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1.
Chockalingam Karunakaran Vaithiyalingam Chidambaranathan 《Monatshefte für Chemie / Chemical Monthly》2000,131(11):1123-1128
Summary. The oxidation of methylphenyl sulfide by imidazolium dichromate in acetonitrile mediated by p-toluenesulfonic acid is first order in IDC and TsOH and zero order in MeSPh in the concentration range studied. The IDC oxidation of 14 para-, meta-, and ortho-substituted phenylmethylsulfides at 20–45°C conforms to the isokinetic relationship but not to any of the linear free energy
relationships; the isokinetic temperature lies within the experimental temperature range.
Received April 18, 2000. Accepted (revised) July 12, 2000 相似文献
2.
Chockalingam Karunakaran Vaithiyalingam Chidambaranathan 《Monatshefte für Chemie / Chemical Monthly》2000,77(1):1123-1128
The oxidation of methylphenyl sulfide by imidazolium dichromate in acetonitrile mediated by p-toluenesulfonic acid is first order in IDC and TsOH and zero order in MeSPh in the concentration range studied. The IDC oxidation of 14 para-, meta-, and ortho-substituted phenylmethylsulfides at 20–45°C conforms to the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental temperature range. 相似文献
3.
When HCrO4 ? is reduced by formate in solutions buffered by 2-ethyl-2-hydroxybutanoic acid and its anion, chelated complexes of both Cr(IV) and Cr(V), both of them stabilized in the medium used, are formed. It appears that Cr(V) is not generated directly from the Cr(VI)-formate reaction but arises instead from oxidation of Cr(IV) by Cr(VI). When the Cr(VI)-formate reaction is allowed to go to completion in the presence of [Cl(NH3)5Co]2+, a scavenger for Cr(II), 84–86% of the Cr(VI) taken is found to be converted to Cr(II), indicating that nearly all of the reacting system proceeds through Cr(IV) and bypasses the more usual state Cr(III). Initial rates for formation of Cr(IV) lead to a rate law pointing to a transition state containing the two redox partners, two ligating carboxyl groups, and two units of H+. Substitution of DCO2 ? for HCO2 ? retards formation of Cr(IV) by a factor of 3.3, whereas the solvent isotope affect, rateD 2O/rateH 2O, favors the deuterated system by a factor of 1.4. Our observations are in accord with a sequence initiated by the ligation of HCrO4 ? to a chelate derived from the buffering carboxylate anion. Conversions of Cr(VI) to Cr(IV), and Cr(IV) to Cr(II) appear to entail hydride shifts from formate to the Cr(=O) function. 相似文献
4.
The electron transfer spectra of adducts of the title metal halides with a series of ligands (nitriles, dialkylchalcogenides, phosphoryl and thiophosphoryl ligands and phosphines) have been studied. The effect of halogen substitution on the halogen metal transitions is discussed by comparing the spectra of the adducts with those of the hexahalometalates. The origin of the two ligand-metal transitions observed in most adducts is discussed, and the splitting of the metal d levels in these almost octahedral adducts is estimated. For each metal halide, the series of adducts with dialkyl chalcogenides show a linear relationship of slope one between the ligand ionisation potential and the ligand-metal charge transfer energy. The ligand optical electronegativities have been estimated. 相似文献
5.
The composition and stability of the complex formed between chromium (VI) and Glycine Thymol Blue (G. T. B.) has been investigated using a spectrophotometric method. The chelate is reddish brown in colour and has λmax 570 nm against a reagent blank. The composition has been determined by different methods as 1: 1. The chelate gives maximum absorbance between pH 6.5 and 7.0. The values of log K as determined by two different methods are 5.21±0.1 and 5.24±0.1 and the values of ΔG° are ?7.08±0.1 and ?7.12±0.1 Kcal respectively at pH 6.8 and at 25°C. 相似文献
6.
