Iodine Chemistry Research Articles

Insights into the Photochemical Transformation of Iodine in Aqueous Systems: Humic Acid Photosensitized Reduction of Iodate

Marine aerosol is highly enriched in iodine, mostly in the form of iodate (IO(3)(-)) ions, compared to its relative abundance in seawater. This paper describes a laboratory study of the photochemical reduction of IO(3)(-) in the presence of humic acid. Spectroscopic analysis showed that ~20% of IO(3)(-) was converted to "free" iodide (I(-)) ions and this fraction remained constant as a function of time. Direct detection of an organically fixed fraction (i.e., ∼ 80%) was not possible, but a number of test reactions with surrogate organic compounds containing functional groups identified in humic acid structures indicate that efficient substitution of iodine occurs at aromatic 1,2 diol sites. These iodinated humic acids are stable with respect to photolysis at near-UV/visible wavelengths and are likely to account for a significant proportion of the soluble iodine-containing organic material occurring within aerosols. In the lower atmosphere, oxidation of I(-) to I(2) in marine aerosol occurs mostly through the uptake of O(3), with H(2)O(2) playing a very minor role. A model of iodine chemistry in the open ocean tropical boundary layer, which incorporates these experimental results, is able to account for the observed enrichment of iodine in marine aerosol.

ChemInform Abstract: Asymmetric Organocatalysis Meets Hypervalent Iodine Chemistry for the α‐Functionalization of Carbonyl Compounds

AbstractReview: 34 refs.

Coastal iodine emissions. 1. Release of I₂ by Laminaria digitata in chamber experiments.

Tidally exposed macroalgae emit large amounts of I(2) and iodocarbons that produce hotspots of iodine chemistry and intense particle nucleation events in the coastal marine boundary layer. Current emission rates are poorly characterized, however, with reported emission rates varying by 3 orders of magnitude. In this study, I(2) emissions from 25 Laminaria digitata samples were investigated in a simulation chamber using incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). The chamber design allowed gradual extraction of seawater to simulate tidal emersion of algae. Samples were exposed to air with or without O(3) and to varying irradiances. Emission of I(2) occurred in four distinct stages: (1) moderate emissions from partially submerged samples; (2) a strong release by fully emerged samples; (3) slowing or stopping of I(2) release; and (4) later pulses of I(2) evident in some samples. Emission rates were highly variable and ranged from 7 to 616 pmol min(-1) gFW(-1) in ozone-free air, with a median value of 55 pmol min(-1) gFW(-1) for 20 samples.

The distribution of iodine in the Croatian marine lake, Mir – The missing iodate

The marine chemistry of iodine has been studied in the marine lake, Mir, regarded as a natural reactor situated in the karstificated carbonate rocks of the Croatian Adriatic coast. The investigation covered the major variables: salinity, temperature, dissolved oxygen, pH and alkalinity, some nutrients, organic carbon, and iodide, iodate and organic-I. Lake Mir was found to be meso-trophic, with dynamic nutrient cycling of a magnitude usually associated with the temperate zone but within a Mediterranean clime. An essentially U-shaped pattern exists in the plot of nutrient concentration versus time for the June–November period studied. Together, the major variables and the nutrient chemistry confirm that Lake Mir is essentially isolated from the nearby (90 m) Adriatic seawater, and this also may explain the meso-trophic nature of the lake, with dry and wet deposition as the source of the extra nutrient. It is of note that iodate was essentially absent from Mir during the sampling period. This appears to be consistent with iodine's behaviour in the oceans in general, where iodate is reduced generally as a result of the presence of the biota. The chemistry of iodine in Lake Mir is consequently dominated by changes in iodide and organic-I concentrations, with the latter at higher concentrations than those found in seawater. Even so, the total iodine concentration in Mir is only about one-quarter of that in the adjacent Adriatic seawater, and again it is argued that this is probably a function of Lake Mir's isolation.

