Synthesis of cyclohexadienylstannanes - Novel example of vinylic SRN1 mechanism: A theoretical and experimental study

The reaction of trimethyltinsodium (1) with 1-(diethoxyphosphoryl)oxy-1,3-cyclohexadienes in liquid ammonia under irradiation affords the corresponding 1-trimethylstannylcyclohexadienes. We suggest that these reactions occur by an S_RN1 mechanism. On the other hand, 2-(diethoxyphosphoryl)oxy-1,3-cyclohexadiene reacts very slowly towards 1 and the substitution product decomposes under the reaction conditions employed. Thus, structurally similar compounds do not behave in the same way under ET conditions. We suggest that this behavior is mainly due to differences in spin density of their radical anions, which affect their fragmentation rates. Our results are supported by computational calculations.     

A novel example of vinylic SRN1: Reactions of 3,3-difluoro-1-iodo-2-phenylcyclopropene with thiolate ions

The reactions of 3,3-difluoro-1-iodo-2-phenylcyclopropene with thiolate ions (with a molar ratio of 1:1) were carried out in laboratory illumination to give the corresponding substituted product. The presence of p-dinitrobenzene (p-DNB) or hydroquinone (HQ) as well as darkness significantly suppressed the reaction. ESR trapping experiments also evidenced the existence of fluorinated radical. All these results demonstrate the reaction involved a vinylic saturated alkyl and aromatic halides (S_RN1) mechanism.     

Syntheses of phenanthridines and benzophenanthridines by intramolecular ortho-arylation of aryl amide ions with aryl halides via SRN1 reactions

The photostimulated reaction of N-(2-halo-benzyl)aryl amines with t-BuOK in liquid ammonia affords fused azaheterocycles by the S_RN1 mechanism. The starting materials are easily obtained by the reaction of 2-halo-benzyl chloride and aromatic amines to prepare the secondary amines. Through this approach, phenanthridine (90%), 4-phenylphenanthridine (87%), benzo[a]phenanthridine (98%), and benzo[c]phenanthridine (84%) were synthesized.     

First Long-Distance SRN1 on a propargylic chloride

We report here the first example of a Long-Distance S_RN1 (LD-S_RN1) reaction on a propargylic chloride. The reaction of 1-(3-chloroprop-1-ynyl)-4-nitrobenzene (1) with nitronate anions led to both the formation of the C-alkylation product through an LD-S_RN1 mechanism and the ethylenic compound resulting from nitrous acid elimination on the C-alkylation product 2. In contrast with previous work on LD-S_RN1 reactivity, no O-alkylation product was observed. Only one original product 4 was isolated under phase transfer conditions, resulting from a nucleophilic attack by 2-nitropropane anion on the electrophilic alkyne. This LD-S_RN1 reactivity did not extend to sulfinate anions; the reaction of 1 with sulfinate anions yielded original ethylenic disulfone compounds which were formed via an ionic process.     

Selective synthesis of mono- and distannylpyridines from chloropyridinols via an SRN1 mechanism

A selective two-step synthesis of either mono- or distannylated pyridines from commercially available pyridinols, involving its conversion to the corresponding diethyl pyridyl phosphates (pyDEP) followed by the reaction with Me₃SnNa in liquid ammonia, is described.The results obtained clearly indicate that the reactions proceed through an unimolecular radical nucleophilic substitution mechanism (S_RN1) with intermediacy of a monosubstitution product.     

A novel synthesis of spiro[(2,2-dimethyl-[1,3]-dioxane)-5,2′-(2′,3′-dihydroindole)] using SRN1 reaction conditions

A concise synthesis of the spiro[(2,2-dimethyl-[1,3]-dioxane)-5,2′-(2′,3′-dihydroindole)] nucleus from substituted benzyl chlorides and 5-(hydroxymethyl)-2,2-dimethyl-5-nitro-1,3-dioxane 5 as starting materials is reported. The nitro intermediates 6 and 7 were prepared under S_RN1 reaction conditions.     

Long distance-SRN1 in nitroimidazole series favored by temperature

New reductive alkylating agents in 4- and 5-nitroimidazole series produce exclusively O-alkylation with nitronate anions under classical S_RN1 conditions at room temperature. Electron-transfer C-alkylation is observed under microwave irradiation or under conventional heating. Furthermore, X-ray spectroscopy shows that the dihedral angles between the phenyl and imidazole rings for the two series are different, which could greatly influence reactivity in 4- and 5-nitroimidazole series.     

Synthesis of arylselenide ethers by photoinduced reactions of selenobenzamide, selenourea and selenocyanate anions with aryl halides

Selenobenzamide (⁻SeCNH(Ph), 1), selenourea (⁻SeCNH(NH₂), 2) and selenocyanate (⁻SeCN, 3) anions afford areneselenolate ions (ArSe⁻) under photostimulation in the presence of tert-butoxide or 2-naphthoxide ions as electron donors (entrainment conditions) in DMSO. In a ‘one-pot’ procedure, ArSe⁻ anions can be trapped by a subsequent aliphatic nucleophilic substitution giving aryl methyl selenides in good to excellent yields (67-100%). This simple approach is compatible with electron-donating and electron-withdrawing substituents, such as nitro and carbonyl groups.     

