Showing papers on "Iodide published in 1991"

Modeling of turing structures in the chlorite--iodide--malonic Acid--starch reaction system.

Abstract: Recent experiments on the chlorite-iodide-malonic acid-starch reaction in a gel reactor give the first evidence of the existence of the symmetry breaking, reaction-diffusion structures predicted by Turing in 1952. A five-variable model that describes the temporal behavior of the system is reduced to a two-variable model, and its spatial behavior is analyzed. Structures have been found with wavelengths that are in good agreement with those observed experimentally. The gel plays a key role by binding key iodine species, thereby creating the necessary difference in the effective diffusion coefficients of the activator and inhibitor species, iodide and chlorite ions, respectively.

Organic Sulfur Chemistry: Structure and Mechanism

Abstract: SULFUR BONDING. INTRODUCTION. PROPERTIES OF SULFUR BONDS. PARTICIPATION OF 3D ORBITALS IN SULFUR BONDING. BONDING IN TRI- AND TETRACOORDINATE SULFUR. WHY ARE "a-DISULFOXIDES" SO UNSTABLE? s-SULFURANE-HYPERVALENCY. HYPERVALENT INTERACTIONS. THE STEREOELECTRONIC EFFECTS OF SULFUR GROUPS. INTRODUCTION. DICOORDINATE SULFUR GROUPS. Electron-Releasing Conjugative Effects. Electron-Sharing Conjugative Effects. Electron-Accepting Conjugative Effects. TRICOORDINATE AND TETRACOORDINATE SULFUR GROUPS. NEIGHBORING GROUP EFFECTS OF SULFUR GROUPS. Dicoordinate Sulfur Groups. Sulfoxides. STEREOCHEMISTRY. INTRODUCTION. TRICOORDINATE SULFUR COMPOUNDS. Structure and Pyramidal Inversion. Sulfoxides. Sulfinate and Thiosulfinate Esters. Sulfonium and Alkoxysulfonium Salts. Sulfilimine and Related Derivatives. Other Tricoordinate Sulfur Compounds. TETRACOORDINATE SULFUR COMPOUNDS. PENTACOORDINATE AND POLYCOORDINATE SULFUR COMPOUNDS. STEREOCHEMISTRY OF a-SULFINYL CARBANIONS. STEREOCHEMISTRY OF a-SULFONYL CARBANIONS. SUBSTITUTION. INTRODUCTION. DICOORDINATE SULFUR COMPOUNDS. Nucleophilic Substitution. Free Radical Substitution. TRICOORDINATE SULFUR COMPOUNDS. Nucleophilic Substitution by SN1-Type Reactions. Nucleophilic Substitution by Ligand Exchange. NUCLEOPHILIC SUBSTITUTIONS ON TETRACOORDINATE SULFUR ATOM-POSSIBLE INVOLVEMENT OF HYPERVALENT INTERMEDIATES. Mode of Bond Fission and Electronic Effects. Effect of Ring Size. Neighboring Group Participation. Reactions at the a-Carbon. PENTACOORDINATE SULFUR COMPOUNDS. LIGAND COUPLING REACTIONS WITHIN HYPERVALENT SPECIES. CONCEPT OF LIGAND COUPLING WITHIN s-SULFURANE INTERMEDIATES. STEREOCHEMISTRY OF LIGAND COUPLING ON SULFUR. LIGAND COUPLING AND LIGAND EXCHANGE ON SULFUR. LIGAND COUPLING AND