Excess Iodide Research Articles

FISSION OF AS-AS BONDS IN ELEMENTAL ARSENIC BY ALKALI METALS IN LIQUID AMMONIA. A ROUTE TO MONOALKYL ARSINES

Addition of two mol equivalents of t-butyl alcohol to a mixture of powdered arsenic and three mol equivalents of lithium in liquid ammonia gives a suspension of lithium arsenide LiAsH2. Subsequent addition of a large excess of t-butyl alcohol and n-octyl iodide at very low temperatures affords n-octyl arsine in -65% yield.

Flow injection biamperometric determination of chloramphenicol and related nitro compounds by on-line chemical photodegradation

An unsegmented continuous-flow assembly for the determination of chloramphenicol is proposed. The determination is based on the on-line photodegradation of the drug in an NH 4 +/NH 3 buffer at pH 10.4 by using a photoreactor consisting of a 697 cm long × 0.8 mm ID piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol is detected by photolytic cleavage of nitrite from the parent compound as well as by organic oxidizing photofragments, and their subsequent reaction with iodide ion, which is monitored biamperometrically. Triiodide thus formed is detected in excess iodide solution by polarizing two platinum electrodes at 100 mV. The calibration graph is linear up to 8 mg l –1 chloramphenicol; the limit of detection is 0.05 mg l –1, the relative standard deviation is 0.4% (for 25 replicates of 10 mg l –1 drug) and the throughput 68 samples h –1. The proposed method was used to determine chloramphenicol in commercially available pharmaceutical formulations and human urine.

The mechanism of the phosphine-modified nickel-catalyzed acetic acid process

The nickel-catalyzed methanol (MeOH) carbonylation reaction was studied with an in situ infrared technique using a high pressure cylindrical internal reflectance reactor (CIR-reactor). The role of phosphine ligands was investigated in order to determine the relationship between the structural and electronic properties of the ligand and catalytic properties. It was found that the highest carbonylation rates occurred for the phosphine ligands having the greatest cone angles. Altering the electronic properties of substituted triarylphosphines resulted in systematic changes in the carbonylation rate, and a Hammett treatment of the rate data using normal sigma constants led to a volcano plot. A modified Hammett plot using Taft polar sigma constants for various trialkylphosphines led to a linear relationship in which the rate increased as the electron-donating properties of the ligand increased. The carbonylation activity was correlated with the steric size of trialkylphosphines by the observation of a linear relationship to the ligands cone angle. The in situ reaction monitoring studies showed that the phosphine ligand was substantially converted to the corresponding phosphonium salt through reaction with excess methyl iodide in the system. The in situ reaction monitoring studies, conducted at typical process conditions, showed that the phosphonium salt reversibly dissociated to differing amounts of the free phosphine depending on the electronic and steric properties of the phosphine. The reaction monitoring studies, using phosphines of widely differing electronic and steric properties showed that the reaction rates increased linearly as the concentration of free PR 3 in solution increased. The results of this ligand study and a prior process parameter study led to a reaction mechanism in which phosphine is mainly transformed to [P(CH 3)R 3] +I −. It was shown that this soluble salt partially dissociates to provide sufficient free phosphine to coordinate to Ni° to form the active catalyst. A low partial pressure of hydrogen was found essential to provide the catalytic cycle with reduced nickel. The Ni° combines with free PR 3, forming Ni(PR 3) 2 which is located within the active catalytic cycle. The kinetic data and in situ reaction monitoring observations are consistent with a reversible slow step in the active cycle consisting of CH 3I reacting with Ni(PR 3) 2, forming an oxidative addition product which is rapidly carbonylated. All other subsequent steps are much faster than the oxidative addition reaction.

Acidity and N-methylation of N-aryl-N ′-cyanoguanidines †

Acid dissociation constants in water have been determined for proton loss from a series of N-aryl-N′-cyanoguanidines 1. Treatment of the same compounds with a strong base, butyllithium, followed by excess methyl iodide leads to successive N-methylation to yield mono-, di- and tri-methylated N-aryl-N′-cyanoguanidines. The mechanism of the methylation is discussed.

