Showing papers on "Iodide published in 1995"

Nitrate-Selective Electrode Developed by Electrochemically Mediated Imprinting/Doping of Polypyrrole

Abstract: Nitrate-selective electrodes have been developed by electropolymerizing pyrrole onto glassy-carbon electrodes in the presence of NaNO 3 . Electrochemical variables were used to optimize the potentiometric response of the electrodes and to maximize the selectivity for nitrate over potentially interferent anions. Calibration plots with near-Nernstian slopes for nitrate were observed, -56±1 mV/decade (n=18), over a linear range of four decades of concentration (5.0×10 -5 -0.50 M nitrate). The electrodes had detection limits of (2±1)×10 -5 M nitrate (n=18). The commercially available nitrate-selective electrodes suffer from interference by lipophilic anions, such as perchlorate and iodide. Compared to these electrodes, the polypyrrole-based nitrate electrodes demonstrated improved selectivity coefficients for perchlorate and iodide by as much as 4 orders of magnitude (K pot NO3-,ClO4- =5.7×10 -2 , K pot NO3-,I- =5.1×10 -2 ). An electrochemically mediated templating mechanism is proposed to explain the observed high selectivity for nitrate

Facile Electrophilic Iodination of Icosahedral Carboranes. Synthesis of Carborane Derivatives with Boron-Carbon Bonds via the Palladium-Catalyzed Reaction of Diiodocarboranes with Grignard Reagents

Abstract: Electrophilic diiodination reactions of icosahedral closo1,2-C2B IOHI 2 and closo1,7-C2B IOHI 2 using 2 molar equiv of iodine monochloride in the presence of catalytic amounts of aluminum chloride yielded the corresponding clos0-9,12-12-1,2-C2B10H10 and closo-9,10-I2-1,7-C2B10H10 complexes in excellent yields. Palladium-mediated cross-coupling reactions of these diiodocarboranes with a variety of alkyl, aralkyl, and aryl Grignard reagents were reinvestigated, and it was demonstrated that the addition of copper(1) iodide as a cocatalyst is crucial to the success of this reaction. A reaction mechanism involving the initial formation of binary organocopper species (RCu; R = alkyl, aralkyl, aryl) followed by the reaction of (a-carborany1)palladium iodides (LzPd(Cb1)I and L2Pd(CbR)I; L = PPh3, Cb = c~oso-~ ,~ -C~BIOHIO, closo-1 7-C2BloHlo) via a four-centered transition state is proposed. The molecular structures of closo-9,10-12-1,7-C2B10H10, 1, and C~O~O-~,~~-(C~H~)~-~,~-C~BIOHIO, 10, have been determined. Crystallographic data are as follows: for 1, monoclinic, space group P21lc, a = 13.2719-

Direct and Indirect Oxidations by Peroxynitrite

Abstract: The mechanism of oxidation of iodide, NiIkyclam, and ferrocyanide by peroxynitrite has been studied in detail. The results demonstrate that the oxidative chemistry of peroxynitrite is highly pH dependent and can take place either directly by the peroxynitrous acid, as in the case of iodide and NiIIcyclam, or indirectly by secondary reactive intermediates formed via the self-decomposition of peroxynitrous acid, as in the case of ferrocyanide. The rate constants of the oxidation of Iand NiIIcyclam by ONOOH have been determined to be (2.3 f 0.1) x lo4 M-' s-' and (3.25 f 0.15) x lo4 M-' s-l, respectively. In the indirect pathway, about 60% of ONOOH isomerizes to nitric acid and about 40% is converted into a highly reactive oxidant which directly oxidized ferrocyanide via the formation of N O i as an intermediate without the involvement of hydroxyl radicals in this process.

