Chain-radical fluoroalkylation of thiophenols with freon ClCF2CFCl2 in the presence of sulfur dioxide

A polyfluoroalkylation of thiophenols with CF₂ClCFCl₂ using substituted pyridine-sulfur dioxide system enables to obtain fluoroalkylated thioethers by a S_RN1-type free-radical route.     

Sodium dithionite initiated fluoroalkylation of trimethoxybenzenes, mesitylene and pyrroles with BrCF2CF2Br

Sodium dithionite initiated reaction of 1,2-dibromotetrafluoroethane with 1,3,5-trimethoxybenzene (1a) in an acetonitrile-water mixture proceeded efficiently at ambient temperature to give 1-(2-bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2) almost quantitatively. Similar reaction with 1,2,3-trimethoxybenzene (1b) gave only reasonable yield of regioisomers of (2-bromotetrafluoroethyl)-trimethoxybenzenes 3 and 4 and small amount of a substitution product of the central trimethoxy group, 1-(2-bromotetrafluoroethyl)-2,6-dimethoxybenzene (5). The reaction with mesitylene (6) gave complex mixtures from which, depending on the temperature and a mesitylene/BrCF₂CF₂Br ratio, the expected (2-bromotetrafluoroethyl)mesitylene (8) or a dimeric product, 4,4′-bis(2-bromo-1,1,2,2-tetrafluoroethyl)-1,3,5,1′,3′,5′-hexamethylbicyclohexyl-2,5,2′,5′-tetraene (7), were isolated in a yield of 18 and 13%, respectively. The reactions of BrCF₂CF₂Br with pyrrole (9) and 1-methylpyrrole (11) gave the respective alkylated compounds, 2-(2-bromotetrafluoroethyl)pyrrole (10) and 2-(2-bromotetrafluoroethyl)-1-methylpyrrole (12) in over 70% yields; the former was found to be fairly unstable. The reactivity of the terminal bromine atom in 1-(2-bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2) was also investigated.     

Condensation of CF2Br2, CF2BrCl and BrCF2CF2Br with enamines and ynamines

BrCF₂X (X : Cl, Br, BrCF₂) react wth enamines and ynamines. A radical chain mechanism is proposed. Halogen (Br or Cl) - fluorine exchange of α halodifluoromethylketones to α trifluoromethylketones using Bu₄⁺N, F^?, 3H₂O is examined.     

Pyrrole synthesis using a tandem Grubbs’ carbene-RuCl3 catalytic system

A straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs’ catalyst (10%) followed by dehydrogenation in the presence of RuCl₃ × H₂O (2%).     

Development and validation of passive samplers for atmospheric monitoring of SO2, NO2, O3 and H2S in tropical areas

Traditionally the monitoring of atmospheric pollutants is aimed at managing accidents and short-term actions for the protection of human health on local and regional scales. These monitoring networks required continuous measurements with high time resolution, involving costly equipment, operation and maintenance. More recent simulations with mathematical models and scenario-building on regional, continental and global scales, as well as studies of environmental personal exposure are demanding three main types of monitoring design, where need for special resolution surpasses the one of temporal resolution: remote places, where no electric power nor trained human resources are available; validation of dispersion simulation by mathematical modeling on regional to larger scales; indoor measurements where people are acting under noise restriction such as residences, school and hospitals. To meet these demands environmental passive samplers for atmospheric gaseous pollutants have been developed and applied for different situations and environments of Brazil. Passive samplers were developed based on molecular diffusion of gas through a static layer of air with fixed filters impregnated with a specific solution for SO₂, NO₂, O₃ and H₂S and used in the following situations: in remote forest area, urban areas with different characteristics - near the sea, with clean ocean air masses coming in and in areas under direct industrial influence. The passive samplers showed good performance when exposed to different types of areas and during different periods: accuracy of measurements, based on standard deviation, were within the recommended limit by the European Union of ± 25% for this type of device and precision below the maximum of 20% cited in the literature, with variation of 2.0 to 16% in the case of these work. The passive devices were able of measuring concentrations very low as those found in the Amazon region (0.58 ± 0.05 µg m^− 3 SO₂ and 1.10 ± 0.07 µg m^− 3 NO₂) and higher concentrations in industrial areas (20.0 ± 1.3 µg m^− 3 SO₂ e 21.0 ± 1.3 µg m^− 3 NO₂).     

