Machine assisted reaction optimization: A self-optimizing reactor system for continuous-flow photochemical reactions

A methodology for the synthesis of oxetanes from benzophenone and furan derivatives is presented. UV-light irradiation in batch and flow systems allowed the [2 + 2] cycloaddition reaction to proceed and a broad range of oxetanes could be synthesized in manual and automated fashion. The identification of high-yielding reaction parameters was achieved through a new self-optimizing photoreactor system.     

Self-optimizing Diffusion Quantum Monte Carlo Calculation: the Potential Energy Curve of C_2

11NTRODUCTIONDiffusionquantumMonteCarlo(DMC)isoneofthesimplestofthevariousMonteCarlotechniquesavailabletosolvetheSchrodingerequation,forarecentre-viewofDMC(seeRef[1i).Foravarietyofsmallatomsandmolecules,DMChasbeenshowntobecapableofprovidinganestimateoftheground-state(nonrelativistic)energywithanaccuracycomparabletogoodqualityClcalculations,evenwhenarelativelysimpletrialwavefunctionisemployed.However,todate,thereareseveralobstaclesinaDMCcalculation:(1)BeforetheDMCcomputation,thepar…     

Greener Synthesis of Pristane by Flow Dehydrative Hydrogenation of Allylic Alcohol Using a Packed-Bed Reactor Charged by Pd/C as a Single Catalyst

Our previous work established a continuous-flow synthesis of pristane, which is a saturated branched alkane obtained from a Basking Shark. The dehydration of an allylic alcohol that is the key to a tetraene was carried out using a packed-bed reactor charged by an acid–silica catalyst (HO-SAS) and flow hydrogenation using molecular hydrogen via a Pd/C catalyst followed. The present work relies on the additional propensity of Pd/C to serve as an acid catalyst, which allows us to perform a flow synthesis of pristane from the aforementioned key allylic alcohol in the presence of molecular hydrogen using Pd/C as a single catalyst, which is applied to both dehydration and hydrogenation. The present one-column-two-reaction-flow system could eliminate the use of an acid catalyst such as HO-SAS and lead to a significant simplification of the production process.     

Continuous‐Flow Synthesis and Derivatization of Aziridines through Palladium‐Catalyzed C(sp3)−H Activation

A continuous‐flow synthesis of aziridines by palladium‐catalyzed C(sp³)?H activation is described. The new flow reaction could be combined with an aziridine‐ring‐opening reaction to give highly functionalized aliphatic amines through a consecutive process. A predictive mechanistic model was developed and used to design the C?H activation flow process and illustrates an approach towards first‐principles design based on novel catalytic reactions.     

Generation and reactions of oxiranyllithiums by use of a flow microreactor system

A flow microreactor system consisting of micromixers and microtubes provides an effective reactor for the generation and reactions of aryloxiranyllithiums without decomposition by virtue of short residence time and efficient temperature control. The deprotonation of styrene oxides with sBuLi can be conducted by using the flow microreactor system at -78 or -68 °C (whereas much lower temperatures (< -100 °C) are needed for the same reactions conducted under macrobatch conditions). The resulting α-aryloxiranyllithiums were allowed to react with electrophiles in the flow microreactor system at the same temperature. The sequential introduction of various electrophiles onto 2,3-diphenyloxiranes was also achieved by using an integrated flow microreactor, which serves as a powerful system for the stereoselective synthesis of tetrasubstituted epoxides.     

Batch and Flow Synthesis of CeO2 Nanomaterials Using Solid-State Microwave Generators

Microwave-assisted synthesis in combination with flow synthesis offers an interesting approach to develop faster and more sustainable procedures for the preparation of homogeneous nanomaterials. Recently, solid-state generators of microwaves appeared as a tool with improved control over power and frequency. Cerium oxide, despite its excellent catalytic activity, has not been prepared before using solid-state generators or microwave-assisted flow chemistry. We report a procedure for the preparation of nanoparticulated CeO₂ (around 4 nm) under 2.45 GHz microwaves in only 30 s. The materials are further calcined at 800 °C to increase particle size, with a better defined particle size and crystallinity. The procedure was tested in batch at pH 11 and 12 and diverse potencies, and the products were characterized by TEM, XRD, DLS, and N₂ adsorption–desorption isotherms. The materials were similar at the diverse pH values and potencies. XRD confirms the crystallinity of the CeO₂ material with a fluorite-like structure. They are composed of particles around 40 nm that aggregate as structures of around 100 nm. The procedure was successfully adapted to flow synthesis, obtaining materials with structure and properties equivalent to batch synthesis. The batch and flow materials offer peroxidase properties, opening the door for their use as ROS scavengers.     

