Facile preparation of organozinc bromides using electrogenerated highly reactive zinc and its use in cross-coupling reaction

Highly reactive zinc was readily prepared by electrolysis of a DMF solution containing pyrene as a mediator with a platinum cathode and a zinc anode. Preferential reduction of pyrene occurred to generate the corresponding radical anion, which reduced zinc ions generated from anodic dissolution to give zero valent zinc with high reactivity. The reactive zinc was successfully used for an efficient transformation of bromoalkanes into the corresponding organozinc bromides. Organozinc bromides obtained were further used successfully in Pd-catalyzed cross-coupling reaction with various aryl iodides and bromides.     

Tandem oxidation/halogenation of aryl allylic alcohols under Moffatt-Swern conditions

Aryl allylic alcohols are converted to halogenated unsaturated ketones or allylic halides using excess Moffatt-Swern reagent. Electron-poor aromatic rings favor formation of the halogenated ketone, while electron-donating substituents in the ortho or para positions favor formation of the allylic halide. The oxidation/halogenation reaction performs well with both oxalyl chloride and oxalyl bromide, providing access to the corresponding chlorides or bromides, respectively.     

Kinetics of the dissolution of copper metal in aqueous solutions containing unsaturated organic ligands and copper(II)

The kinetics of the dissolution of copper metal in an aqueous solution containing copper(II) and an unsaturated organic ligand was followed by using an automated flow-injection analysis technique to determine the concentration of copper(I) in solution as a function of time. The results suggest that the rate of dissolution of the copper metal is dependent on electron transfer between the copper(II) and copper atoms on the surface of the copper metal, and on the stabilization of copper(I) by the unsaturated organic ligand in solution.     

Kinetics and mechanism of the reaction of substituted benzyl bromides with copper in dimethylformamide

The reaction of copper metal with various substituted benzyl bromides in dimethylformamide has been studied and the kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log(k/k°) vs the substituent constant σ gave good correlations (ρ = 0.24, S_ρ = 0.03, r = 0.951). The structure of the organic group has little effect on the rate of reaction of substituted benzyl bromides with copper. In the absence of atmospheric oxygen, oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethanes and copper(I) complexes. The stereochemistry and intermediate compound were also studied and the reaction mechanism is discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Zinc-Mediated Intermolecular Reductive Radical Fluoroalkylsulfination of Unsaturated Carbon–Carbon Bonds with Fluoroalkyl Bromides and Sulfur Dioxide

A versatile and general zinc-mediated intermolecular reductive radical fluoroalkylsulfination of unsaturated C−C bonds has been developed using readily available fluoroalkyl bromides and 1,4-diazabicyclo[2.2.2]octane-bis(sulfur dioxide) adduct (DABSO) with wide substrate scope and excellent functional group tolerance. Sulfur dioxide anion radical generated in situ from the reduction of sulfur dioxide with zinc may be involved in the reaction mechanism.     

铜-有机配位体不饱和配合物的催化化学发光活性及其分析应用

铜(Ⅱ)离子与许多有机配位体组成饱和配合物后, 均导致铜(Ⅱ)在Luminol-H2O2和o-Phen-H2O2体系中催化化学发光活性的消失。本文首次发现, 当铜(Ⅱ)离子与某些有机配位体组成1:1不饱和配位化合物时, 它们非但不抑制化学发光,而且比铜(Ⅱ)离子具有更高的催化化学发光活性, 据此, 本文建立了用配合溶解Cu(OH)2, 流动注射化学发光技术测定氨基酸的新方法, 检测限均可达pmol级,比文献普遍使用的抑制化学发光法灵敏度高10~150倍, 线性范围达三个数量级,相对偏差在5.4%以下。     

Determination of cobalt, nickel, lead, bismuth and indium in ores, soils and related materials by atomic-absorption spectrometry after separation by xanthate extraction

A method for determining approximately 0.5, mug/g or more of cobalt, nickel and lead and approximately 3 mug/g or more of bismuth and indium in ores, soils and related materials is described. After sample decomposition and dissolution of the salts in dilute hydrochloric-tartaric acid solution, iron(III) is reduced with ascorbic acid and the resultant iron(II) is complexed with ammonium fluoride. Cobalt, nickel, lead, bismuth and indium are subsequently separated from iron, aluminium, zinc and other matrix elements by a triple chloroform extraction of their xanthate complexes at pH 2.00 +/- 0.05. After the removal of chloroform by evaporation and the destruction of the xanthates with nitric and perchloric acids, the solution is evaporated to dryness and the individual elements are ultimately determined in a 20% v/v hydrochloric acid medium containing 1000 mug/ml potassium by atomic-absorption spectrometry with an air-acetylene flame. Co-extraction of arsenic and antimony is avoided by volatilizing them as the bromides during the decomposition step. Small amounts of co-extracted molybdenum, iron and copper do not interfere.     

