Copper-Mediated Radical Cyclopropanation of Activated Alkenes under Continuous-Flow Conditions.

The mobility of azoxystrobin in sandy loam soil was studied under continuous and discontinuous flow conditions in soil columns under laboratory conditions at two application rates (50 and 100 μg), with simulated rainfall of 300 mm. Residues of azoxystrobin in soil and leachate were estimated by gas-liquid chromatography and confirmed by gas chromatography-mass spectrometry. Though maximum concentration of azoxystrobin was found in the top 10 cm layer under both continuous and discontinuous flow conditions but azoxystrobin residues under continuous flow conditions were recorded down to a depth of 15-20 cm and under discontinuous flow conditions residues, were recorded at depths of up to 20 and 25 cm for the single and double dose treatments, respectively. The retention of azoxystrobin residues was greater under continuous flow conditions at the higher dose, whereas a low retention of azoxystrobin residues at the lower dose and under discontinuous flow conditions was observed. The low mobility of azoxystrobin in soil indicated that it represents a low risk to groundwater systems. Leachate fractions were free from azoxystrobin residues.   Key words: Leaching, azoxystrobin, sandy loam soil, column, residues.

Abstract: Active methylene and methyne compounds can bechemoselectively brominated in high yields using potassiumbromide, hydrochloric acid, and hydrogen peroxide at room temper-ature. Key words: halogenation, halaides, green chemistry, bromination,active methylene compounds Halogenated active methylene and methyne compoundsare very important synthetic intermediates for the nucleo-philic substitutions in synthetic organic chemistry. Theclassical methods of halogenation of active methylene andmethyne compounds 1 are the reaction with bromine 1 orsulfuryl chloride, 2 however, they suffer from drawbackssuch as toxicity of the reagents, generation of acidicgasses after the reaction, or overhalogenation of thearomatic rings in 1 . Although a number of new methodsof this transformation have previously been developed,most of them have severe disadvantages such as theproduction of undesirable waste. 3–5 Khan and co-workers recently developed chemoselectivebromination of active methylene compounds by employ-ing the vanadium pentoxide catalyzed (V

Two trifluoromethyl-substituted building blocks β-(trifluoromethyl)vinyl sulfonium salts 1 and 2 were developed. Reactions of β-(trifluoromethyl)vinyl sulfonium salt 1 with active methylene compounds containing electron-withdrawing groups using DBU as the base in DMSO occurred to give trifluoromethyl-substituted cyclopropane derivatives 7 as the major products. In contrast, reactions of β-(trifluoromethyl)vinyl sulfonium salt 2 with active methylene compounds occurred with the migration of one of the electron-withdrawing groups to give the products 8 as the major products when NaH was used as the base in DMSO. Moreover, when NaH was used as base in THF/CH(2)Cl(2) at -78 °C, reaction of β-(trifluoromethyl)vinyl sulfonium salt 1 gave trifluoromethyl-substituted 2,3-dihydrofuran derivatives 9 as the major products. A working mechanism was proposed to explain the different behaviors of the β-(trifluoromethyl)vinyl sulfonium salts 1 or 2 with active methylene compounds under these different conditions.

Epoxidation of Crotyl Alcohol Using Ti-Containing Heterogeneous Catalysts: Comments on the Loss of Ti by Leaching

An efficient method for the synthesis of functionalized 4H‐chromenes via a one‐pot three‐component condensation reaction of a 2‐hydroxybenzaldehyde with an active methylene compound and a carbon‐based nucleophile in the presence of a catalytic amount of ZrOCl2·8H2O in water under thermal condition has been described. High yields, simple work‐up procedure, performing reactions in water and synthesis of complex molecules with a one‐pot procedure are the main advantages of this procedure. In addition, the structure of the product from the condensation of salicylaldehyde, 2‐naphthol, and dimedone was confirmed by X‐ray crystallography.

