Mild oxidation of benzyl alcohols to benzyl aldehydes or ketones catalyzed by visible light

Tuning the physicochemical features of titanium oxide nanomaterials by ultrasound: Elevating photocatalytic selective partial oxidation of lignin-inspired aromatic alcohols

The research for "green" and economically feasible approaches such as (photo)catalysis especially for biomass valorization such as selective oxidation of biomass derived compounds like aromatic alcohols to corresponding aldehyde by avoiding the harsh reaction conditions and the addition of reagents concentrate the focus of attention the last years. Hence, design and development of novel photocatalyst for the partial selective oxidation is highly desirable. In this research work, ultrasonication of different frequencies (22, 40, 80 kHz) and different amplitudes was utilized as synthesis tool in order to obtain novel materials by precipitation method. The synthesized samples were characterized by using different techniques such as N₂ sorption, TEM, XPS, XRD, thermal analysis, and diffuse reflectance spectroscopy. The synthesized sample by using low ultrasound frequency (22 kHz) and amplitude showed a mixed morphological and structural nature consisting of asymmetric 1-dimensional (nanorods-like), layered nano-structures and not well-defined areas, leading to elevate for metal oxide specific surface areas up to 155 m²/g. The observed 1-D nanostructures have diamentions in the range of 20-60 nm. This sample revealed the highest photo-oxidation efficiency for the selective conversion of two biomass-derived, and more specifically lignin-inspired model compounds, benzyl alcohol and cinnamyl alcohol to benzaldehyde and cinnamyl aldehyde, respectively, and hence the highest yield towards the desired aldehydes. The selective photo-oxidation activity was retained even after 5 photocatalytic cycles, while no leaching of Ti was recorded.

Transition Metal Complex Catalyzed Photo- and Electrochemical (De)hydrogenations Involving C=O and C=N Bonds

Herein, we summarize the photo- and electrochemical protocols for dehydrogenation and hydrogenations involving carbonyl and imine functions. The three basic principles that have been explored to interconvert such moieties with transition metal complexes are discussed in detail and the substrate scope is evaluated. Furthermore, we describe some general thermodynamic and kinetic aspects of such electro- and photochemically driven reactions.

1 Introduction

2 Dehydrogenation Reactions

2.1 Electrochemical Dehydrogenations Using High-Valent Metal Species

2.2 Electrochemical Dehydrogenations Involving Metal Hydride species

2.3 Photochemically Driven Dehydrogenation

3 Hydrogenation Reactions

3.1 Electrochemical Protocols

3.2 Photochemical Protocols

4 Conclusion

5 Abbreviations