Selective Mild Oxidation of Anilines into Nitroarenes by Catalytic Activation of Mesoporous Frameworks Linked with Gold-Loaded Mn3 O4 Nanoparticles.

This work reports the synthesis and catalytic application of mesoporous Au-loaded Mn3 O4 nanoparticle assemblies (MNAs) with different Au contents, i. e., 0.2, 0.5 and 1 wt %, towards the selective oxidation of anilines into the corresponding nitroarenes. Among common oxidants, as well as several supported gold nanoparticle platforms, Au/Mn3 O4 MNAs containing 0.5 wt % Au with an average particle size of 3-4 nm show the best catalytic performance in the presence of tert-butyl hydroperoxide (TBHP) as a mild oxidant. In all cases, the corresponding nitroarenes were isolated in high to excellent yields (85-97 %) and selectivity (>98 %) from acetonitrile or greener solvents, such as ethyl acetate, after simple flash chromatography purification. The 0.5 % Au/Mn3 O4 catalyst can be isolated and reused four times without a significant loss of its activity and can be applied successfully to a lab-scale reaction of p-toluidine (1 mmol) leading to the p-nitrotulene in 83 % yield. The presence of AuNPs on the Mn3 O4 surface enhances the catalytic activity for the formation of the desired nitroarene. A reasonable mechanism was proposed including the plausible formation of two intermediates, the corresponding N-aryl hydroxylamine and the nitrosoarene.

Highly Efficient Sorption of Methyl Orange by a Metal-Organic Resin-Alginic Acid Composite.

The composite anion-exchange material MOR-1-HA (metal-organic resin-1-alginic acid) was investigated as sorbent for the capture of the methyl orange anion (MO- ) from aqueous solutions. MOR-1-HA shows a remarkably high sorption capacity (up to 859 mg g-1 ) and rapid sorption kinetics, the fastest among the reported metal-organic sorbents. It is capable of absorbing MO- over a wide pH range (1-8) and, in addition, it exhibits significant MO- sorption affinity even in the presence of large excesses of competing anions (e.g., Cl- , NO3 - , SO4 2- ). The exceptional MO- -sorption properties of MOR-1-HA arise not only from its highly porous structure and easily exchangeable Cl- anions, but also from a multitude of interaction effects, such as electrostatic interactions between MO- and the NH3 + groups of the material, hydration/dehydration, hydrophobicity/hydrophilicity, size and capacity of generating lateral interactions, and intercalation as revealed by theoretical studies. An ion-exchange column with a stationary phase containing MOR-1-HA and silica sand showed high efficiency for the removal of MO- from various types of aqueous samples. The column can be readily regenerated and reused for many runs with minimal loss (2.3-9.3 %) of its exchange capacity. The simplicity of the MOR-1-HA/sand column and its high regeneration capability and reusability make it particularly attractive for application in the remediation of MO- -contaminated industrial wastewater.

Mesoporous Assembled Mn3 O4 Nanoparticle Networks as Efficient Catalysts for Selective Oxidation of Alkenes and Aryl Alkanes.

The design of nanoscale materials has been considered important for enhancing their surface properties for catalysis. Metal oxide nanoparticles have a large number of exposed surface active sites, but they suffer from low reactivity and poor stability resulting from excessive aggregation into less active microscopic structures. Herein, the synthesis of mesoporous Mn3 O4 nanoparticle assemblies by polymer-assisted self-assembly is presented and their catalytic activity is demonstrated in the oxidation of various saturated and unsaturated hydrocarbons, including aromatic alkenes and aryl alkanes, in the presence of tert-butyl hydroperoxide as a mild oxidant. It is also shown through comparative studies that the high catalytic activity and stability of these Mn3 O4 assemblies arise from the unique three-dimensional open-pore structure, high internal surface area (90 m2 g-1 ) and uniform mesopores (≈6.6 nm in size).