Hindered Phenol Derivative as a Multifunctional Additive in Lithium Complex Grease

This paper describes 3-(3,5-Di<i>tert</i>-butyl-4-hydroxy-phenyl)-propionic acid 2-(4-meth yl-thiazol-5-yl)-ethyl ester (BHMT) as a high-performance multifunctional additive in lithium complex grease (LCG). The tribological properties and antioxidant behaviors of BHMT were evaluated by the tribological test and thermal analysis, respectively, and compared with those of zinc dialkyldithiophosphate (ZDDP). The tribochemical film BHMT generated on the worn surface was analyzed by X-ray photoelectron spectroscopy (XPS). Tribological results indicated that BHMT exhibited better friction-reduction and antiwear properties than ZDDP. The thermal analysis demonstrated that the antioxidation ability of BHMT was superior to that of ZDDP. Moreover, XPS results showed that lubrication film composed of iron oxide, iron sulfate, and nitrogen oxide was formed on the worn surface, which was an explicit explanation of the tribochemical mechanism of BHMT

Radical-Smiles Rearrangement by a Vitamin B2-Derived Photocatalyst in Water

Herein, we report a catalytic radical-Smiles rearrangement system of arene migration from ether to carboxylic acid with riboflavin tetraacetate (RFT), a readily available ester of natural vitamin B2, as the photocatalyst and water as a green solvent, being free of external oxidant, base, metal, inert gas protection, and lengthy reaction time. Not only the known substituted 2-phenyloxybenzoic acids substrates but also a group of naphthalene- and heterocycle-based analogues was converted to the corresponding aryl salicylates for the first time. Mechanistic studies, especially a couple of kinetic isotope effect (KIE) experiments, suggested a sequential electron transfer-proton transfer processes enabled by the bifunctional flavin photocatalyst

Aerobic Alcohol Oxidation with a Cerium–Phenanthrolinedione Complex: A Mimic of Lanthanide-Based Methanol Dehydrogenase

The development of efficient catalytic systems that use an environmentally friendly oxidant, such as molecular oxygen, remains an ongoing challenge in the oxidative transformation of hydrocarbons. Herein, we report the synthesis and characterization of a bioinspired cerium(III) catalyst bearing a commercially available 1,10-phenanthroline-5,6-dione (phd) ligand, an inexpensive and efficient molecular model of the pyrroloquinoline quinone (PQQ) cofactor. This Ce–phd complex, in which the cerium(III) ion acts as a Lewis acid center and the phd ligand regulates the redox process, shows good reactivity in the catalytic oxidation of various alcohols using air as an oxidant and no need for any cocatalyst, base, desiccant, or solvent pretreatment. Secondary benzylic and aliphatic alcohols and aromatic primary alcohols were converted to the corresponding ketones and aldehydes with good yields, respectively. In addition, this Ce–phd complex exhibited good chemoselectivity for the oxidation of alcohols over other labile groups, the secondary alcohols over primary alcohols, and benzylic alcohols over aliphatic alcohols by intramolecular and intermolecular competitive reactions. The catalytic reaction mechanism is proposed as a possible hydride transfer process on the basis of the studies of probe substrates, the kinetic isotope effect (KIE), Hammett plot, UV–vis spectra analysis, and stoichiometric reactions. The present results provide not only a practical mimic of PQQ-dependent methanol dehydrogenases (MDH) with earth-abundant cerium and a simple ligand but also an efficient, selective, and sustainable approach to the catalytic aerobic oxidation of alcohols