Iodine Chemistry Research Articles

Hypervalent Iodine Chemistry: 25 Years of Development at the University of Thessaloniki

In this Account we review the reactivity of organic hypervalent compounds through reactions developed mainly at Thessaloniki University over the last 25 years. A number of the reactions discussed were not previously covered adequately in review articles and books. After an introduction and a general brief discussion on structure and reactivity, we examine some early work of ours involving transformations of miscellaneous substrates using (diacyloxyiodo)benzenes. Then, we discuss various aspects of the chemistry of iodonium compounds, including salts, ylides and 1,4-dipoles.

Upper Limit of Iodine Oxide in the Lower Stratosphere

It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2σ), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small.

Experimental analyses of iodine behavior under severe accident conditions with ART

The fission products (FP) behavior analysis code ART developed at JAERI simulates a FP transport and deposition in a reactor coolant system and containment during severe accidents. As part of the code development and verification, several experimental analyses have been conducted. In the JAERI's WAVE experiment, the effect of nitrogen or steam carrier gases on the cesium iodide (CsI) behavior in piping was recently investigated. The ART analysis for nitrogen agreed with the experimental results by reflecting the detailed thermo-fluiddynamic calculation on the CsI aerosol behavior analysis. On the contrary, the analysis for steam did not agree well with the experimental results because observed enhancement of aerosol growth cannot be explained by existing models. Moreover, the newly developed empirical models on iodine chemistry in water were examined for the ACE/RTF 3B experiment. The analysis showed that those models have a fundamental analytical capability.

Hypervalent Iodine Chemistry: Mechanistic Investigation of the Novel Haloacetoxylation, Halogenation, and Acetoxylation Reactions of 1,4-Dimethoxynaphthalenes

Treatment of 1,4-dimethoxynaphthalenes with iodosobenzene diacetate and trimethylsilyl chloride or bromide furnished the haloacetoxylated, acetoxylated, and halogenated 1,4-dimethoxynaphthalenes in excellent yield. The reaction pathway for each transformation was shown to be a function of reagent stoichiometry. A mechanistic hypothesis is presented that rationalizes the reaction pathways and explains the subtle differences in the halogenation reactions. The acetoxylation, for example, is thought to involve the formation of an iodonium ion that promotes the nucleophilic addition of acetate ion and subsequent 1,2-acetyl migration. Bromination occurs as a direct result of the oxidation of trimethylsilyl bromide to bromine, followed by electrophilic aromatic substitution. Chlorination is thought to proceed via a radical process and not the formation of molecular chlorine from the dissociation of iodosobenzene dichloride. The haloacetoxylation reaction also appears to be fairly specific for 1,4-dimethoxynaphthalenes, since the analogous reaction with a 1,4-dimethoxybenzene derivative was unsuccessful.

Silicon Dry Etching in Hydrogen Iodide Plasmas: Surface Diagnostics and Technological Applications

We have investigated hydrogen iodide (HI) as an alternative to conventional chlorine or bromine chemistry for dry etching. Plasma exposed Si surfaces show damage, as revealed by photoluminescence studies. These defects can be annealed out by thermal treatment at 550° C. We have developed an anisotropic polysilicon gate etch process for 0.35 µ m MOS technology based on iodine chemistry. The selectivity between polysilicon and oxide is determined as a function of various process parameters. Decreasing the rf source power from 350 to 100 W increases the selectivity between polysilicon and SiO2 from approx. 30:1 to 180:1. Profiles with a degree of anisotropy close to unity can be obtained without trenching or other undesirable anomalies. Iodine-based plasmas are characterized by very low self-biased voltages, typically less than 70 V.

The atmospheric column abundance of IO: Implications for stratospheric ozone

Absorption attributable to atmospheric IO is observed in high‐resolution, high air mass solar spectra taken at the National Solar Observatory, Kitt Peak, Arizona, in March 1995. These observations, together with cross sections measured in the laboratory for the IO {A2Π3/2←X2Π3/2 (2,0)} rotationally resolved electronic transition, are consistent with a total stratospheric iodine mixing ratio of 0.2 (+0.3 −0.2) parts per trillion by volume. This result, combined with recent laboratory measurements of the rate of the reactions of IO with other halogen species, suggests that iodine chemistry is not responsible for the reductions observed in lower stratospheric ozone during the last several decades.

