Homogeneous continuous flow nitration of O-methylisouronium sulfate and its optimization by kinetic modeling.

Nitration of O-methylisouronium sulfate under mixed acid conditions gives O-methyl-N-nitroisourea, a key intermediate of neonicotinoid insecticides with high application value. The reaction is a fast and highly exothermic process with a high mass transfer resistance, making its control difficult and risky. In this paper, a homogeneous continuous flow microreactor system was developed for the nitration of O-methylisouronium sulfate under high concentrations of mixed acids, with a homemade static mixer eliminating the mass transfer resistance. In addition, the kinetic modeling of this reaction was performed based on the theory of NO2 + attack, with the activation energy and pre-exponential factor determined. Finally, based on the response surface generated by the kinetic model, the reaction was optimized with a conversion of 87.4% under a sulfuric acid mass fraction of 94%, initial reactant concentration of 0.5 mol/L, reaction temperature of 40 °C, molar ratio of reactants at 4.4:1, and a residence time of 12.36 minutes.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D-Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with selectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, and continuous-flow process for precise control over production selectivity of value-added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

Evaluating the efficacy of microalgal-bacterial granular sludge system in lake water remediation.

The microalgal-bacterial granular sludge (MBGS) process is attracting attention as a green wastewater treatment technology. However, research on the application of MBGS in lake water remediation is limited. Thus, this experiment investigated the feasibility and the efficacy of the MBGS process for the treatment of natural lake water in a continuous-flow tubular reactor. The average removal efficiencies of COD, NH4+-N, NO3--N, NO2--N, TN, PO43--P, TP, and turbidity by MBGS system in the day/night cycles were 50.10/61.39%, 63.52/75.23%, 43.37/73.57%, 90.72/93.48%, 78.30/80.02%, 71.13/74.62%, 65.08/70.57%, 92.32/89.84%, respectively. As the experiment progressed, the total chlorophyll content in MBGS decreased as the granule size increased, while the extracellular polymeric substances content increased, suggesting that the lake water contributed to bacterial growth and favored the stability of MBGS. Moreover, the eukaryotic microorganisms were dominated by Chlorophyta and Rotifera, and prokaryotic microorganisms were dominated by Proteobacteria in MBGS. By promoting the decomposition of various organic compounds in the lake water and inhibiting sludge expansion, these microorganisms help the MBGS system to maintain excellent granular characteristics and performance. Overall, the MBGS system proved to be a feasible option for the remediation of natural lake waters.

Solvent Minimized Synthesis of Amides by Reactive Extrusion.

Herein, we report on the translation of a small scale ball-milled amidation protocol into a large scale continuous reactive extrusion process. Critical components to the successful translation were: a) understanding how the different operating parameters of a twin-screw extruder should be harnessed to control prolonged continuous operation, and b) consideration of the physical form of the input materials. The amidation reaction is applied to 36 amides spanning a variety of physical form combinations (liquid-liquid, solid-liquid and solid-solid). Following this learning process, we have developed an understanding for the translation of each physical form combination and demonstrated a 7-hour reactive extrusion process for the synthesis of an amide on 500 gram scale (1.3 mols of product).

Stable and Versatile Pd Precursors for the Preparation of Robust Pd Catalysts under Continuous-Flow.

The chemical and engineering communities require the development of versatile precursors that can be used to synthesize robust catalysts to achieve global sustainability. To meet this demand, we developed a new Pd precursor for incorporating fine Pd metal into supports in a highly efficient manner. An atmospherically stable Pd precursor (Pd-80) was prepared by the thermally promoted aerobic oxidation of tetrakis(triphenylphosphine)palladium. The physical properties of Pd-80 were investigated using NMR spectroscopy, SEM, XPS, solvent-relaxation NMR spectroscopy, and dynamic light scattering (DLS) experiments. We also prepared a cordierite-supported Pd catalyst (Pd/cordierite) by stirring Pd-80 and cordierite powder in chloroform at room temperature. Pd/cordierite selectively catalyzes the hydrogenation of various reducible functional groups, including alkynes, azides, nitro groups, olefins, CO2Bn, N-Cbz, O-Bn, aromatic ketones, and styrene oxide, in continuous-flow hydrogenation reactions. The Pd/cordierite-catalyzed continuous-flow hydrogenation of nitrobenzene derivatives afforded the corresponding anilines, with catalyst activity maintained for over 250 h of continuous operation and a turnover number (TON) of 61,090 recorded.

Photosensitizer-Free Benzo[1,4]oxazin-2-one Synthesis by Continuous-Flow Photochemistry.