Evidence for polyelectrolyte/ionomer behavior in the collapse of polycationic gels

Abstract: The interaction of slightly cross-linked positively charged gels of poly(diallyldimethylammonium chloride) (PDADMACl) with sodium salts of chloride, bromide, iodide, and acetate in aqueous media has been investigated. At the critical concentration of sodium iodide, a phase transition of the network to the collapsed state was observed. A wide hysteresis accompanied this transition. The presence of other salts did not initiate the network collapse in the investigated concentration range. A decrease in the charge density of the cationic network by copolymerization of DADMACl with acrylamide resulted in the disappearance of the phase transition. In this case, the usual contraction of polyelectrolyte gels in the presence of the mentioned salts was observed. The rate of volume change increased sharply with increasing concentration of sodium iodide. For some cases, two well distinct regions in the kinetic behavior were observed: a region of fast polyelectrolyte contraction and a region of slow collapse which, to our knowledge, had not been observed previously. The experimental results can be explained by the formation of ion pairs and multiplets (ionomer effect) for the sufficiently charged networks in the collapsed state. As a result, the collapsed ionomeric state of the network becomes competitive with the swollen polyelectrolyte state at high enough fractions of the ion-containing segments because of the tendency of the ion pairs to associate. A potential barrier which separates the ionomeric and the polyelectrolyte states of the gel can be used to explain the two-step kinetics of the collapse

Infrared spectroscopic studies on photolysis of methyl iodide and its clusters in solid parahydrogen

Abstract: Methyl iodide is trapped as the monomer and as clusters in the parahydrogen, known as a quantum crystal, at temperatures below about 8 K. UV illumination of the deposited sample at about 5 K causes the dispersal of clusters and the production of the methyl radical, methane, and ethane as evidenced by their infrared absorption spectra. Thermal annealing of the photolyzed sample at temperatures up to 11 K results in the disappearance of the methyl radical, the enhancement of ethane, and the regeneration of methyl iodide. When the initial concentration of the iodide is small, the clusters in the deposited sample are suppressed. For such a sample the UV excitation produces the methyl radical and methane but the formation of ethane is negligibly small. Relevance of the present work to studies of photolysis in gaseous clusters of methyl iodide is discussed.

Langmuir Film-Forming and Second Harmonic Generation Properties of Lanthanide Complexes

Abstract: A series of amphiphilic lanthanide complexes were designed and synthesized, in which the lanthanide complex anions act both as the counterions of hemicyanine and as the spacer within a Langmuir-Blodgett (LB) film. Studies on the surface pressure-area ({pi}-A) isotherms of these complexes show that the film-forming properties can be clearly improved if appropriate {Beta}-diketone ligands were chosen. The effects of molecular structures of the complexes, including the variation of lanthanide central ions, the structures of {Beta}-diketone ligands, and the length of alkyl chains in hemicyanines, on the film-forming properties of the materials are discussed. From second-harmonic generation experiments, the largely enhanced second-order molecular hyperpolarizability of lanthanide complexes with good film-forming properties were obtained compared with the hemicyanine iodide. This effect may be due in part to the local field effect but primarily molecular ordering and ordered segregation of hemicyanine chromophores by the bulky lanthanide complex anions. The charge separation of the hemicyanine chromophores was supported by the crystal structure of a model complex. The homogeneity of the film was verified by low angle X-ray diffraction and also by the linear relationship of the absorbance vs the number of layers of the LB films of a selected complex. 37 refs., 7more » figs., 3 tabs.« less

Charge Transfer Salts of Benzene-Bridged 1,2,3,5-Dithiadiazolyl Diradicals. Preparation, Structures, and Transport Properties of 1,3- and 1,4-[(S2N2C)C6H4(CN2S2)][X] (X = I, Br)

