Visible Light-Mediated Selective Aerobic Oxidation of Alcohols Catalyzed by Disulfide in Batch and Flow.

Selective aerobic oxidation of alcohols in batch and flow can be realized under light irradiation, utilizing disulfide as the photocatalyst, and a variety of primary and secondary alcohols were converted to the corresponding aldehydes or ketones in up to 99% yield and high selectivity. The reaction efficiency could be increased even further by combining a continuous-flow strategy. Detailed mechanistic studies have also been achieved to determine the role of oxygen and disulfides in this oxidation.

Determination of the Lower Limit of Physical Properties of Tight Oil Reservoirs: A Case Study of the Lower Es3 in the Jiangjiadian Area, Linnan Sag.

The tight oil reservoir in Linnan Sag has great potential, a wide distribution range, and large total predicted resources. The rapid accumulation and burial of sediments in multiple source directions have resulted in the characteristics of low porosity and low permeability of the Lower Es3 in the Jiangjiadian area, Linnan Sag. Based on conventional core analysis data, mercury injection data, and oil testing data, this paper comprehensively determines the lower limit of effective physical properties of reservoirs in the Jiangjiadian area of Linnan Sag and studies its main influencing factors. The results show that (1) the lower Es3 reservoir in the Jiangjiadian area of Linnan Sag mainly develops feldspar sandstone and lithic feldspar sandstone. The porosity is mainly distributed at about 12%, and the permeability is mainly distributed at 0.3 mD; (2) based on the study of reservoir characteristics, the empirical statistical method based on core analysis data and the pore-permeability intersection method, the mercury injection parameter method based on test data, and the oil test verification method are used to comprehensively determine the lower limit of physical properties in the study area. The lower limit of porosity is 7.87%, and the lower limit of permeability is 0.16 mD; (3) sedimentation mainly affects the lower limit of physical properties by controlling reservoir lithology and pore structure. The existence of compaction and cementation in diagenesis will reduce the reservoir porosity and affect the lower limit of effective physical properties. The secondary dissolution pores formed by dissolution have a certain improvement effect on the effective physical properties of the reservoir.

Bridging Effect of Carbon Nitride with More Negative Conduction Potential and Halogens Promotes the Liquid-Phase Oxidation of Aromatic C-H Bonds.

The selective oxidation of benzyl C-H bonds of alkyl aromatic hydrocarbons under solvent-free conditions by using heterogeneous catalysis is a challenging task. In this work, we designed a carbon nitride photocatalyst with a high charge separation efficiency and a directed charge transfer path, which was doped with Ni and Br in the carbon nitride skeleton. Br was deposited directionally onto the electron-rich Ni surface traps to form a bond with Ni, which acted as a charge transfer bridge connecting CN and Br, resulting in a bridging effect. Photogenerated electrons were transferred from Ni target to Br, and electrons were aggregated to form a directional charge transfer path, thereby enhancing the photocatalytic performance of CN. The photocatalyst was utilized for the selective oxidation of ethylbenzene at room temperature, atmospheric pressure, and solvent-free conditions. Under batch conditions simulating solar irradiation, the conversion of ethylbenzene was 43.3% and the selectivity of the product acetophenone was up to 92.0%. With the continuous flow strategy, the conversion of ethylbenzene was increased to 52.4 and 48.1%, respectively, while the selectivity reached 92.7 and 91.0%, and the reaction time was reduced from 24 to 2.1 h. The catalyst was also found to be broadly applicable for the selective oxidation of C-H bonds in the benzyl position of alkyl aromatic hydrocarbons.

A DFT and kinetic study: Is it possible to prepare epoxides without catalysts using the in-situ generated peroxy radicals or peroxides by one-step method?