Phase formation and structural characteristics of Cd-Pb-S nanopowder compositions produced by modification of CdS powder in a citrate-ammonia solution of a lead salt

Nanopowders obtained by modification of a cadmium sulfide powder in a citrate-ammonia solution of lead acetate have been studied by X-ray diffraction, electron microscopy, and thermal analysis. The type of crystal structure and composition of Cd-Pb-S nanopowders depend on the conditions of their synthesis. The thermoanalytical curves show a well-defined endotherm in the temperature range 284–321°C. The position of this endotherm depends on the duration of contact of a CdS powder with an aqueous solution of a lead salt. Heating nanopowders to 600°C in an argon flow leads to formation of oxygen-containing phases: lead sulfate and cadmium oxide.     

A Modular Flow Design for the meta‐Selective C−H Arylation of Anilines

Described herein is an effective and practical modular flow design for the meta ‐selective C−H arylation of anilines. The design consists of four continuous‐flow modules (i.e., diaryliodonium salt synthesis, meta ‐selective C−H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta ‐arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances.     

Flow‐Assisted Synthesis of [10]Cycloparaphenylene through Serial Microreactions under Mild Conditions

Cycloparaphenylene (CPP) has been recognized as an attractive template for the bottom‐up synthesis of carbon nanotubes with uniform diameter, and is important for the chemistry of graphitic as well as ring‐shaped macromolecules. However, the reported routes from halogenated benzenes have suffered from low yields even under time‐ and labor‐consuming multistep conditions. Herein we report a flow‐assisted synthesis of [10]CPP in four steps under mild conditions. For the synthesis, a selective nucleophilic addition of the unprotected diketone without the double‐added byproduct was achieved within 3 s in high yield. Subsequently, the obtained compound was reacted with dilithiated benzene at 25 °C to form a U‐shaped precursor for CPP in a separate microreactor, which was finally dimerized and aromatized to obtain [10]CPP by a two‐step in‐flask reaction. Precise control of time and flow facilitated by the flow‐assisted system enabled the development of an efficient synthetic route for [10]CPP.     

Development of a Fully Continuous-Flow Approach Towards Asymmetric Total Synthesis of Tetrahydroprotoberberine Natural Alkaloids

Continuous flow synthetic technologies had been widely applied in the total synthesis in the past few decades. Fully continuous flow synthesis is still extremely focused on multi-step synthesis of complex natural pharmaceutical molecules. Thus, the development of fully continuous flow total synthesis of natural products is in demand but challenging. Herein, we demonstrated the first fully continuous flow approach towards asymmetric total synthesis of natural tetrahydroprotoberberine alkaloids, (−)-isocanadine, (−)-tetrahydropseudocoptisine, (−)-stylopine and (−)-nandinine. This method features a concise linear sequence involving four chemical transformations and three on-line work-up processing in an integrated flow platform, without any intermediate purification. The overall yield and enantioselectivity of this four-step continuous flow chemistry were up to 50 % and 92 %ee, respectively, in a total residence time of 32.5 min, corresponding to a throughput of 145 mg/h.     

A protecting group free synthesis of (+/-)-neostenine via the [5 + 2] photocycloaddition of maleimides

A concise, linear synthesis of the Stemona alkaloid (+/-)-neostenine is reported. Key features include an organocopper-mediated bislactone C2-desymmetrization for the stereoselective construction of the cyclohexane-lactone C,D-rings. The assembly of the fused pyrrolo[1,2-a]azepine core was achieved by application of a [5 + 2] maleimide photocycloaddition. A custom FEP flow reactor was used to successfully overcome the scale limitations imposed by a classical immersion well batch reactor. The synthesis was completed in 14 steps from furan, in 9.5% overall yield, without the use of any protecting groups.     