Novel synthesis of meso-tetraarylporphyrins using CF3SO2Cl under aerobic oxidation

meso-Tetraarylporphyrins are synthesized from pyrrole and aryl aldehydes cleanly and efficiently in one pot at room temperature using equimolar amount of CF₃SO₂Cl in the presence of air as oxidant. By this novel method 5,10,15,20-tetraarylporphyrins can be prepared in excellent yields.     

Reductive sulfur extrusion reaction of 2,1,3-benzothiadiazole compounds: a new methodology using NaBH4/CoCl2·6H2O(cat) as the reducing system

A new simple and efficient methodology for reductive sulfur extrusion from 2,1,3-benzothiadiazole compounds has been developed using NaBH₄ in the presence of catalytic amounts of CoCl₂·6H₂O (1 mol %). This method is an efficient alternative for the generation of various 1,4-disubstituted-2,3-diaminobenzene derivatives from 4,7-disubstituted-2,1,3-benzothiadiazoles. The diamines can be easily converted into 4,7-disubstituted-quinoxaline compounds by simple reaction with glyoxal-sodium bisulfite.     

Study on the catalytic reduction mechanism of SO2 by CO over doped copper perovskite catalyst in presence of oxygen

Summary The reduction mechanism of SO₂ by CO using LaCoO₃ and doped copper as catalysts was investigated. The activity, selectivity of sulfur and the COS amount under various reaction conditions were tested. The results showed that the Cu doped catalysts were better than the undoped catalyst and 10% copper-doping gave the optimum catalyst.     

Photocatalytic degradation of organic dyes on visible-light responsive photocatalyst PbBiO2Br

The layered compound of lead bismuth oxybromide PbBiO₂Br, prepared by conventional solid-state reaction method, has an optical band gap of 2.3 eV, and possesses a good visible-light-response ability. The references, PbBi₂Nb₂O₉, TiO_2−xN_x, BiOBr and BiOI_0.8Cl_0.2, which are excellent visible-light-response photocatalysts, were applied to comparatively understand the activity of PbBiO₂Br. Degradation of methyl orange and methylene blue was used to evaluate photocatalytic activity. The results show that PbBiO₂Br is more photocatalytically active than PbBi₂Nb₂O₉, TiO_2−xN_x and BiOBr under visible light.     

Low-temperature hydrothermal synthesis of S-doped TiO2 with visible light photocatalytic activity

A one-step low-temperature hydrothermal route was developed for the synthesis of S-doped TiO₂ photocatalysts from TiS₂ and HCl. Crystalline TiO₂ was formed and sulfur could be efficiently doped into the anatase lattice under hydrothermal conditions. When the initial TiS₂ concentration is increased, the content of S-dopant and optical absorption in the visible region also increase. The photocatalytic activity of the S-doped TiO₂ was evaluated through the degradation of 4-chlorophenol under visible light irradiation. Our results show that the S-doped TiO₂ prepared by this hydrothermal approach possesses much higher photocatalytic activity than that obtained by the traditional high-temperature thermal annealing method.     

A SO2-selective electrode based on a Zn-porphyrin for wine analysis

This work describes the assessment of a SO₂-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2 mol L⁻¹ diethylamine solution for 24 h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of −59.5 mV dec⁻¹, a practical detection limit of 3.7 × 10⁻⁶ mol L⁻¹ and a low limit of linear range of 7.2 × 10⁻⁶ mol L⁻¹. The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method.     

Free radical (phenylsulfonyl)difluoromethylation of alkynes with PhSO2CF2I reagent: stereoselective preparation of PhSO2CF2- and CF2H-substituted alkenes

Stereoselective free radical (phenylsulfonyl)difluoromethylation of terminal alkynes with iododifluoromethyl phenyl sulfone (PhSO₂CF₂I) has been accomplished by using Et₃B/air as an initiator. The obtained PhSO₂CF₂-substituted vinyl iodides, which can be further subjected to Suzuki coupling and Sonogashira coupling reactions, are useful precursors for the preparation of many structurally diverse PhSO₂CF₂- and CF₂H-substituted alkenes.     