Asymmetric Organocatalysis Meets Hypervalent Iodine Chemistry for the α‐Functionalization of Carbonyl Compounds

Keywords: asymmetric synthesis ; enantioselectivity ; hypervalent compounds ; iodine ; organocatalysis ; Diaryliodonium Salts ; Beta-Ketoesters ; Ketones ; Arylation ; Aldehydes ; Iodoarenes ; Oxidation ; Reagents ; Trifluoromethylation Reference EPFL-ARTICLE-180009doi:10.1002/cctc.201200116View record in Web of Science Record created on 2012-07-13, modified on 2017-12-03

Uncertainties in gas-phase atmospheric iodine chemistry

We present a comprehensive chemical mechanism for gas-phase iodine, to be used for modelling tropospheric chemistry. The mechanism has been compiled from evaluated data and individual literature studies, where available; a number of key processes have not been studied experimentally or theoretically and in these cases estimations have been made. The uncertainty associated with these assumptions is evaluated. We analyze the mechanism using a box-model under a variety of boundary layer scenarios – representative of environments where iodine species have been observed – to study the response of the chemical system to changes in the kinetic parameters of selected reactions. We focus in particular on key species such as IO, OIO, INO3 and I2Oy and the impact of iodine chemistry on ozone formation and HOx levels. The results indicate that the chemical system is most sensitive to reactions leading to comparatively stable iodine compounds, which should be a focus of future laboratory studies.

ChemInform Abstract: Hypervalent Iodine Induced Metal‐Free C—H Cross Couplings to Biaryls

AbstractReview: ca. 100 refs.

Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

Abstract. The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr−1 for CHBr3 and 67.3 Gg yr−1 for CH2Br2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere – lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH2ICl, CH2IBr, CH2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.

Modeling and Interpretation of Iodine Behavior in PHEBUS FPT-1 Containment with ASTEC and COCOSYS Codes

The Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France, and the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Germany, have been involved in the analyses and modeling of PHEBUS tests and particularly in iodine chemistry behavior in the containment. To analyze the accuracy of the chemistry models developed and reproduce volatile iodine formation, iodine behavior in PHEBUS FPT-1 containment was modeled by both IRSN and GRS with two different codes: ASTEC and COSOSYS. The ways of modeling (using the ASTEC/IODE and COCOSYS/AIM respective modules) and the nodalization of both approaches are presented and compared, as well as the assumptions made to perform the calculations. The results of the comprehensive analyses are compared with the experimental results, and interpretation of the iodine behavior in the PHEBUS FPT-1 containment is given. Then, a common point of view is concluded that highlights the lack of knowledge for some phenomena of significant impact on the iodine behavior in the containment during a severe accident. Organic iodide and iodine oxide formation models in particular are pointed out for the gaseous phase. The need for improving iodine behavior models including their coupling to thermal hydraulics and aerosol physics is also explained.

LWR severe accident simulation: Iodine behaviour in FPT2 experiment and advances on containment iodine chemistry

The Phebus Fission Product (FP) Program studies key phenomena of severe accidents in water-cooled nuclear reactors. In the framework of the Phebus program, five in-pile experiments have been performed that cover fuel rod degradation and behaviour of fission products released via the coolant circuit into the containment vessel. The focus of this paper is on iodine behaviour during the Phebus FPT2 test. FPT2 used a 33 GWd/t uranium dioxide fuel enriched to 4.5%, re-irradiated in situ for 7 days to a burn-up of 130 MWd/t. This test was performed to study the impact of steam-poor conditions and boric acid on the fission product chemistry. For the containment vessel, more specifically, the objective was to study iodine chemistry in an alkaline sump under evaporating conditions. The iodine results of the Phebus FPT2 test confirmed many of the essential features of iodine behaviour in the containment vessel provided by the first two Phebus tests, FPT0 and FPT1. These are the existence of an early gaseous iodine fraction, the persistence of low gaseous iodine concentrations and the importance of the sump in suppressing the iodine partitioning from sump to atmosphere. The main new insights provided by the Phebus FPT2 test were the iodine desorption from stainless steel walls deposits and the role of the evaporating sump in further iodine depletion in the containment atmosphere. The current paper presents an interpretation of the iodine behaviour in the FPT2 containment vessel based on dedicated small-scale analytical experiments and computer codes calculations. Other investigations dealing with primary circuit and sump chemistry are also reported. These could help to scale the results of Phebus-FP tests to reactor accidents. Modelling studies were generally successful when a gaseous iodine injection from the primary circuit was assumed. Indeed, though each of the iodine codes has specific iodine chemistry features that should be further developed and each approach to the modelling is distinct, the overall iodine behaviour in the FPT2 containment is generally well reproduced by the models that predict: a low final gaseous iodine concentration in the containment atmosphere, a predominant iodine concentration in the sump and to a lesser extent a significant iodine deposition on containment surfaces. The main code-to-code differences, in the results obtained in gaseous iodine speciation, come from the various treatments of gaseous radiolytic reactions. Calculations that include the radiolytic conversion of volatile iodine into iodine oxide particulate show there is a persistence of both gaseous iodine and iodine oxide particles in the atmosphere. There are also some variations between the predicted organic iodine concentrations that depend mainly on the initial assumptions. A key aspect of the Phebus FPT2 test interpretation is that the long term iodine behaviour in the containment can be explained by exchanges between organic iodide released from painted surfaces and inorganic iodine released from deposited aerosol on the containment walls. Further studies of regulatory significance on sump chemistry showed that the gaseous iodine control that was evident in the Phebus tests through silver release and/or alkaline buffered sump solutions may not be assured. As most of the past iodine aqueous chemistry studies were done with rather pure systems and because of the uncompleted understanding of the gaseous iodine speciation, the results may not be extrapolated easily to conditions of reactor accidents thus necessitating deeper investigations.