An Immobilized‐Dirhodium Hollow‐Fiber Flow Reactor for Scalable and Sustainable C−H Functionalization in Continuous Flow

A scalable flow reactor is demonstrated for enantioselective and regioselective rhodium carbene reactions (cyclopropanation and C?H functionalization) by developing cascade reaction methods employing a microfluidic flow reactor system containing immobilized dirhodium catalysts in conjunction with the flow synthesis of diazo compounds. This allows the utilization of the energetic diazo compounds in a safe manner and the recycling of the dirhodium catalysts multiple times. This approach is amenable to application in a bulk‐scale synthesis employing asymmetric C?H functionalization by stacking multiple fibers in one reactor module. The products from this sequential flow–flow reactor are compared with a conventional batch reactor or flow–batch reactor in terms of yield, regioselectivity, and enantioselectivity.     

From p-Xylene to Ibuprofen in Flow: Three-Step Synthesis by a Unified Sequence of Chemoselective C−H Metalations

Ibuprofen was prepared from an inactive and inexpensive p-xylene by three-step flow functionalizations through chemoselective metalations of benzyl positions in sequence using an in situ generated LICKOR-type superbase. The flow approach in the microreactor facilitated the comprehensive exploration of over 100 conditions in the first-step reaction by varying concentrations, temperatures, solvents, and equivalents of reagents, enabling optimal conditions to be found with 95 % yield by significantly suppressing the formation of byproducts, followed by the second C−H metalation step in 95 % yield. Moreover, gram-scale synthesis of ibuprofen in the final step was achieved by biphasic flow reaction of solution-phase intermediate with CO₂, isolating 2.3 g for 10 min of operation time.     

Effect of Potassium Promotion on the Formation of a Fe/C<Subscript>act</Subscript> Catalyst in the Course of Reduction in CO and CO/H<Subscript>2</Subscript>

The process of formation of a Fe/C catalyst was considered as a sequence of topochemical reactions. It was demonstrated that potassium promotion accelerated the formation of magnetite at the stage of catalyst calcination in a flow of argon. The particle size of iron oxides decreased with the concentration of potassium. Potassium promotion also led to an increase in the concentration of Hägg carbide in the course of catalyst reduction by synthesis gas.     

Synthesis and characterization of 3-phenylethynyl endcapped matrix resins

The synthesis of 3-phenylethynylphenol, and its applicability as a high temperature cross-linking endcap for high T_g polyarylene ethers is described. It was synthesized in high yields and purity using the palladium catalyzed coupling reaction between the protected 3-bromo or iodo phenol and phenylacetylene. The yield of the reaction was found to be highly dependent on the structure of the halide used, the reaction temperature, and the concentration of phenylacetylene. The use of the protected phenol in the palladium catalyzed reaction was also extended to the high yield synthesis of 3-ethynylphenol and protected 4-ethynylphenols. The complete synthesis of 3-phenylethynylphenol, 3-ethynylphenol, and protected 4-ethynylphenol in high yields has been demonstrated and is discussed herein. Three new phenylethynyl functionalized arylene ether matrix resins have been synthesized in high yields and purity by reacting 3-phenylethynylphenol with 4,4′-dichlorodiphenyl sulfone, 4,4′-difluorobenzophenone, and bis(4-fluorophenyl)phenyl phosphine oxide, via nucleophilic poly(arylene ether) synthesis conditions. These low molecular weight materials undergo thermally induced chain extension/branching to yield an insoluble three-dimensional network at reaction temperatures of around 380°C. The low molecular weight arylene ethers endcapped with the phenylethynyl group demonstrate excellent flow characteristics and a wide processing window of about 250°C. Crosslinking of the 4,4′-bis(3-phenylethynyl phenoxy)diphenyl sulfone system for 30 min at 350°C in air afforded a T_g value of 265°C by differential scanning calorimetry measurements. Trace metal analysis for palladium and copper showed absence of these metals that would otherwise detract from the excellent thermal stability. The synthesis and characterization of these phenylethynyl endcapped arylene ether matrix resins is discussed. © 1995 John Wiley & Sons, Inc.     

