3 research outputs found
Two new chromone derivatives from the rhizosphere soil fungus <i>Ilyonectria robusta</i>
Two new chromone derivatives (1 and 2), and two known compounds (3 and 4) were isolated from the rhizosphere soil fungus Ilyonectria robusta. Their planar structures and absolute configurations were determined by extensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. Additionally, all the isolated compounds were evaluated for their antibacterial activity against Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli, but no obvious activity was observed at a concentration of 128āĪ¼g/mL.</p
Correction to Highly Selective Liquid-Phase Oxidation of Cyclohexane to KA Oil over Ti-MWW Catalyst: Evidence of Formation of Oxyl Radicals
Correction to Highly Selective Liquid-Phase Oxidation
of Cyclohexane to KA Oil over Ti-MWW Catalyst: Evidence of Formation
of Oxyl Radical
Highly Selective Liquid-Phase Oxidation of Cyclohexane to KA Oil over Ti-MWW Catalyst: Evidence of Formation of Oxyl Radicals
Various types of Ti-containing zeolites,
i.e., Ti-MWW, TS-1, Ti-MOR, and Ti-BEA, have been evaluated as candidates
for the liquid-phase oxidation of cyclohexane using <i>t</i>-butyl hydroperoxide (TBHP, 7ā8 wt %) as model oxidant. Ti-MWW
zeolite displayed the highest activity for cyclohexanol and cyclohexanone
(KA oil) with an overall selectivity higher than 90% at 80 Ā°C,
making this catalyst a candidate of choice for industrial KA oil production
by deperoxidation of cyclohexyl hydroperoxide. The effect of the reaction
temperature, reaction time, catalyst amount, and catalyst stability
on Ti-MWW was surveyed in detail. The Ti-MWW catalyst showed a stable
performance and could be recycled at least four times without detectable
Ti leaching and loss of structural stability. The active sites for
cyclohexane oxidation appeared to be located near external 12-ring
cups in the Ti-MWW framework as suggested by a series of position-selective
poisoning tests with tripropyl- and triphenylamine, impelling cyclohexane
diffusion within the internal 10-ring channels. EPR experiments supported
by DFT calculations suggested the coexistence of both TiĀ(IV)-OO<sup>ā¢</sup> (peroxyl) and TiĀ(IV)-O<sup>ā¢</sup> (oxyl) species
generated through bimolecular pathways, implying simultaneously (SiO)<sub>3</sub>TiĀ(OOtBu) species and tBuOOH. The catalytic activity was strongly
inhibited in the presence of alkenes, leading to the preferential
formation of the epoxidation product with no detectable formation
of radicals. Notably, this is the first time that oxyl species have
been detected particularly with the help of DFT calculations. Predicted
differences of <i>g</i> tensors between peroxyl and oxyl
species at various hydration levels in the presence of cyclohexane
were consistent with the EPR spectra