A combination of water and microwave irradiation promotes the catalyst-free addition of pyrroles and indoles to nitroalkenes

A combination of water and microwave irradiation was used for the first time to perform a catalyst-free nitro-Michael addition of pyrroles and indoles. Under superheated conditions, the water trends to ionize by changing its chemical and physical properties. Therefore, we performed a new green-protocol using the water either as environmentally no harm solvent or as catalyst. The reaction success is independent from the kind of pyrrole, indole or nitroalkenes rapidly affording the corresponding adducts and giving excellent yields.     

湿空气饱和水蒸汽曲线计算模型的建立与分析

湿空气物性的高精度计算中,饱和水蒸汽曲线的计算建模是关键所在。在对已有的饱和水蒸汽压力公式进行误差分析比较后,得到了Gerry方程误差最小的结论。为解决计算的连续性问题,重新界定了该方程中冰面及水面方程的分界点。其次,建立了两种高精度的t-p公式,可方便直接的计算湿空气露点温度。最后,分析了饱和蒸汽曲线斜率的意义,推导出它的计算式。以上建立的湿空气饱和水蒸汽曲线计算模型,不仅具有快速方便的物性计算功能,还提供了准确判定湿空气状态变化的准则。     

一种自制的蒸馏水器保护装置

本装置由检测、控制、执行、报警和电源五部分组成。检测部分采用了靠正常水位导通的两根信号线。当蒸馏水器在正常运行时遇停水,本装置可立即实现断电保护,同时发出声光报警,有效防止干烧,杜绝事故发生。本装置制作简便,元器件均为市售,成本低廉,性能可靠。     

SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURES THROUGH COPOLYMERIC MEMBRANES: Ⅰ. ACRYLIC ACID AND ACRYLONITRILE COPOLYMER AND ITS IONIZED MEMBRANES

The copolymer of acrylic acid and acrylonitrile has been synthesized and pervaporation properties of the copolymeric membranes have been investigated. In order to elucidate the influence of membrane-permeate interaction on the pervaporation of water-ethanol mixtures and to prepare much improved membranes, the membranes have been treated with alkali metal, alkali earth metal and transition metal salt aqueous solutions. The treated membranes (ionized membranes) exhibited higher separation factors than the untreated membranes. The separation factors of various alkali metal cation membranes decreased in the following order : Li~+>Na~+>K~+, and the permeation rates showed an opposite tendency. The dependence of pervaporation behavior on the copolymer composition ,feed concentration and operating temperature have been studied with both ionized and non-ionized membranes. The apparent activation energies of water and ethanol permeation were calculated.     

Water mediated deprotective intramolecular hydroamination of N-propargylaminopyridines: synthesis of imidazo[1,2-a]pyridines

Metal-free synthesis of substituted imidazole [1,2-a]pyridines from deprotective N-(prop-2-yn-1-yl)pyridin-2-amines in water is elucidated. Electron releasing substituents on pyridine ring provided pure products in quantitative yields without separation by column chromatography.     

Immobilization of Ru(III) complex on silica: a heterogenized catalyst for selective oxidation of alcohols in water at room temperature

We have developed a heterogenized catalyst (‘SiO₂’–NH₂–Ru^III) by the immobilization of [Ru(acac)₂(CH₃CN)₂]PF₆ on SiO₂. The catalyst was characterized by SEM, solid state NMR, EPR, FT-IR, ICP, and BET surface area analyses. ‘SiO₂’–NH₂–Ru^III catalyzed the selective oxidation of alcohols with periodic acid in water at room temperature. This protocol was applicable to the controlled oxidation of structurally diverse primary and secondary alcohols. The catalyst could be quantitatively recovered and reused up to six cycles without significant loss of catalytic activity.     

Fabrication and application of a new modified electrochemical sensor using nano-silica and a newly synthesized Schiff base for simultaneous determination of Cd,Cu and Hg ions in water and some foodstuff samples

A new chemically modified carbon paste electrode was constructed and used for rapid, simple, accurate, selective and highly sensitive simultaneous determination of cadmium, copper and mercury using square wave anodic stripping voltammetry (SWASV). The carbon paste electrode was modified by N,N′-bis(3-(2-thenylidenimino)propyl)piperazine coated silica nanoparticles. Compared with carbon paste electrode, the stripping peak currents had a significant increase at the modified electrode. Under the optimized conditions (deposition potential, −1.100 V vs. Ag/AgCl; deposition time, 60 s; resting time, 10 s; SW frequency, 25 Hz; pulse amplitude, 0.15 V; dc voltage step height, 4.4 mV), the detection limit was 0.3, 0.1 and 0.05 ng mL⁻¹ for the determination of Cd²⁺, Cu²⁺ and Hg²⁺, respectively. The complexation reaction of the ligand with several metal cations in methanol was studied and the stability constants of the complexes were obtained. The effects of different cations and anions on the simultaneous determination of metal ions were studied and it was found that the electrode is highly selective for the simultaneous determination of Cd²⁺, Cu²⁺ and Hg²⁺. Furthermore, the present method was applied to the determination of Cd²⁺, Cu²⁺ and Hg²⁺ in water and some foodstuff samples.     

Ammonium Determination in Water Samples by Using Opa-Nac Reagent: A Comparative Study with Nessler and Ammonium Selective Electrode Methods

A selective and sensitive method based on the ammonium derivatisation with o -phthaldialdehyde (OPA) and N -acetyl-cysteine (NAC) has been developed for ammonium determination in real water samples. The proposed procedure has been compared with ammonium reference methods such as Nessler reagent method and ammonium selective electrode. All procedures have been chemometrically tested and compared in terms of the main analytical properties. These procedures have been used to determine ammonium in unknown water samples. The OPA-NAC reagent method does not present any systematic error (proportional or constant), while Nessler reagent presents both of them for some samples assayed. The ammonium selective electrode is free of corrigible systematic errors, however presents amine interference. The OPA-NAC ammonium method is able to achieve a detection limit (LOD) of 0.07 mg/L in the sample, with a linear dynamic range up to 1.4 mg/L of ammonium.     

Evaluation of Pesticide Contamination of Ground Water in Two Agricultural Areas of Portugal

In two Portuguese agricultural areas, "Beira Litoral" and "Ribatejo e Oeste", several pesticides regularly applied in vineyards, maize, potato, tomato for industry, apple, pear and rice were detected in ground water. Atrazine was the most frequently detected, being found in 70% of the total of 79 sites selected in the year 2000, followed by its metabolites desethylatrazine and desisopropylatrazine with frequencies of detection, respectively, of 56% and 48% and by simazine (37%), alachlor (25%), metolachlor (24%) and metribuzin (15%). Other pesticides and metabolites i.e. 3,4-dichloroaniline, dimethoate, f and g -endosulfan, lindane, molinate and prometryn were also detected but at lower occurrences. Pesticides were detected mainly in ground water wells used for irrigation purposes, although in some locations they were also found in water wells used for human consumption. In this study, it was also observed a seasonal variation of pesticide residues in ground water of shallow and deep wells.