Redox reaction iodide/iodate

Dushman Reaction Investigated in Micro Reactors Organic synthesis 91 [OS 91] Redox reaction of iodate and iodide... 

Inorganic anions such as iodide, iodate, nitrate, and chlorate have been determined on the basis of redox reactions. Iodides have been determined by their reaction with chromium(vi) in an acidic medium. The unreacted Cr is then extracted into MIBK from a 3 M HCl solution. The iodide concentration is quantitatively related to the increase of the Cr atomic signal in aqueous solution or the decrease of the Cr signal in the organic phase. Selenium(iv) is reduced by iodide to elemental selenium. The atomic absorption signal of selenium is then measured in the selenium precipitate. 

P 35] A reaction system with two competitive parallel reactions was used for mixing characterization [36], The Dushman reaction involves the mixing of iodate, iodide and sodium acetate in one solution and a strong acid such as sulfuric acid or hydrochloric acid in another solution. If mixing is fast, the neutralization of the acid and the base dominates as the faster reaction. The redox reaction of iodide and iodate then is a slow process nearly no iodine is formed as the redox product... 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

The efficiency of mixing is usually determined by a standard chemical method, the so-called Dushman reaction.Mixing of a strong acid (FICl) and a solution of I , lOs , and CFi3C02Na (sodium acetate) leads to a combination of an ultrafast reaction (neutralization of the acid) and a fast reaction (I2 formation by an acid promoted redox reaction between iodide ions and iodate ions) as shown in Scheme 7.1. These two reactions having H as a common reaction component compete in a parallel way. If the mixing is very fast, the ultrafast process masks the slower second... 

As the experiments showed, iodide and iodate were formed in a ratio of about 5 1 upon contact of I2 with the basic aerosol materials. Apparently, it is easier for I2 to disproportionate on the surface than it is for it to undergo a redox reaction with ions in the crystal to form Csl alone. Thermochemical data show that the formation of iodide and iodate would result in a lower free energy of reaction than formation of iodide alone. Formation of iodate alone would give a lower iodine potential than formation of iodide and iodate however, iodate formation seems to be limited by reaction kinetics. The extent of I2 reaction with anhydrous CS2O and CS2CO3 is probably limited only by the surface concentration of iodide and iodate which prevents or delays further interaction between I2 and the host crystal. In tests in which saturated aqueous solutions of these compounds were present, no such limitation was observed, nor had it been expected. 

KI -f- 3 0 until the fused mass has reached a temperature above 560 C. Therefore, potassium iodate remains unchanged after several hours at 300-400 . If, however, the salt is mixed with carbonic material and then heated, a redox reaction producing potassium iodide and carbon dioxide occurs within a short time (1-5 minutes), and it begins even at 250-300 C. The presence of the resulting potassium iodide in the heated mixture is readily shown by extracting the cooled mass with a little water and adding dilute sulfuric acid to the extract. Iodine is set free ... 

Even in the cold, iodates are reduced by hypophosphorous acid iodides and phosphoric acid result. This redox reaction does not occur instantane-ousl and directly, but via partial reactions with different velocities. Phosphorous acid and iodide are formed initially (1) the latter then reacts with the iodate to produce free iodine (2), which then oxidizes the phosphorous acid produced in (1) to phosphoric acid ... 

Reaction System The iodide-iodate reaction (Villermaux-Dushman reaction) is based on a system of two competing parallel reactions as described above (Equation 2.60). The neutralization reaction ri is very fast and can be considered as instantaneous. The redox reaction T2 is fast. By adding an add to a mixture of iodide and iodate in a H2B03 /H3B03 buffer, iodine will be formed only if a local proton excess exists. Therefore, the amount of iodine formed can be used to characterize the mixing time in the reactor. Best results are obtained if the mixing time is on the same order as the reaction time (t = tr2). 

In the fractional precipitation method for the separation of radioiodide, radioiodate, and radioperiodate (27,45), the sample was dissolved in aimonia water and iodine carriers were added. (The basic nature of the solution prevents redox reactions which might occur between the oxo species and iodide in an acidic or neutral medium.) Silver iodide was then precipitated from the ammo-niacal solution. The solution which remained was acidified with nitric acid and silver lodate precipitated. The periodate, which was left in solution, was reduced to iodide by means of sulfite and the iodide precipitated as the silver salt. The separation is not entirely satisfactory high results for periodate are generally obtained because some iodate appears in the periodate fraction as a result of the slight solubility of silver iodate. 

Thermodynamic data for U and its adsorption reactions have already been discussed. Among other important radioisotopes, the behavior of iodine in is relatively simple and well understood. Iodine occurs as iodate (lOj) in highly oxidized waters and iodide (I ) under more reducing conditions, including in most groundwaters (cf. Pourbaix 1966). At 25°C and below pH = 5, the redox boundary defining equal concentrations of these species for = 10 M is given by... 

The oxidation numbers of oxygen and hydrogen have not changed in the course of the reaction. However, that of iodine has changed. It went from +V (iodate ion) and -I (iodide ion) to 0 (iodine). The two redox couples are... 

The actinide ions in aqueous solution resemble the tripositive lanthanide ions in their precipitation reactions, allowing for differences in the redox properties of early members of the actinide series. The chloride, bromide, nitrate, bromate, and perchlorate anions form water-soluble salts, which can be isolated as hydrated solids by evaporation. The acetates, iodates, and iodides are somewhat less soluble in water. The sulfates are sparingly soluble in hot solutions, somewhat more soluble in the cold. Insoluble precipitates are formed with hydroxide, fluoride, carbonate, oxalate, and phosphate anions. Precipitates formed from aqueous solution are usually hydrated, and the preparation of anhydrous salts from the hydrates without formation of hydrolyzed species can only be accomplished with difficulty. The actinide(iv) ions resemble Ce(iv) in forming fluorides and oxalates insoluble even in acid solution. The nitrates, sulfates, perchlorates, and sulfides are all water-soluble. The iv state actinide ions form insoluble iodates and arsenates even in rather strong acid solution. The... 

For the production of I from Cs, the target, CsIO, was irradiated with fast neutrons obtained from the reaction of deuterons on beryllium (109). After irradiation, the cesium iodate was dissolved in an aqueous solution of molecular iodine and the iodine extracted into carbon tetrachloride. Several I,I redox cycles were then carried out and the iodine was finally precipitated as silver iodide. The product was contaminated with I and I (the extent of contamination was not given) formed from iodate. 

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