The reaction of CrO2Cl2 with 2, 2′‐bipyridyl or 1, 10‐phenanthroline (diimine) in CCl4 or anhydrous CH3CO2H solution, produces orange‐brown diamagnetic [CrO2Cl2(diimine)]. The X‐ray structure of [CrO2Cl2(2, 2′‐bipy)] shows a six‐coordinate central chromium(VI) atom with cis‐dioxo groups trans to the diimine. In contrast, the diimines react with CrO3 in CH3CO2H / conc. aqueous HCl to form bright red paramagnetic CrV complexes, [CrOCl3(diimine)]. The X‐ray structure of [CrOCl3(2, 2′‐bipy)] shows a six‐coordinate central chromium atom with mer‐chlorines and the diimine trans to O/Cl. The addition of [2, 2‐bipyH2]Cl2 to a solution of CrO3 in CH3CO2H saturated with HCl gas, produces the CrV anion [2, 2′‐bipyH2][CrOCl4]Cl, which loses HCl on heating in vacuo to form [CrOCl3(2, 2′‐bipy)]. IR, UV/Vis, and 1H NMR spectra (CrVI only) are reported for the new complexes. Attempts to extend these routes to oxygen donor ligands, including ethers and phosphine oxides, were unsuccessful. The diimine complexes are the first structurally autheticated adducts of chromium(VI) and (V) oxide‐chlorides with neutral ligands. 相似文献
7.
IntroductionSingleelectrontransferinaromaticnucleophilicsub stitutionhasattractedmuchattentioninrecentyears .Inadditiontothewell knownSRN1mechanismreportedbyBunnett,1manyotheractivatedaromaticsystems ,i .e .,nitroarylhalides ,dinitrobenzenes ,etc .,havebeenre p… 相似文献
8.
Jun YAO Lin TIAN Fei WANG Hui‐Lun CHEN Chao‐Qian XU Chun‐Li SU Ming‐Fa CAI Thomas MASKOW Gyulad ZARAY Yan‐Xin WANG 《中国化学》2008,26(1):101-106
The effects of Cr(III) and Cr(VI) species (Cr2O72?, CrO42? and Cr3+) on the growth of Escherichia coli (E. coli) have been investigated in detail by microcalorimetry at 37 °C. Parameters including the growth rate constant (k), inhibitory ratio (I), half‐inhibitory concentration (IC50), total heat output (Qtotal), time of the maximum heat production (tlog) in the log phase have been obtained. The results showed that Cr(VI) and Cr(III) had the inhibition effect on the growth of E. coli in aquatic environment; however, the inhibitory ratio of Cr(III) to E. coli was smaller than that of Cr(VI). The k values of E. coli in the presence of Cr(VI) and at high concentrations of Cr(III) were decreased with increasing the concentrations of these chromium species. Among the three chromium species investigated, Cr2O72? was found to be the most poisonous species against E. coli with an IC50 value of 35.52 µg·mL?1. CrO42? exhibited moderate toxicity on E. coli with an IC50 of 50.24 µg·mL?1, and Cr3+ had the lowest toxicity with an IC50 of 84.30 µg·mL?1. Microcalorimetry can provide a convenient, sensitive and reliable method to study the effect of various metal species on the growth of bacteria or other microorganisms. 相似文献
9.
The electron transfer spectra of the hexachloro- and hexabromoniobate (V), and-tantalate(V) anions are investigated with particular care to avoid hydrolysis products. New interpretations are given, and the optical electronegativities χ of Nb(V) and Ta(V) are recalculated. The difference between both χ values is 0.2, in better agreement with the differences observed for metals of the second and third transition series. 相似文献
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13.
《Analytical letters》2012,45(8):1447-1451
Abstract A fluorescence quenching method for the determination of Cr(VI) in aqueous solution is described. The fluorescence intensity of the system is linear ever the range 5×10?6 - 1.0×10?4 M Cr(VI). The method has been applied to the determination of Cr(VI) In cast iron and waste water. 相似文献
14.
IntroductionFreeradicalformationfromhalogenatedhydrocarbonshasreceivedconsiderableattentionbecauseofitsscientif icandenvironmentalrelevance .1 6 Thisreactionseemstoplayanimportantroleinvariousprocesses .Bond break ingreactionisapowerfulsynthetictooltoprov… 相似文献
15.
L. N. Polyshchuk E. S. Yanovskaya V. V. Yanishpol’skii V. A. Tertykh K. M. Sukhoi M. V. Burmistr 《Russian Journal of Applied Chemistry》2007,80(9):1590-1593
The sorption of polyionene 1,4-MePh on the silica gel surface was studied. The silica gel modified with polyionene sorbed was used for sorption preconcentration of MoO 4 2? , WO 4 2? , Cr2O 7 2? , and VO 3 ? anions from aqueous solutions. The sorption isotherms of these anions on the initial and modified silica gels were obtained and analyzed. 相似文献
16.
