Selective photocatalytic oxidation of alcohols to corresponding aldehydes in solvent-free conditions using porphyrin sensitizers

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C-N/C-O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

Performing synthetic transformation using visible light as energy source, in the presence of a photocatalyst as a promoter, is currently of high interest, and oxidation reactions carried out under these conditions using oxygen as the final oxidant are particularly convenient from an environmental point of view. This review summarizes the recent developments achieved in the oxidative dehydrogenation of C-N and C-O bonds, leading to C=N and C=O bonds, respectively, using air or pure oxygen as oxidant and metal-free homogeneous or recyclable heterogeneous photocatalysts under visible light irradiation.

Tracking down the brominated single electron oxidants in recent organic red-ox transformations: photolysis and photocatalysis

A wide range of organic and inorganic brominated compounds including molecular bromine have been extensively used as oxidants in many organic photo-redox transformations in recent years, an area of ever growing interest because of greener and milder approaches. The oxidation power of these compounds is utilized through both mechanistic pathways (by hydrogen atom transfer or HAT in the absence of a photocatalyst and a combination of single electron transfer or SET and/or HAT in the presence of a photocatalyst). Not only as terminal oxidants for regeneration of photocatalysts, but brominated reactants have also contributed to the oxidation of the reaction intermediate(s) to carry on the radical chain process in several reactions. Here in this review mainly the non-brominative oxidative product formations are discussed, carried out since the last two decades, skipping the instances where they acted as terminal oxidants only to regenerate photocatalysts. The reactions are used to generate natural products, pharmaceuticals and beyond.

Photodegradation of metoprolol in the presence of aquatic fulvic acids. Kinetic studies, degradation pathways and role of singlet oxygen, OH radicals and fulvic acids triplet states

Metoprolol is a pharmaceutical used for the treatment of cardiovascular diseases and disorders, whose frequent detection in surface waters raises concern. Indirect photodegradation is an important degradation pathway in waters and dissolved organic matter has a major role as photosensitizer. In this study, metoprolol photodegradation, in the absence and in the presence of fulvic acids extracted from the Vouga River (Portugal) (VRFA), was assessed under simulated sunlight. While metoprolol direct photodegradation was deniable, indirect photolysis occurred under the presence of VRFA. It followed a pseudo-first order kinetics and after 72 h of irradiation there was a decrease of metoprolol concentration of ∼80 %. The OH radical (OH) was verified to be the main reactive species (RS) responsible for the photosensitized degradation of metoprolol, but other RS are also involved, probably triplet excited states of FA (³FA*) and singlet oxygen (¹O₂), as demonstrated by the higher inhibition of the photodegradation in presence of sodium azide than in presence of 2-propanol. Based on a previous identification of photoproducts, tentative degradation mechanisms were here proposed. Photoproducts analysis after 24 h irradiation in the absence and presence of scavengers, shown that different RS are involved in the formation of different products/intermediates.

Photocatalytic asymmetric epoxidation of trans-stilbene with manganese–porphyrin/graphene-oxide nanocomposite and molecular oxygen: axial ligand effect

An efficient, visible light-driven manganese–porphyrin photocatalyst was developed for the asymmetric epoxidation of trans-stilbene by molecular oxygen under mild conditions.