The sulfonic acid functionalization of sufficiently electron-deficient benzene sulfonic acids undergoes ipso nucleophilic substitution with various active methylene compounds, leading to new C-C bond formation. Good to excellent yields are obtained under mild conditions without transition-metal (Pd or Cu) catalyst, PTC, and ligand. No solid waste is generated. It is a highly effective strategy for incorporating various active methylene compounds into the o-nitro-substituted benzene ring. This method has been applied not only for synthesizing APIs but also in materials chemistry. It shows a novel route for creating heavily crowded all-carbon quaternary centers. Carbon-carbon bond formation by substituting a sulfonic acid group was unknown.

Effects of flow interruption on transport and retention of iron oxide colloids in quartz sand

The use of a polymer inclusion membrane for separation and preconcentration of orthophosphate in flow analysis

Background: Simple and efficient method has been developed for the Knoevenagel condensation of novel 3-chloro-3-(4-oxo-4H-pyrido[1,2-a]pyrimidin-3yl)acrylaldehyde (5) with active methylene compounds such as malononitrile (6), 3-methyl-1-phenyl-pyrazole-5(4H)-one (7), 3-methyl-1Hpyrazole- 5(4H)-one (8), Meldrum’s acid (9), Barbituric acid (10) and 4-hydroxycoumarin (11) by stirring in ethanol at room temperature for 2 h in the presence of L-proline as a catalyst yielding the products 12a, b to 17a, b respectively. Methods: In this article, we reported a new synthesis of 3-chloro-3-(4-oxo-4H-pyrido[1,2-a]pyrimidin- 3yl)acrylaldehyde (5) which was prepared from the 2-aminopyridine 1 condensed with ethyl ethoxymethyleneacetoacetate (2) in ethanol under refluxing conditions for 4 h giving a product which has been characterized as ethyl 3-oxo-2-((pyridin-2-ylamino)methylene)butanoate 3 on the basis of its spectral data. On thermal cyclization, in diphenyl ether for 30 min at 255oC, 3a gave a product 4. Vilsmeier-Haack formylation of 4 at RT for 4 h gave a product 5. Condensation of 5 with malononitrile, 3-methyl-1-phenyl-pyrazole-5(4H)-one, 3-methyl-1H-pyrazole-5(4H)-one, Meldrum’s acid, Barbituric acid and 4-hydroxycoumarin (11) by stirring in ethanol at room temperature for 2 h in the presence of L-proline as a catalyst yielding the products 12a, b to 17a, b respectively. Result: A novel preparation of 3-chloro-3-(4-oxo-4H-pyrido[1,2-a]pyrimidin-3yl)acrylaldehyde (5) method is reported in this article, along with the condensation of 5 with various active methylene compounds by stirring in ethanol at room temperature for 2 h in the presence of L-proline as a catalyst yielding the products 12a, b to 17a, b respectively. The structures of the synthesized compounds were confirmed by 1H-NMR, 13C-NMR, GC-MS and IR spectral data. All of the intermediates were structurally characterized IR (KBr): 1747 and 1697 cm-1 (strong, sharp of absorptions due to the -CHO and -N-CO-). 1H-NMR (DMSO-d6/TMS): δ 7.4-7.8 (t, 3H, Ar-H), 8.7 (s, 1H, α-H to the enamine nitrogen), 9.2 (q, pyridine ring proton), 10.2 (s, 1H, -CHO). LC-MS (HR-MS): m/z 235.0271, [(C12H14N2O3) +H]+. Conclusion: In conclusion, L-proline has been employed as an efficient catalyst for the preparation of a simple, efficient method for the synthesis of condensed compounds and a novel synthetic route to 3- chloro-3-(4-oxo-4H-pyrido[1, 2-a]pyrimidin-3yl)acrylaldehyde(5), whose condensation with active methylene compounds (6-11) reactions at RT, led to products 12-17. Keywords: Active methylene compounds, Knoevenagel condensation, L-proline, Pyridopyrimidines, Vilsemeier-Haack formylation.

