The synthesis of propylene oxide from propylene and hydrogen peroxide and the side reactions of propylene oxide were studied in a broad range of experimental conditions (25−80 °C, 2.5−8.5 bar) in a laboratory-scale trickle-bed reactor using commercial titanium silicate (TS-1) as a heterogeneous catalyst. The reaction solvent was methanol. A very precise gas chromatographic analysis method was developed to study the reactant conversion and product distribution. Long-term experiments in the continuous reactor revealed excellent catalyst stability. Besides the main product propylene oxide, side products such as 1-methoxy-2-propanol and propylene glycol were formed via ring-opening reactions with methanol and water. A prominent maximum in the activity at optimal temperatures was observed. The formation of the side products and the catalytic activity was related to the concentration of water and hydrogen peroxide. An extensive study of propylene oxide transformations was conducted, illustrating the importance of lower water concentration and shorter residence times for selective production of propylene oxide. The reaction mechanisms of the epoxidation process and the side reactions were discussed: a consecutive-parallel reaction scheme was confirmed by the propylene synthesis experiments and separate experiments with propylene oxide and methanol and water.
Ethylene epoxidation
with hydrogen peroxide was studied in a laboratory-scale
trickle bed reactor under a broad range of experimental conditions
(15–80 °C, 2.5–8.5 bar) utilizing a commercial
titanium-silicate catalyst (TS-1). The catalyst was very stable and
selective over 150 h time-on-stream. The main reaction product was
ethylene oxide, while 2-methoxyethanol and ethylene glycol were observed
as kinetic byproducts. In most of the experiments, ethylene glycol
was not detected at all. An increase in temperature and pressure affected
negatively the ethylene oxide selectivity, while an increase in the
hydrogen peroxide concentration improved both the ethylene oxide selectivity
and ethylene conversion. Ethylene epoxidation was comparable with
propylene epoxidation, displaying, however, important differences
in activity and selectivity, which were attributed to the partial
pressures studied in the present work. It was demonstrated that TS-1
is a very selective and active catalyst for the selective epoxidation
of ethylene with hydrogen peroxide.
An evaluation of antioxidant and anticancer activity was screened in Leptocarpha rivularis DC flower extracts using four solvents (n-hexane (Hex), dichloromethane (DCM), ethyl acetate (AcOEt), and ethanol (EtOH)). Extracts were compared for total extract flavonoids and phenol contents, antioxidant activity (2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH), ferric reducing antioxidant potential (FRAP), total reactive antioxidant properties (TRAP) and oxygen radical absorbance capacity (ORAC)) across a determined value of reduced/oxidized glutathione (GSH/GSSG), and cell viability (the sulforhodamine B (SRB) assay). The most active extracts were analyzed by chromatographic analysis (GC/MS) and tested for apoptotic pathways. Extracts from Hex, DCM and AcOEt reduced cell viability, caused changes in cell morphology, affected mitochondrial membrane permeability, and induced caspase activation in tumor cell lines HT-29, PC-3, and MCF-7. These effects were generally less pronounced in the HEK-293 cell line (nontumor cells), indicating clear selectivity towards tumor cell lines. We attribute likely extract activity to the presence of sesquiterpene lactones, in combination with other components like steroids and flavonoids.
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