DFT calculations and kinetic analysis have been employed to comprehensively explore the possibility to prepare epoxides by one-step method using the in-situ generated peroxy radicals or hydroperoxides as epoxidizing agents. Computational studies demonstrated that the selectivities for the reaction systems of O2 /R2/R1, O2 /CuH/R1, O2 /CuH/styrene, O2 /AcH/R1 were 68.2%, 69.6%, 100% and 93.3%, respectively. The in-situ generated peroxide radicals, such as HOO˙, CuOO˙ and AcOO˙, could react with R1 or styrene by attacking the CC double bond to form a CO bond and subsequently undergoing a cleavage of OO bond to yield epoxides. Peroxide radicals could abstract a hydrogen atom from methyl group on R1, forming unwanted by-products. It should be noted that the hydrogen atoms of HOO˙ is easy to be abstracted by CC double bond and simultaneously the oxygen atom is connected to the CH moiety to form an alkyl peroxy radical (Rad11), greatly limiting the selectivity. The comprehensive mechanistic studies provide a deep understanding on preparing epoxides by one-step method.

Effects of Oxygen: Experimental and VTST/DFT Studies on Cumene Autoxidation with Air under Atmospheric Pressure.

The mechanism of how oxygen affects cumene autoxidation related to temperature is still bewildering. Kinetic analysis of cumene autoxidation with air at a pressure of 1.0 atm was investigated by experiments and variational transition state theory/DFT. Oxygen was the limiting factor for cumene autoxidation above 100 °C, although it had negligible impacts on cumene autoxidation at 70-100 °C. The kinetic analysis by VTST coupled with DFT calculations proved that {k 6,reverse[ROO•]}/{k 7,forward[RH]0 [ROO•]} > 103 (70-120 °C), suggesting that ROO• tended to decompose back to R• and O2 rapidly, whereas it was much slower for ROO• abstracting a hydrogen atom from RH to form ROOH. When the concentration of oxygen was higher than the critical value ([O2]critical), it could not significantly affect the equilibrium concentration of ROO•, which in turn could not affect the autoxidation rate significantly. Besides, the critical oxygen concentration ([O2]critical) was exponentially related to 1/T, which was consistent with Hattori's experimental results.

Visible-Light-Driven Oxidative Cleavage of Alkenes Using Water-Soluble CdSe Quantum Dots.

The oxidative cleavage of C=C bonds is an important chemical reaction, which is a popular reaction in the photocatalytic field. However, high catalyst-loading and low turnover number (TON) are general shortcomings in reported visible-light-driven reactions. Herein, the direct oxidative cleavage of C=C bonds through water-soluble CdSe quantum dots (QDs) is described under visible-light irradiation at room temperature with high TON (up to 3.7×104 ). Under the same conditions, water-soluble CdSe QDs could also oxidize sulfides to sulfoxides with 51-84 % yields and TONs up to 3.4×104 . The key features of this photocatalytic protocol include high TONs, wide substrates scope, low catalyst loadings, simple and mild reaction conditions, and molecular O2 as the oxidant.

Rose bengal as photocatalyst: visible light-mediated Friedel-Crafts alkylation of indoles with nitroalkenes in water.

A novel and facile visible-light-mediated alkylation of indoles and nitroalkenes has been developed. In this protocol, rose bengal acts as a photosensitizer, and environmentally benign water was used as the green and efficient reaction medium. Indoles reacted smoothly with nitroalkenes under the irradiation of visible-light and generated corresponding 3-(2-nitroalkyl)indoles in moderate to good yields (up to 87%).

Visible light-mediated selective α-functionalization of 1,3-dicarbonyl compounds via disulfide induced aerobic oxidation.

A visible light-mediated α-functionalization of 1,3-dicarbonyl compounds with switchable selectivity induced by disulfide is disclosed. Upon irradiation with visible light, the metal- and base-free α-hydroxylation or α-hydroxymethylation reaction proceeded smoothly through a disulfide-catalyzed oxidation under mild conditions. The combination of a continuous-flow strategy could further improve the reaction efficiencies.

Preparation of O-Protected Cyanohydrins by Aerobic Oxidation of α-Substituted Malononitriles in the Presence of Diarylphosphine Oxides.

A mild, reagent-cyanide-free, and efficient synthesis of O-phosphinoyl-protected cyanohydrins from readily available α-substituted malononitriles was realized using diarylphosphine oxides in the presence of O2. Mechanistic studies indicated that in addition to the initial aerobic oxidation of the malononitrile derivative notable features of this process include the formation of a tetrahedral intermediate and a subsequent intramolecular rearrangement. The phosphinoyl-protecting group can be removed by alcoholysis or by reduction with DIBAL-H.