An efficient and robust fluoroketone catalyst epoxidation

Radical and Cationic Pathways in C(sp3)-H Bond Oxygenation by Dioxiranes of Bicyclic and Spirocyclic Hydrocarbons Bearing Cyclopropane Moieties

A product and DFT computational study on the reactions of 3-ethyl-3-(trifluoromethyl)dioxirane (ETFDO) with bicyclic and spirocyclic hydrocarbons bearing cyclopropyl groups was carried out. With bicyclo[n.1.0]alkanes (n = 3-6), diastereoselective formation of the alcohol product derived from C2-H bond hydroxylation was observed, accompanied by smaller amounts of products derived from oxygenation at other sites. With 1-methylbicyclo[4.1.0]heptane, rearranged products were also observed in addition to the unrearranged products deriving from oxygenation at the most activated C2-H and C5-H bonds. With spiro[2.5]octane and 6-tert-butylspiro[2.5]octane, reaction with ETFDO occurred predominantly or exclusively at the axial C4-H to give unrearranged oxygenation products, accompanied by smaller amounts of rearranged bicyclo[4.2.0]octan-1-ols. The good to outstanding site-selectivities and diastereoselectivities are paralleled by the calculated activation free energies for the corresponding reaction pathways. Computations show that the σ* orbitals of the bicyclo[n.1.0]alkane cis or trans C2-H bonds and spiro[2.5]octanes axial C4-H bond hyperconjugatively interact with the Walsh orbitals of the cyclopropane ring, activating these bonds toward HAT to ETFDO. The detection of rearranged oxygenation products in the oxidation of 1-methylbicyclo[4.1.0]heptane, spiro[2.5]octane, and 6-tert-butylspiro[2.5]octane provides unambiguous evidence for the involvement of cationic intermediates in these reactions, representing the first examples on the operation of ET pathways in dioxirane-mediated C(sp3)-H bond oxygenations. Computations support these findings, showing that formation of cationic intermediates is associated with specific stabilizing hyperconjugative interactions between the incipient carbon radical and the cyclopropane C-C bonding orbitals that trigger ET to the incipient dioxirane derived 1,1,1-trifluoro-2-hydroxy-2-butoxyl radical.

Electron Affinity and Electronic Structure of Hexafluoroacetone (HFA) Revealed by Photodetaching the [HFA]•- Radical Anion

A great deal of effort has been focused on developing a metal-free catalytic system for epoxidation of unreactive alkenes. Fluoroketones are thought as remarkably promising catalysts for epoxidation reactions. The combination of fluorinated alcohols and catalytic amounts of hexafluoroacetone (HFA) gives a versatile and effective medium for epoxidation of various olefins with hydrogen peroxide. However, the fundamental physicochemical properties of HFA remained largely unclear, although they were very important to understand the related interactions. Here, we performed a joint study on the electron affinity and electronic structure of HFA employing negative ion photoelectron (NIPE) spectroscopy and quantum chemistry calculations. Two distinct bands with complicated vibrational progressions were observed in the 193 nm NIPE spectrum. The adiabatic/vertical detachment energies (ADE/VDE) were derived to be 1.42/2.06 and 4.43/4.86 eV for the ground singlet state and excited triplet state, respectively. Using the optimized geometries and vibrational frequencies of the anion and the neutral, the Franck-Condon factors were calculated for electron detachments to produce HFA in its lowest singlet and triplet states. Good agreements are obtained hereby for both bands between the experimental and calculated NIPE spectra, when taking into account combination vibrational excitations, unequivocally revealing that HFA possesses a singlet ground state with a giant singlet-triplet energy difference (ΔE_ST). The electron affinity (EA) and ΔE_ST of HFA were therefore determined to be EA = 1.42 ± 0.02 eV and ΔE_ST = -3.01 eV.

Simple spectrophotometric determination of monopersulfate

A simple, sensitive and accurate spectrophotometric method has been developed and validated for the determination of monopersulfate (MPS) which is an active part of potassium monopersulfate triple salt that has the commercial name - Oxone. This work proposes a spectrophotometric determination of monopersulfate based on modification of the iodometric titration method. The analysis of absorption spectra was made for the concentration range from 1.35 to 13.01 ppm of MPS (with a detection and quantification limit of 0.41 and 1.35 ppm, respectively) and different pH values. The influence of several anions on the measurement was also investigated. Furthermore, the absorbance of iron and cobalt (often used as free radical initiators) proved to have no effect on the measurement of MPS concentrations. On the basis of the conducted studies, we propose 395 nm as an optimal wavelength for the determination of MPS concentrations.