Computational studies of the isomers of ClIO and ClIO2 Implications for the stratospheric chemistry of iodine

A. Misra and P. Marshall, J. Chem. Soc., Faraday Trans., 1997, 93, 3301 DOI: 10.1039/A702360J

Sorption of hypoiodous acid on activated carbon

In spite of good adsorption characteristics of activated carbon for molecular iodine, from water solution, problems arising due to complexity of chemistry of iodine and hydrolysis as well as influences of other relevant factors in water solutions which easily change the equilibrium concentrations toward domination of species with lower absorbability. Sorption of hypoiodus acid as predominant chemical form of iodine in neutral and weak alkaline solution within the range of micro concentrations has been studied in great details. In the experiments sorption of hypoiodous acid from water solutions on activated carbon with surface area of 1000 m2/g, under static and dynamic conditions, has been performed. Isotherms on various temperatures (25°C, 50°C, 70°C) has been obtained. Parameters of the sorption are determined and mechanism of adsorption of hypoiodous acid molecules on activated carbon has been discussed.

The variation of iodate and total iodine in some UK rainwaters during 1980–1981

A complete sequence of daily rainfall (bulk precipitation) samples collected between January 1980 and April 1981 at Wallingford, in central Southern England, together with a few month's samples from other sites in west Wales, northern England and southern Scotland, have been analysed for iodate and total iodine concentration. The wet deposition of iodine depended mainly upon the amount of rainfall, and the average monthly total iodine concentration was nnt found to vary seasonally as had been anticipated. This behaviour contrasted markedly with that of chloride and sodium ions, whose average monthly concentration decreased during summertime. On average, iodate composed one-half of the total iodine. The iodine chemistry of the rainfall is discussed in terms of the equilibrium between HOI and I2, and between iodine and other redox systems, e.g. peroxide and ozone.

Potential impact of iodine on tropospheric levels of ozone and other critical oxidants

A new analysis of tropospheric iodine chemistry suggests that under certain conditions this chemistry could have a significant impact on the rate of destruction of tropospheric ozone. In addition, it suggests that modest shifts could result in the critical radical ratio HO2/OH. This analysis is based on the first ever observations of CH3I in the middle and upper free troposphere as recorded during the NASA Pacific Exploratory Mission in the western Pacific. Improved evaluations of several critical gas kinetic and photochemical rate coefficients have also been used. Three iodine source scenarios were explored in arriving at the above conclusions. These include: (1) the assumption that the release of CH3I from the marine environment was the only iodine source with boundary layer levels reflecting a low‐productivity source region, (2) same as scenario 1 but with an additional marine iodine source in the form of higher molecular weight iodocarbons, and (3) source scenario 2 but with the release of all iodocarbons occurring in a region of high biological productivity. Based on one‐dimensional model simulations, these three source scenarios resulted in estimated Ix (Ix = I + IO + HI + HOI + 2I2O2 + INOx) yields for the upper troposphere of 0.5, 1.5, and 7 parts per trillion by volume (pptv), respectively. Of these, only at the 1.5 and 7 pptv level were meaningful enhancements in O3 destruction estimated. Total column O3 destruction for these cases averaged 6 and 30%, respectively. At present we believe the 1.5 pptv Ix source scenario to be more typical of the tropical marine environment; however, for specific regions of the Pacific (i.e., marine upwelling regions) and for specific seasons of the year, much higher levels might be experienced. Even so, significant uncertainties still remain in the proposed iodine chemistry. In particular, much uncertainty remains in the magnitude of the marine iodine source. In addition, several rate coefficients for gas phase processes need further investigating, as does the efficiency for removal of iodine due to aerosol scavenging processes.

Clinical and epidemiological correlates of iodine deficiency disorders

Abstract The iodine deficiency disorders, endemic goitre, stillbirths, abortions, congenital abnormalities, endemic cretinism, and impaired mental function, are found worldwide. Known for millenia, they currently put 29% of the world’s population at risk. The most important is cretinism, found in two forms. Neurological cretinism possibly develops due to an insult in early pregnancy, hypothyroid cretinism to an insult late in pregnancy or in early life. The classical medical causes of environmental iodine deficiency, glaciation and leaching, do not adequately explain the prevalence and distribution of iodine deficiency disorders, nor have the new insights into the environmental chemistry of iodine been assimilated properly with medical knowledge. Joint studies would be of help. The presence of various factors other than iodine deficiency in the causation of the disorders is recognized. These are often thought to be geologically related. Recent work suggests plate tectonics as the unifying factor, since iodine deficiency disorders are found along many plate collision zones. Concentration of major and trace elements as a result of plate subduction provides a possible source of goitrogens. A systematic search is needed. The iodine goitrogen ratio could provide the link between environmental iodine and differing intensities of the iodine deficiency disorders found in affected communities.