Polymer-Supported Hypervalent Iodine as Green Oxidant in Organic Synthesis

2-Iodoxy benzoic acid (IBX) and Dess-Martin periodin­ane (DMP, Scheme [¹] ) have been extensively employed in organic synthesis as mild and highly selective reagents for the oxidation of alcohols to carbonyl compounds as well as for a variety of other synthetically useful oxidative transformations. However, IBX and DMP are not perfect with respect to the principles of green chemistry since they are normally used as non-recyclable, stoichiometric reagents in non-recyclable organic solvents, which have potentially damaging environmental effects. [¹] [²] Reactions of monomeric hypervalent iodine reagents with organic substrates lead to the respective iodoarenes as byproducts, which in general are not recoverable from a reaction mixture. The discovery of recyclable reagents and catalytic systems based on the iodine redox chemistry has initiated a major surge of research activity and added a new dimension to the field of hypervalent iodine chemistry. Polymer-supported modifications of hypervalent iodine reagents retain the useful reactivity of their monomeric analogues with the added advantage of being readily recyclable and reusable. Numerous new organoiodine(V) reagents have recently been developed, and it is anticipated that these safe and efficient derivatives and analogues of IBX will find widespread synthetic application in the future.

A containment analysis for SBLOCA in the refurbished Wolsong-1 Nuclear Power Plant

A small break leading to a loss of coolant accident (SBLOCA), being one of the topic accidents in the nuclear plant diagnosis in recent years, has been analysed and evaluated for the refurbished Wolsong-1 Nuclear Power Plant (NPP). The Industry Standard Toolset (IST) codes developed by CANDU (Canadian Deuterium Uranium reactor) Owners Group and updated models including design change parameters are applied newly to the event analyses. The GOTHIC code has been used for the containment thermal-hydraulic analysis of Wolsong-1. Also, the SMART-IST code fitted in the Iodine Chemistry (IMOD-2) model has been used to predict nuclide behavior within the containment considering various aspects. The IMOD-2 was incorporated into SMART-IST as a module dealing with chemical transformations and mass transfer of iodine species in containment. IMOD-2 model is very sensitive to paint and chemicals. The parametric studies for the IMOD-2 model are performed to decide the analysis value set. The iodine release amount increases as the paint thickness increases. But, the iodine release amount increases as the water pH (dousing and primary heat transport (PHT)) decreases. The developed containment analysis methodology and the results of SBLOCA without Emergency Coolant Injection (ECI) are presented herein. Under the most heat-up conditions, the radionuclide release from the failed fuel into the containment and subsequently to the environment is such that the radioactive doses to the public are below the acceptable limits.

Chemistry of radioactive iodine in aqueous media: Basic and applied aspects

The results of studies on chemistry of radioactive iodine in aqueous media of various compositions, performed in the world in the past decade, are systematized and analyzed. Prospects for using the data obtained in various fields of nuclear power engineering are assessed.

Nutrient speciation and hydrography in two anchialine caves in Croatia: tools to understand iodine speciation