PSEUDOROTATION. OTHER EXAMPLES. LIGAND COUPLING ON OTHER ATOMS. OXIDATION OF SULFOXIDES WITH METAL OXIDES. REDUCTION OF SULFILIMINES WITH METAL HYDRIDES. OXIDATION AND OXYGENATION. INTRODUCTION. OXIDATION OF THIOLS TO DISULFIDES. Air Oxidation. Metal Oxides and Metallic Ions. Sulfoxides, Amine N-Oxides and Peroxides. Halogens and Halogenating Agents. Nitrogen Compounds. Flavin Derivatives. Photo-Oxidation. OXIDATION OF THIOLS AND DISULFIDES TO SULFUR SPECIES OF HIGHER OXIDATION STATES. Nucleophilic Oxidation. Electrophilic Oxidation. Oxygenation with Enzymes. OXIDATION AND OXYGENATION OF SULFIDES AND SULFOXIDES. Electrophilic Oxidation. Nucelophilic Oxidation. One-Electron Transfer Oxygenation-A Comparison of Cytochrome P-450 and FAD-Containing Monooxygenase. Stereochemistry. REDUCTION. INTRODUCTION. REDUCTION OF DISULFIDES TO THIOLS. Metal Hydrides. Electron Transfer and Photolysis. Thiols and Selenols. Formamidinesulfinic Acid. Tricoordinate Phosphorus Compounds. REDUCTION OF SULFENIC ACID AND SULFENIC ACID DERIVATIVES. Thiols. Electrode Reduction. Silicon and Tin Hydrides. REDUCTION OF SULFINIC ACID AND SULFINIC ACID DERIVATIVES. Phosphorus Compounds. Hydrogen Halides and Trimethylsilyl Iodide. Lithium Aluminum Hydride. Hydrazine. Trichlorosilane. Sodium Metal. Thiols. Grignard Reagents. REDUCTION OF THIOLSULFINATES. Thiols. Phosphines. Cyanide. REDUCTION OF SULFOXIDE, SULFILIMINE AND SULFONIUM YLIDES. Metal Hydrides. Carbenes. Metal and Metal Complexes. Tricoordinate Phosphorus Compounds. Iodide Ion. Sulfur Compounds. Other Procedures. REDUCTION OF SULFONES AND SULFOXIMINES. Elemental Sulfur. Metal Hydrides. Zinc and Hydrochloric Acid and Samarium Iodide. Aryldiazonium Salts. Metals-Reductive Cleavage. Electrochemical Reduction. Nitrosation of Sulfoximines. Carbenes. REDUCTION OF SULFONYL DERIVATIVES. Sodium Sulfite. Halide Ions. Lithium Aluminum Hydride. Metals and Metal Salts. One-Electron Transfer Reactions. Electrochemical Reduction. Free Radical Reductions. Tricoordinate Phosphorus Compounds. Thiols. Other Procedures. REDUCTION OF SULFONIC ACIDS. Nickel-Aluminum. Electrochemical and One-Electron Transfer Reductions. Iodide/Trifluoroacetic Anhydride. Triphenyl Phosphine with Iodine or Disulfides. Borane Derivatives. Polyphosphoric Acid Derivatives with Iodide. Phosphorus Pentasulfide. REDUCTION OF SULFURIC ACID AND SULFATE. REARRANGEMENTS. INTRODUCTION. THE STEVENS REARRANGEMENT. THE SOMMELET-HAUSER OR THE MOFFATT-PFITZNER REARRANGEMENT. THE PUMMERER REARRANGEMENT. SIGMATROPIC REARRANGEMENTS. [1,j]-Sigmatropic Reactions. [3,3]-Sigmatropic Reactions. [2,3]-Sigmatropic Reactions. OTHER REARRANGEMENTS.

