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A Mechanistic Change Results in 100 Times Faster CH Functionalization for Ethane versus Methane by a Homogeneous Pt Catalyst

Author:
Konnick, Michael M., Bischof, Steven M., Yousufuddin, Muhammed, Hashiguchi, Brian G., Ess, Daniel H., Periana, Roy A.
Source:
Journal of the American Chemical Society 2014 v.136 no.28 pp. 10085-10094
ISSN:
1520-5126
Subject:
catalysts, energy, ethane, ethanol, ethylene, methane, oxidation, platinum, shale, solvents, sulfuric acid, temperature
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 Ptᴵᴵ “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 Ptᴵᴵ-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 Ptᴵᴵ-hydride, which is then rapidly oxidized by H₂SO₄ to regenerate Ptᴵᴵ-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.
Agid:
5391883