Air oxidation of iodide

Standardization of Na Og with Cu. To prevent air oxidation of iodide in the acidic solution, use a 180 mL tail-form beaker (or a 150 mL standard beaker) loosely fitted with a 2-hole stopper. One hole serves as inlet for a brisk flow of N2 or Ar that leaks out the side of the stopper. The other hole is used for the buret. Pipet 10.00 mL of standard Cu solution into the beaker and flush with inert gas. Remove the cork briefly to add 10 mL of water containing 1.0-1.5 g of freshly dissolved KI and begin magnetic stirring. Titrate with Na2S2Os from a 50 mL buret, adding 2 drops of starch just before the last trace of I2 disappears. Premature addition of starch leads to irreversible binding of I2 to the starch, and makes the end point harder to detect. 

Boyer and Ramsey found that the air oxidation of iodide is induced by the reaction of iodide with peroxydisulfate, Fe(III), ferricyanide, or V(V). The reaction with V(V) was investigated in detail and found to behave as a typical induced chain reaction. The proposed mechanism involves the formation of atomic iodine I or the ion I2" as an intermediate that reacts with oxygen. The chain is initiated by the reaction... 

In accordance with this mechanism, an induced air oxidation of iodide is to be expected whenever 1° or Ij is formed as the primary oxidation product of iodine. Titrations of iodide with Ce(IV) or Mn04 are not sensitive to induced air oxidation, evidently because 2 is rapidly oxidized to I2. The induction factor and therefore the relative error due to air oxidation (oxygen error. Section 19-2) are decreased by an increasing concentration of iodide and oxidant, because the importance of the termination reaction (15-64) increases. 

Iodine can be purified by sublimation from potassium iodide and calcium oxide and weighed as a primary standard. Because of the limited solubility and volatility of iodine, it must be dissolved in concentrated potassium iodide solution and diluted to volume. Air oxidation of iodide should be minimized by preparing the solution with water free of heavy-metal ions and storing it in a cool, dark place. Because of the inconvenience of weighing iodine accurately, its solutions are commonly standardized against arsenic(III) oxide (primary standard) or thiosulfate. ... 

Two common sources of error in the quantitative use of iodine are (/) loss of iodine due to its volatility and (2) air oxidation of iodide. The first is most likely to be encountered if the concentration of iodide is so low that solid iodine is present. Sufficient iodide should be present to decrease the concentration of free iodine below the saturation value. Loss of iodine is enhanced by evolution of gases (such as carbon dioxide generated for deaeration) and by elevated temperatures. Determinations should be carried out in cold solutions. 

Because the reaction is not instantaneous at moderate acidity, a relatively high acidity is used, with the concomitant danger of air oxidation of iodide. Accurate results can be obtained by regulating the concentrations of acid and potassium iodide closely (for example, using 0.2 M hydrochloric acid and 2% potassium iodide) and allowing the mixture to stand 10 min. 

Actually, a strongly acidic solution of iodine can be titrated if the thiosulfate is added slowly with vigorous stirring. In the reverse titration (thiosulfate with iodine), however, a weakly acidic solution must be used to avoid decomposition. A low concentration of acid tends to prevent appreciable air oxidation of iodide. 

Air oxidation of iodide ion also causes changes in the molarity of an iodine solution ... 

The quantitative conversion of thiosulfate to tetrathionate is unique with iodine. Other oxidant agents tend to carry the oxidation further to sulfate ion or to a mixture of tetrathionate and sulfate ions. Thiosulfate titration of iodine is best performed in neutral or slightly acidic solutions. If strongly acidic solutions must be titrated, air oxidation of the excess of iodide must be prevented by blanketing the solution with an inert gas, such as carbon dioxide or... 

Inasmuch as the soil used was slightly alkaline (pH 7.70) it was believed that some of the triiodide produced in the soil distillate by Reaction 1 would be lost. The addition of a small quantity of acetic acid to this distillate considerably increased the percentage of ethylene dibromide recovered in the analysis (Table I). However, the addition of acid aids the oxidation of iodide ion to triiodide ion by oxygen of the air according to Equation 3. 

