Iodine oxidation states

Operated in a CSTR, the CIMA reaction produces, as a function of iodide or chlorite feed concentrations, bistability between an iodine reduced state (high iodine, high iodide concentration) and an iodine oxidized state (low iodide concentration) at relatively low malonic acid feed concentration. Sustained oscillations are produced at higher concentration [14,59]. Using starch as iodine color indicator, the reduced state colors daric blue while the oxidized state is clear or pale yellow. 

Chemical Properties. The electron configuration of the iodine atom is [Kr]4d ° and its ground state is. Principal oxidation states... 

Reactions in Aqueous Media. The chemistry of aqueous iodine has been extensively studied because of the role of iodine as a disinfectant (see Disinfectants AND antiseptics). The system is very complex, owing to the number of oxidation states available to iodine under ambient conditions (48). 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

In the black, lustrous Pd2Sel3, four quadratic PdSei Isa entities are connected by a common Se to a Pd4Se2l4l4/2 group (see Fig. 27). These groups combine via common iodines to form corrugated layers. The formal oxidation state of Pd is 2-1-. 

During oxidation of tin(II) ions by hydrogen peroxide, iodine, bromine, mercury(ir) and thallium(III) the induced reduction of cobalt(in) complexes cannot be observed. Therefore, it was concluded that these reactions proceed by 2-equivalent changes in the oxidation states of the reactants. 

Attempts to oxidise silver dithiocarbamato complexes with halogens to compounds with the metal in higher oxidation states obviously failed. By addition of iodine to a solution of [Ag(Bu2 fc)]g in CHQ3, an insoluble product is formed with the composition rjA% S> X2dtc) 141). With other alkyl groups similar complexes are obtained. Investigations about the nature of this type of compounds are in progress. 

An extremely rare example of a six-coordinate platinum(II) complex has been prepared by the reaction of [Pt(dmpe)2]2+ with three equivalents of I2 in H20/EtOH solution which affords black crystals of [PtI(dmpe)2(K-I2)]I3 (102). X-ray crystallography reveals a neutral I2 ligand that is coordinated to the metal center through one of the iodine atoms.278 XPS (X-ray photoelectron spectroscopy) measurements are consistent with the platinum center having a +2 oxidation state. 

Since the iodine is oxidized (from - l to 0), the oxygen must be reduced. It starts out in the - 1 oxidation state it is reduced to the -2 oxidation state. Water (or OH") is the probable product. 

Perhaps the most important application of redox chemicals in the modern laboratory is in oxidation or reduction reactions that are required as part of a preparation scheme. Such preoxidation or prereduction is also frequently required for certain instrumental procedures for which a specific oxidation state is essential in order to measure whatever property is measured by the instrument. An example in this textbook can be found in Experiment 19 (the hydroxylamine hydrochloride keeps the iron in the +2 state). Also in wastewater treatment plants, it is important to measure dissolved oxygen (DO). In this procedure, Mn(OH)2 reacts with the oxygen in basic solution to form Mn(OH)3. When acidified and in the presence of KI, iodine is liberated and titrated. This method is called the Winkler method. 

The morning session was devoted to a general explanation of the areas of application in studying magnetic properties, oxidation states, compounds, and metal structure. In the afternoon, reviews of the Mossbauer investigations of iron, tin, iodine, tellurium, and some of the rare earth elements were presented. The meeting concluded with a discussion on the future of Mossbauer Spectroscopy in which an interested audience participated. 

Iodine is present in the environment predominantly in the oxidation states —1 (1, iodide) and - -5 (lOs", iodate). Reduction of lOs" to 1 occurs at pe = 13.3 at pH 5 and pe° = 11.3 at pH 7. Hence 1 is expected to predominate in the soil solution except in oxic alkaline soils (Whitehead, 1984). However Yuita (1992) found predominantly IO3 in acid Japanese soils contaminated with iodine the concentrations in solution were some 20 times those of 1 and I2. On flooding the soils, the total concentration of 1 in solution increased 10- to 50-fold, predominantly as I. The concentrations of sorbed 1 were not measured, but both lOs and 1 are expected to be bound to organic matter and oxides and hence their concentrations in solution are expected to increase with reductive dissolution reactions. Further, for a given concentration in solution, 1 is more rapidly absorbed by plants than IO3 (Mackowiak and Grossl, 1999). Hence flooding is expected to increase accumulation in plants both through increased solubility and increased absorption. 

Following a similar strategy, an ingenious mixed resin bed quench and purification strategy was devised for the Dess-Martin periodinane mediated conversion of alcohols to carbonyls. This hypervalent iodine oxidant was viewed as containing an inherent masked carboxylic acid functionality that was revealed at the end of the reaction (Species (11) Scheme 2.30). Therefore purification was easily achieved by treatment of the reaction mixture with a mixed-resin bed containing both a thiosulfate resin and a polymeric base. The thiosulfate polymer was used to reduce excess hypervalent iodine lodine(V) and (III) oxidation states species to 2-iodoben-zoic acid (11), which was in turn scavenged by the polymeric base [51]. 

Iodine also has an oxidation state of+5, when forming the iodate— ion ... 

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