Visible-light photolysis of hydrogen iodide using sensitized layered semiconductor particles

Abstract: Surface sensitization of internally platinized layered oxide semiconductors K 4-x H x Nb 6 O 17 .nH 2 O (x≃2.5),H 2 Ti 3 O 7 , and HTiNbO 5 by RuL 3 2+ (L=4,4'-dicarboxy-2,2'-bipyridine) yields photocatalysts for the production of H 2 and I 3 - in aqueous iodide solutions. Flash photolysis experiments show that, at pH 3.0 excited state RuL 3 2+ injects an electron into K 4-x H x Nb 6 O 17 .nH 2 O and is rapidly re-reduced by I - . Steady-state photolysis at 450 nm in 50mM aqueous KI (pH 3.0) yields H 2 and I 3 - in stoichiometric amounts, with an initial quantum yield of 0.3%

Selectivity of membrane electrodes based on derivatives of dibenzyltin dichloride

Abstract: Selectivity properties are established for membrane electrodes prepared by incorporating bis(p-methylbenzyl)tin dichloride, dibenzyltin dichloride, and bis(p-chlorobenzyl)tin dichloride in plasticized polymer membranes. These electrodes display an unusually high level of selectivity for dibasic phosphate over many common anions. Electrodes prepared with the p-chloro derivative possess the best detection limit and the highest degree of selectivity for phosphate. Selectivity coefficients are calculated for phosphate relative to the following groups of anions: salicylate, benzoate, thiocyanate, iodide, nitrate, bromide, chloride, acetate, fluoride, pyrophosphate, arsenate, adenosine 5'-cyclic monophosphate, adenosine 5'-monophosphate, adenosine 5'-diphosphate, and adenosine 5'-triphosphate. Tin-carbon hyperconjugation within the organotin compound is hypothesized to be critically important in the selective response to phosphate. Enhancement of tin-carbon hyperconjugation by increasing the electron-withdrawing power of substituents on the benzyl ring is predicted to provide even higher levels of selectivity for phosphate.

A facile synthesis of bicyclo[m.n.1]alkan-1-ols. Evidence for organosamarium intermediates in the samarium(II) iodide promoted intramolecular Barbier-type reaction

Abstract: Samarium(II) iodide (SmI 2 ) has been successfully employed as a reductive coupling agent for the intramolecular Barbier-type synthesis of bicyclo[m.n.1]alkan-1-ols. Thus, a variety of 3-(ω-iodoalkyl)cycloalkanones, upon treatment with SmI 2 and a catalytic quantity of iron complex in tetrahydrofuran (THF), provide the title compounds in excellent yields. The reaction is quite general for the construction of diverse bicyclic ring systems, including the highly strained bicyclo[2.1.1]hexan-1-ol

Iodine speciation in the water column of the Black Sea

Abstract: Iodine speciation was determined on water samples collected from the upper 250 m of the Black Sea during 11–14 June 1988. Iodate, iodide and total iodine were determined by three separate voltammetric methods. In most samples, the sum of iodide plus iodate equalled the total iodine. In four samples obtained near the oxic/anoxic nonsulfidic interface, however, the sum of the iodide plus iodate was less than the total iodine (range 17–38% lower). Thus, a third form of iodine is present. Addition of sulfite to the samples did not increase the iodide concentration which would be expected if I 2 or OI − were present. It is suggested that the third form of iodine is organic and probably of high molecular weight (peptide or aromatic?). The differences with the previous results of Wong and Brewer (1977, Geochimica et Cosmochimica Acta , 41 , 151–159) can be attributed to different methods used and to differences in the water column chemistry of the Black Sea over time and perhaps season. In the previous work, O 2 and H 2 S coexisted in the zone between the oxic and sulfidic zones whereas in this work, O 2 and H 2 S were not present in the zone between the oxic and sulfidic zones.

Anodic underpotential deposition and cathodic stripping of iodine at polycrystalline and single-crystal gold: studies by LEED, AES, XPS, and electrochemistry

Abstract: The oxidative chemisorption and cathodic stripping reductive desorption of iodine have been compared at smooth polycrystalline and well-defined Au(111) single-crystal electrodes. Experimental measurements were based upon cyclic voltammetry, thin-layer coulometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction. The results indicate that iodide is oxidatively adsorbed as zerovalent atomic iodine at potentials between −0.4 V and +0.4 V (Ag/AgCl reference); at lower potentials, surface iodine is reductively desorbed as aqueous iodide, while at considerably more positive potentials, it is oxidized to aqueous iodate

Transient near-infrared spectroscopy of visible light sensitized oxidation of iodide at colloidal titania

Abstract: Visible light induced photooxidation of iodide at dye-sensitized TiO 2 colloid has been monitored in real time by near-infrared absorption spectroscopy.