Kinetics and Mechanism of the Reduction of Chromium(VI) and Chromium(V) by D‐Glucitol and D‐Mannitol
VivianaP. Roldn VernicaA. Daier Bernard Goodman MabelI. Santoro JuanCarlos Gonzlez Nancy Calisto SandraR. Signorella LuisF. Sala 《Helvetica chimica acta》2000,83(12):3211-3228
The oxidation of D ‐glucitol and D ‐mannitol by CrVI yields the aldonic acid (and/or the aldonolactone) and CrIII as final products when an excess of alditol over CrVI is used. The redox reaction occurs through a CrVI→CrV→CrIII path, the CrVI→CrV reduction being the slow redox step. The complete rate laws for the redox reactions are expressed by: a) −d[CrVI]/dt {kM2 H [H+]2+kMH [H+]}[mannitol][CrVI], where kM2 H (6.7±0.3)⋅10 M s−1 and kMH (9±2)⋅10 M s−1; b) −d[CrVI]/dt {kG2 H [H+]2+kGH [H+]}[glucitol][CrVI], where kG2 H (8.5±0.2)⋅10 M s−1 and kGH (1.8±0.1)⋅10 M s−1, at 33°. The slow redox steps are preceded by the formation of a CrVI oxy ester with λmax 371 nm, at pH 4.5. In acid medium, intermediate CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five‐ and six‐coordinate oxo‐CrV intermediates are formed, with the alditol or the aldonic acid acting as bidentate ligands. Pentacoordinate oxo‐CrV species are present at any [H+], whereas hexacoordinate ones are observed only at pH<2 and become the dominant species under stronger acidic conditions where rapid decomposition to the redox products occurs. At higher pH, where hexacoordinate oxo‐CrV species are not observed, CrV complexes are stable enough to remain in solution for several days to months. 相似文献
17.
Ab initio methods are used to investigate ring strain effects on sulfide-singlet oxygen reaction intermediates. The optimized persulfoxide and thiadioxirane structures derived from 3-, 4-, and 5-membered ring sulfides showed minor albeit systematic changes in geometry. These persulfoxides and thiadioxiranes are best described as distorted tetrahedral and trigonal bipyramidal in nature, respectively. We find that the persulfoxy sulfur becomes less sulfonium-ion-like in character with decreasing ring size. In addition, the persulfoxide and the thiadioxirane are nearly isoenergetic in all cases and their interconversion barriers are nearly identical. We speculate that the anticipated ring strain effect in the persulfoxide is compensated for by a weaker sulfur-oxygen interaction and the corresponding relaxation of the need to attain the energetically preferred tetrahedral geometry. 相似文献
18.
The complexation of the shift reagent tris-(dipivalomethanato)-europium with pyridine in deuteriochloroform has been studied by means of 1H-NMR. Shift parameters S = 28.0, 9.9, and 9.2 ppm respectively for pyridine protons 2, 3 and 4 are obtained. The results indicate that the shift reagent complexes a single pyridine molecule with an association constant K1 > 100 mole?1l. 相似文献
19.
The free-energy surface profile for an adiabatic electron transfer reaction in a polar solvent is calculated. The calculation allows for the dependence of electron wavefunctions of reactants on the environment polarization and for nonsphericity of electron wavefunctions. Allowance for the nonsphericity reduces significantly the activation barrier and increases the reaction rate. 相似文献
20.
The mechanism of dediazoniation of arenediazonium tetrafluoroborates in 2,2,2-trifluoroethanol (TFE) is strongly dependent on the concentration of added pyridine. The added base complexes with the diazonium ion and diverts it to a homolytic pathway. Complex formation is indicated by the disappearance of the \documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus \equiv {\rm N}\raise1pt\hbox{---}$\end{document} stretching vibration and appearance of a new band at about 1640–1690 cm?1 ascribed to the \documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} {\rm N}\raise1pt\hbox{=\kern-3.45pt=} {\rm N}\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus {\rm C}_5 {\rm H}_5$\end{document} system. UV. and NMR. results support this conclusion. Chemically induced dynamic nuclear polarization (CIDNP) experiments clearly implicate a radical-pair as an important intermediate in the decomposition of these complexes. 相似文献