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Visible light induced green transformation of primary amines to imines using a silicate supported anatase photocatalyst.

ABSTRACT: Catalytic oxidation of amine to imine is of intense present interest since imines are important intermediates for the synthesis of fine chemicals, pharmaceuticals, and agricultural chemicals. However, considerable efforts have been made to develop efficient methods for the oxidation of secondary amines to imines, while little attention has until recently been given to the oxidation of primary amines, presumably owing to the high reactivity of generated imines of primary amines that are easily dehydrogenated to nitriles. Herein, we report the oxidative coupling of a series of primary benzylic amines into corresponding imines with dioxygen as the benign oxidant over composite catalysts of TiO2 (anatase)-silicate under visible light irradiation of ? > 460 nm. Visible light response of this system is believed to be as a result of high population of defects and contacts between silicate and anatase crystals in the composite and the strong interaction between benzylic amine and the catalyst. It is found that tuning the intensity and wavelength of the light irradiation and the reaction temperature can remarkably enhance the reaction activity. Water can also act as a green medium for the reaction with an excellent selectivity. This report contributes to the use of readily synthesized, environmentally benign, TiO2 based composite photocatalyst and solar energy to realize the transformation of primary amines to imine compounds.

SUBMITTER: Zavahir S

PROVIDER: S-EPMC6272701 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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Visible light induced green transformation of primary amines to imines using a silicate supported anatase photocatalyst.

Zavahir Sifani S Zhu Huaiyong H

Molecules (Basel, Switzerland) 20150126 2

Catalytic oxidation of amine to imine is of intense present interest since imines are important intermediates for the synthesis of fine chemicals, pharmaceuticals, and agricultural chemicals. However, considerable efforts have been made to develop efficient methods for the oxidation of secondary amines to imines, while little attention has until recently been given to the oxidation of primary amines, presumably owing to the high reactivity of generated imines of primary amines that are easily de ...[more]

PMID: 25629455

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Project description:Titanium dioxide is an ubiquitous photocatalyst in water-cleaning technologies, being presently the most promising tools to resolve the global issue of sewage treatment. In this framework, titanium dioxide-graphene nanocomposites are discussed as promising visible-light activated photocatalysts but little is hitherto known about the surface and interface chemistry bridging the metal oxide and carbon phases. In an attempt to spotlight this overlooked issue, we herein designed two different hybrid nanocomposites through covalent grafting and growth of titanium dioxide clusters on graphene oxide and on phosphorylated graphene oxide, which affords GO@TiO2 and PGO@TiO2, respectively. While anatase could be selectively harvested on the surface of GO@TiO2, biphasic anatase-rutile nucleates could be obtained on PGO@TiO2. Thermal annealing treatments improve the metal oxide crystallization and further remove oxygenated groups from the surface of graphene. The interfacial stability of these photocatalysts was also investigated under irradiation, with the graphene support being sensitive to the proximal presence of titanium dioxide. The resulting nanocomposites were also assessed for methylene blue removal through adsorption and photocatalysis. Regardless of their composition, superior photoactivity was noticed for the nanocomposites compared to commercially available degussa that display marginal visible-light photoactivity (11% removal). Within our study, PGO@TiO2-500 stands as the most active catalyst, allowing nearly quantitative removal of the pollutant from water. The superior performance of PGO@TiO2-500 can be explained by the highest stability reached through P-O-Ti bonding, its improved crystallinity, and the reduction of the graphene surface during thermal treatment. On a whole, this study provides a blueprint for comparing semiconducting metal oxide grown on tuneable surface-interfacial graphene environments and highlights the utility of surface-engineering graphene sheets to access efficient visible-light oxidation photocatalysts.

Dataset Information

Visible light induced green transformation of primary amines to imines using a silicate supported anatase photocatalyst.

Publications

Visible light induced green transformation of primary amines to imines using a silicate supported anatase photocatalyst.

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