Iodine chemistry in the water column of the Chesapeake Bay : evidence for organic iodine forms

Abstract: During the summer of 1987, we collected and analysed Chesapeake Bay water samples for the inorganic iodine species: iodide (by cathodic-stripping squarewave voltammetry) and iodate (by differential pulse polarography); and total iodine (by hypochlorite oxidation of the seawater sample to iodate). The difference between the sum of the inorganic iodine species and the total iodine was significant for about one-third of the samples collected from the Bay. Thus, in these samples, a third (or more) ‘new’ form(s) of iodine was present. These samples were primarily from oxygen-saturated surface waters of high biological activity (primary productivity and bacterial processes). This ‘new’ form can make up as much as 70% of the total iodine. Waters containing low oxygen concentrations showed less of this ‘new’ form of iodine whereas anoxic and sulphidic bottom waters contained only iodide. This ‘new’ form of iodine is organic in nature and probably non-volatile. It may reside in the peptide and humic fractions. Only reduced iodine (iodide and organic iodine) was detected in waters from the northern section of the Bay, whereas only iodide and iodate were detected in the southern section of the Bay. In only two samples were iodide, iodate and the ‘new’ form of iodine found to coexist. Iodide and organic iodine are probably cycled in the surface waters of the northern section of the Bay via a combination of biogeochemical and photochemical processes which produce the reactive intermediates, molecular iodine and hypoiodous acid. These react quickly with reduced inorganic and organic compounds to maintain the reduced forms of iodine in the water column. Only total iodine is conservative throughout the estuary. The inorganic iodine forms can be used as geochemical tracers.

Preferential solvation in mixed binary solvents by ultraviolet–visible spectroscopy: N-ethyl-4-cyanopyridinium iodide in alcohol–acetone mixtures

Abstract: Preferential solvation of N-ethyl-4-cyanopyridinium iodide has been studied by monitoring its solvatochromic charge-transfer band in an alcohol–acetone binary mixture. Solvation by alcohols is found to be preferred over acetone over the entire range of composition. The role of (i) self-association in alcohols, (ii) the size effect of the solvents and (iii) solvent–solvent interaction in determining the preferential solvation in the binary mixture has also been discussed.

X-ray photoelectron spectroscopic studies of poly(2,2'-bithiophene) and its complexes.

Abstract: The charge distributions in chemically synthesized poly(2,2'-bithiophene) (PBT) complexes have been studied by x-ray photoelectron spectroscopy (XPS). XPS results suggest the presence of multiple chemical states for the ``dopants'' in perchlorate, iodide, and ${\mathrm{FeCl}}_{4}^{\mathrm{\ensuremath{-}}}$ complexes. Properly curve-fitted C 1s and S 2p core-level spectra reveal the simultaneous presence of neutral and polarized (or partially charged) species in both carbon and sulfur. The relative amounts of the neutral and polarized species vary in accordance with the oxidation level of the polymer. These results suggest that each dopant anion is associated with a thiophenium ion in the polymer chain. Similar results are also observed for the poly(3-methylthiophene) complexes. The present XPS results differ from most of the earlier XPS studies that have reported overall binding-energy shifts for the C 1s and/or S 2p core-level spectra of the oxidized thiophene polymer complexes. The undoped PBT is susceptible to reoxidation by iodine, ferric chloride, and strong organic acceptors, such as 2,3-dichloro-5,6-dicyano-p-benzoquinone and tetracyanoethylene.

ESCA studies of phase-transfer catalysts in solution : ion pairing and surface activity

Abstract: Phase-transfer catalysts in solution have been studied by means of electron spectroscopy. Different anion-cation distributions at the surface were found depending on the anion identity. Thus, tetrabutylammonium perchlorate and tributyl-3-iodopropylammonium iodide show strong evidence of the formation of contact ion pairs at the surface. Conversely, the tetrabutylammonium nitrate and chloride show a more diffuse character of the anion distribution with respect to the surface. The observed differences in surface structure between the salts correlate with the variation in transfer coefficients from aqueous to organic phase

Microwave acid digestion and preconcentration neutron activation analysis of biological and diet samples for iodine.

Abstract: A simple preconcentration neutron activation analysis (PNAA) method has been developed for the determination of low levels of iodine in biological and nutritional materials. The method involves dissolution of the samples by microwave digestion in the presence of acids in closed Teflon bombs and preconcentration of total iodine, after reduction to iodide with hydrazine sulfate, by coprecipitation with bismuth sulfide. The effects of different factors such as acidity, time for complete precipitation, and concentrations of bismuth, sulfide, and diverse ions on the quantitative recovery of iodide have been studied. The absolute detection limit of the PNAA method is 5 ng of iodine. Precision of measurement, expressed in terms of relative standard deviation, is about 5% at 100 ppb and 10% at 20 ppb levels of iodine. The PNAA method has been applied to several biological reference materials and total diet samples.