Field Tests for Iodate in Salt

Commercially available field test kits for the determination of iodate in salt were tested to evaluate their performance and to devise improvements in their range and accuracy. Dropper tests based on the blue colour of the starch-iodine complex formed with iodine released by excess potassium iodide gave rapid qualitative indication of the presence of iodate. Because of the dark colour of the complex, the tests were found to be quantitative over only a limited range, typically 0 to 20 μg of iodine per gram of salt. We have developed methods for improving the reliability and colour reproducibility of these types of kits. Instructions for producing reliable kits of this type with improved colour reproducibility are presented. Improved qualitative tests in the range of 0 to 50 μg/g were obtained with a simple liquid-phase colourimetric system, based on the same chemistry. A field test kit was developed and tested in laboratories in India and Zimbabwe, as well as in our laboratory in Toronto. the test gave reproducible results, comparable to those of titration, with a typical standard deviation of ± 5 μg/g. the range of measurements can be extended to 100 μg/g by dilution. Instructions for preparing these kits are presented.

The carbonylation of methyl iodide and methanol to methyl acetate catalysed by palladium and platinum iodides

Palladium(II) salts catalyse the carbonylation of methyl iodide in methanol to methyl acetate (5 atm CO, 140 °C) in the presence of a large excess of iodide, even without amine or phosphine co-ligands; platinum(II) salts show similar reactions but are a little less effective.

Amperometric detection with microelectrodes in flow injection analysis: theoretical aspects and application in the determination of nitrite in saliva

The construction of a wall-jet cell with amperometric detection using a set of disc electrodes whose radii ranged from 5 to 750 μm has been proposed. The influence of some experimental parameters like flow rate and electrode radius on hydrodynamic voltammograms recorded for a 0.5 mmol dm −3 potassium ferrocyanide solution also containing 0.1 mol dm −3 KCl has been discussed. Some considerations regarding the current signals obtained from flow injection experiments using both a 5- and a 750-μm radius platinum electrode were carried out in order to achieve the lowest limit of detection, a value of 0.03 μmol dm −3 ferrocyanide being calculated by using the 5-μm radius microelectrode as amperometric detector. The wall-jet cell has been used in the determination of nitrite in saliva by quantifying the triiodide formed in the reaction of the analyte with excess iodide in acidic medium. A 12.5-μm platinum disc microelectrode maintained at +0.2 V vs. Ag/AgCl was used as amperometric detector. Peaks obtained in fiagrams after injection of diluted saliva to the carrier stream containing 0.1 mol dm −3 sulphuric acid and 20 mmol dm −3 potassium iodide were compared to an analytical curve obtained in the same conditions ( r 2=0.997) for a nitrite concentration in the range 1–10 μmol dm −3. The concentration of nitrite in the saliva sample after the appropriate correction for dilution was found to be 2.3 ppm (0.05 mmol dm −3), in a good agreement with results obtained by using a standard spectrophotometric procedure (2.5 ppm). The limit of detection of the method was calculated as 0.2 μmol dm −3, and the reproducibility was checked by measuring the peak current for 19 injections of 10 μM nitrite, the standard deviation being 3.7%.

Flow-injection biamperometric determination of nitrate (by photoreduction) and nitrite with the NO −2/I − reaction

An unsegmented continuous-flow method for the determination of nitrite and nitrate is proposed. Nitrate is photoreduced by UV irradiation with a low-pressure 8 w mercury lamp. The nitrite in the sample and that resulting from the photoreduction of nitrate are used to oxidize iodide ion. Tri-iodide thus formed is detected biamperometrically in excess iodide by using a flow-cell furnished with two platinum electrodes polarized at 100 mV. The limits of detection, throughput and reproducibility ( n=26) thus achieved for nitrite and nitrate are 25 and 50 μg l −1, 27 and 25 h −1, and 1.2 and 1.6%, respectively. The proposed method was used to determine nitrate and nitrite in natural waters, waste waters, soils, meat products and fertilizers.

Trimethylsilyl iodide as a halide exchange reagent in inorganic chemistry: synthesis and structure of Cp 2*ThI 2 (Cp* = η 5-C 5Me 5)

The bis(pentamethylcyclopentadienyl)thorium(IV) complex Cp 2*ThI 2 (Cp* = η 5-C 5Me 5) was readily synthesized from the dibromo derivative Cp 2*ThBr 2 using a slight excess of trimethylsilyl iodide (Me 3SiI). The thorium complex Cp 2*ThI 2 exhibits a ‘bent metallocene’ structure, as determined by single-crystal X-ray diffraction (monoclinic, space group P2 1/ n; a = 8.572(2), b = 16.718(3), c = 15.881(2) Å; β = 98.16(2) o; V = 2252.8(8) Å 3; Z = 4).

