Iodate oxidation with

Soluble sulphides. Hydrogen sulphide and soluble sulphides can also be determined by oxidation with potassium iodate in an alkaline medium. Mix 10.0 mL of the sulphide solution containing about 2.5 mg sulphide with 15.0 mL 0.025M potassium iodate (Section 10.126) and 10 mL of 10M sodium hydroxide. Boil gently for 10 minutes, cool, add 5 mL of 5 per cent potassium iodide solution and 20 mL of 4M sulphuric acid. Titrate the liberated iodine, which is equivalent... 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Determinations of iodate without pre-oxidation in Pacific seawater by the previous method gave a mean result of 583 ig/l with a standard deviation of 0.23 xg/l. For samples containing between 40 and 60 xg/l, standard deviations of 0.19 xg/l (iodate method with pre-oxidation), 0.12 xg/l (iodate method without pre-oxidation), and 0.43 ig/l (total iodine method) were obtained. 

A set of Pacific open-ocean samples were analysed for iodate-iodine using both the procedure which incorporates pre-oxidation with iodine water and that which does not. Also, in a similar exercise total iodine was determined using both the method that incorporates pre-oxidation with bromine water and the catalytic method using the reaction between Ce(IV) and As(III) [81]. Variance tests showed that differences between either replicates or methods was not significant. 

Silver foil is transformed by an aq. soln. of the trichloride into silver chloride and iodide silver oxide with an excess of the trichloride is transformed into the chloride and iodic acid with more silver oxide, silver iodate is formed and with an excess of the oxide and a boiling soln. some silver periodate is formed. Mercuric oxide is slowly transformed into mercuric chloride and oxide chlorine, oxygen, and possibly chlorine monoxide are evolved. Aq. soln. of the trichloride give a precipitate of iodine with a little stannous chloride with more stannous chloride, some stannous iodide is formed. Consequently, although chloroform extracts no iodine from the aq. soln., it will do so after the addition of stannous chloride. Sulphur dioxide and ferrous sulphate are oxidized. 

The element was obtained by the reduction of an acidic solution of the iodate ion with sodium hydrogen sulfite, (a) Write the chemical equation for the reaction, assuming the oxidized product to be HS04. (b) Calculate the mass of sodium hydrogen sulfite needed to produce 50.0 g of iodine. 

Oxidants often tend to disproportionate by interaction of the acidic or undissociated oxidant with the anion of the same oxidant 1 this is a nucleophilic displacement, by the OX- anion, of X- from the oxygen atom of the electrophilic HOX [Eq. (11)]. Two points should be emphasized here. First, the maximum decomposition occurs when HOX and OX- are in equal concentrations, that is, when the pH of the reaction is equal to the pKa of the oxidant [Eq. (12)]. Second, since this is a displacement, the reaction goes more readily when the group X- is easily displaced thus formation of iodate from hypoiodite is more extensive than chlorate formation from hypochlorite. 

Other methods were developed for various anions. Bromides were oxidized with permanganate and the bromine so produced reacted with cyclohexene to form 1,2-dibromocyclohexane [577]. Similarly, iodides were analysed in milk as monoiodoacetone after oxidation with iodate and after reaction of the released iodine with acetone [578]. Pennington [579] utilized the same oxidation reaction for the analysis of iodates the iodine released was analysed as such. Cyanides were chlorinated prior to analysis with chloramine-T and the cyanogen chloride so produced was subjected to GC [580]. Analogously, cyanides and isocyanates form cyanogen bromide with bromine water, which can be analysed by GC [581]. 

It will be appreciated that iodate is incompatible with both iodide (cf. Section IV.21, reaction 6) and with thiocyanate (Section IV.21, reaction 9) since iodine is liberated in acid solution. Also sulphide is incompatible with both bromate and iodate (oxidation to sulphate occurs), and an arsenite is oxidized by iodate in acid solution. These facts should therefore be borne in mind when interpreting Table V.30. An independent test for iodate (test 11) is provided below this can be performed before the silver nitrate tests. 