Despite iodine being one of the most abundant of the minor elements in oxic seawater, the principal processes controlling its interconversion from iodate to iodide and vice versa, are still either elusive or largely unknown. The two major hypotheses for iodate reduction involve either phytoplankton growth in primary production, or bacteria during regeneration. An earlier study intended to exploit the unusual nature of anchialine environments revealed that iodide is oxidised to iodate in the bottom of such caves, whereas reduction of iodate occurs in the shallower parts of the water column. This investigation was made on the hypothesis that study of the nitrogen and phosphorus nutrient systems within the caves might offer a bridge between the iodine chemistry and the marine bacteria which are assumed to be the agent of change of the iodine in the caves. Accordingly, the hydrography, the nutrient chemistry, and some further iodine studies were made of two anchialine caves on the east coast of the Adriatic Sea in Croatia. Iodate and iodide were determined by differential pulse voltammetry and cathodic stripping square-wave voltammetry, respectively. Total iodine was determined indirectly, as iodate, after oxidation of reduced iodine species with UV irradiation and strong chemical oxidants. Nutrient concentrations were measured by spectrophotometry. Nutrient profiles within the well stratified water columns indicate a relatively short-lived surface source of nitrate and phosphate to the caves, with a more conventional, mid-water, nutrient regeneration system. The latter involves nitrite and ammonium at the bottom of the halocline, suggestive of both autotrophic and heterotrophic microbial activity. High iodate/low iodide deep water, and conservative behaviour of total inorganic iodine were confirmed in both systems. Iodate is reduced to iodide in the hypoxic region where nutrient regeneration occurs. The concentrations of organic iodine were surprisingly high in both systems, generally increasing toward the surface, where it comprised almost 80% of total iodine. As with alkalinity and silica, the results suggest that this refractive iodine component is liberated during dissolution of the surrounding karst rock. A major, natural flushing of one of the caves with fresh water was confirmed, showing that the cave systems offer the opportunity to re-start investigations periodically.

Raman scattering studies of the condensed phase of the HIx feed of the sulfur-iodine thermochemical cycle

The species present in the condensed phase of the HI x , hydrogen producing, feed in the water-splitting, sulfur―iodine thermochemical cycle have been investigated using spontaneous Raman scattering. Measurements of I 2 -containing species in the low Raman-shift region from 50 to 400 cm ―1 in samples of the two aqueous binary systems, I 2 /H 2 O and HI/H 2 O, and the ternary system HI/I 2 /H 2 O with and without the addition of H 2 SO 4 have provided a consistent picture of the aqueous iodine and polyiodide chemistry. Samples were contained in sealed silica ampoules and were heated to temperatures in the range 20―300°C. The results, which cover a wide range of I 2 and HI mole fractions, and x I2 /x HI mole ratios, in the HI/I 2 /H 2 O system, reveal the co-occurrence of H + I ― 3 , H + ―I ― (I 2 ), and H + ―I ― (I 2 ) 2 solvated species in the condensed phase of HI x . Thus, while the first is mostly evident by its strong fundamental band with Raman shift in the range from 110 to 115 cm ―1 , the other two species appear convoluted in a broad prominent band whose Raman shift ranges between 153 and 172 cm ―1 depending on the x I2 /x HI mole ratio. These well characterized Raman features are proposed as an in situ diagnostic for process control of the cycle.

Hypervalent Iodine Induced Metal-Free C-H Cross Couplings to Biaryls

Hypervalent iodine reagents, such as phenyliodine diacetate (PIDA) and phenyliodine bis(trifluoroacetate) (PIFA), are promising alternatives to metal-based oxidants for developing environmentally benign oxidation reactions, due to their low toxicities, mild reactivities, ready availability, high stabilities, and easy handling. During the study on the hypervalent iodine chemistry, we first determined in the 1990’s the single-electron-transfer (SET) oxidation ability of the hypervalent iodine(III) reagent toward electron-rich aromatic rings, such as the phenyl ether compounds, affording the corresponding aromatic cation radicals. This discovery led us to develop a series of metal-free carbon-hydrogen (C-H) bond functionalizations of aromatic compounds using the hypervalent iodine oxidants. We have extended the strategy to the carbon-carbon bond formation of biaryls based on the double aromatic C-H bond couplings, which can now provide a novel technology to the synthetic area of metal-free cross couplings for producing mixed biaryls from two molecules of unfunctionalized aromatic compounds. These achievements found by us during the development of hypervalent iodine-induced metal-free C-H cross couplings are now summarized in detail.

Measurements and modelling of molecular iodine emissions, transport and photodestruction in the coastal region around Roscoff