Effect of Dimers on the Temperature-Dependent Absorption Cross Section of Methyl Iodide

Due to the implication of iodine chemistry in stratospheric ozone depletion, an accurate atmospheric lifetime of methyl iodide has recently become of interest. To calculate this lifetime, a reliable temperature-dependent UV photodissociation cross section, in the region that overlaps with available solar light, is vital. Unfortunately, measurement of this cross section is complicated by the fact that, at typical laboratory pressures, methyl iodide readily forms dimers whose ultraviolet absorption differs from that of the monomer and that dimer formation is also temperature-dependent. We use a combination of theory and experiment to separate the changes in the absorption due to the temperature dependence of dimer formation from the narrowing of the absorption band that results from rotational and vibrational cooling of isolated methyl iodide molecules. Calculation of the predicted absorption cross section shows that the valence band absorption spectrum narrows only slightly upon cooling from 25 to −73 °C (200 K). Absorption spectra were also measured experimentally at a range of pressures from 0.1 to 2.4 Torr and a range of temperatures from −22 to 100 °C. The temperature-dependent cross section measured at 0.1 Torr agrees well with the calculated temperature dependence. The spectra at higher pressures show strong pressure as well as temperature dependence. This pressure dependence allowed us to constrain the temperature-dependent equilibrium constant for dimer formation.

Molecular iodine reduction by natural and model organic substances in seawater

The reactivity of 2 µM molecular iodine in seawater toward various organic compounds containing aromatic, α-keto, amino, olefinic and sugar functional groups was investigated. More detailed studies have been made of the reduction kinetics with salicylic acid, α-ketoglutaric acid and the polypeptide oxidized glutathione, particularly to establish whether variation over the pH range 4–9 would provide a similar reduction reactivity or “fingerprint” to that of molecular iodine added to natural seawater. The data indicates that compounds with only one functional group react with first order kinetics whereas compounds with multiple functional groups show more complex behaviour. Kinetic and thermodynamic modelling indicates that HOI is the main iodine species reacting with organic matter at seawater pH of 8.2. Based on the pH “fingerprints”, peptides and compounds containing carbonyl or α-keto groups are the key reductants of molecular iodine added to seawater. These compounds form C-I and N-I bonds which can allow for a rich organic iodine chemistry in seawater. The model compound results are discussed in relation to oceanic processes.

Novel N-Acyl α-Azidopyrrolidines (N-Acyliminium-Ion Precursors)

As an alternative to the electrochemical procedure [Shono (1984). Tetrahedron, 40, 811-850], N-acyliminium-ion precursors may be generated utilizing novel hypervalent iodine chemistry. The crystal structures of 2-azido-N,N-diphenylpyrrolidine-1-carboxamide, C 17 H 17 N 5 O, and 2,5-diazido-N-(3,4,5-trimethoxybenzoyl)pyrrolidine, C 14 H 17 N 7 O 4 , are reported. In both instances the pyrrolidine ring is found in the half-chair conformation. The azido groups are non-linear with an average bond angle of 172.9 (1)°

Co-ordination chemistry of iodine(I) with tetraazamacrocycles or monodentate ligands. Comparisons with bromine(I) and with some d-block metals

Co-ordination compounds of iodine(I), including those with tetraazamacrocyclic ligands, have been prepared either by direct reaction with the [I(NCMe)2]+ cation or by the previously reported ligand-induced disproportionation reaction of I2. The syntheses and the properties of the iodine complexes so prepared are compared with analogous work involving bromine, iron(II) or copper(II).