Continuous spectrophotometric determination of copper, nickel and zinc in copper-base alloys by flow-injection analysis

Flow-injection methods have been developed for the determination of copper, nickel and zinc in copper-base alloys, including several types of brasses, deoxidized copper, beryllium copper and German silver. The system for copper and nickel involves the measurement of the absorbance of the copper(II) and nickel(II) aquo-complexes at 805 and 410 nm, respectively, after simple dissolution of the sample in a nitric acid-phosphoric acid mixture. The system needs no further reagents and the sample solutions can be analysed at rates of up to 280 /hr for copper (or nickel in German silver) without any carry-over. The system for zinc consists of automatic dilution of the injected sample with a thiosulphate-acetate buffer solution and the subsequent measurement of the absorbance of the zinc-Xylenol Orange complex at 568 nm. This system permits analysis rates of up to 90/hr for zinc solutions, with no carry-over. The procedures have been applied to standard copper-base alloys. The results agreed satisfactorily with the certified values. The precision ranges are 0.2-0.7% for copper and nickel and 0.5-0.8% for zinc.     

The determination of trace amounts of zinc, cadmium, lead and copper in airborne particulate matter by anodic stripping voltammetry

The application of anodic stripping voltammetry, with a hanging mercury drop electrode, to the determination of zinc, cadmium, lead and copper in airborne particulate matter collected by filtration is discussed. This procedure allows for the destruction of the filter material followed by the complete dissolution (including silicates) of the collected particulate matter. A low-temperature ashing process is described and the recovery of cadmium in this procedure is studied. Analytical data obtained by anodic stripping and atomic absorption for zinc, cadmium, lead and copper are compared.     

Aminomethylation of organic halides promoted by zinc in protic medium

Organic halides undergo smooth aminomethylation by secondary amines and aqueous formaldehyde promoted by metallic zinc under copper(I) catalysis. Good to excellent yields are obtained with primary, secondary, and tertiary iodides, allylic, propargylic, and benzylic bromides and with α-bromoesters. In most cases, DMSO is the best solvent, but dioxane is preferable for some more reactive halides. Additional experiments with radical quenchers and promoters and the use of ‘radical clocks’ indicate a stepwise reaction mechanism initiated by the attack of an alkyl radical to iminium ion.     

Dosage De L′antimoine Dans Le Zinc Electrolytique Et Le Sulfate De Zinc

Abstract

Anmodic-stripping voltammetry at a haning-drop mercury electrode has been applied to the precise and accurate trace analysis of antominy in metalic zinc and in solutions of zinc sulfate. A sample preparation methos is described which obviates loss of antimony by voltalization. A mixture of zinc sulfate and 6M hydrochloricacid is used as supporting electrolyte, in order to enhance the separation o the closely spaced dissolution peaks of copper and antimony.     

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k^o) vs the substituent constant σ gave good correlations (ρ = 0.15, S_ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated. The reaction mechanism is discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 296–305, 2005     

(Series Editor) Transform Techniques in Chemistry,P.R. Griffiths,D. Hercules (Eds.), in: Modern Analytical Chemistry Series,Plenum, New York,NY (1978), 385 pp. $47.40

Concentration potentials in zinc sulphate, copper sulphate, nickel sulphate and cobalt sulphate solutions across liquid membranes based on myristates and laurates of zinc, copper, nickel and cobalt and caprate and caprylate of copper have been studied in concentration cells in which the liquid membrane separates the two solutions of the same electrolyte. The behaviour of the cell with heavy metal soap liquid ion-exchange membranes becomes more and more nernstian as the number of carbon atoms in the hydrocarbon chain of the fatty acid soap increases. Concentration potential values with copper, zinc, nickel or cobalt soap follow the order of their insolubility in water. The failure to record the theoretical potentials as calculated by Nernst's equation has been explained by considering the transport of water across organic phase by hydrated ions and the dissolution of heavy metal soaps in aqueous solutions. Liquid membranes based on heavy metal myristate soaps when used in concentration cells could measure the activities of zinc, copper, nickel and cobalt ions in the concentration range of 10^?4–10^?1M.     