The catalyst system of TOP18 and TOT is remarkably stable and long-lived if the reaction system is kept free of water and air. Contamination of the reaction mixture with water will lead to TOT decomposition (17). This reaction produces hydrogen iodide which reacts with epoxide 1. Air is deleterious to both catalyst components. Introduction of air into the process can cause oxidation of iodide anion to iodine which will dealkylate TOT. These reactions lead to loss of iodine value from the catalyst system which is monitored by XRF during production. 

A sample (approximately 0.2 g.) is weighed accurately and dissolved in 25 ml. of water then 25 ml. of 0.1 N hydrochloric acid and 0.2 g. of potassium bromide are added. The solution is titrated with 0.017 M potassium bromate until a permanent yellow color is produced. Potassium iodide (0.1 g.) is added, and the solution is backtitrated to a starch end point with 0.1 N sodium thiosulfate. The blue color returns in about a minute since the high acidity promotes air oxidation of excess iodide. The accuracy is only slightly less if the appearance of a faint yellow bromine color is taken as the end point. One mole of potassium bromate is equivalent to 3 of sodium /8-styrenesul-fonate. 

Sparingly soluble salts of the complex cation, such as the iodide, the picrate, the reineckate, the perchlorate, and the tetraphenylborate, are prepared in pure form by air oxidation of bisbenzenechromium(O) in a mixture of benzene and water according to the reaction ... 

The tetrahydrobianthryl products formed by protonation of the dimeric dianions have been isolated (up to 90% yield) in some cases after addition of acids [253.255,256]. Unless the dimer dianion is trapped by acid (or in a single case by methyl iodide [259]), air oxidation of the dimer dianion to starting material takes place during work-up [249-254]. 

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. 

Bromide is most often separated by distillation after oxidation to bromine [1]. Distillation is carried out in a stream of gas such as air, nitrogen, or carbon dioxide. It is possible to separate iodide, bromide, and chloride from each other by selective oxidation. First, the iodine produced by oxidation of iodide with hydrogen peroxide in phosphoric acid medium (pH 1) is distilled. Then dilute nitric acid (2.5 M) is used to oxidize bromide to bromine. Iodide in the presence of bromide can also be oxidized with nitrite in acetic acid medium. The iodide (and subsequently the bromine) liberated can be separated by extraction into CHCI3, CCI4, and other solvents [1,2],... 

The titration should be performed rapidly to minimize air oxidation of the iodide. 8tirring should be efficient to prevent local excesses of thiosulfate because it is decomposed in acid solution ... 

When the fuel rod segments were heated in a dry air atmosphere, much higher release fractions were observed (Collins et al., 1988). At 500 and 700 °C test temperatures, the iodine release fractions were considerably larger than those obtained in steam tests conducted at the same temperature likewise, at 700 °C the cesium release fraction was larger by about a factor of 60 than it was in a steam atmosphere. This increase in release rates was assumed to be caused by an increased porosity of the fuel pellet as a consequence of superficial UO2 oxidation, as well as of oxidation of iodide originally present in the fuel and in the gap to elemental iodine. 

The solution is immediately titrated with standard 0.1 N sodium thiosulfate solution from a 25-mL buret (with efficient swirling, but not shaking) to near disappearance of the yellow color. At this point, a few drops of a 1% soluble starch solution may be added to form the intensely blue iodine-starch complex for easier detection of the endpoint. The titration should take no more than about 1 min to minimize air oxidation of the iodide to additional iodine. The titration reaction is... 

It must be achieved under very precise experimental conditions in order to avoid the formation of nitrogen dioxide NO2 from nitric oxide NO by reaction with the air dioxygen. Nitric acid itself is formed by the oxidation reaction of iodide ions. Nitrogen oxides, present in the medium, catalyze the oxidization of iodide ions by dioxygen and result in too great a release of iodine. 

Some experimental conditions must be respected in order to obtain satisfactory results. The hydrochloric acid concentration must be high, about 4 mol/L. The oxidization of iodide ions by the air dioxygen must be avoided and we must wait five... 