Cyano phosphate : an efficient intermediate for the chemoselective conversion of carbonyl compounds to nitriles

Abstract: Cyanohydrin diethyl phosphates, readily obtained from various ketones and aldehydes by reaction with diethyl phosphorocyanidate and lithium cyanide, reacted chemoselectively with samarium(II) iodide in THF to give the corresponding nitriles in excellent yields. This method was also found applicable to α,β-unsaturated carbonyl compounds via cyano phosphates to give β,γ-unsaturated nitriles, not obtainable by standard methods, without isomerization of the double bonds

Determination of trace iodine in food and biological samples by cathodic stripping voltammetry.

Abstract: This paper describes a sensitive and selective method for the determination of iodine in food and biological samples. The method involves treatment of samples by combustion in an oxygen flask and determination of iodide by cathodic stripping voltammetry of the solid phase formed with the quaternary ammonium salt Zephiramine as the ionic associating agent; Br- is used as the complexing agent in the preconcentration process. We have studied the effect of concentration of Zephiramine, Br-, I-, and some other elements presented, deposition potential, preelectrolysis time, and scan rate, on the stripping curve shape and maximum stripping current. Determinations of trace iodine in table salt, laver, and eggs were demonstrated as practical examples.

Structure determination of zinc iodide complexes formed in aqueous solution

Abstract: Structures of the complexes formed in aqueous solutions between zinc(II) and iodide ions have been determined from large-angle X-ray scattering, Raman and far-IR measurements. The coordination in the hydrated Zn2+ hexaaqua ion and the first iodide complex, [ZnI]+, is octahedral, but is changed into tetrahedral in the higher complexes, [ZnI2(H2O)2], [ZnI3(H2O)]− and [ZnI4]2−. The Zn-I bond length is 2.635(4)A in the [ZnI4]2− ion and slightly shorter, 2.592(6)A, in the two lower tetrahedral complexes. In the octahedral [ZnI(H2O)5]+ complex the Zn-I bond length is 2.90(1)A. The Zn-O bonding distances in the complexes are approximately the same as that in the hydrated Zn2+ ion, 2.10(1)A.

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXIII. Stereochemistries and Structures of the 1 : 1 Adducts of Cu1X (X = Cl, Br, I) With 2,2'-Bipyridine

Abstract: Syntheses and single-crystal X-ray structural characterizations (at c. 295 K) are recorded for the 1 : 1 adducts of copper(I) chloride, bromide and iodide with L = 2,2′-bipyridine. The chloride is triclinic, Pī , a 14.069(5), b 10.520(3), c 7.872(2)Ǻ, α 69.00(2), β 88.62(3), γ 70.70(2)°, Z = 4 formula units; R was 0.041 for No 1805 'observed' [I > 3σ(I)] reflections. The bromide is monoclinic, P21/c, a 8.788(3), b 13.206(6), c 9.895(3)Ǻ, β 117.90(2)°, Z = 4 formula units; R 0.036 for No 1007. The iodide is monoclinic, C2/c, a 17.571(3), b 8.587(7), c 16.796(3)Ǻ, β 120.17(2)°, Z = 8 formula units; R 0.041 for No 1038. The chloride is ionic, [CuL2]+ [ ClCuCl ]-; in the cation, Cu-N are 2.005(6)-2.039(6)Ǻ with interligand N-Cu-N 114.4(3)-132.4(2)°, while, in the anion, Cl-Cu-Cl is 177.3(1)°, with Cu-Cl 2.086(2) and 2.091(2)Ǻ. The bromide (unlike its 1,10-phenanthroline counterpart, which is ionic) is a centrosymmetric dimer , as also is the iodide. In the bromide, Cu-N are 2.083(6), 2.099(5), and Cu-Br 2.428(2), 2.463(1)Ǻ, Cu…Cu and Br…Br being 2.850(1) and 3.975(2)Ǻ respectively. In the iodide, Cu-N are 2.070(8), 2.08(1), and Cu-I, 2.583(3)Ǻ (×2), and Cu…Cu and I…I are 2.610(2) and 4.420(1)Ǻ.