Fischer–Tropsch synthesis: Iron-based catalysts supported on nitrogen-doped carbon nanotubes synthesized by post-doping

Solution combustion synthesis of zirconia-stabilized calcium oxide sorbents for CO2 capture

Cyclopropanes are prevalent in natural products, pharmaceuticals, and bioactive compounds, functioning as a significant structural motif. Although a series of methods have been developed for the construction of the cyclopropane skeleton, the development of a direct and efficient strategy for the rapid synthesis of cyclopropanes from bench‐stable starting materials with a broad substrate scope and functional group tolerance remains challenging and highly desirable. Herein, we present an electrochemical method for the direct cyclopropanation of unactivated alkenes using active methylene compounds. The strategy shows a broad substrate scope with a high level of functional group compatibility, as well as potential application as demonstrated by late‐stage cyclopropanation of complex molecules and drug derivatives. Further mechanistic investigations suggest that Cp2Fe (Fc) plays an essential role as an oxidative mediator in generating radicals from active methylene compounds.

Cyclopropanes are prevalent in natural products, pharmaceuticals, and bioactive compounds, functioning as a significant structural motif. Although a series of methods have been developed for the construction of the cyclopropane skeleton, the development of a direct and efficient strategy for the rapid synthesis of cyclopropanes from bench-stable starting materials with a broad substrate scope and functional group tolerance remains challenging and highly desirable. Herein, we present an electrochemical method for the direct cyclopropanation of unactivated alkenes using active methylene compounds. The strategy shows a broad substrate scope with a high level of functional group compatibility, as well as potential application as demonstrated by late-stage cyclopropanation of complex molecules and drug derivatives. Further mechanistic investigations suggest that Cp2Fe (Fc) plays an essential role as an oxidative mediator in generating radicals from active methylene compounds.

In the pulmonary circulation, resistive and compliant properties overlap in the same vessels. Resistance varies nonlinearly with pressure and flow; this relationship is driven by the elastic properties of the vessels. Linehan et al. correlated the mean pulmonary arterial pressure and mean flow with resistance using an original equation incorporating the distensibility of the pulmonary arteries. The goal of this study was to validate this equation in an in vivo porcine model. In vivo measurements were acquired in 6 pigs. The distensibility coefficient (DC) was measured by placing piezo-electric crystals around the pulmonary artery (PA). In addition to experiments under pulsatile conditions, a right ventricular (RV) bypass system was used to induce a continuous pulmonary flow state. The Linehan et al. equation was then used to predict the pressure from the flow under continuous flow conditions. The diameter-derived DC was 2.4%/mmHg (+/-0.4%), whereas the surface area-based DC was 4.1 %/mmHg (+/-0.1%). An increase in continuous flow was associated with a constant decrease in resistance, which correlated with the diameter-based DC (r=-0.8407, p=0.044) and the surface area-based DC (r=-0.8986, p=0.028). In contrast to the Linehan et al. equation, our results showed constant or even decreasing pressure as flow increased. Using a model of continuous pulmonary flow induced by an RV assist system, pulmonary pressure could not be predicted based on the flow using the Linehan et al. equation. Measurements of distensibility based on the diameter of the PA were inversely correlated with the resistance.

A novel heating efficiency analysis of the microwave heated stop-flow (i.e. stagnant liquid) and continuous-flow reactors has been presented. The thermal losses to the surrounding air by natural convection have been taken into account for heating efficiency calculation of the microwave heating process. The effect of the load diameter in the range of 4–29 mm on the heating efficiency of ethylene glycol was studied in a single mode microwave cavity under continuous flow and stop-flow conditions. The variation of the microwave absorbing properties of the load with temperature was estimated. Under stop-flow conditions, the heating efficiency depends on the load diameter. The highest heating efficiency has been observed at the load diameter close to the half wavelength of the electromagnetic field in the corresponding medium. Under continuous-flow conditions, the heating efficiency increased linearly. However, microwave leakage above the propagation diameter restricted further experimentation at higher load diameters. Contrary to the stop-flow conditions, the load temperature did not raise monotonously from the inlet to outlet under continuous-flow conditions. This was due to the combined effect of lagging convective heat fluxes in comparison to volumetric heating. This severely disturbs the uniformity of the electromagnetic field in the axial direction and creates areas of high and low field intensity along the load length decreasing the heating efficiency as compared to stop-flow conditions.