Heat release during the hydration of calcinated α-C<Subscript>2</Subscript>SH and its mixture with killalaite

In this work, the influence of the mineral composition of the synthesized calcium silicate hydrates on their hydraulic activity after thermal treatment was determined. Primary mixture, consisting of quartz sand and burnt limestone (CaO/SiO₂ = 2), was treated hydrothermally with NaOH additive at 200 °C. It was determined that α-C₂SH prevailed in the product after 4 h of the synthesis. The results of DSC and XRD analysis revealed that α-C₂SH was partially decomposed after 12 h of the synthesis and newly formed compounds were identified—killalaite, portlandite and C–S–H. The products of 4 and 12 h synthesis were treated thermally at temperatures between 450 and 1000 °C. It was determined that dellaite and x-C₂S formed already at 450 °C, β-C₂S at 600 °C and α′_L-C₂S at 800 °C when the 4 h synthesis product, in which α-C₂SH prevailed, was treated thermally. On the other hand, killalaite remained stable up to 600 °C, and the temperature values, at which mentioned calcium silicates formed, increased in case of a 12 h synthesis product. Heat flow values of the main hydration reaction and total heat release exceeded 3.1 mW g^?1 and 140 J g^?1 accordingly in case of the samples in which α-C₂SH prevailed. However, increase in the thermal treatment temperature resulted in a decrease in the mixtures hydraulic activity. It was proved that killalaite formation in the product of the 12 h hydrothermal synthesis vividly decreases its hydraulic activity after the thermal treatment in the temperature range of 450–1000 °C. No increment in the heat flow values that could be attributed to the main hydration reaction (acceleration period) was witnessed in all the curves of the heat flow analysis in this case.     

Conversion of Methane and Carbon Dioxide in a DBD Reactor: Influence of Oxygen

A continuous plug flow reactor supported by a dielectric barrier discharge (DBD) is used to study the conversion of methane, carbon dioxide, and oxygen at different compositions. The three studied gases were diluted with helium to 3 % with an overall flow rate of 200 sccm. The 13.56 MHz plasma was ignited at atmospheric pressure. The product stream and the inlet flow were analyzed by a FTIR spectrometer equipped with a White-cell and by a quadrupole mass spectrometer. The DBD reactor generates hydrogen, carbon monoxide, ethane, ethene, acetylene, formaldehyde, and methanol. Additional oxygen in the feed has positive effects on the yield of methanol, formaldehyde and carbon monoxide and reduces the total consumed energy. The hydrogen yield reaches its maximum at medium amounts of oxygen in the inlet flow. The conversion of methane increases to a limiting value of about 35 %. Methane rich feeds increase the yield of hydrogen, ethane and methanol. On the other hand, additional oxygen has a negative influence on the produced amount of C2 hydrocarbons. The conversion of methane and carbon dioxide as well as the yield of synthesis gas components and C2 hydrocarbons increases by changing the plasma power to higher values.     

量子相干控制化学反应的进展和机遇

1995年,人们曾预言"量子控制多体动力学将成为化学物理的主流"(引自第20届Solvay化学会议上Stuart A.Rice的主旨演说.Solvay会议是研讨未来科学的高级会议.这一届会议的主题是"光化学: 化学反应及其飞秒尺度上的控制"). 现在, 我们看到了这股潮流正源源而来,每年都不断地在Nature、 Science等杂志上刻下了里程碑.     

Thermal degradation of CTAB in as-synthesized MCM-41

Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal surfactant degradation outside and inside pores were identified at various temperatures using ¹³C solid-state nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and ¹³C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41 synthesis on molecular level.     

Exact Fixed-node Quantum Monte Carlo： Self-optimizing Procedure

In this paper, a novel exact fixed-node quantum Monte Carlo (EFNQMC) algorithm was proposed, which is a self-optimizing and self-improving procedure. In contrast to the previous EFN-QMC method, the importance function of this method is optimized synchronistically in the diffusion procedure, but not be-fore beginning the EFNQMC computation. In order to optimize the importance function, the improved steepest descent tech-nique is used, in which the step size is automatically adjustable.The procedure is quasi-Newton type and converges super linear-ly. The present method also uses a novel trial function, which has correct electron-electron and electron-nucleus cusp condi-tious. The novel EFNQMC algorithm and the novel trial func-tion are employed to calculate the energies of 1 ^1A1 state of CH2, ^1Ag state of Cs and the ground-states of H2, LiH, Li2 and H2O.