The metastable Ni7±xS6, and mixed Ni6±x(S1−ySey)5, phases

The closely related, narrowly non-stoichiometric, metastable as well as thermodynamically stable “phases” in the metal-rich part of the Ni–S phase diagram near the nominal composition Ni_7±xS₆ have been carefully re-investigated via electron diffraction and transmission electron microscope imaging. Two quite distinct polymorphs have been identified, a minority incommensurate interface-modulated polymorph and a (heavily twinned) majority I1a1, a=2a_p, b=2b_p, c=−a_p+c_p superstructure (of an underlying Bmmb, a_p3.3, b_p16.4, c_p11.3 Å parent structure) polymorph. The incommensurate polymorph is shown to be very closely related to the only known polymorph of Ni_6±xSe₅ and is rapidly stabilized to room temperature upon doping of the sulfide compounds with selenium.     

Photoluminescent BaMoO4 nanopowders prepared by complex polymerization method (CPM)

The BaMoO₄ nanopowders were prepared by the Complex Polymerization Method (CPM). The structure properties of the BaMoO₄ powders were characterized by FTIR transmittance spectra, X-ray diffraction (XRD), Raman spectra, photoluminescence spectra (PL) and high-resolution scanning electron microscopy (HR-SEM). The XRD, FTIR and Raman data showed that BaMoO₄ at 300 °C was disordered. At 400 °C and higher temperature, BaMoO₄ crystalline scheelite-type phases could be identified, without the presence of additional phases, according to the XRD, FTIR and Raman data. The calculated average crystallite sizes, calculated by XRD, around 40 nm, showed the tendency to increase with the temperature. The crystallite sizes, obtained by HR-SEM, were around of 40-50 nm. The sample that presented the highest intensity of the red emission band was the one heat treated at 400 °C for 2 h, and the sample that displayed the highest intensity of the green emission band was the one heat treated at 700 °C for 2 h. The CPM was shown to be a low cost route for the production of BaMoO₄ nanopowders, with the advantages of lower temperature, smaller time and reduced cost. The optical properties observed for BaMoO₄ nanopowders suggested that this material is a highly promising candidate for photoluminescent applications.     

Aflatoxin B1 and M1 in milk

The aflatoxin M₁ (AFLAM₁) is a mycotoxin that results from the hydroxylation of the aflatoxin B₁ (AFLAB₁). It contaminates the milk of animals fed with a diet containing its precursor. In this work, we determined the occurrence of AFLAB₁ and AFLAM₁ in milk, as well as the chromatographic conditions to quantify these mycotoxins. The extraction and quantification of AFLAB₁ and AFLAM₁ in naturally contaminated and artificially spiked milk samples which are produced and marketed in the state of RS were performed using the AOAC official method and UHPLC with fluorescence detection. We obtained a separation factor of 2.3 for AFLAB₁ and AFLAM₁ using a mobile phase consisting of 1% acetic acid:acetonitrile:methanol (55:10:35). The analytical curves had a wide linearity range and the limit of quantification (LOQ_m) concentrations of AFLAB₁ and AFLAM₁ were equal to 0.5 and 0.25 μg L⁻¹, respectively. Samples of pasteurized and ultra-high-temperature processed (UHT) milk showed natural contamination, and the levels for both aflatoxins ranged from 0.7 to 1.5 μg L⁻¹. Raw and concentrated milk samples only contained AFLAM₁, with a maximum average concentration of 1.7 μg L⁻¹. These concentrations, higher than permitted by legislation, confirm the existence of a health risk, as well as highlight the relevance of searching for alternatives to reduce this contamination.     

Free radical SH2′ reaction mechanism study by comparing free radical SH2′ reaction with free radical addition reaction

It is not clear whether the mechanism of the S_H2′ reaction of allyl chloride is concerted or stepwise. The relative rates of the competitive free radical addition to two different double bonds in (2-chloroallyl)-(2-choromethylallyl) ether have been determined. There are two competitive free radical addition reactions, one is free radical S_H2′ reaction and the other is free radical addition reaction. The mechanism of the S_H2′ reaction is discussed by comparing free radical S_H2′ reaction with free radical addition reaction.     

CCl2自由基被无机小分子猝灭的速率常数

对CCl4/Ar混合气体脉冲直流高压放电产生CCl2自由基,用541.52 nm激光将电子基态CCl2激励到A 1B1(0,4,0)振动能级上. 通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1和a 3B1)被O2、N2、NO、 CO2、 CS2、H2O、SO2,和SF6分子猝灭的实验结果.用我们提出的三能级模型分析处理实验数据,获得了CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.     