Seaweeds. The eadiest successful manufacture of iodine started in 1817 using certain varieties of seaweeds. The seaweed was dried, burned, and the ash lixiviated to obtain iodine and potassium and sodium salts. The first process used was known as the kelp, or native, process. The name kelp, initially apphed to the ash of the seaweed, has been extended to include the seaweed itself. About 20 t of fresh seaweed was used to produce 5 t of air-dried product containing a mean of 0.38 wt % iodine in the form of iodides of alkah metals. The ash obtained after burning the dried seaweed contains about 1.5 wt % iodine. Chemical separation of the iodine was performed by lixiviation of the burned kelp, followed by soHd-Hquid separation and water evaporation. After separating sodium and potassium chloride, and sodium carbonate, the mother Hquor containing iodine as iodide was treated with sulfuric acid and manganese dioxide to oxidize the iodide to free iodine, which was sublimed and condensed in earthenware pipes (57). 

Methylene iodide [75-11-6], CH2I2, also known as diio dome thane, mol wt 267.87, 94.76% I, mp 6.0°C, and bp 181°C, is a very heavy colorless Hquid. It has a density of 3.325 g/mL at 20°C and a refractive index of 1.7538 at 4°C. It darkens in contact with air, moisture, and light. Its solubiHty in water is 1.42 g/100 g H2O at 20°C it is soluble in alcohol, chloroform, ben2ene, and ether. Methylene iodide is prepared by reaction of sodium arsenite and iodoform with sodium hydroxide reaction of iodine, sodium ethoxide, and hydroiodic acid on iodoform the oxidation of iodoacetic acid with potassium persulfate and by reaction of potassium iodide and methylene chloride (124,125). Diiodoform is used for determining the density and refractive index of minerals. It is also used as a starting material in the manufacture of x-ray contrast media and other synthetic pharmaceuticals (qv). 

Detection of Bromine Vapor. Bromine vapor in air can be monitored by using an oxidant monitor instmment that sounds an alarm when a certain level is reached. An oxidant monitor operates on an amperometric principle. The bromine oxidizes potassium iodide in solution, producing an electrical output by depolarizing one sensor electrode. Detector tubes, usefiil for determining the level of respiratory protection required, contain (9-toluidine that produces a yellow-orange stain when reacted with bromine. These tubes and sample pumps are available through safety supply companies (54). The usefiil concentration range is 0.2—30 ppm. 

The Iodometric method has also been utilized in analyzing hydrogen sulfide in the air (EPA 1978). The method is based on the oxidation of hydrogen sulfide by absorption of the gas sample in an impinger containing a standardized solution of iodine and potassium iodide. This solution will also oxidize sulfur dioxide. The Iodometric method is suitable for occupational settings. The accuracy of the method is approximately 0.50 ppm hydrogen sulfide for a 30-L air sample (EPA 1978). 

Some evidence to suggest that peroxo complexes can be intermediates in the oxidation of Pt(II) by 02 has been presented. As shown in Scheme 41, a Pt(IV) peroxo complex was obtained by reacting cis-PtCl2(DMSO)2 and 1,4,7-triazacyclononane (tacn) in ethanol in the presence of air (200). An alkylperoxoplatinum(IV) complex is obtained in the reaction of (phen)PtMe2 (phen = 1,10-phenanthroline) with dioxygen and isopropyl-iodide. Under conditions that favor radical formation (light or radical initiators), an isopropylperoxoplatinum(IV) compound was obtained (201,202), depicted in Scheme 42. 

A dramatic departure of ozone measurements from total oxidant measurements has b Mi reported for the Houston, Texas, area. Side-by-side measurements suggested that either method was a poor predictor of the other. Consideration was given to known interferences due to oxides of nitrogen, sulfur dioxide, or hydrogen sulfide, and the deviations still could not be accounted for. In the worst case, the ozone measurements exceeded the national ambient air quality standard for 3 h, and the potassium iodide instrument read less than 15 ppb for the 24-h period. Sulfur dioxide was measured at 0.01-0.04 ppm throughout the day. Even for a 1 1 molar influence of sulfur dioxide, this could not explain the low oxidant values. Regression analysis was carried out to support the conclusion that the ozone concentration is often much higher than the nonozone oxidant concentration. 

The corresponding nickel complexes of these ligands were synthesized through deprotection of the acetyl groups via saponification in methanol, followed by addition of Ni(H20)6Cl2 and air oxidation. The monoanions 4a-e were then precipitated by treatment with tetrabutylammonium bromide, and recrystallized to give shiny, crystalline materials. 7V-Methylpyridinium salts were also produced by substituting A -methylpyridinimn iodide for tetrabutylammonimn bromide. 

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