Highly efficient degradation of ofloxacin by UV/Oxone/Co2+ oxidation process

INTRODUCTION

In this study, UV/Oxone/Co(2+) oxidation process was applied to degradation of ofloxacin (OFL) in the presence of Co(2+) as the catalytic and Oxone as the oxidant. The operation parameters including pH, temperature, dosages of reagents, and reaction time were studied in detail.

RESULTS

The results showed that the optimum conditions for the UV/Oxone/Co(2+) processes were determined as follows: temperature = 25°C, pH = 5.0, [Oxone] = 0.6 mmol/L, [Oxone]/[Co(2+)] = 1,000, and reaction time = 60 min. Under these conditions, 100% of the OFL degraded. The kinetics was also studied, and degradation of OFL by the UV/Oxone/Co(2+) process could be described by first-order kinetics.

CONCLUSIONS

Mineralization of the process was investigated by measuring the total organic carbon (TOC), and the TOC decreased by 87.0% after 60 min. This process could be used as a pretreatment method for wastewater containing ofloxacin.

Oxone/Co(2+) oxidation as an advanced oxidation process: comparison with traditional Fenton oxidation for treatment of landfill leachate

In this paper, the application of Fenton and Oxone/Co(2+) oxidation processes for landfill leachate treatment was investigated. The removal of the chemical oxygen demand (COD), suspended substances (SS) and the color of the landfill leachate by Fenton oxidation to that by Oxone/Co(2+) oxidation were compared under optimal operational conditions. For Fenton oxidation process, the optimal conditions were determined as: [H(2)O(2)]=80 mmol L(-1), [H(2)O(2)]/[Fe(2+)]=2.0, initial pH=2.5, reaction temperature=37.5+/-1 degrees C, reaction time=160 min, number of stepwise addition=3. Under the given conditions, 56.9% of the COD removal efficiency was achieved, but the SS and the color of the treated landfill leachate increased due to the generation of a large quantity of ferric hydroxide sludge. In reference to Oxone/Co(2+) oxidation process, the optimal conditions were determined as: [Oxone]=4.5 mmol L(-1), [Oxone]/[Co(2+)]=10(4), pH=6.5, reaction temperature=30+/-1 degrees C, reaction time=300 min, number of stepwise addition=7, the COD, SS and the color removal efficiencies were 57.5, 53.3 and 83.3%, respectively. From this work, it can be concluded that Oxone/Co(2+) oxidation process demonstrated higher degradation efficiencies of the COD, SS and color for landfill leachate treatment than that by Fenton oxidation process. It also suggested that Oxone/Co(2+) oxidation process could be considered as one of the most promising technologies for practical applicability to treat landfill leachate in large scale. For further improving the efficiency of Oxone/Co(2+) oxidation process, we proposed that combination of it with other technologies in future such as ultraviolet, ultrasound and biological methods.

Regioselectivity and diasteroselectivity in Pt(II)-mediated "green" catalytic epoxidation of terminal alkenes with hydrogen peroxide: mechanistic insight into a peculiar substrate selectivity

Recently developed electron-poor Pt(II) catalyst 1 with the "green" oxidant 35% hydrogen peroxide displays high activity and complete substrate selectivity in the epoxidation of terminal alkenes because of stringent steric and electronic requirements. In the presence of isolated dienes bearing terminal and internal double bonds, epoxidation is completely regioselective toward the production of terminal epoxides. Insight into the mechanism is gained by means of a reaction progress kinetic analysis approach that underlines the peculiar role of 1 in activating both the alkene and H2O2 in the rate-determining step providing a rare example of nucleophilic oxidation of alkenes by H2O2.

Practical Synthesis of Fluorous Oxazolidinone Chiral Auxiliaries from α-Amino Acids

[reaction: see text] A series of new fluorous-supported oxazolidinone chiral auxiliaries has been prepared using a versatile and general five-step pathway, starting from readily available chiral alpha-amino acids. The key feature of this synthesis is the efficient generation of a suitably active perfluoroalkyllithium species. By use of this protocol, the auxiliaries can be obtained in high enantiomeric purity and on multigram scales from L-phenylalanine and L-valine with overall yields as high as 55%. The new methodology also incorporates fluorous solid-phase extraction on the large scale, allowing bulk quantities (up to 25 g) of fluorous compounds to be purified from the crude reaction mixture.

Enantioselective epoxidation of alkenes catalyzed by 2-fluoro-N-carbethoxytropinone and related tropinone derivatives

Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities.