摘要:

AbstractThe kinetics of the hydrolysis of hydrazone de rived from nitropyridine 2‐carboxaldehyde and 2‐hydrazino‐4‐substituted thiazoles Ia‐e in 10% (v/v) DMF‐buffer mixture has been investigated by applying two in dependent and different techniques viz UV‐spectrophotometry and differential pulse, polarography (DPP). The hydrolysis has been found to follow general acid‐base catalysis. Mechanism for the hydrolysis in acidic medium has been postulated. The observed rate constants, activation and thermodynamic parameters for the hydrolysis have been calculated. The effects of pH, molecular structure, temperature and change in percent age of water in the DMF‐buffer mixture on the rate of hydrolysis ha

ISSN:0009-4536    

DOI:10.1002/jccs.200100159

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe conductivity of some transition metal perchlorates, M(ClO4)2(M2+= Mn, Co, Ni, Cu and Zn) has been measured in urea‐water mixtures at 288–318 K. The limiting molar conductivities and the ion association constants of these electrolytes were calculated by the Shedlovsky extrapolation method. The ion association constants de creased in the order Co>Ni>Zn with increasing the atomic number, whereas Cu>Mn in the ionic association constants as are suit of the maximum temperature dependencies of Cu2+.The thermodynamic functions,ΔH° andA S°, for the formation of that ion pair have also been obtained.BothΔH° andΔS°for all the salts under study are positive values. On the other hand, the Walden products, Δoη, of the salts in crease with an in crease in temperature at 288–318 K, which indicate that these electrolytes be have as structure‐makers or promotors. Also, the activation energies, E, have been calculat

ISSN:0009-4536    

DOI:10.1002/jccs.200100160

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe relative polarizability effect of alkyl substituent can be conveniently obtained by calculating the so‐called Polarizability Effect Index (PEI) value, pro posed firstly in our laboratories,PEI = Σ(α/Ni2), whereaiis the polarizability of primary units CH3, CH2‐, CHC‐, and the Niis the carbon atom number from reaction site to the primary unit. By using the PEI and atomic charge in a molecule, the ionization potential of alkyl halide, the enthalpy of reaction for the gas‐phase addition of a proton to an alcohol or ether (proton affinity), the gas‐phase basicity of alcohols or ethers (proton affinity), and gas‐phase acidity of alcohols can be quantitatively modeled by the two‐parameter expr

ISSN:0009-4536    

DOI:10.1002/jccs.200100161

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe water1H and17O NMR relaxation properties of aqueous solutions containing Gd(III) che lates of the DTPA‐BIPA, DTPA‐BAA, DTPA‐BDEA and DTPA‐BMA ligands were investigated, and the results were compared with those previously reported for the Gd(III) complex with DTPA ligand. The significant deviation from the monoexponential behavior at the estimation of temperature dependence of1H longitudinal relaxation rate for Gd(III) complexes with DTPA‐BIPA, DTPA‐BAA and DTPA‐BDEA ligands is characteristic of the slow chemical ex change. The measurements of17O NMR trans verse relaxation rates and EPR transverse electronic relaxation rates in the range 276–343 K, allowed the assessment of the water‐exchange lifetime between the coordination site and the bulk solvent. With this approach, we obtained the water‐exchange life time (τM) of 1515, 1429, 1538 and 2128 ns for [Gd(DTPA‐BIPA)(H2O)], [Gd(DTPA‐BAA)(H2O)], [Gd(DTPA‐BDEA)(H2O)] and [Gd(DTPA‐BMA)(H2O)], respectively. Compared with the τMvalue of 303 ns for [Gd(DTPA)(H2O)]2−, we are able to conclude that the water residence life time in creases when the two terminal carboxylate groups of DTPA were

ISSN:0009-4536    

DOI:10.1002/jccs.200100162

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA new method for the in direct determination of thiocyanate with ammonium sulfate and isopropyl alcohol by extraction‐flotation of cop per in the presence of ascorbic acid is described. A small amount of Cu(II) is reduced to Cu(I) by ascorbic acid, then Cu(I) is precipitated with SCN−. In the course of phase separation of isopropyl alcohol from water, the precipitated CuSCN stays in the interface of isopropyl alcohol and water. A good linear relationship is observed between the flotation yield of Cu(II) and the amount of SCN−. The detection limit for thiocyanate is 1.0 × 10−5M, and the linear range is 1.0 × 10−5∼ 7.8 × 10−5M. Every parameter was optimized and the reaction mechanism was studied. The method is simple and rapid and it was successfully applied to the determination of thiocyanate in urine and saliva of smokers and non‐smokers and in venous blood of patients in fused with so

ISSN:0009-4536    

DOI:10.1002/jccs.200100163

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe color reaction of palladium(II) with the new reagent OPT was studied. In the presence of cetyltrimethyl ammonium bromide (CTMAB), in pH 5.0–5.6 HAc‐NaAc buffer solution, a yellow‐brown soluble complex with the ratio of 1:4 was formed. The maximum absorption was at 299.0 nm, the apparent molar absorptivity ϵ299.0 nm= 1.38×105l mol−1cm−1. Beer's law was obeyed in the range of 2–12 μg Pd(II)/25 mL. The method's sensitivity and selectivity were very good. It could be used to determine palladium(II) in a catalyst with satisf

ISSN:0009-4536    

DOI:10.1002/jccs.200100164

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe distribution equilibria of Pd(II) between aqueous bromide media and Cyanex‐923 as well as Cyanex‐ 471X in toluene was studied as a function of the concentration of extractants and the acid concentration. The extraction behaviour of Cyanex‐471X is compared with Cyanex‐923 as they contain different donor atoms. The quantitative extraction of Pd(II) was observed with Cyanex‐923 in toluene from 4.0–8.0 mol l−1HBr media and was stripped out with 2.0 mol l−1hydrochloric acid. Similarly Pd(II) was quantitatively extracted with Cyanex‐471X in toluene from 6.0–8.0 mol l−1HBr media and was stripped out with 7.0 mol l−1NH3solution as well as 1.0 mol l−1of stabilized sodium thiosulfate solution at pH 4.4. The stoichiometry of the Cyanex‐923 and Cyanex‐471X extracted species determined from slope analysis was 1:2 and 1:1, respectively. Palladium(II) was extracted and separated from its binary and ternary mixture.These methods were successfully employed for analysis

ISSN:0009-4536    

DOI:10.1002/jccs.200100165

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractDesign and fabrication of microcapillary electrophoresis (CE) chips on quartz substrates are described. The micro capillary channels are formed by the combination of a metal etch mask and wet chemical etching. In this paper, a simple but reliable one‐mask process is applied to fabricate micro structures on quartz substrates, which are commercially‐available blank photomasks. The selection of the quartz substrates greatly simplifies the fabrication process. The substrates with micro channels are then bonded with an other quartz cover plate at low temperature by using diluted hydrofluoric acid (HF) solution. Good channel sealing is observed. The low temperature bonding yields low residual stress and makes chemical surface modification prior to bonding feasible, if necessary. The quartz chips with higher UV transmittance allow us to use a laser induced fluorescence detection system for chemical analysis successfully. Solutions containing Nile blue are first per formed in the CE chips as a demonstration of electrophoretic injection. The capability of the microfabricated CE chips for electrophoretic injection and separation is then characterizedviathe analysis of DNA fragments φX174 digested byHaeIII. An excellent signal/noise ratio is obtained. In addition to single‐channel sample injection and separation, multi‐channel de vices capable of parallel electro‐migration of multi‐samples have also been demonstrated

ISSN:0009-4536    

DOI:10.1002/jccs.200100166

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe photolytic reactions of 2‐substituted αlyl chloride witht‐BuHgCl In different solvents were Investigated. The reactions proceed the SH2′ reaction mechanism except the substituent is a strong electron‐releasing group. The electron transfer process becomes more competitive with the radical addition process when the substituent is a strong electron‐releasing group. When the substituent is a strong electron‐releasing group such as ‐CH2SiMe3, there action in CH2CN shows pronounced electron transfer process while the reaction in DMSO or THF involves both of the SH2′ and the electron transfer processes. The reaction is sol vent dependent. An electron transfer mechan

ISSN:0009-4536    

DOI:10.1002/jccs.200100167

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

Abstract2‐Aryl‐2H‐[1,2,4]triazolo[4,3‐a]pyridin‐3‐ones4were synthesized by cycloaddition of α‐chloroformylarylhydrazines7with pyridines1. The inductive and mesomeric effects of substituents on pyridines were also investigated in this study. In reactions of 3‐substituted pyridines bearing a π‐electron‐donating substituent, the ortho site, C(2), of the pyridine ring is more favored for cycloaddition than the para site, C(6). As the substituent is a σ‐electron‐donating group, the cycloaddition only occurs on the ortho position. For reactions of 2‐substituted pyridines, however, cycloadditions were controlled solely by inductive effect, regard less of mesomeric effect. Only when the substituent is an electron‐donating group, would the cycloaddition proceed to afford expected cycloadducts. Further more, it is found that the inductive effect plays a more important role than the steric effect for reactions

ISSN:0009-4536    

DOI:10.1002/jccs.200100168

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY