Chlorine dioxide chlorite complex

The concentration of chlorine dioxide, chlorite and total oxidants was determined on site using a portable colorimeter (Palintest Photometer 5000) and a modification of the DPD test in which any chlorine species are complexed with glycine to ensure only chlorine dioxide reacts with DPD. The chlorite and total oxidants are then determined on a fresh sample by acidification and neutralisation in the presence of potassium iodide. The initial dose level was set at 0.3ppm chlorine dioxide injected in the water feed to the cold... 

Mechanisms in Chlorine Dioxide Generation from Chlorite. The reactions between sodium chlorite and chloriue-based oxidizers and acids are complex and involve the formation of the proposed unsymmetrical intermediate, [CI2O2] (16,18,22,36,108,135—140). 

Chlorine Dioxide. Chlorine dioxide, C102. is a gas that is more hazardous than chlonne. Large amounts for pulp bleaching are made by several processes in which sodium chlorate is reduced with chloride, methanol, or sulfur dioxide in highly acidic solutions by complex reactions. For most other purposes chlorine dioxide is made from sodium chlorite. 

The kinetics of the oxidation of l-phenyl-2-thiourea by chlorite, in aqueous acidic media, are strongly influenced by the pH and show a complex acid dependence. The proposed mechanism involves HOC1 as a major intermediate whose autocatalytic production determines the observed kinetics of the reaction. The oxidation involved the formation of two stable intermediates, the sulfinic acid and the sulfonic acid, on the pathway towards total desulfurization to form phenylurea. A comprehensive 29-reaction scheme has been proposed to describe the observed complex kinetics.96 The oxidation of trimethylthiourea (TMTU) by chlorite in slightly acidic media is very fast. The oxidation of TMTU proceeds through the formation of sulfinic acid then to the sulfoxylate anion. The direct reaction of chlorine dioxide and TMTU is autocatalytic and is also inhibited by acid. A series of 28 reactions have been proposed to describe the mechanism.97... 

When chlorine dioxide is obtained by anodic chlorite oxidation, with or without the addition of sulphate, it is relatively stable in the minute-to-hour time scale at room temperature in the dark. Complex formation probably stabilises the chlorine dioxide (Gordon and Emmenegger 1966). Unfortunately, observation of this complex under these conditions in water electrolysis is compromised by low optical sensitivity. 

The oxidation pathways of chlorine dioxide under actual conditions are complex because a number of species including chlorine, hypochlorous, chlorous, and chloric acids are formed as intermediates. A rapid conversion of chlorine dioxide to chloride and chlorite (chlorous acid, pK 2.0) may first take place, followed then by a slow phase during which mainly the chlorite reacts with the pulp components. However, continuous generation of chlorine dioxide during bleaching takes place, for example, by the reaction between chlorite and chlorine (or hypochlorous acid) ... 

Solid chlorine dioxide polyhydrate cem be handled safely at low temperatures, usually in the form of blocks encased in ice coatings (227), and it is frequently shipped cold and regenerated as a gas (228) for bleaching flour. Stable liquid mixtures of chlorine dioxide with chlorine at low temperatures are also reported (212). It has been alleged that pyridine and chlorine dioxide form a stable solid complex that can be used to furnish free chlorine dioxide on addition of water (216). Chlorine dioxide is reported (2) to form a complex of low volatility in solution with neutral or basic perborate, which supposedly can be again dissociated by acidification of the solution with release of chlorine dioxide. In fact, the stabilized solutions have all the properties of neutral or slightly basic solutions of chlorite ion, which disproportionate upon the addition of acid. 

This steady state is attained in 1 to 2 hr. Thereafter, the color lightens and, if the stream of chlorine dioxide is continued, in 4 to 6 hr the color of the solution is the same as that of a saturated chlorine dioxide solution in pure water. When all the gases have been removed, the solution has no oxidizing power and consequently contains no chlorite ion and is neutral. These observations by Barnett (10) indicate that a highly colored complex is formed apparently the complex is [CIO2 C102"]. The gas formed when this complex decomposes is presumably a mixture of chlorine and oxygen (10, 226). The existence of this complex has been perceived by several other researchers (78,... 

Emmenegger and Gordon (78) noted that, at pH 7, a mixture of chlorine dioxide and sodium chlorite appeared to be stable, as evidenced by its visible and ultraviolet spectra. They determined that the formation constant Q for the charge transfer complex in this mixture is about 1.6J f . ... 

Turing strucmres have been widely studied in CIMA reaction [67] and its derivatives. When the CIMA reaction is performed in gel media by using starch as an indicator, some striped and hexagonal (spotted) structures [68] are observed. These strucmres are shown in Fig. 1.7. First, a starch-iodide complex is formed. The activator (iodine species) and the starch-triiodide complex generate Turing strucmres which diffuse much more slowly in the gel medium than inhibitor species (chlorite or chlorine dioxide). 

However, standards and samples caimot be prepared in eluent or diluted with eluent as chlorite is complexed by tetraborate. Because chlorine dioxide is also complexed by perborate, it is recommended that standards and samples be prepared with water containing 0.1 mmol/L NaOH and 12 mmol/L H2O2. As an... 

The kinetics of this last reaction have been studied as a function of pH. Another reaction in the complex series of interactions among the oxoacids of chlorine, the disproportionation of chlorine dioxide to chlorate and chlorite, follows the rate law below, with E - 10.8 kcal mol ... 

After all the iodide has been consumed, the iodine reacts rapidly with chlorite until all the chlorite has disappeared as well. In this second stage, iodine(I) intermediates (HOI, ICl), chloride ions and, under some conditions, chlorine dioxide are produced. The iodine(I) intermediates disproportionate comparatively slowly to produce iodine and iodate in the third stage of the reaction. After the iodide is consumed, the stoichiometry becomes very complex it depends on the ratio and the absolute concentrations of the reactants iodine and chlorite [23] it cannot be described by a single stoichiometric equation. Production of chlorine dioxide [23-25] becomes important at higher (> 10 M) initial reactant concentrations. 

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