a homogeneous Pt catalyst.
abstract: The selective, oxidative functionalization of ethane, a significant component of shale gas, to products such as ethylene or ethanol at low temperatures and pressures remains a significant challenge. Herein we report that ethane is efficiently and selectively functionalized to the ethanol ester of H2SO4, ethyl bisulfate (EtOSO3H) as the initial product, with the Pt(II) "Periana-Catalytica" catalyst in 98% sulfuric acid. A subsequent organic reaction selectively generates isethionic acid bisulfate ester (HO3S-CH2-CH2-OSO3H, ITA). In contrast to the modest 3-5 times faster rate typically observed in electrophilic CH activation of higher alkanes, ethane CH functionalization was found to be ~100 times faster than that of methane. Experiment and quantum-mechanical calculations reveal that this unexpectedly large increase in rate is the result of a fundamentally different catalytic cycle in which ethane CH activation (and not platinum oxidation as for methane) is now turnover limiting. Facile Pt(II)-Et functionalization was determined to occur via a low energy β-hydride elimination pathway (which is not available for methane) to generate ethylene and a Pt(II)-hydride, which is then rapidly oxidized by H2SO4 to regenerate Pt(II)-X2. A rapid, non-Pt-catalyzed reaction of formed ethylene with the hot, concentrated H2SO4 solvent cleanly generate EtOSO3H as the initial product, which further reacts with the H2SO4 solvent to generate ITA.
authors.affiliation: The Scripps Energy & Materials Center, Department of Chemistry, The Scripps Research Institute , Jupiter, Florida 33458, United States.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Konnick
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bischof
authors.forename: Muhammed
authors.initials: M
authors.lastname: Yousufuddin
authors.forename: Brian G
authors.initials: BG
authors.lastname: Hashiguchi
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Ess
authors.forename: Roy A
authors.initials: RA
authors.lastname: Periana