Model reactions of a carbonylation catalyst: phosphite induced migratory CO insertion in [MeIr(CO) 2I 3] −

Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO) 2I 3] − ( 1) is an important step in the new iridium-based process for acetic acid manufacture. A model study of the migratory insertion reactions of 1 with P-donor ligands is reported. Complex 1 reacts with phosphites to give neutral acetyl complexes, [Ir(COMe)(CO)I 2L 2] (L = P(OPh) 3 ( 2), P(OMe) 3 ( 3)). Complex 2 has been isolated and fully characterised from the reaction of Ph 4As[MeIr(CO) 2I 3] with AgBF 4 and P(OPh) 3; comparison of spectroscopic properties suggests an analogous formulation for 3. IR and 31P NMR spectroscopy indicate initial formation of unstable isomers of 2 which isomerise to the thermodynamic product with trans phosphite ligands. Kinetic measurements for the reactions of 1 with phosphites in CH 2Cl 2 show first order dependence on [ 1], only when the reactions are carried out in the presence of excess iodide. The rates exhibit a saturation dependence on [ L] and are inhibited by iodide. The reactions are accelerated by addition of alcohols (e.g. 18× enhancement for L = P (OMe) 3 in 1:3 MeOH-CH 2Cl 2). A reaction mechanism is proposed which involves substitution of an iodide ligand by phosphite, prior to migratory CO insertion. The observed rate constants fit well to a rate law derived from this mechanism. Analysis of the kinetic data shows that k 1, the rate constant for iodide dissociation, is independent of L, but is increased by a factor of ∼18 on adding 25% MeOH to CH 2Cl 2. Activation parameters for the k 1 step are Δ H ≠ = 71 (±3) kJ mol −, Δ S ≠ = −81 (±9) J mol −1 K −1 in CH 2Cl 2 and Δ H ≠ = 60(±4) kJ mol −1, Δ S ≠ = −93(± 12) J mol −1 K −1 in 1:3 MeOH-CH 2Cl 2. Solvent assistance of the iodide dissociation step gives the observed rate enhancement in protic solvents. The mechanism is similar to that proposed for the carbonylation of 1.

Synthesis and Characterization of the Bis-Cyclometalating Ligand 3,3‘,5,5‘-Tetrakis[(dimethylamino)methyl]biphenyl and Its Use in the Preparation of Bimetallic M(II), M(IV) (M = Pt, Pd), and Mixed-Valence Pt(II)−Pt(IV) Complexesviaa Dilithio-Derivative. Crystal Structure of the Pd Dimer [ClPd{2,6-(Me2NCH2)2C6H2}]2

The potentially bis-cyclometalating ligand 3,3‘,5,5‘-tetrakis[(dimethylamino)methyl]biphenyl, was prepared from 3,5-(Me2NCH2)2C6H3Br in a one-pot synthesis involving lithium−halogen exchange, transmetalation, and reductive-elimination reactions. This ligand undergoes selective dilithiation in the 4 and 4‘ positions of the biphenyl group to form [Li2{2,6-(Me2NCH2)2C6H2}2]n, which is a versatile precursor to bimetallic complexes via a double transmetalation reaction. The syntheses and characterization of the new homobinuclear Pt(II) and Pd(II) compounds, [(MeCN)Pt{2,6-(Me2NCH2)2C6H2}−]2(CF3SO3)2 and [ClPd{2,6-(Me2NCH2)2C6H2}−]2, is reported in addition to a novel synthetic route to the complex [ClPt{2,6-(Me2NCH2)2C6H2}−]2. The solid-state structure of Pd dimer was determined by single-crystal X-ray diffraction. Oxidative addition of Cl2 to the latter Pt compound produced the bis-platinum(IV) complex [Cl3Pt{2,6-(Me2NCH2)2C6H2}−]2, which reacts with 2 equiv of Ag(O3SCF3) in MeCN solution to form [(MeCN)Cl2Pt{2,6-(Me2NCH2)2C6H2}−]2(CF3SO3)2. This complex could also be obtained directly by reaction of the former PtII dimer with 2 equiv of Cl2IPh. 1H NMR spectroscopic studies show that mixtures of the PtII and PtIV dimers in acetonitrile solution are in equilibrium with a mixed-valence (PtII,PtIV) species [(MeCN)PtII{2,6-(Me2NCH2)2C6H2−C6H2(CH2NMe2)-2,6}PtIVCl2(NCMe)](CF3SO3)2, which, however, could not be isolated in pure form. The reaction of the PtII dimer with ≤1 equiv of Cl2IPh also gave a PtIV dimer, along with unreacted starting material and the mixed-valence complex. A reversible double C−C bond formation has been achieved by reaction of the PtII dimer with excess of methyl iodide. This procedure yields the bis(arenonium) species [IPtII{2,6-(Me2NCH2)2-1-MeC6H2}−]2(CF3SO3)2 in which both the Me groups derived from I−Me bond cleavage are bound to the Cipso of the aryl rings. The mono(arenonium) compound [IPtII{2,6-(Me2NCH2)2-1-MeC6H2-C6H2(CH2NMe2)2-2‘,6‘}PtII](CF3SO3)2 has been identified as an intermediate in this reaction by 1H NMR spectroscopy.

