Syntheses and Fe(II)/Fe(III) equilibria of the new multidentate ligands pyridine-2-phosphonic- 6-carbo×ylic acid and 2,6-pyridinediphosphonic acid for the use of their iron chelates as catalysts for the o×idation of H<sub>2</sub>S to S<sub>8</sub> by air
摘要:
The syntheses of two terdentate chelating agents, pyridine-2-phosphonic-6-carboxylic acid (2PP6C) and 2,6-pyridinediphosphonic acid (2,6PDPA), are described. The stepwise stability constants for the ferric complexes at 25.0 degrees C and mu=,0.100 M (KNO3) are log K-ML = 15.97 and log K-ML2 = 9.50 for 2PP6C, and log K-ML = 20.87 and log K(ML)2 = 7.81 for 2,6PDPA. Under the same conditions the stepwise formation constants for the ferrous chelates are log K-ML = 8.70 and log K-ML2 = 5.10 for 2PP6C, and log K-ML = 10.12 and log K-ML2 = 5.33 for 2,6PDPA. The stabilities of the Fe(III) and Fe(II) chelates are high enough to prevent precipitation of Fe(OH)(3) and FeS, respectively, from solutions having pH as high as 10.0. The rates of oxidative degradation of these ligands are very slow when the iron chelates are used as redox catalysts for the oxidation of H2S to S-8 by air. The rates of oxidative degradation are immeasurably slow when the iron chelates are used with sodium thiosulfate as a radical scavenger.
α-Heteroarylation of Thioethers via Photoredox and Weak Brønsted Base Catalysis
作者:Edwin Alfonzo、Sudhir M. Hande
DOI:10.1021/acs.orglett.1c02151
日期:2021.8.6
thioethers to α-thio alkyl radicals and their addition to N-methoxyheteroarenium salts for the redox-neutral synthesis of α-heteroaromatic thioethers. Studies are consistent with a two-step activation mechanism, where oxidation of thioethers to sulfide radical cations by a photoredox catalyst is followed by α-C–H deprotonation by a weak Brønsted base catalyst to afford α-thio alkyl radicals. Further,
Intermolecular Hydropyridylation of Unactivated Alkenes
作者:Xiaoshen Ma、Seth B. Herzon
DOI:10.1021/jacs.6b05271
日期:2016.7.20
A general method for the hydropyridylation of unactivatedalkenes is described. The transformation connects metal-mediated hydrogen atom transfer to alkenes and Minisci addition reactions. The reaction proceeds under mild conditions with high site-selectivities and allows for the construction of tertiary and quaternary centers from simple alkene starting materials.
Cobalt bis(acetylacetonate)–<i>tert</i>-butyl hydroperoxide–triethylsilane: a general reagent combination for the Markovnikov-selective hydrofunctionalization of alkenes by hydrogen atom transfer
作者:Xiaoshen Ma、Seth B Herzon
DOI:10.3762/bjoc.14.201
日期:——
and practical reagent combination to initiate a broad range of Markovnikov-selective alkene hydrofunctionalization reactions. These transformations are believed to proceed by cobalt-mediated hydrogen atom transfer (HAT) to the alkene substrate, followed by interception of the resulting alkyl radical intermediate with a SOMOphile. In addition, we report the first reductivecouplings of unactivated
Photochemical C–H Silylation and Hydroxymethylation of Pyridines and Related Structures: Synthetic Scope and Mechanisms
作者:Fatima Rammal、Di Gao、Sondes Boujnah、Aqeel A. Hussein、Jacques Lalevée、Annie-Claude Gaumont、Fabrice Morlet-Savary、Sami Lakhdar
DOI:10.1021/acscatal.0c03726
日期:2020.11.20
Considering the synthetic relevance of heteroarenes in various areas ranging from organic synthesis to medicinal chemistry, developing practically simple methodologies to access functionalized heteroarenes is of a significant value. Described herein is an efficient approach for C–H silylation and hydroxymethylation of pyridines and related heterocycles by the combination of silanes or methanol with readily