We report a photosynthetic method for producing 2H-benzo[b][1,4]oxazin-2-ones from aryl azides and α-ketoacids. This method is highly sustainable, requiring only visible light irradiation of the substrates and no external additives. Furthermore, we implemented a continuous-flow system to achieve efficient light irradiation and rapid mixing, significantly improving reaction efficiency and reducing reaction time compared to the batch process. The flow system enabled gram-scale synthesis. We also demonstrated the utility of the products, by employing the benzo[1,4]oxazin-2-one moiety as a directing group for C-H activation on the 3-aryl substituent. This green approach highlights the potential for developing environmentally friendly synthetic processes.

Fibrous catalyst based on atomic Pd and N-doped holey graphene functionalized cotton fiber for continuous-flow reaction.

Continuous-flow catalysis bridges the gap between bench-scale laboratories and production-scale factories and thus should be a green and promising technology for the manufacture of value-added chemicals. Here, we present the construction of a continuous-flow catalytic system by integrating a tubular reactor with novel catalytic fibers, which are comprised of single-atomic Pd (Pd1) and nitrogen-doped holey graphene (NHG) functionalized cotton fibers (CFs). Due to the loosely packed structure, highly exposed dual-active sites (i.e., single-atomic PdN4 sites and activated C sites in the NHG carbocatalyst) of the CF@(Pd1/NHG) catalytic fibers, the corresponding flowing system exhibites remarkably high catalytic performance (activity and durability) and processing rate in organic reactions, including oxidative hydroxylation of phenylboronic acid and reduction of nitroarenes. Typically, the processing rate of the catalytic system toward 4-nitrophenol (a representative nitroarene) reduction can reach up to 2.46 × 10-3 mmol·mg-1·min-1, significantly higher than that of those packing catalysts reported in recent years.

Isolation of ß-O-4-rich lignin from Birch in high yields enabled by continuous flow supercritical water treatment.

The continuous flow supercritical water (scH2O) treatment of Birch wood (T = 372-382 °C; t = 0.3-0.7 s; p = 260 bar) followed by alkali extraction of lignin allowed for the isolation of lignin and lignin carbohydrate complexes (LCCs) with a high number of ß-O-4 moieties in the range 29-57/100 Ar (evaluated by quantitative 13C NMR analysis) in yields ranging between 13-19 wt% with respect to the initial wood. A "lightning rod effect" of carbohydrates has been claimed to explain the low degradation of ß-O-4 bonds during the process. The structure of the isolated lignin was thoroughly elucidated via comprehensive NMR studies (HSQC, 13C and 31P). A low degree of condensation (DC) < 5% was found for all the lignin samples, which was only slightly dependent on the reaction severity. The number of aliphatic -OH, phenolic -OH, and -COOH groups was in the range 3.37-5.25, 1.41-2.31 and 0.39-0.73 mmol/g, respectively. The number of -COOH groups increased with increased severity, suggesting that oxidation can occur during the scH2O treatment. Furthermore, by simply varying the reaction severity, it was possible to tune important lignin properties, like the molar mass and the glass transition temperature (Tg).

Electrooxidative C(sp3)‒H Cyanation of Sparteine and Lupanine in Undivided Batch and Continuous-Flow Cells.

Sparteine is widely used as a chiral ligand in asymmetric synthesis, but methods for providing efficient access to functionalized sparteine derivatives are still limited. Herein, we describe an electrochemical α-cyanation of sparteine-type bis-quinolizidine alkaloids. This method features commercially available setups for batch and single-pass continuous flow conditions, enabling easy gram scale synthesis of valuable racemic and enantiopure products. Moreover, insights into the selectivity of the reaction and overoxidation mechanisms are disclosed. This allows for the development of divergent oxidation pathways depending on the electrolysis conditions.

Formation to Transportation: En-Route Fission-Facilitated Formation of Spheres in a Phosphorus-Based Porous Organic Polymer for Transportation of Iodine.

Despite its potential as a clean power source to meet rising electricity demands, nuclear energy generates radioactive waste, including isotopes of iodine, that pose significant environmental and health risks. There is a growing demand to capture radioactive iodine and repurpose it effectively. However, achieving this dual functionality with a single material remains a significant challenge. This study explores phosphorus-based porous organic polymers (P-POPs) as probes for these dual functionalities. By employing 4-formyl(triphenyl)phosphine (BB1) and phenyl-1,4-diacetonitrile (BB2) under the Knoevenagel polycondensation method, P-POPs (PKPOPs) have been synthesized that exhibit a smooth spherical morphology, which efficiently captures and release iodine under ambient conditions, facilitating efficient transportation of molecular iodine. This novel approach aims to potentially transform nuclear waste into valuable organic feedstock via an iodination reaction. The innovative application of PKPOP has also been demonstrated for iodination reactions using ball mills and under continuous flow conditions, showcasing its potential for safer waste management and utilization.