SYNTHESIS OF 1,4,7,10-TETRA-N-ALKYL-1,4,7,10-TETRAAZA-CYCLODODECANES

ABSTRACT

We report a concise method for the preparation of 1,4,7,10-tetra-N-alkyl-1,4,7,10-tetraaza-cyclododecanes via deprotonation to the fourfold lithium amide followed by alkylation with alkyl bromides. The procedure circumvents the problem of ammonium salt formation and provides direct access to hydrophobic 1,4,7,10-tetraaza-cyclododecanes in moderate yield. The so obtained hydrophobic macrocycles were converted into the corresponding zinc(II), copper(II), nickel(II) and cobalt(II) complexes, that may be used as water stable Lewis-acids in catalysis and anion extraction.     

Highly efficient,general procedure for the preparation of alkylzinc reagents from unactivated alkyl bromides and chlorides

[reaction: see text] Alkylzinc bromides have been efficiently prepared by the direct insertion of zinc metal (dust, powder, granule, shot), activated with 1-5 mol % I(2), into alkyl bromides in a polar aprotic solvent. The zinc reagents thus formed undergo Ni- and Pd-catalyzed cross-coupling with aryl halides to produce functionalized alkylarenes in excellent yields.     

Heck reactions of alkenes with aryl iodides and aryl bromides: Rate-determining steps deduced from a comparative kinetic study of competing and noncompeting reactions

Joint kinetic analysis of competition and noncompetition experiments can provide important information and sometimes a direct answer concerning the rate-determining step of a catalytic reaction. Applying this approach to the Heck reaction has demonstrated that alkenes; reactive aryl iodides; and, contrary to the conventional opinion, unactivated aryl bromides participate in rapid steps of the Heck reaction. For aryl iodides, the rate-determining step includes the dissociation of a C-H bond. At the same time, kinetic data for the dissolution of palladium reacting with aryl bromides suggest that the rate of the catalytic reaction is determined by the slow dissolution of palladium aggregates.     

高效液相色谱化学发光检测法测定氨基酸

本文根据铜与氨基酸组成的１：１不饱和络合物对Ｌｕｍｉｎｏｌ－Ｈ２Ｏ２化学发光体系的催化活性，设计了一种新型氨基酸高效液相色谱化学发光检测器，即在色谱柱后安装一个氢氧化铜柱，从柱后流出的氨基酸通过氢氧化铜柱时，产生配合溶解形成氨基酸－铜（１：１）络合物，进行化学发光检测，１４种常见氨基酸的检测限均在ｐｍｏｌ级，已用于血清、尿和啤酒中氨基酸的测定。     

Adsorption properties of new Silochrome-based chelate-containing gas chromatographic materials

Adsorbents were obtained on the basis of Silochrome S80 modified with complex compounds of copper(II) and nickel(II) with bidentate nitrogen-containing organic ligands. The gas-chromatographic method was used to study the thermodynamic characteristics of the adsorption of organic compounds belonging to various classes on Silochrome S80 before and after its modification. It was found that supported metal complexes strongly affect the chromatographic polarity and favor a more selective separation of mixtures of close-boiling carbonyl compounds and saturated and unsaturated light hydrocarbons.     

A Facile Synthesis of Bridged‐tricyclic Skeletons via Intramolecular Diels‐Alder Reaction of Cyclic 1,3‐Dienes Containing an α,β‐Unsaturated Ester

Intramolecular Diels‐Alder reaction (IMDA) precursors are easily available starting from addition of ester functionalized zinc‐copper reagents to cyclohexadienyl‐ and cycloheptadienylirontricarbonyl cation salts. The resulting cyclic 1,3‐dienes containing an α,β‐unsaturated ester functionality underwent smoothly IMDA reaction to afford bridged tricyclic compounds. Bridged heterotricyclic skeletons were also available via IMDA reaction of cyclic 1,3‐dienes bearing an imine or aldehyde functionality.     

Direct Formation of Secondary and Tertiary Alkylzinc Bromides and Subsequent Cu(I)-Mediated Couplings

Secondary and tertiary alkylzinc bromides can be generated from the direct oxidative addition of Rieke zinc to secondary and tertiary alkyl bromides in high yield. These organozinc reagents have been found to undergo copper-catalyzed conjugate addition, cross-coupling with acid chlorides, and carbocupration to activated alkynes.