Abstract. Iodine emissions from the dominant six macroalgal species in the coastal regions around Roscoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLe) undertaken in September 2006. A two-dimensional model is used to explore the relationship between geographically resolved regional emissions (based on maps of seaweed beds in the area and seaweed I2 emission rates previously measured in the laboratory) and in situ point and line measurements of I2 performed respectively by a broadband cavity ringdown spectroscopy (BBCRDS) instrument sited on the shoreline and a long-path differential optical absorption spectroscopy (LP-DOAS) instrument sampling over an extended light path to an off-shore island. The modelled point and line I2 concentrations compare quantitatively with BBCRDS and LP-DOAS measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLe. Total I2 emissions over the 100 km2 region around Roscoff are calculated to be 1.7×1019 molecules per second during the lowest tides. During the night, the model replicates I2 concentrations up to 50 pptv measured along the LP-DOAS instrument's line of sight, and predicts spikes of several hundred pptv in certain conditions. Point I2 concentrations up to 50 pptv are also calculated at the measurement site, in broad agreement with the BBCRDS observations. Daytime measured concentrations of I2 at the site correlate with modelled production and transport processes. However substantial recycling of the photodissociated I2 is required for the model to quantitatively match measured concentrations. This result corroborates previous modelling of iodine and NOx chemistry in the semi-polluted marine boundary layer which proposed a mechanism for recycling I2 via the formation, transport and subsequent reactions of the IONO2 reservoir compound. The methodology presented in this paper provides a tool for linking spatially distinct measurements to inhomogeneous and temporally varying emission fields.

Modelling of iodine-induced stress corrosion cracking in CANDU fuel

Iodine-induced stress corrosion cracking (I-SCC) is a recognized factor for fuel-element failure in the operation of nuclear reactors requiring the implementation of mitigation measures. I-SCC is believed to depend on certain factors such as iodine concentration, oxide layer type and thickness on the fuel sheath, irradiation history, metallurgical parameters related to sheath like texture and microstructure, and the mechanical properties of zirconium alloys. This work details the development of a thermodynamics and mechanistic treatment accounting for the iodine chemistry and kinetics in the fuel-to-sheath gap and its influence on I-SCC phenomena. The governing transport equations for the model are solved with a finite-element technique using the COMSOL Multiphysics® commercial software platform. Based on this analysis, this study also proposes potential remedies for I-SCC.

Evidence of reactive iodine chemistry in the Arctic boundary layer

Although it has recently been established that iodine plays an important role in the atmospheric chemistry of coastal Antarctica, where it occurs at levels which cause significant ozone (O3) depletion and changes in the atmospheric oxidising capacity, iodine oxides have not previously been observed conclusively in the Arctic boundary layer (BL). This paper describes differential optical absorption spectroscopy (DOAS) observations of iodine monoxide (IO), along with gas chromatographic measurements of iodocarbons, in the sub‐Arctic environment at Kuujjuarapik, Hudson Bay, Canada. Episodes of elevated levels of IO (up to 3.4 ± 1.2 ppt) accompanied by a variety of iodocarbons were observed. Air mass back trajectories show that the observed iodine compounds originate from open water polynyas that form in the sea ice on Hudson Bay. A combination of long‐path DOAS and multiaxis DOAS observations suggested that the IO is limited to about 100 m in height. The observations are interpreted using a one‐dimensional model, which indicates that the iodocarbon sources from these exposed waters can account for the observed concentrations of IO. These levels of IO deplete O3 at rates comparable to bromine oxide (BrO) and, more importantly, strongly enhance the effect of bromine‐catalyzed O3 depletion in the Arctic BL, an effect which has not been quantitatively considered hitherto. However, the measurements and modeling results indicate that the effects of iodine chemistry are on a much more localized scale than bromine chemistry in the Arctic environment.

Determination of total and non-water soluble iodine in atmospheric aerosols by thermal extraction and spectrometric detection (TESI)

Iodine has recently been of interest in atmospheric chemistry due to its role in tropospheric ozone depletion, modification of the HO/HO(2) ratio and aerosol nucleation. Gas-phase iodine chemistry is tightly coupled to the aerosol phase through heterogeneous reactions, which are dependent on iodine concentrations and speciation in the aerosol. To date, the only method available for total iodine determination in aerosols is collection on filters by impaction and quantification by neutron activation analysis (NAA). NAA is not widely available to all working groups and is costly to commission. Here, we present a method to determine total iodine concentrations in aerosol impact filter samples by combustion of filter sub-samples (approximately 5 cm(2)) at 1,000 degrees C, trapping in deionised water and quantification by UV/Vis spectroscopy. Both quartz and cellulose filters were analysed from four separate sampling campaigns. The method proved to be sensitive (3sigma = 6 ng absolute iodine approximately 3 pmol m(-3)) precise (RSD approximately 5%) and accurate, as determined by external and standard addition calibrations. Total iodine concentrations ranged from 10 pmol m(-3) over the Southern Ocean to 100 pmol m(-3) over the tropical Atlantic, in agreement with previous estimates. The soluble iodine concentration (extracted with water and measured by ICP-MS) was then subtracted from the total iodine to yield non-water-soluble iodine (NSI). The NSI fraction ranged from 20% to 53% of total iodine, and thus can be significant in some cases.