Oxides iodine

The most extensively studied oxide of iodine is I2O5. It is prepared by the dehydration of iodic acid, 

The white solid decomposes at high temperatures ( 300 °C) to give I2 and 02. Chemically, I205 is a strong oxidizing agent and this property has been extensively exploited. In one use, it is employed to oxidize CO for quantitative determination. 

This oxide reacts with water, and it is the anhydride of iodic acid, 

The only other oxides of iodine that appear to have been prepared are I204, I4O9, and I207, but they are of no real importance. 

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Titration Indicators. Concentrations of arsenic(III) as low as 2 x 10 M can be measured (272) by titration with iodine, using the chemiluminescent iodine oxidation of luminol to indicate the end point. Oxidation reactions have been titrated using siloxene the appearance of chemiluminescence indicates excess oxidant. Examples include titration of thallium (277) and lead (278) with dichromate and analysis of iron(II) by titration with cerium(IV) (279). 

Sodium thiosulfate is determined by titration with standard iodine solution (37). Sulfate and sulfite are determined together by comparison of the turbidity produced when barium chloride is added after the iodine oxidation with the turbidity produced by a known quantity of sulfate iu the same volume of solution. The absence of sulfide is iadicated when the addition of alkaline lead acetate produces no color within one minute. 

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

The nitrogen of these aminocarboranes can be alkylated to give, eg, 7-[N(CH3)3]-7-CB2qH22 [31117-16-5]. These compounds give closo-2-(Z. . ]Y, [38102-45-0] upon treatment with Na in tetrahydrofuran (THF) followed by iodine oxidation (eq. 63) (126). 

Finally in this section we mention iodine oxide pentafluoride, F5IO, obtained as a colourless liquid, mp 45°, when IF7 is allowed to react with water, silica, glass or I2O5. As implied... 

Molecular iodine oxidatively adds to 156 (M = Rh, Ir) to yield 157 (M = Rh, Ir X = I), the species containing a metal-metal bond (970M4718). 

In reaction (19) the iodine shown on the left has an oxidation number of zero. After the reaction, some of the iodine atoms have oxidation number +5 and some —1. In other words, the iodine oxidation number has gone both up and down in the reaction. This is an example of selfoxidation-reduction, sometimes called disproportionation. It is a reaction quite typical of, but not at all restricted to, the halogens. 

The Dess-Martin reagent can be shock sensitive under some conditions and explode > 200°C. Other hypervalent iodine oxidizing reagents are known, including PhI(OAc)2/TEMPO and PhI(OAc)2 supported on alumina with microwave irradiation. 

The hypervalent iodine oxidation of (pyridylalkyl)trimethylsilanes to the corresponding alcohols and esters has been reported <96H(43)1151>. Oxidation of 2-(phenylethynyl)p5nidine with HjOj/AcOH followed by ROH/NajCOj provides 6-alkoxy-2-phenacylpyridines 42 via an intermediate iV-oxide <96H(43)1179>. 

Finally, phthalocyanine iron catalysts were also used for the oxidation of alcohols to yield corresponding carbonyl compounds with nonbenign hypervalent iodine oxidants [147]. 

The water content should be and is increasingly determined during RM preparation by Karl Fischer titration. The principle of this method is that it quantifies water selectively by measuring the consumption of iodine. During the titration, iodine oxidizes methylsulfite, formed from methanol and sulfur dioxide in a first step, to methylsulfate under stoichiometric involvement of water. Complete reac-... 

Omura, K. Iodine oxidation of alpha -tocopherol and its model compound in alkaline methanol unexpected isomerization of the product quinone monoketals. J. Org. Chem. 1989, 54, 1987-1990. 

Me2CH, were obtained by iodine oxidation of dimeric platinum(II) complexes.419,420 The Pt—Pt bond lengths in the latter two compounds are 2.598(1) A and 2.578(1) A respectively,420 substantially longer than that in the acetate analogue. 

This compound, readily formed by iodine oxidation of azidodithioformic acid or its salts, is a powerful explosive. It is sensitive to mechanical impact or heating to 40°C, and slow decomposition during storage increases the sensitivity. Preparative precautions are detailed. 

Iodine oxides and bromine oxides are solid compounds which are beyond the scope of this article and will therefore not be discussed in any detail. Clyne and Coxon410 have found that BrO decays in a similar manner to CIO, with the second order rate coefficient of the order of 2x 108 1.mole-1.sec-1. In view of the important role of CIO in the decomposition of chlorine oxides, it is conceivable that BrO may play a similar role in the decomposition of bromine oxides. However, no kinetic information on the decomposition of bromine oxides in the gas phase appears to be available at the present time. 

D Sahal. Removal of iodine by solid phase adsorption to charcoal following iodine oxidation of acetamidomethyl-protected peptide precursors to their disulfide bonded products oxytocin and a Pre-S, peptide of hepatitis B illustrate the method. Int J Pept Res 53, 91, 1999. 

Figure 2.1-9 shows that the iodine oxidation of NaBH4 also leads to B[Pg.48]

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]. 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

In the reaction of l-hydroxy-2-oxo-l-cyclohexanecarboxamide and cyan-amide, the 2-aminooxazole 282 was formed. Treatment of 282 with hydrazine yielded the semicarbazide 283, which on iodine oxidation gave the perhydro-2,4-quinazolinedione 284 (87JPR177). Although the configuration of the product was not given, the cis annelation can be deduced from the published NMR data. 

While the silver and zinc salts were effective Lewis acids for these cyclizations, Kikugawa and coworkers reported that the alkoxynitrenium ions could be generated directly from hydroxamic esters (4) using hypervalent iodine oxidants such as hydroxy(tosyloxy) iodobenzene (HUB) and phenyliodine(lll)bis(trifluoroacetate) (PIFA) . Presumably, with such reagents the reactions proceed through A-(oxoiodobenzene) intermediates (54), which can themselves be regarded as anomeric hydroxamic esters and sources of alkoxynitrenium ions (55) (Scheme 11). 

In dilute aqueous solutions, iodine oxidizes sulfur dioxide to sulfuric acid I2 + SO2 + 2H2O —> H2SO4 + 2HI... 

Kamber B, Hartmann A, Eisler K, Riniker B, Rink H, Sieber P, Rittel W. The synthesis of cystine peptides by iodine oxidation of 5-trityl-cysteine and S-acetamidomethyl-cysteine peptides. Helv Chim Acta 1980 63 899-915. 

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