First single electron transfer reaction on propargylic chloride in 5-nitroimidazole series

We report here the first example of an S_RN1 reaction on propargylic chloride in heterocyclic series. The reaction of 4-(3-chloroprop-1-ynyl)-1,2-dimethyl-5-nitro-1H-imidazole with nitronate anions led to both the formation of the C-alkylated product through an S_RN1 mechanism and the predominant ethylenic compound resulting from nitrous acid elimination on the C-alkylated product. Interestingly, in contrast to our previous works on S_RN1 reactivity, no O-alkylated product was observed.     

CCl2(A 1B 1,a3B1)自由基被烷烃类分子猝灭动力学

用放电 LIF实验装置,对CCl4/Ar混合气体放电产生CCl2自由基,再用541.52 nm激光将电子基态CCl2激励到激发态A 1B1(0,4,0)振动能级上,通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1)被烷烃类分子猝灭的实验结果,用我们提出的三能级模型分析处理实验数据,获得CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.     

高温固相法合成LiNi1/3Mn1/3Co1/3O2及其性能研究

采用高温固相法合成出层状锂离子电池正极材料LiNi_1/3Mn_1/3Co_1/3O₂。通过XRD、ICP、SEM和电化学测试手段对产物的结构、组成、形貌及电化学性能进行了研究。XRD结果表明此方法合成的LiNi_1/3Mn_1/3Co_1/3O₂具有标准的α-NaFeO₂型层状结构，SEM照片显示颗粒粒径大约在500 nm左右，粒径分布较窄。以20 mA·g^-1电流密度放电，充放电电压在2.8～4.4 V之间，其首次放电比容量为170 mAh·g^-1，40次循环容量保持率为85.3%。进一步加入石墨导电剂后，同样条件下首次放电比容量变为179 mAh·g^-1，50次循环容量保持率为89.6%。容量衰减主要发生在前10次循环。XRD和SEM测试表明循环初期容量衰减的原因是由材料本体结构变化和界面反应共同作用的结果。     

Preparation and photocatalytic activity of Sb2S3/Bi2S3 doped TiO2 from complex precursor via gel-hydrothermal treatment

Sb₂S₃/Bi₂S₃ doped TiO₂ were prepared with the coordination compounds [M(S₂CNEt)₃] (M=Sb, Bi; S₂CNEt=pyrrolidinedithiocarbamate) as precursors via gel-hydrothermal techniques. The doped TiO₂ were characterized by XRD, SEM, XPS and UV-vis diffuse reflectance means. The photocatalyst based on doped TiO₂ for photodecolorization of 4-nitrophenol (4-NP) was examined. The optimal Bi₂S₃/Sb₂S₃ content, pH and different doped techniques have been investigated. Photocatalytic tests reveal that M₂S₃ doped TiO₂ via the gel-hydrothermal route performs better photocatalytic activity for photodegradation reaction of 4-nitrophenol (4-NP).     

TsOH-SiO2 as an efficient and eco-friendly catalyst for Knoevenagel condensation

Tosic acid on silica gel (TsOH-SiO₂) was synthesized and characterized using microscopic and spectroscopic techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy. Thermal behaviour of the catalyst was investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TsOH-SiO₂ showed excellent catalytic activity for the Knoevenagel condensation and was recyclable for six cycles.     

电解Co-Ni-Mn合金制备LiCo1/3Ni1/3Mn1/3正极材料

由Co-Ni-Mn合金出发，采用电解方法合成了含3种过渡金属元素的前驱物，再利用该前驱物制备了锂离子二次电池正极材料LiCo_1/3Ni_1/3Mn_1/3。XRD测试结果表明通过该方法制备的正极材料具有较好的层状结构，SEM测试则显示材料由规则形状的1 μm左右颗粒组成。通过XPS实验证明Co、Ni、Mn 3种过渡金属元素在该材料中的价态分别为+3，+2，+4。采用循环伏安法对材料的电化学行为进行了研究，表明该材料具有较好的充放电可逆性。该材料在150 mA·g^-1电流下经过50周的恒电流充放循环后容量仍能保持在160 mAh·g^-1。     

表面活性剂控制合成不同形貌的纳米硫化铋

采用硝酸铋和硫脲为反应物,通过添加不同的表面活性剂如Triton X-100+OP-10、TX-10、Triton X-100,用回流法合成了硫化铋纳米花。所得产物用XRD、EDS、TEM、SAED、SEM以及UV-Vis进行了表征。结果表明,经85～110 ℃回流反应3 h,可以得到结晶良好、具有各种形貌的正交晶相的硫化铋纳米花。经计算,其晶胞参数为a=0.439 34 nm, b=0.965 64 nm, c=1.118 5 nm。UV-Vis分析表明,硫化铋