Ozone depletion and global warming potentials of CF3I

Laboratory measurements of the infrared and near‐ultraviolet absorption characteristics of CF3I (a potentially useful substitute for halons) are presented. Using these data together with a detailed photochemical model, it is shown that the lifetime of this gas in the sunlit atmosphere is less than a day. The chemistry of iodine in the stratosphere is evaluated, and it is shown that any iodine that reaches the stratosphere will be very effective for ozone destruction there. However, the extremely short lifetime of CF3I greatly limits its transport to the stratosphere when released at the surface, especially at midlatitudes, and the total anthropogenic surface release of CF3I is likely to be far less than that of natural iodocarbons such as CH3I on a global basis. It is highly probable that the steady‐state ozone depletion potential (ODP) of CF3I for surface releases is less than 0.008 and more likely below 0.0001. Measured infrared absorption data are also combined with the lifetime to show that the 20‐year global warming potential (GWP) of this gas is likely to be very small, less than 5. Therefore this study suggests that neither the ODP nor the GWP of this gas represent significant obstacles to its use as a replacement for halons.

On the role of iodine in ozone depletion

Ozone depletions in the lower stratosphere outside of polar regions are difficult to explain using only local chlorine and bromine chemistry. We speculate that iodine chemistry in combination with trends in anthropogenic chlorine and bromine may also be a factor in determining the widespread current depletion of lower stratospheric ozone. We also speculate on a related role for iodine in the sudden springtime surface ozone loss observed in the Arctic.

Thermochemical considerations in source term evaluation

The calculation of the release of fission products from degraded fuel in a light water reactor core uncovery accident is the first step in determining the overall radiological source term. It is the aim of costly experiments to improve our knowledge about the release behavior of the relevant fission products. Since this depends greatly on their chemistry, a thermodynamic evaluation about compound formation and vaporisation in a fuel-fission product-coolant system should precede such tests. It shows how the volatility of these products may change with test conditions. It will need more reduction of the steam atmosphere to get a noticable release of barium and strontium than to have europium show up. It is very unlikely that ruthenium is significantly released even in a nonreduced steam environment. Molybdenum will be released with the cesium in oxidising and slightly reducing atmospheres. Boron has an effect on the iodine and cesium chemistry. This, however, depends greatly on test or accident conditions. It is practically nonexistent at high steam pressures. Low oxygen potential and high boron content of the atmosphere increase the effect.

Determination of iodide ion in impregnated charcoals by flow injection

A procedure for the determination of iodide in charcoals impregnated with potassium iodide is described. An aqueous extract is prepared and the iodide ion concentration in this extract (up to 4 × 10–3 mol dm–3) is determined by injection into a water stream that is merged with an aqueous solution containing potassium iodate and sulfuric acid, followed by absorptiometric measurement at 460 nm. The analysis is simple and rapid, with a limit of detection of 6 × 10–5 mol dm–3 iodide and a relative standard deviation (n= 10) of 1.2% for 1 × 10–3 mol dm–3 iodide. The procedure was used to measure the levels and the distribution of potassium iodide in impregnated charcoals. The flow method is discussed with reference to the chemistry of elementary iodine in aqueous solution.

The phebus fission product project

A new facility is being built at the Phebus test reactor in Cadarache, France, for investigations into phenomena of fuel damage and fission product (FP) release under severe power reactor accident conditions, as part of a large international research program. Phebus FP simulates core, cooling system and containment of an accidented reactor by appropriate scaled-down experimental components. The test fuel, with 25 to 30 GWd/t burnup, is re-irradiated in situ and then overheated up to UO 2 melting. Fission products and other aerosols are swept through the primary pipework into the containment vessel, by hot steam and hydrogen. Experimental instrumentation and posttest analyses will enable the following main phenomena to be studied: structural material and fuel dislocation, final fuel state; release, chemical form and transport/depletion of fission products in the facility, particularly aerosol physics, including nonfission product material and iodine chemistry in terms of volatile species formation through radiolysis, reactions with organic material, aerosol-vapor reactions, etc. Design and development of equipment and experimental procedures are supported by modeling and code calculations with the scope of predicting the experimental sequence, on one hand, and to prepare code validation through the results, on the other hand. More than 25 organisation from Europe and overseas, collaborate in the scientific and technological development of the Phebus FP program. The first in-pile test is planned for spring 1993, and five subsequent experiments are scheduled to follow in yearly intervals. This paper describes facility and support activities, and highlights a number of nuclear materials aspects involved.