Abstract: Cosublimation of 1,3- and 1,4-benzene-bis(1,2,3,5-dithiadiazolyl) and iodine/bromine affords crystals of the mixed valence salts 1,3- and 1,4-[(S2N2C)C6H4(CN2S2)][X] (X = I, Br). The crystal structures of the two iodide salts consist of perfectly superimposed stacks of molecular units with interannular spacing along the stacks of 3.487(3) and 3.415(2) A, for the 1,3- and 1,4-derivatives. In both compounds the iodines are disordered along the stacking direction. The 1,3-derivative has a highly one-dimensional structure; there are no short intercolumnar S-S interactions. In the 1,4-derivative, however, lateral S-S contacts of 3.911 A, afford some measure of three-dimensionality. The bromide salt of the 1,4-derivative consists of ribbons of alternating 1,4-[(S2N2C)C6H4(CN2S2)]+ units and bromide ions. Within each molecule one heterocyclic ring is closed shell, i.e., a [CN2S2]+ cation, while the other is a discrete radical. The ribbons are layered in zigzag fashion that maximizes ion pairing and isolates the radical centers. The bromide salt of the 1,3-derivative also forms ribbon-like arrays, but the unit cell repeat consists of four layers of ribbons. Within these layers the [CN2S2] rings are approximately stacked. The four rings within the repeat unit along each stack consists of three rings clustered into a trimeric [CN2S2]3+ cation, while the remaining ring is a discrete [CN2S2]+ cation. Magnetic susceptibility and conductivity measurements on the two iodide salts indicate weakly metallic behavior at room temperature, with a charge density wave (CDW) driven metal-insulator phase transition occurring near 270 and 190 K for the 1,3- and 1,4-derivatives, respectively. For the 1,4-derivative, analysis of the CDW wavevector associated with the transition affords a degree of charge transfer of 1/4 of electron per radical, i.e., an overall formulation of [(S2N2C)C6H4(CN2S2)]0.5+[I]0.5-. The bromide salt of the 1,3-derivative is a closed shell insulator, while in the 1,4-bromide the isolated radical centers are antiferromagnetically coupled.

Process for producing high purity acetic acid

Abstract: A high purity acetic acid is prepared by reacting methanol with carbon monoxide in the presence of a rhodium catalyst, iodide salts, and methyl iodide, wherein an acetaldehyde concentration in the reaction liquid is maintained at 400 ppm or lower. This may be attained by contacting the liquid containing carbonyl impurities with water to separate and remove the carbonyl impurities. After that, the liquid can be returned to the reactor.

Sorption of fluoride ions from aqueous solutions by a yttrium‐loaded poly(hydroxamic acid) resin

Abstract: Yttrium‐loaded poly(hydroxamic acid) ion‐exchange resin (YPHA) has been studied to sorb fluoride ion from aqueous solutions The resin was effective in decreasing the fluoride concentration from 5 mM down to 0002 mM in the pH range of 28 to 42 The rate constant for the sorption was found to be 56 x 10‐2 min‐1 The sorption of the fluoride was the Langmuir type and its capacity was 068 mmol‐F/g resin The sorption selectivity shows that the fluoride removal may be interfered by the presence of phosphate and sulphate but was not affected by chloride, bromide, iodide and nitrate ions The removal of fluoride from actual industrial wastewaters was more than 96% A column test shows that fluoride ion was retained on the column until the breakthrough point The fluoride ion sorbed can be eluted from the resin with 100 mM sodium hydroxide, and the column can be reused after being conditioned with 1 mM hydrochloric acid

Fate of ClNO2 over aqueous solutions containing iodide

Abstract: The uptake of nitryl chloride ClNO2 by pure water and NaI solutions was studied as a function of temperature in the range from 268 to 279 K with the droplet train technique. An upper limit of 10−5 was derived for the uptake on pure water, while the uptake rate was observed to be greatly enhanced in the presence of 10−3–10−2 M iodide, yielding uptake coefficients in the range from 1.1 × 10−3 to 6.6 × 10−3. This enhancement is a consequence of a reaction between I− and ClNO2 where we suggest that a transfer of Cl+ to iodide is involved. We also suggest that bulk kinetics alone is unable to describe the measured uptake rate which is influenced by surface reactions. These results show that heterogeneous chemistry in concentrated aerosols may play an important role for the fate of ClNO2, and may affect the concentration of atomic chlorine in the marine boundary layer.