Rubidium periodate, RbI04.—When a mixture of rubidium iodate and hydroxide in hot concentrated solution is oxidized with chlorine, the periodate is formed in colourless quadratic crystals isomorphous with those of potassium periodate, and with the density 3-918 at 16° C. At 13° C. its solubility is 0-65 gram in 100 grams of water.18... 

Reactions (63) and (65) often occm simultaneously. For example, iodate or iodine in acidic conditions and cyano-ferrate(III) in alkaline solutions prefer reaction (62), while iron(III) or manganate prefer reaction (64). The oxidation to dinitrogen either takes place directly or stepwise in a one-electron oxidation with hydrazyl radicals N2H3-(A/ff = 231 kJmol ) as intermediates. 

The method (16) describes the titrimetric microdetermination of salicylic acid, aspirin and p-hydroxybenzoic acid by amplification reactions. The cited acids are brominated with Br to form tribromophenyl hypobromite, which after removal of unconsumed Br wtih formic acid, is treated with iodide to give tribromophenol and free iodine. The liberated iodine is extracted with CHCI3 and reduced to iodide, which is determined by oxidation with Br and iodimetric titration of the iodate produced with Na2S203 solution. This six fold amplification... 

Pyrogullol U OXldlMtl by Ihc reagent in aqueous buffer to purpurogallin," but the yield (39%) is lowif thbn In oxidation with sodium iodate. Tropolone does nut react end hence behevilJMliyihi e eerboxylic ncid then e phenol. 

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. 

In the presence of a small excess of iodide, Pd gives Pdt which is sparingly soluble in acidic media. When shaken with benzene or DIPE, PdE passes into the organic phase it has been the basis for a sensitive indirect determination method. The suspension of Pdh in the organic solvent is stripped by dilute ammonia. The aqueous solution is acidified, then the iodide is oxidized by bromine to IO3. This iodate reacts with added T to liberate iodine, which is determined as its coloured complex with starch (see Section 25.2.1). One Pd atom in PdE is equivalent to twelve atoms of iodine. 

Oxidation of the 1,1-disubstituted hydrazine, 3-amino-2-oxazolidinone (1), with bromine water, with potassium iodate-HN03, or with potassium bromate in 6 N HC1 affords a compound melting at 299° and now recognized as the trans-3,3 -azobis(2-oxazolidinone) of formula (2). Forgione et al. 5 explored oxidation with yellow mercuric oxide in dioxane or THF at 25° and obtained an isomeric product, m.p. 171°, in 50% yield along with a little of the trans isomer (2). Infrared, UV,... 

Iodine, in acid solution, reacts with acetone to form monoiodoacetone, which can be detected at low concentrations by electron-capture detection. The reaction is specific for iodine. Iodide can be determined after oxidation with potassium iodate. The other halide anions are not oxidized by iodate to the reactive molecular form and thus do not interfere in the derivatization reaction. 

Distillation Methods Distillation methods have been widely used in iodine isotope production. Since iodine may be converted to a volatile form (I2), either wet distillation or dry distillation has been employed. A general distillation procedure for carrier-free purification has been reported earlier by Kahn and Freedman (1954). In a wet distillation method (IAEA, 1966), irradiated Te metal is dissolved in a chromic acid-H2S04 mixture. After complete dissolution, the iodate (IO3) formed is reduced to elemental iodine (I2) with oxalic acid and then distilled off from the solution. The distillate is trapped in alkaline sulfite solution. This solution is then purified by an oxidation-reduction cycle and finally redistilled into dilute alkaline solution. In another wet distillation method, irradiated Te02 is dissolved in NaOH and the sodium tellurite is oxidized with H2O2 in the presence of a catalyst, sodium molybdate. The mixture is then acidified with H2SO4 and the iodine is distilled off and trapped in ice-cold water. 

Iodate oxidizes iodide to Ij (which is volatile), thus increasing the instability of iodide. This interaction has important practical consequences when iodized with a mixture of potassium iodate and iodide, bread loses 34% of its iodine over one week of storage, while with either iodide or iodate alone its iodine content remains stable (Anke et al., 1998). 

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