N-Difluoromethylation of imidazoles and pyrazoles using BrCF2PO(OEt)2 under mild condition

A simple and efficient protocol for the direct N-difluoromethylation of imidazoles and pyrazoles has been developed. The reaction makes use of commercially available, non-ozone-depleting and easy handling BrCF₂PO(OEt)₂ as difluorocarbene precursor, and provides a cost-efficient and environmentally benign access to some difluoromethylated biologically relevant molecules.     

Preparation and structure of a ruthenium dicarbonyl derivative of the P2N4S2 ring

The reaction of Ru(CO)₄(C₂H₄) or Ru(CO)₅ with 1,5-Ph₄P₂N₄S₂ in CH₂Cl₂/hexane at 23°C produces the dimer [Ru(CO)₂(Ph₄ P₂N₄S₂)]₂ (2), which was shown by X-ray crystallography to have a centrosymmetric structure in which the P₂N₄S₂ ring is attached to one ruthenium atom through two (geminal) nitrogen atoms and the remote sulfur atom and serves as a bridge to the other ruthenium atom via the second sulfur atom. Crystals of 2 ·2(CH₂Cl₂) are triclinic, space group P (No. 2), a = 12.901(1) Å, b = 13.072(1) Å, c = 10.123(1) Å, = 100.88(1)°, β = 98.90(1)°, γ = 67.50(1)°, V = 1542.4(3) Å, Z = 1 with final R and R_w values of 0.040 and 0.027, respectively.     

Regioselective synthesis of 5-aryl-2-oxazolidinones from carbon dioxide and aziridines using BrPh3PPEG600PPh3Br as an efficient, homogenous recyclable catalyst at ambient conditions

Polyethylene glycol functionalized phosphonium salt (Br⁻Ph₃⁺PPEG₆₀₀P⁺Ph₃Br⁻) was found to be an efficient, homogenous, recyclable catalyst for coupling of CO₂ with a variety of aziridines producing corresponding 5-aryl-2-oxazolidinones with good yields and excellent regioselectivity under relatively mild and solvent free conditions. Furthermore, the catalyst was effectively recycled for four consecutive cycles without any significant loss in its catalytic activity and selectivity.     

Ni/TiO2-SiO2上光催化重整葡萄糖以低CO选择性制H2（英文）

Nano-sized Ni particles on TiO2-SiO2 were synthesized by the two methods of photo-assisted deposition(PAD) and impregnation.H2,which is a promising energy carrier,with a low CO concentration was produced by the photocatalytic reforming of glucose(a model biomass) on the Ni/TiO2-SiO2 catalyst.The supported Ni enhanced the rate of H2 production while it suppressed CO selectivity.The catalysts were characterized by X-ray diffraction,X-ray absorption fine structure,transmission electron microscope,and nitrogen adsorption analysis.Both H2 production and CO selectivity were strongly dependent on the preparation method,and PAD-Ni/TiO2-SiO2 was the better catalyst for H2 production with the lowest CO concentration.     

MnOx/MWCNTs低温氨选择性催化还原NOx硫中毒机理

以经过浓硝酸和等离子体放电预处理后的多壁碳纳米管(MWCNTs)为载体, 锰氧化物(MnO_x)为活性组分, 采用等体积浸渍法制备MnO_x/MWCNTs 催化剂. 利用热重分析(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原/脱附(TPR/TPD)以及傅里叶变换红外(FTIR)光谱对催化剂进行表征, 探讨SO₂对催化剂低温氨选择性催化还原(SCR)NO_x活性的影响及SO₂中毒机理. 结果表明, 低温下SO₂对MnO_x/MWCNTs 催化剂活性有明显毒化作用. 反应温度越高, SO₂浓度越大, 催化剂SCR活性下降越快. 活性中心Mn原子硫酸化是催化剂失活的主要原因. 另外, 催化剂表面生成硫酸铵盐以及SO₂对NO吸附的抑制作用也一定程度上造成了催化剂的失活.