Anodic Polarization Behavior of Copper in Aqueous Bromide and Bromide/Benzotriazole Solutions

Abstract: Theoretical potential-pH equilibria and anodic polarization studies were used to show that formation of the aqueous CuBr 2 - complex in 1M NaBr at ∼24 o C promotes active behavior of copper at pH values ≥3<7 in a manner similar to that observed in chloride solutions. A region of apparent Tafel behavior is observed with a position and slope (dE/d log i) of 60 mV that is consistent with mass transport control of the CuBr 2 - species. Careful analysis of this region provides a method for checking the value of the chemical-free energy of the cuprous complex. Polarization studies in benzotriazole containing 1M NaBr show that benzotriazole interacts with the active oxide-free copper surface to inhibit anodic dissolution of copper. The interaction is potential-dependent, similar to the behavior in chloride solutions, and inhibition is less effective at the lower pH values. Furthermore, a potential occurs above which the spontaneous repair of a damaged inhibiting film is unlikely. The inhibition process is discussed and the observations are shown to be reasonably consistent with a mechanism whose first step is the adsorption of the neutral benzotriazole molecule. Some possible similarities and differences between the active behavior of copper in iodide and bromide solutions are discussed on the basis of differences in their potential-pH equilibria

Application of a quartz crystal microbalance to the study of copper corrosion in acid solution inhibited by triazole-iodide protective films

Abstract: When one uses one side of a quartz crystal microbalance as the working electrode in electrochemical experiments, mass changes can be monitored continuously with a sensitivity of a few nanograms per square centimeter. In this study the working electrode consisted of electrolytically deposited copper, exposed to 0.1M sodium sulfate at pH 3, open to the atmosphere and in some cases containing H{sub 2}O{sub 2}. Upon addition of one of the inhibitors, benzotriazole (BTA), tolyltriazole (TTA), carboxy-benzotriazole (CBT), or these inhibitors plus potassium iodide, the rate of frequency change decreases markedly. After removal of the inhibitors from the corrosive medium by fast solution exchange there is a marked continuing protective effect of the inhibitor films in the cases of BTA + KI and TTA + KI with the latter being the most stable and protective of all of the films. The results were qualitatively the same in the more corrosive solution containing H{sub 2}O{sub 2}.

Electrochemical response of poly(vinylferrocenium)-coated Pt electrods to some anions in aqueous media

Abstract: The electrooxidation behavior of iodide, thiocyanate, and cyanide on poly(vinylferrocenium)-coated Pt electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. IR and UV spectroscopic data, and differential scanning calorimetry (DSC) measurements indicated that these anions were incorporated in the polymeric structure as a result of anion exchange. Anodic stripping of these anions from the film was carried out after the initial preconcentration. Cyanide uptake was found to cause an irreversible change in the physical properties of the film, whereas thiocyanate and iodide are merely incorporated in the film structure as counter ions.

Iodine speciation in size fractionated atmospheric particles by isotope dilution mass spectrometry.

Abstract: An isotope dilution mass spectrometric method has been developed for the accurate and sensitive determination of iodide and iodate in aerosol particles of the atmosphere. The direct iodine speciation has been possible by the use of species specifically 129I enriched spike solutions and separation of the isotope diluted species by anion exchange chromatography after water extraction of the filters. Size fractionated collection of aerosol particles by a six stage impactor system shows different distributions of iodide and iodate for particles of different size with specific patterns for anthropogenically influenced continental and unpolluted marine aerosols, respectively. The detection limit for particulate iodide and iodate has been (3–5) pg/m3 for sampling volumes of 3000 m3. Oil, used for heating plants, could be identified as one but not the only anthropogenic iodine source.