Iodide to iodate

Carbon impregnated with potassium iodide was used as an ozone-scrubbing filter in a chemiluminescence NO analyser. When the level of iodide was inadvertently increased to the high level of 40%, the filter exploded violently dining replacement after use. This was attributed to oxidation of iodide to iodate by ozone, and frictional initiation of the iodate-carbon mixture when the filter was dismantled. 

Carpenter et al. [3] suggest that this method may have underestimated the true value by a factor of three or more. The error was proposed to be due to the oxidation of iodide to iodate by molecular bromine and/or hypobromous acid (reaction (4.6)),... 

The practical application of these observations is to minimise the effect of iodate by rapidly carrying out the iodometric titration of chlorine residual in seawater at pH 4. Moreover, if desired, a titration correction curve can be generated using iodate at the specific concentration of iodide in the sample in question, as there appears to be a complete conversion of seawater iodide to iodate in the presence of excess chlorine. 

In order to remove effectively iodide by RNDS , oxidation of iodide to iodate or periodate is necessary. Iodide is oxidised to iodate with excess chlorine. Through contact of dechlorinated brine with the ion-exchange resin containing zirconium hydroxide, the iodide is therefore removed from the brine. 

In the case of well brine, the anolyte is not circulated as the iodide content is too high. In this situation, a portion of the anolyte containing chlorine is added to the well brine and after oxidising the iodide to iodate the brine is sent to the RNDS . 

Solutions of periodic add and of sodium metaperiodate in water are quite stable at room temperature. The periodate content is readily determined by titrating, with standard sodium arsenite solution, the iodine liberated from iodide in neutral solution.49 103-197 Periodate also may be determined accurately in the presence of iodate, since in neutral solution periodate is reduced by iodide to iodate. The reaction in the presence of a boric add-borax buffer is shown by the following equation. 

The best known amplification reactions are used in connection with the determination of small amounts of iodide. By oxidation of iodide to iodate,... 

Methoxyl. Methoxyl groups are determined by a modified method (53). Methyl iodide is formed by hydrolysis of the methoxyl groups of wood lignin in hydriodic acid and is distilled under CO2 into a solution of bromine and potassium acetate in glacial acetic acid. Bromine oxidizes iodide to iodate which is then titrated with standard thiosulfate. The method is difficult and time-consuming, and some experience is necessary before satisfactory results can be obtained. Details are in ASTM Standard D 1166 and Tappi Standard T 209 (withdrawn in November 1979). Additional discussion can be found in Reference 54. 

One per cent potassium iodide in neutral buffered or alkali solutions is more stable and useful than 20% potassium iodide in bubblers for collection and determination of ozone in air. Either 1 % solution may be used to determine low concentrations of ozone however, there is a difference in their stoichiometry. Over the range of 0.01 to 30 p.p.m. (v./v.) results by the alkaline procedure should be multiplied by 1.54 to correct for stoichiometry. The neutral reagent does not require acidification and has more nearly uniform stoichiometry. The alkaline procedure is preferable when final analysis may be delayed. Experiments with boric acid for acidification of samples in the alkaline reagent show that some mechanism other than oxidation of iodide to iodate or periodate is involved, possibly formation of hypoiodite. Preliminary experiments with gas phase titrations of nitrogen dioxide and nitric oxide against ozone confirm the stoichiometry of the neutral reagent as 1 mole of iodine released for each mole of ozone. 

This chapter considers the oxidation of iodide in seawater by natural oxidants (02, H202, and 03). The oxidation of iodide to iodate is considered slow, yet the six-electron T-IOj redox couple normally used to represent the process (or predict stability) is thermodynamically favorable (2). We will discuss both one- and two-electron-transfer processes with these oxidants, focusing on the first step of electron transfer and using the frontier molecular orbital theory approach in conjunction with available thermodynamic and kinetic data. The analysis shows that the chemical oxidation of I to I03 is not a very important process in seawater, except perhaps at the surface microlayer. 

I" solutions are stable to oxidation for long periods of time in the presence of 02. The half-time for the iodide-to-iodate conversion is unknown (2). Conversely, the reaction of HS" (which is isoelectronic with I ) with 02 has a half-... 

The mechanism for the iodide-to-iodate conversion in seawater is still not well understood. This conversion is not a facile process. Here we compare iodide with other isoelectronic ions, including SH and its congeners Cl" (0.545 M in seawater) and Br (840 xM). The analysis indicates the conservative nature of Cl" under photochemical and thermal conditions. 

Bromine water is usually used for the oxidation of iodide to iodate [4,5]. The excess of bromine is removed by boiling, or by the addition of phenol (to form tribromophenol). Permanganate oxidizes iodide to iodate in alkaline media. The excess of permanganate is reduced with nitrite, the residual nitrite being reduced with urea. 

Polarographic determination. Free chlorine oxidizes iodides to iodates in moderately alkaline medium (pH 10), which are determined by a polarographic method. 

In a slightly basic solution (ca. pH 8) such as seawater, both iodate and iodide are present, but iodate is more stable than iodide under oxic conditions (Wong, 1991). However, direct oxidation of iodide to iodate is very slow due to the kinetic barrier, and thus iodide is stable for a long time in seawater once it is formed by biological and/ or abiological process. On the other hand, as iodate is thermodynamically stable, the reduction of iodate to iodide does not occur spontaneously. 

Since one iodide ion gives one molecule of iodate, which in turn liberates six atoms of iodine, the sensitivity of the test is thus markedly multiplied. The oxidation of iodide to iodate may be carried out by means of bromine water in neutral solution ... 

The method proposed by Martinez et al. [78] also allows the determination of bromide, nitrite, and nitrate together with iodide. Complete separation of the four inorganic anions was reached in less than 3 min. Sulfate added to prevent the oxidation of iodide to iodate does not interfere the determination of iodide, up to a ratio of 1 1000 (I S03 ), but it does not allow the simultaneous analysis of bromide, nitrite, and nitrate. 

Leipert s method for determination of iodide is widely used, especially on solutions derived from the combustion of organic compounds containing iodine. This method depends upon the oxidation of iodide to iodate with bromine water, removal of the excess bromine by addition of some suitable reagent (phenol is widely used—see under Chiniofon Sodium, p. 315—but formic acid is most convenient), addition of iodide and titration of the liberated iodine with thiosulphate. The method has the great advantage that it gives a six-fold increase in the quantity of iodine to be titrated. A detailed procedure for its application will be found in Appendix IV, p. 800. 

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