Deoxygenation of Steroidal Ring-D 16,17-Ketols with Timethylsilyl Iodide.

Reaction of various steroidal 16, 17-ketols, 16α-hydroxy-17-ketones 1-3, and 15, 16β-hydroxy-17-ketone 4, and 17β-hydroxy-16-ketones 5-7, and 17, along with methyl ethers of 16α- and 17β-ketols, 1 and 5, with an excess of trimethylsilyl iodide (TMSI) or with HI in CHCl3, produced the deoxygenated products, a mixture of the corresponding 17-and 16-ketones, in low to quantitative yields, in which the 17-ketone was the major product in each case. When the 16β-deuterated 16α-ketol 3 and the 17α-deuterated 17β-ketol 7 were reached with TMSI for a brief period (15 min), the deuterium content at C-16β and C-17α of the recovered steroids 3 and 7 was reduced by 17 and 35%, respectively. The present results indicate that the deoxygenation proceeds not only through a direct iodination pathway producing α-iodoketone but also through other reaction pathways.

Polymerization of 1-methyl-2,5-bis[1-(4-phenylurazolyl)] pyrrole dianion with alkyldihalides

1-Methyl-2,5-bis[1-(4-phenylurazolyl)] pyrrole was prepared from the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with N-methylpyrrole in methylene chloride solution. This compound was converted to its potassium dianion salt upon reaction with potassium hydroxide in absolute ethanol. The reaction of this dianion salt with excess methyl iodide in dimethyl sulphoxide gave the methylated adduct in high yield. Polymerizations of this dianion salt with 1,2-dibromoethane, 1,2-diiodoethane and 1,4-diiodobuthane were performed in dimethyl sulphoxide and led to the formation of new polymers. Some structural characterization and physical properties of these novel polymers are reported. © 1998 SCI.

Mechanistic Studies on the Aryl−Aryl Interchange Reaction of ArPdL2I (L = Triarylphosphine) Complexes

The aryl−aryl interchange reaction of ArPdL2I complex 1m was found to follow pseudo-first-order kinetics. A marked inhibition in the presence of excess phosphine and/or excess iodide was observed, suggesting that a dissociative pathway was involved, contrary to the analogous alkyl−aryl interchange reaction studied previously. Phosphine flooding experiments could not be performed due to a competing phosphonium salt formation reaction that occurred in the presence of excess phosphine. A deuterium labeling experiment indicated that the interchange reaction proceeded via the reductive elimination to form the phosphonium salt, suggesting that excess phosphine was acting as a trap for intermediate palladium(0) species preventing the generation of the interchanged palladium(II) complex. Substituent effect studies of the interchange reaction indicated that it was inhibited by electron-withdrawing groups on both the phosphine and palladium-bound aryl groups and by increased steric bulk on both the phosphine and pa...

Methyl iodide mediated cleavage of the nitrogen-oxygen bond of isoxazolidines

A novel method of NO bond cleavage in isoxazolidines is described. Treatment of isoxazolidine with excess of methyl iodide in THF under reflux gave the quaternary ammonium iodide alcohol and the α,β-unsaturated aldehyde. The former can be converted to the latter via the Swern oxidation.

PENTAALKYL-6-DIPHENYLPHOSPHINO-2,3,4,5-TETRACARBA-NIDO-HEXABORANES(6)

Pentaalkyl-6-bromo-2,3,4,5-tetracarba-nido-hexaboranes(6) (3-carb-Br and 4-cab-Br) react with lithium-diphenylphosphide to give the 6-diphenylphosphino substituted carboranes 3-carb-PPh2 and 4-carb-PPh2. 3-carb-PPh2 can be oxidized to give the respective oxide, sulfide and selenide. Treatment of 4-carb-PPh2 with an excess of methyl iodide cleaves the P-B bond and 4-carb-I is formed together with [Me2Ph2P]+I. 4-carb-PPh2 reacts with borane in tetrahydrofuran (BH3-THF/THF) or W(CO)5-THF/THF to give the BH3 and W(CO)5 complexes. All products were characterized by 1H, 11B, 13C and 31P NMR spectroscopy.

