A Facile Oxidation of Thiols to Disulfides Catalyzed by CoSalen

Aerobic Thiols Oxidative Coupling to Disulfides over Robust CoOx Nanoclusters Confined within Hierarchical Silicalite-1 Zeolite

Disulfide is an important organic reagent and synthetic intermediate that is widely used in organic synthesis, polymers, and other fields, but its synthesis still suffers from many environmental pollution and economic problems. Here, we present an environmentally friendly and efficient base-free aerobic oxidative thiol coupling catalyzed by heterogeneous CoOx nanoclusters entrapped in hierarchical silicalite-1 zeolite, synthesized by combining silane pore expansion and metal coordination methods under hydrothermal conditions. It is confirmed that open hierarchical channels favor mass diffusion, and the chemical valence of Co species in CoOx/h-S-1-H is +2, which is different from that of Co3O4 particles in CoOx/h-S-1-I. CoOx nanoclusters, are strongly fixed in the channels of silicalite-1 zeolite via Co-O-Si bonds, which is of great importance for the high catalytic activity in both symmetrical and unsymmetrical oxidative thiol coupling reactions. After recycling experiments four times, the CoOx/h-S-1-H used has almost the same chemical state and the same distribution of Co(II) species as the fresh catalysts. Based on DFT calculations and inhibition experiments, the oxidative coupling of thiols undergoes a free radical mechanism in which Co(III) causes RS-H cleavage into RS· and H· species. Subsequently, two RS· radicals are coupled to disulfides, while H· radicals react with the O species to form H2O molecules. This work not only provides guidance on catalyst design and parameter optimization for oxidative thiol coupling but also advances the understanding of the aerobic oxidation mechanism.

Application of Iodine as a Catalyst in Aerobic Oxidations: A Sustainable Approach for Thiol Oxidations

Iodine is a well-known oxidant that is widely used in organic syntheses. Thiol oxidation by stoichiometric iodine is one of the most commonly employed strategies for the synthesis of valuable disulfides. While recent advancements in catalytic aerobic oxidation conditions have eliminated the need for stoichiometric oxidants, concerns persist regarding the use of toxic or expensive catalysts. In this study, we discovered that iodine can be used as a cheap, low-toxicity catalyst in the aerobic oxidation of thiols. In the catalytic cycle, iodine can be regenerated via HI oxidation by O2 at 70 °C in EtOAc. This protocol harnesses sustainable oxygen as the terminal oxidant, enabling the conversion of primary and secondary thiols with remarkable efficiency. Notably, all 26 tested thiols, encompassing various sensitive functional groups, were successfully converted into their corresponding disulfides with yields ranging from >66% to 98% at a catalyst loading of 5 mol%.

Reactive Epoxy Nanofiltration Membranes with Disulfide Bonds for the Separation of Multicomponent Chemical Mixtures

This article reports the fabrication of organic solvent nanofiltration membranes containing a labile disulfide bond, which is broken by reaction with a chemical stimulus. These membranes are a new generation of smart membranes that have tailored selectivities and flux that can be altered by reacting with a chemical stimulus. The selectivity and flux of chemicals through the membranes was controlled by varying the concentration of disulfide bonds in the membrane. When the disulfide bonds were cleaved, the pores in the membrane became larger and yielded different separation properties. The membrane selectivity was changed by up to 70% and flux was increased up to 5×. The rapid change in selectivity of the membrane allowed for the separation of three-component mixtures. A three-component mixture of 33.3% m-dinitrobenzene, 33.3% triphenylmethane, and 33.3% 1,3,5-tris(diphenylamino)benzene (TDAB) was separated into three different fractions that were significantly enriched in one of the three molecules. The first fraction contained m-dinitrobenzene at 82% purity and 84% yield, the second fraction contained triphenylmethane at 67% purity and 49% yield, and the third fraction contained TDAB at 71% purity and 88% yield.