Optical properties and oxidative potential of aqueous-phase products from OH and ³C^*-initiated photolysis of eugenol

In ambient air, aqueous-phase oxidation may turn precursors into more light-absorbing and toxic products, leading to air quality deterioration and adverse health effects. In this study, we investigated eugenol degradation in aqueous phase under direct photolysis, and triplet excited organic (3C*) and hydroxyl radical (OH) as oxidants. Results showed degradation rates of eugenol followed the order of 3C* > OH > direct photolysis. Relative contributions of reactive oxygen species (ROS) and 3C* were evaluated via quenching and O2-free experiments. 3C* played a dominant role in eugenol degradation for 3C*-initiated oxidation, while both O2 and O2•-generated were important for eugenol degradation for OH-initiated oxidation. Rate constants under O2, air and N2 followed the order of ko2＞kAir＞kN2 under both direct photolysis and OH oxidation, and it changed to kAir＞kN2＞ko2 in 3C*-initiated oxidation. Light absorption spectra showed absorbance at 300–400 nm increased as photolysis progressed, and there were new broad fluorescent spectra at excitation/emission (Ex/Em) = 250/(400–500) nm, suggesting the formation of new chromophores and fluorophores, such as humic-like substances (HULIS). Additionally, distinct fluorescence peaks appeared at Ex/Em=(300–350)/300 nm at different stages. Concentration of generated HULIS increased gradually over time, then leveled off. Dithiothreitol (DTT) assay was applied to assess the oxidation potential of products, which was greater than pure eugenol, suggesting more harmful species were produced during oxidation. Detailed reaction pathways were elucidated via analyses of chemical characteristics of the products.

LIQUID-PHASE OXIDATION OF 4-ETHYLECYCLOHEX-1-ENE BY OXYGEN OF AIR IN. PRESENCE OF CATALYTIC

The liquid-phase oxidation of 4-ethylecyclohexene by oxygen in the presence of a catalytic system (NH4)6Mo7O24 CoBr2) was investigated. The influence of various factors (temperature, duration, quantity of catalyst, molar ratios of reagents) on the oxidation reaction rates (conversion of feedstock, selectivity of reaction on oxy products) is determined

Versatility of Supported Gold Nanoparticles on Hydrotalcites used for Oxidation and Reduction Reactions

Regardless of their size, supported gold nanoparticles are largely used for liquid-phase oxidation reactions. Small gold nanoparticles exhibit good performance during the reduction of organic compounds. The direct reduction of carboxylic acid to aldehyde is a famous and familiar reaction in the field of organic chemistry and is considered as one of the fundamental chemical transformations. Herein, we present Au/hydrotalcite, Au/MgO, and Au/Al2O3 systems as heterogeneous versatile catalysts to realize the oxidation of furfural (FF) to furoic acid (FA) and realize the reduction of FA to FF. Experiments showed that in standard aqueous conditions under air, FF can be easily oxidized to FA. When DMSO was used as a solvent to conduct the experiments under an atmosphere of CO2, FA was reduced to FF. The Au/HT series of catalysts was found to be active in both transformations, pointing out the versatility of the gold-based catalysts. The activity significantly depends on the acid-base properties of the catalyst.

Activity of Manganese Carboxylates in the Process of Liquid-Phase Oxidation of Ethylbenzene with Atmospheric Oxygen

The process of oxidation of hydrocarbon with oxygen proceeds with formation of the corresponding hydroperoxide as the primary product [1,2]. A catalyst is the most important factor that influences on the direction of flow of the oxidation reaction. Catalysts based on metals of variable valency, and their derivatives are the most active in reactions of oxidation of hydrocarbon [3].