The catalytic effect of Mo V on the oxidation of iodide by chlorate

The kinetics of the catalytic effect of Mo 2O 4(H 2O) 2+ 6 on the iodide oxidation by chlorate was studied at different temperatures (25–45°C) in Ar-saturated acid aqueous solutions under conditions of excess iodide ion by monitoring the formation of I − 3 at 352 nm. The initial reaction rate at 30°C is represented by the following equation: v = 1 3 d[I − 3]/d t = k Mo[H +] 2[I −][ClO − 3] with k Mo = 9 × 10 −5 s −1 · M −3 + 0.73 s −1 · M −3 [H +] −1[Mo 2O 2+ 4] where the brackets indicate molar concentrations and time is expressed in seconds. A mechanism, which includes the formation of a dimeric molybdenum complex as rate determining step, is proposed to account for the experimental results.

Amiodarone induces a different pattern of ultrastructural change in the thyroid to iodine excess alone in both the BB/W rat and the Wistar rat.

Amiodarone (AMD)-induced toxicity can be a life-threatening complication which limits the use of amiodarone as an anti-arrhythmic agent. The aim of the present study was to determine the nature of AMD toxicity by comparing ultrastructural changes induced by AMD and equivalent amounts of iodide in two animal models, the Wistar and the autoimmune BB/W rat. Rats were divided into control (water), AMD- (30 mg AMD/kg) or iodide-treated (10 mg/kg) groups. Thyroids were removed at 15 weeks and processed for electron microscopy. We found that AMD induced specific ultrastructural changes of thyroid cytotoxicity in both rat models, which were distinct compared with changes induced by excess iodide alone. Specific changes included marked distortion of thyroid architecture, evidence of necrosis and apoptosis, inclusion bodies, lipofuscinogenesis and markedly dilated endoplasmic reticulum (ER). Our data indicate that AMD is directly cytotoxic to the thyroid an effect mediated by disruption of subcellular organelle function. ER dilatation is suggestive that AMD cytotoxicity may be mediated through disruption of the protein sorting pathways leading to a drug-induced form of ER storage disease. The predilection of the thyroid to AMD may be explained by the additive effects of excess iodine and AMD drug toxicity on protein sorting pathways.

Protection of the Maternal and Fetal Thyroid from Radioactive Contamination by the Administration of Stable Iodide during Pregnancy. An Experimental Evaluation in Chimpanzees

The safety and efficacy of the administration of stable iodide to protect the fetal thyroid from exposure to radioactive iodide were investigated in chimpanzees in weeks 19 to 21 of pregnancy. The mean 24-h uptake of iodide in the fetal thyroid, determined with 123I-, was 1.8%. Administration of stable potassium iodide (KI), 0.65, 1.95 or 6.5 mg per kg body weight, 1 h before tracer injection reduced the fetal uptake satisfactorily. Only the higher doses were effective after 20 h. Excess iodide may impair a child's thyroid status. However, adverse effects were not found during the 11 days the animals ingested these doses. Tracer concentrations in the amniotic fluid were 30- to 130-fold lower than in the urine. The dose to the fetus from radioactivity in the maternal bladder was estimated by computer simulation. The potential increment of the risk from this dose during the ingestion of stable iodide is smaller than the reduction of risk achieved by inhibiting the uptake of radioactive iodide by the fetal thyroid. The conclusion of the experiments is that stable iodide can be used safely and effectively to protect the fetal thyroid against contamination with radioactive iodine.

Connecting Cluster Anion Properties to Bulk: Ion Solvation Free Energy Trends with Cluster Size and the Surface vs Internal Nature of Iodide in Water Clusters

There is disagreement in the literature on whether small water clusters (up to ∼60 waters) accommodate an excess iodide anion at the surface, in the interior, or in states intermediate between the two extremes. Small cluster solvation data, the results of ion simulations in model polar solvent clusters of intermediate size, and limiting continuum dielectric trends at large cluster size have been combined to illustrate the progression of the free energy of ion solvation from the smallest cluster size to bulk, establishing a set of general expectations for cluster ion solvation properties vs cluster size. The surface vs internal state issue for iodide in water clusters is examined in the context of the cluster ion properties of solvation thermochemistry, electron vertical detachment thresholds, and vertical detachment energies with specific regard to variation with cluster size and extrapolation to bulk. In aqueous systems, the anionic cluster property of vertical detachment threshold is shown to bear a bet...